Chevy 12 Bolt Rear End Oil Type? The 92 Correct Answer

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Table of Contents

What kind of fluid goes in a Chevy rear end?

Differential fluid, also called gear oil, is the fluid that is poured into the rear differential housing. It needs to lubricate the clutches, gears, and bearings in the rear end. It also keeps all of those components cool so that all of the parts in the differential don’t overheat and belt.

What kind of fluid goes in a Chevy differential?

Chevy Silverado Differential Lubricants. GM Original Equipment SAE 75W-85 Synthetic API GL-5 Differential Fluid by ACDelco®.

How much oil does a GM rear end take?

GM-Tech. Valsport said: The rear diff (1/2 ton 10 bolt) takes more like 3 quarts, not 2. The recommended fluid level is 10-15mm below the fill plug.

Are all Chevy 12-bolt rear ends the same?

They are not interchangeable. That doesn’t mean the truck rearend is not capable of receiving performance upgrades. To the contrary, aftermarket 30-spline differentials and axles are available. GM car and truck 12-bolt rearends are easily distinguishable by the cover shape.

What kind of oil do I put in rear differential?

There are two types of differential fluid. One is mineral oil, which is a natural, crude oil-based fluid. The other is synthetic differential fluid, which is created in a lab. As with all synthetic oils, synthetic differential fluid oils can be fine-tuned for optimal performance.

GM 12-Bolt Rearend Guide. How-To Identify That Swap Meet Find

Cornering without rattling, bouncing or bouncing is a given. That’s all thanks to the differential (sometimes referred to as a transaxle), a component that compensates for the difference in distance the inside and outside wheels travel when a car is cornering.

The differential, which is part of the drivetrain, helps distribute vehicle power evenly to each wheel. The differential keeps you in control when turning.

The differential relies on differential fluid to operate in optimal condition. What is differential fluid? It is the oil that lubricates the differential’s internal components such as the ring gear and pinion, preventing the differential from starting to wear and causing major problems.

Brian Murphy, Universal Technical Institute (UTI) Curriculum Education and Development Program Manager, shares more about why differential fluid is important and why it’s important to preserve it.

What does differential fluid do?

Differential fluid ensures that the differential stays in top condition for a long time. Sometimes referred to as transmission oil, differential oil is found in the axle housing. It is designed to work under high pressure situations, not high temperatures like engine oil.

differential fluid:

Lubricates clutch packs, gears and bearings

Lubricates the ring gears and pinions that transmit power from the driveshaft to the wheel axles

Cools and lubricates the differential

Without differential fluid, the differential would overheat due to metal-to-metal contact. That means it would burn itself out, potentially causing safety issues and requiring expensive repairs.

What does differential fluid look like?

Differential fluid looks like engine oil but is thicker.

There are two types of differential fluid. One is mineral oil, which is a natural crude oil-based liquid.

The other is synthetic differential fluid made in a lab. Like all synthetic oils, synthetic differential oils can be fine-tuned to achieve optimal performance.

What is rear differential oil?

Rear-wheel drive vehicles use a rear differential but not a front differential. A front-wheel drive vehicle uses a transaxle, which is part of the transmission. Rear differential oil is used on rear-wheel drive vehicles.

Trucks use the same fluid in both the interaxle differential and the rear differential.

How often should the differential fluid be changed?

The answer depends on the manufacturer. It’s always best to refer to your owner’s manual for the correct service interval. In most cases, you will need to change the differential fluid every 30,000 to 50,000 miles.

It’s important to keep track of when changing differential oil because the metal-to-metal contact generates heat through friction. It also weakens gears and wears down surfaces. This can lead to differential failure, which is a costly problem.

What happens when differential fluid levels are low?

When differential fluid levels are low, gears begin to grind, which can lead to differential failure.

Unlike motor oil, which works with an oil filter, differentials do not have a filter. When a differential experiences unwanted friction, small metal shavings or pieces can result and cause significant damage to the differential.

Learn more about differentials at UTI

Students in the UTI Automotive Technology and Diesel Technology programs learn about differentials and how they affect these vehicles. These are dealt with in different courses.

In the “Diesel truck manual transmission” course, one of the most important learnings is the disassembly, inspection and reassembly of single and double countershaft transmissions, differentials and drive shafts. Students will learn about the function of rear differentials as well as an interaxle differential and disassemble both components in a supportive learning environment.

In the Automotive Powertrains & Transmissions course, students will learn how to assemble and disassemble rear differentials and driveshafts and learn to understand drive train angles.

“UTI gives its students the skills they need to start as a diesel or automotive technician and advance quickly,” says Brian. “It provides students with the operational knowledge and troubleshooting experience needed to succeed.”6

If you are interested in a career as an automotive or diesel technician, contact UTI online or at 1-800-834-7308 for more information.

What weight oil goes in rear differential?

In a rear-wheel-drive car, the differential has its own housing and lubrication, a thick, dark oil usually heavier than 80 weight.

GM 12-Bolt Rearend Guide. How-To Identify That Swap Meet Find

Changing a car’s differential oil is one of the most overlooked maintenance tasks on light trucks, SUVs and non-front wheel drive passenger cars. Because the differential is in the back and under the car, it doesn’t get star treatment like the engine in the front.

But if the lubrication in the car differential fails, you won’t get very far. Luckily, you only need to change this oil every 30,000 to 50,000 miles.

⚠️As always, check your owner’s manual for how often to service your differential. Every car is different.

The differential is a component in all cars and is designed to compensate for the difference in the distance that the inside wheels and the outside wheels travel when the car is cornering. In a rear-wheel drive car, the differential has its own housing and lubrication, a thick, dark oil usually heavier than 80.

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Front drivers typically integrate the differential into the transmission case and share the same fluid. The differential oil lubricates the ring gears and pinions that transmit power from the drive shaft to the wheel axles. If your car is equipped with a limited slip differential, it also keeps all the moving parts in that assembly healthy.

A differential allows your car to take corners without drama. If both driving wheels turned together, they would jump because the outer tire goes farther than the inner one. There are many variations on the design, but they fall into three categories: open, limited slip, and torque vectoring.

Changing this oil is just as important as changing the engine oil, and for the same reason. Metal-to-metal contact wears surfaces and generates frictional heat, which inevitably weakens gears and leads to failure. Checking and changing the differential oil on a light truck is actually quite easy, but on a passenger car it’s a bit more difficult.

Either way, this little procedure can save you a big headache later.

Prepare the area

Loosen the screw at the very top of the cover, but leave the screw in place to prevent the cover from falling off completely and soaking the floor—and you—in differential oil. Nick Ferrari/Popular Mechanics

Depending on the design of your differential, this can be a very dirty job or a very clean job. Some differentials have a drain plug; others require you to remove the case cover. In both cases you need a wide drip tray; a plastic sheet underneath would be good insurance. Drive your vehicle for a few minutes to warm up the oil, then put on your dirty clothes – you’re likely to get dirty.

It’s just an oil change, right? Not that complicated, but get ready because old auto differential oil has the worst smell in the automotive world. At this warning, remove the filler hole plug at the top of the differential case, then unscrew the drain plug. If you don’t have a drain plug, unscrew the case screws and leave a few screws loose at the top to hold the cover in place.

Carefully pry the cover open with a regular screwdriver or the oil will spurt out and cover you in that unholy stench. Be careful not to damage the surface of the differential case. Drain the oil completely and then remove the cover.

Clean and seal everything

Nick Ferrari Nick Ferrari

Assume that all of the leftover oil in the axle is loaded with metal filings. If you’re an oil change scout, you don’t need to worry about this, but the rest of us should take the time to wipe the remaining oil from the case, gears, and the wet side of the home. Make sure you get everything as there might be some shavings hiding in the nooks and crannies.

💡A simple degreaser or just a set of shop towels is all you need to clean the case cover. Use gloves that you are happy to throw away. Once the cover is shiny, run a magnet around the inside to pick up any stray metal shavings.

Also clean the tip of the fill hole plug; Most are equipped with a magnet to grab fine metal particles. Don’t get mad about harsh cleaners – you don’t want the residue messing with your new oil. Take a razor scraper or light abrasive pad and scrape away the mating surface of the case and cover. Wipe both surfaces with a lint-free shop towel and brake cleaner.

Some cars have pre-made gaskets. If not, use a liquid gasket product rated for harsh conditions and oil exposure such as: B. Permatex Ultra Black. Place a single bead on the mating surface of the cover and draw a circle around each mounting hole, then screw the cover on using just enough clamping force to flatten the bead. Allow to cure according to directions, then use a torque wrench to tighten the bolts to your vehicle’s specifications.

Fill to the brim

Use a hose or pump to fill the differential with new oil if you cannot use the bottle alone. Nick Ferrari

Use the highest quality gear oil you can afford to fill the differential. The weight and capacity are listed in your owner’s manual; Your differential usually lasts up to 3 liters. However, be sure to read this manual as some limited slip differentials require a secondary friction modifying additive.

Fill the differential straight from the bottle if you have space, but if space is tight you can get a pump or extension hose to make the job easier. The bottom of the plug hole is the maximum fill line. So if oil drips out, you’re done.

Plug in, torque to spec, and you’re good for tens of thousands of miles.

Now look at this:

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Is differential oil the same as gear oil?

Differential oil, which is also known as gear oil, is thicker compared to engine oil. As a lubricating oil, gear oil prevents vehicles’ metallic components from damage and increases their overall performance. The oil also makes it easy for cars to make corners in a hassle-free way.

GM 12-Bolt Rearend Guide. How-To Identify That Swap Meet Find

Differential oil, also known as gear oil, is thicker than engine oil. As a lubricating oil, gear oil protects metallic components of vehicles from damage and increases their overall performance. The oil also makes it easy for cars to corner smoothly.

The high-performance automotive fluid works under high pressure to ensure all gears, clutch packs and bearings are continuously lubricated and all differentials operate smoothly and safely.

If the gear oil leaks or becomes dirty or contaminated with water, the metal components can be permanently damaged. To avoid damage to transmissions, clutch packs, and differentials, you need to be aware of the symptoms of bad transmission fluid.

Burnt smell from the differential

If you notice a bad smell coming from your transmission, you should take this as a sign of bad differential oil, which may be contaminated and therefore not working as it should. The bad smell is a sign that the gearbox is overheating because the lubricating oil is either used up or dirty and is not able to lubricate the gears properly.

The oil can also be expired or too old to lubricate vehicle parts, causing the same bad smell because the metals are burning due to metal-to-metal friction. Once you discover your differential oil is contaminated, the next step is to replace it immediately.

Strange noise

Another symptom of bad differential oil is whirring, howling, or howling noises, which indicate that metal parts, clutches, gears, and differentials have not been lubricated due to a dirty lack of clean oil.

vibrations

If you feel unusual vibrations while driving, it could be a sign of a bad differential or gear oil. However, it can be a sign of other vehicle problems that a professional mechanic may need to check.

The strange noises increase as your vehicle turns and as it speeds up. For this reason, you should take your vehicle to a reliable and professional mechanic to perform the necessary inspections and fix the problem.

To repair the gears and other metal parts, our professional and trained mechanics can do the job. If you need a differential repair, call our auto repair shop today!

Can I use ATF in differential?

Never try swapping ATF for gear oil in a manual transmission. My friend who builds Diffs for a living has confirmed that ATF should work on in my differential– So I reckon it may be worth a shot- now to get the time to do it!

GM 12-Bolt Rearend Guide. How-To Identify That Swap Meet Find

Quote: oil pan 4 quote from differential kits can use ATF.

Millions of front-wheel drive cars do it every day.

Most “open” spindle gear sets seem to work well in ATF, the GM Zexel-Torson LSD is approved for use with ATF. I don’t see why Detroit lockers and various aftermarket lockers should have problems.

Any spindle kit with couplers like a GM posi unit will not do as well with ATF.

The cogs and pinions shouldn’t really care what kind of oil they’re in as long as they stay wet.

I think you might have problems installing ATF in a differential used for applications other than light car stuff (I wouldn’t mind being wrong about that).

It seems like it should work on paper, but I haven’t found anyone who has ever tried it.

Never attempt to replace ATF with transmission oil in a manual transmission.

My friend who builds diffs for a living confirmed that ATF should work in my diff – so I think it might be worth a try – now to get the time to do it!

It’s also common for us BMW folks here to run ATF in the gearboxes – makes cold shifting a lot easier – I have no qualms about doing that – or I can try motor oil as a half (It seems to suggest that the oil in the subway trans is similar to 5w30 motor oil.) Thanks for confirming that ATF should be fine in an “open” differential (no clutch plates). My friend who builds diffs for a living confirmed that ATF should work in my differential. So I think it might be worth trying – now to find the time! It’s also common for us BMW folks here to run ATF in the gearboxes – makes cold shifting a lot easier – I have no qualms about doing that – or I can try motor oil as a half way (It seems to suggest that the oil in the Subway Trans 5w30 motor oil is similar.)

My blog about cars – Fu’Gutty Cars

http://fuguttycars.wordpress.com/

US MPG for my Renault Clio 182

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Is axle oil and gear oil the same?

Well, yes, they are all gear lubricants, but no, you can’t just use them interchangeably. Axles, differentials, final drives and other gear sets used in mobile equipment applications all require specific lubricants designed for the heavy loads and the sliding and rolling forces associated with the operation of gears.

GM 12-Bolt Rearend Guide. How-To Identify That Swap Meet Find

GL-4, GL-5, FD1, TO-4. You’ve probably seen these gear oil specifications in equipment maintenance and lubrication manuals for years, but do you know what they all mean? All those letters and numbers can be confusing. Is it really necessary to know what each of these specifications means? And can’t you just use one of them in a gear set? It’s all gear oil, isn’t it?

Well yes they are all gear lubes but no you can’t just use them interchangeably. Axles, differentials, final drives, and other gear sets used in mobile equipment applications all require specialty lubricants designed to withstand the high loads and sliding and rolling forces associated with transmission operation.

Gear lubricants are definitely not the same as gear oils. There are differences in the additive technology used in lubricants for each specification, and just because one type of gear oil works well for one type of transmission application doesn’t mean it will work well for all.

Different industry associations and different device manufacturers issue unique specifications. Most of the time these specifications are not interchangeable. Swapping one type of transmission oil for another is sometimes possible, but making this swap can be difficult and you should seek advice from a lubricants specialist to make the right decision.

For these reasons, it is important for equipment owners, operators and lubrication technicians to determine what specification is recommended by the equipment manufacturer for each machine and gear set to ensure the correct lubricant is being used.

The following are some of the most common gear lubricant specifications and their intended applications:

API GL-4 – Intended for gear sets with light to high loading and sliding forces. GL-4 lubricants are commonly used in synchronous manual transmissions for on-road and off-road trucks.

API GL-5 – Intended for heavily loaded gear sets with high sliding forces such as hypoid differentials. GL-5 lubricants contain high concentrations of extreme pressure additives to provide protection under boundary lubrication conditions. Common heavy-duty applications include differentials in on-highway and off-highway trucks, differentials, final drives in Caterpillar scrapers, and differentials and planetary gears in Euclid transporters. Some manual transmissions can use GL-5 but should not normally be used in synchromesh transmissions as the EP additives can be corrosive to yellow metals found in these types of transmissions. Limited slip differentials also typically require a special lubricant with a limited slip additive.

Cat FD-1 – Intended for final drives and axles in Caterpillar equipment types that do not contain friction materials (i.e. wet brakes). A Cat FD-1 SAE 50 or SAE 60 petroleum based product will allow a 4,000 hour drain interval and a multigrade 80W-140 synthetic or semi-synthetic product will allow a drain interval of up to 6,000 hours – if the operator uses a drain interval used oil analysis program such as: . B. Castrol Labcheck. Common applications include final drives in bulldozers and differentials, final drives and front wheel bearings in Cat off-highway trucks.

Cat TO-4 – SAE 50 and SAE 60 grades can be used in final drives and axles with a 2,000 hour drain interval. Common applications include differentials, final drives and planetary gears in Caterpillar wheel loaders, wheel dozers, excavators and landfill compactors. TO-4 fluids are also used in lower viscosity grades in transmissions and hydraulics in some machines.

General purpose tractor fluids – This category includes many specifications such as: B. John Deere J20C, Volvo WB-101, Case (IH) Hy-tran, Ford M2C-134A (and others), and is included for axles and differentials in certain units intended for wet brakes. These fluids contain friction modifiers to reduce wet brake chatter, but should not be used in equipment designed for TO-4 fluids as the friction modifiers used can adversely affect braking performance. Universal Tractor Fluids are also used in the transmissions and hydraulics of many brands of equipment.

SAE 50 Motor Oil – While not strictly a “gear oil,” this type of lubricant is often recommended as a lubricant for some truck manual transmissions.

This article is not intended to provide a complete recommendation of all possible uses for these fluids, or for all gear sets. It provides a quick guide to clarify the differences between these liquid types and to make users aware that these products are not interchangeable. Please note that using the wrong type of product can result in poor performance and accelerated wear as there is no universal fluid that fits all gear sets for mobile devices.

Please be sure to follow the actual OEM recommendation or ask your Castrol HD Account Manager or Field Engineer for help before making a transmission oil decision.

How much oil does a Silverado rear end take?

2.75 quarts (rear with 9.5” and 10.5” diff.)

GM 12-Bolt Rearend Guide. How-To Identify That Swap Meet Find

maintenance schedule

The following intervals are based on the assumption that you will perform the service yourself and will not pay to have the work performed. These are our recommended minimum service intervals for vehicles that are driven every day and in many cases are less than factory recommendations. Because regular maintenance increases your car’s efficiency, performance and resale value, we encourage you to follow our schedule. If you are driving in dusty areas, towing a trailer, idling or driving at low speeds for long periods of time, or driving in freezing temperatures for short periods of time (less than four miles at a time), even shorter intervals are recommended.

If the vehicle is new, follow the maintenance schedule closely, record it in your owner’s manual and keep all receipts to protect the warranty. In many cases, the initial service check is free (contact the service department for more information).

Every 250 km or weekly

Check the engine oil level

Check the coolant level

Check the windshield washer fluid level

Check the brake fluid levels

Check the tires and tire pressure

Every 3,000 km or 3 months

…all the items listed above, as well

Change engine oil and filter

Check the power steering fluid level

Check the automatic transmission oil level

Every 6,000 km or 6 months

…all the items listed above, as well

Spin the hoops

Check the wiper blades

Check and service the battery

Check the engine accessory drive belt

Inspect the hoses under the hood

Check the cooling system

Check the seat belts

Every 15,000 km or 12 months

…all the items listed above, as well

Lubricate the chassis

Check the differential oil level in the front (4×4) and rear axles

Check the fuel system

Check the braking system*

Check the exhaust system

Check Transfer Case Oil Level (4×4)

Check the air filter*

Every 30,000 km or 30 months

…all the items listed above, as well

Change brake fluid

Change automatic transmission oil and filter**

Change transfer case oil (4×4)

Flush Cooling System (if ethylene glycol antifreeze is colored green)

Replace the air filter*

Check the boots of the steering, suspension and drive axle

Check the evaporative emission control system

Every 60,000 miles or 48 months

…all the items listed above, as well

Replace the spark plugs

Check/replace the spark plug wires

change differential oil**

Every 100,000 km or 60 months

…all the items listed above, as well

Flush Cooling System (If Orange Dex-Cool Antifreeze)

*Perform at half the specified intervals if the vehicle is operated under one or more of the following conditions:

Driving in dusty areas

Tow a trailer

idle for a long time

Driving at low speeds or short journeys in freezing temperatures

** Perform at half the specified interval when operating under one or more of the following conditions:

How much gear oil does a 99 Silverado take?

It will hold about 2.7 quarts.

GM 12-Bolt Rearend Guide. How-To Identify That Swap Meet Find

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Is a GM 12-bolt rear end good?

When the 12-bolt rearend is properly assembled, it’s the strongest passenger-vehicle rearend Chevy ever produced. GM engineers designed the 12-bolt to be a durable piece that could handle the torque output of its big displacement engines.

GM 12-Bolt Rearend Guide. How-To Identify That Swap Meet Find

See all 12 photos See all 12 photos

Let’s face it, performance cars are about discovering the weak link in the chain. What happens once you start putting out some serious horsepower? You break a gearbox or a rear end because it’s too weak. Darwin taught us that only the strong survive. That means you can forget about the spindly 7.5- and 8.2-inch 10-bolts. They are cannon fodder. For this story we will compare the 12-inch to the much-vaunted Ford 9-inch to assess the pros and cons of both rear triangles. To help us in our search we contacted Randy’s Ring and Pinion to track all the variables.

The 12-hole and 9-inch butts are actually more similar than different. The main difference between the two is the design of the cases. The 12-bolt integral design features a carrier housing and sprocket mount that are part of the rear housing, while the 9″ model uses a dropped third member that takes advantage of an independent carrier housing and sprocket mount that is integrated into the rear Housing to be screwed.

12-bolt to glory The GM 12-bolt debuted in 1965 and was mass-produced until 1972. It features an 8.875 inch cog carrier held in place with two internal main caps. The pinion shaft is 1.625″ in diameter and is shimmed to achieve proper pinion depth. The pinion gear meshes with a yoke that mates with the driveshaft rear universal joint. The three most common types of yokes are the 1310, 1330, and 1350 series units, but the 12-bolt generally uses the smallest 1310-style U-joint.

Factory axles are available in a 30-spline configuration and slide into the side gears. Rather than bolting the axles, the stock GM >> 10 and 12 bolts use small C-clips over the ends of the axles to hold them in place. This involves removing the rear cover, draining the oil, and pulling out the center pin to pull the C-clips to remove the axles (phew!). Axle bearings are pressed into the tube, with the outside diameter of the axle shaft serving as the inner bearing brace. The downside to this idea is that if the bearing fails, the axle will fail as well.

The 12-bolt assembly is more complicated as it uses a shim between the sprocket and the inner sprocket bearing. Since this bearing is pressed on, it must be removed with a press to change the sprocket disc to adjust the sprocket depth. The ring gear play is also adjusted with shims. This requires the correct thickness of shims on both sides to ensure the carrier bearings are preloaded and that the backlash is correct. All of this is not difficult, but requires special tools to achieve it. While original 12-hole cases are becoming rare, Moser has stepped into the void with a brand new case configured for all major Chevy body styles.

When properly assembled, the 12-bolt rear end is the strongest passenger car rear end Chevy has ever produced. GM engineers designed the 12-bolt engine to be a durable part that could handle the torque output of its large displacement engines.

The big 9 inch

The 9-inch Ford rear has established itself as the pinnacle of rear axle strength and durability. The 9-inch is so pervasive in the performance market that you can buy bolt-on 9-inch cases from companies like Currie Enterprises and Randy’s Ring and Pinion for every Chevrolet body style you can imagine.

The 9-inch rear was first mass-produced by Ford Motor Company in 1957 and continued for 30 years. While the 9-inch uses many similar parts to the 12-hole, it configures them in a slightly more convenient and durable package. A 9-inch rear has a stamped body with nothing but axle tubes welded on each end. This type of rear triangle is easier to service due to the removable center section that houses the gear set. This detachable gear case houses a differential assembly onto which the ring gear bolts. The 9-inch uses a bolt-on external sprocket stay that locates the large sprocket bearing. However, an added plus for the 9-inch is an internal rear sprocket support that also supports the gear end of the sprocket to limit gear deflection under high torque loads.

Like the 12-bolt sprocket, the 9-inch sprocket uses shims to achieve proper sprocket depth with a small 1.313-inch pinion shaft diameter. Another difference between the two rear wheels is that the 9-inch places its pinion lower on the ring gear to improve tooth contact. This strengthens the rear assembly, but at the cost of about 2 to 3 percent loss of power to drive the gears compared to a 12 bolt. Of course, gear, housing and bearing sizes are relevant to strength, so you’ll need to make the strength comparison to the 9-inch with its .125-inch larger sprocket diameter and internal pinion retainer.

Another advantage of the 9-inch is that the axles are easier to install and remove. Ford designed the factory 28- and 31-spline axles to be removable by pulling four bolts per axle flange, which allows the axle to slip out. The axles have pressed bearings and retaining plates that are bolted to the housing flanges. There are no C-clips inside the chainstay holding it in place like a 12 hole. The plus here for the 9-inch is that if you break an axle in the case, the axle holder will hold the axle in place. On a 12-hole, breaking an axle means it will slide right out of the case, causing massive body damage in the process. You can convert a 12-bolt axle to a 9″ axle mount, but this requires a C-clip eliminator kit and body modifications.

Ultimately, the choice between 9″ and 12 bolts comes down to personal preference. If you’re building a cruiser and want to keep all GM, the 12-hole is more than able to take the abuse. On the other hand, if you plan on whipping up your Bow Tie machine with slicks and plenty of torque, the 9-inch’s strength and serviceability is hard to beat. Both are great pieces so we’ll let you decide.

See all 12 photos See all 12 photos

What is the strongest rear end?

Dana 60 Rear End Assemblies

If you want a big brute of a rear end under your car, look no further than a Dana 60. Even in the heyday of muscle cars, Dana 60 rear differentials were renowned for their strength, along with their difficulty to locate.

GM 12-Bolt Rearend Guide. How-To Identify That Swap Meet Find

You’d think picking a rear end for a project car would be easy.

It is not.

Search the Summit Racing website or catalog and you will find that there are almost too many choices.

For example, on the GM site, you can find 8.20″ 10-bolt sprockets, 8.50″ 10-bolt sprockets, and 8.875″ 12-bolt sprockets.

Popular FoMoCo options include the rear end with 8.00 inch cog, the rear end with 8.8 inch cog and of course the 9 inch cog.

For Mopars, the 8¾ and the Dana 60 are second to none. And then there’s the Dana 44 and others including several quick-change assemblies.

The possibilities are manifold.

But it gets easier if you narrow it down to the top three options:

The Dana60

The GM 12 hole

The Ford 9 inch

There are several reasons why the “Big 3” are proving popular, from absolute strength to parts availability. And just as importantly, the aftermarket now has you covered when it comes to these popular and trusted rear axle assemblies. You don’t have to look for them in junkyards, nor do you have to deal with worn out 40 year old components.

In no particular order, here’s what’s hot and what’s not in relation to everyone.

…

Dana 60 tail assemblies

If you want a big brute tail under your car, look no further than a Dana 60.

Even in the heyday of muscle cars, Dana 60 rear differentials were known for their strength, along with their difficulty in locating them.

Today they are actually incredibly easy to find. Strange Engineering and others offer a full line of heavy duty bolted rear end assemblies for a wide variety of common applications.

The truth is, for racing purposes you can now build a better rear end than a Dana, but for street cars it’s a good choice. Here’s why:

Dana 60 rears feature a huge 9¾ inch diameter sprocket and when fitted with a modern limited slip setup (there are several including Detroit Lockers) the axle splines increase to a whopping 35.

The sprocket is a large 1-5/8-inch diameter (29-spline) that can be set up to accept massive Spicer 1350-series universal joints. Gear ratio options are also plentiful, ranging from 3.31:1 all the way up to 7.17:1.

Strange Engineering’s Dana 60 (dubbed the “S60″) isn’t exactly a piece-for-piece clone of the original.

Instead, it includes several user-friendly modifications.

For example, there is additional material underneath both main caps (similar to some aftermarket 12-bolt casings). This means you don’t need to add billet caps to the rear end. With a standard Dana 60, the axle tubes are simply pressed in and plug welded. With the Strange S60, on the other hand, the tubes are neatly welded in a rosette and then each tube is completely welded to the housing. Stock Dana 60 rears usually require the housing to be spread apart to remove the luggage rack (some more than others).

That’s not the case with an S60 – it doesn’t need to be spread to reinstall the carrier as it comes with adjusters like an aftermarket 9″ which eliminates the side carrier shims.

…

GM 12 hole rear triangle

One of the most popular high performance rear ends in use today is the 12 hole Chevy.

But it too (like the Ford and Dana) has flaws.

For example, the area behind the rear caps is heavily corrugated (more or less hollow) in a stock 12-bolt GM casting. This affects strength. The solution is to use a billet main cap.

Why go to all this trouble? Easy. The hypoid action of the rear differential attempts to push the carrier rearward out of the case.

Another reason is the bore size limitation. The bore size of the case will determine which axles you can use. Remember that as the axle spline increases, the diameter of the axle shaft increases (which in turn dictates the need for a special large bore housing). In stock form, you can press in a 33-spline axle, but that’s it. Certain new aftermarket cases can be built to accommodate a large 35 spline setup. And many of these don’t require billet caps.

On a stock 12-bolt, the axle tubes are only held in place by plug welds.

If you look at old 12 hole bolts you will see that in many cases the GM factory welds were not intact and upon closer inspection you will find pinholes in the welds. This doesn’t affect the strength of a case like this (since the tubes have been fully welded to the coconut), but does introduce a small problem: the factory spot welding system will often leak or ‘wet’ lubricant.

Because of this, many car owners have had their 12-bolt gaskets replaced, gaskets replaced, and drain plugs replaced – only to find the leak was in the area of a factory spot weld.

The solution is simple but time consuming. Each tube spot weld is filled using a plug weld or “rosette” welding process, resulting in a clean, leak-free body.

Another area to be aware of is the entry point for the axle tubes in the coconut. With a stock 12-hole bolt, this spot is fragile. In the case of aftermarket castings, they’ve been seriously beefed up to handle much greater loads than a stock GM 12-bolt.

Another issue is the stock C-clip method of axle mounting.

Break a C-clip attached axle and the entire axle will detach from the car. For this reason, C-clips are required by every racing club. The solution is either a C-clip eliminator kit or a welded-on housing end that uses a sealed bearing and bolt-on bearing retainer.

Of course, most aftermarket 12-bolt cases are already set up for sealed bearings and bolt-on bearing retainers.

…

9 inch Ford rear assemblies

The 9″ Ford is definitely a very popular rear differential, but you have to keep in mind that the 9” hasn’t been built in decades, which means the latest junkyard parts you’ll come across are at least 20 years old .

On the downside, it’s pretty much the standard rear end for drag racing (and for good reason).

Aside from age, the 9-inch has three major disadvantages from a drag racing perspective: First, the axle tubes of the standard housing are not round. Not only do they taper from 3½ inches to 3 inches, but the tubes all have “flats” that are more or less crimped onto the tubes.

Both of these factors force a chassis builder to build each mount individually, as none is symmetrical.

Also, the front of the OEM Ford case is approximately 24 inches wide. Because of this, some cars require you to weld mounts to the face, which means you lose adjustment holes for items like the four-bar linkage.

Most of the detail that goes into a good 9-inch is hidden, making many of these cases look more original than they actually are.

Many of the new aftermarket 9-inch cases require a lot of work.

While we can’t give you a full, step-by-step examination of the methods of fastening a Ford, we can give you a little insight into some of the techniques.

…

It’s common on high-performance cars to add a brace to the rear of a Ford 9-inch, essentially connecting the ends of the axle tubes together while also anchoring the rear of the case.

This greatly increases the strength of the case and prevents it from physically moving forward and backward.

But the back brace scenario has a catch that some chassis builders forget, ignore, or just don’t know: when the back brace is added, the chassis doesn’t flex fore and aft. Instead, it bends down under power, which can negatively impact performance and damage parts.

The solution? A hose attached between the four-bar brackets (see the attached photos for a closer look). Of course, most builders use custom-made 360-degree four-link mounts (which wrap completely around the respective axle tubes).

But the nine-inch preparation has even more to offer.

Almost all 9 inch body ‘banjos’ are formed by stamping. Stressed by sticky tires, extra weight and a powerful motor, the design doesn’t really work because what ends up happening is the housing deflects at the beam, reducing ring and pinion life.

A big problem is the back cover on the case.

The back of a 9-incher isn’t one piece – it’s a stamped cover that’s pressed into the case. The hypoid action of the third element attempts to push the carrier out of the back of the case. Welding the cover to the back of the case will not fix the problem.

The solution is to weld the stamped parts of the case together and then add internal case “supports”. These supports are essentially a series of tubes connecting the front of the case to the back. This extends the life of the sprocket.

What about the middle part? Ford centers were typically made with a separate screw-in bracket for the sprocket.

Ford did a good thing with the 9-inch’s design and layout. No secret.

If you’re inclined, it’s possible to track down most of the stock parts to piece together a factory-style nodular iron. 31-spline 9-inch, complete with a Daytona sprocket support and even a Detroit locker.

But the truth is what you will find is old, worn out hardware. And you should be prepared to drop a serious coin to get the old stuff in shape. Not good. And probably not racing either.

There are many options for updated aftermarket brute force Ford center sections.

Several companies manufacture and sell ductile iron housings. Ductile iron is a type of cast iron that first saw the light of day in 1943. While most grades of cast iron are brittle, nodular iron is much more ductile due to its “ductile iron” inclusions.

When considering aftermarket cases, keep upgrade availability in mind. Several companies (Strange Engineering and Mark Williams, to name two) offer reinforced ductile iron cases that are stronger than stock but comparable in weight to a stock Ford assembly.

Some of the better aftermarket 9″ cases come complete with drilled billet steel rear end caps. They also include custom billet steel adjusters and studs to secure the sprocket assembly. They are available in stock and larger bore sizes (the larger the bore, the larger the axle diameter/spline you can use – the larger the axle diameter and spline, the stronger the axle).

There are other options, too, including examples of aluminum cases with “through-bolts”. Isn’t aluminum weaker than ductile iron? Not necessarily.

These are highly engineered, ultra-tough components that have become pretty much standard on NHRA Pro Stock. It is also used regularly in slower drag race cars, pro street cars and a range of really fast street machines.

Which tail is the best?

As always, it depends.

In terms of weight, the Dana 60 is the heaviest of the group (although the S60 is quite a bit lighter than a stock Dana 60). Typically they are 20-40 pounds heavier than a 12 hole or 9 inch. We can’t give you specific weights as case width and part selection obviously affects weight.

In terms of power loss, the 12-hole has about 2-3 percent less parasitic losses than a 9-inch due to the sprocket position, sometimes referred to as the hypoid centerline.

The Ford 9″ sprocket is mounted lower in the carrier and has the largest hypoid offset, requiring more power to drive than the Dana 60 or GM 12-bolt.

The Dana 60 has so much bulk that it also uses a lot of energy to drive (although many say it feels a little less than a 9-inch Ford).

In terms of serviceability, the 9-inch Ford is the big winner simply because you can remove the center section and wait on a bench (which is a big reason it’s favored by drag racers). But wrestling a center section around on the floor or a bench isn’t the easiest unless you have a bench stand with an axle assembly adapter.

This allows you to machine the 9″ center section on your workbench or engine stand.

And finally, Dana 60 parts are not as easy to figure out in the wild as 12-hole and 9-inch Ford parts.

There are many things to consider when choosing a rear end (not least your budget). All three of these rear triangles are very good when built with the right parts.

How can you tell if a 12-bolt is posi?

If you see springs in the window of the carrier, either coil springs like this or an S-shaped spring, it’s a Posi unit.

GM 12-Bolt Rearend Guide. How-To Identify That Swap Meet Find

They should both turn. That’s all there is to it. If you step on the long pedal on a sports car and the smoke clears, you should see two black bands of equal length on the ground.

When they were new they did just that. But most of us don’t think of a limited slip differential as a wearing part, like brake shoes or a clutch. Eventually limited slip stops limiting wheel spin and you have a really snazzy open differential.

You can refurbish a limited slip the same way you would refurbish a clutch or brake: replace the parts with worn friction material.

The mystery of a limited slip differential may put some people off. A limited slip differential is a compact piece with a number of parts inside it, and people generally don’t understand how the parts work together to keep both wheels turning. To put it in a nutshell, there are two sets of clutch discs and metal discs that come in two packs. Each pack is connected to a side gear. A stub on the outside diameter of the side gear is splined, and the clutch pack rides on it. The inner diameter of the side gear is also splined and holds the end of the axle shaft. On a GM Positraction unit, springs in the center of the unit force the clutch packs together, causing the side gears to act essentially as a solid unit, connecting both axles.

When the car corners, the outside wheel spins faster than the inside wheel, overcoming the pressure of the springs and causing the clutch to slip. In a straight line, the clutches hold and the tires spin together. The clutches in a differential wear out and when they do you have two choices: replace the entire differential with a new one or replace the worn out clutches. It seems that most people don’t realize that they have the second option.

Ultimate Driveline of Shelbyville, Michigan offers all internal parts to rebuild an Eaton-style limited slip differential, as well as complete new units. You can buy a set of new metallic clutches for $115. a set of carbon fiber clutches is $140; A complete unit costs $420. If you know your hand tools, the decision is a no-brainer.

The factory matched the stiffness of the Posi units with a variety of springs available in 200, 400, and 800 pound pressures. The 200-pounders will spin both tires when driving on ice or snow; think “the posi for the family station wagon”. The 400-pound springs are good for all-around street performance. The 800-pounders will hook up on the drag strip with sticky tires, but on the road they’re generally considered to be on the limit. A set of 800-pound springs will make the rear end chatter and shake when it comes to turns, and it will also put undue pressure on the clutch packs, shortening their lifespan.

For this story we took apart two different GM 12 bolt rear triangles to rebuild one and show the damage to the other. A new set of clutches and stiffer springs were fitted to the first while we are still deciding what to do with the second as teeth on a final gear have snapped off. “Actually, the spider and end gears are the weak link,” Ultimate’s Jay Prosch-Jensen told us. “They’re designed to break before the more expensive pieces.”

According to him and other Chevy guys we spoke to, it’s not uncommon for 12 bolts to break. When considering what to do with your own 12 hole bolt, you need to figure out which parts to replace rather than simply buying a complete unit. If the pieces save a few hundred dollars, that’s not a decision at all. On the other hand, if it needs a full internal kit plus couplers, you can get a brand new unit for a few bucks more.

We can’t make the decision for you, but at least we can clear up some mysteries.