Menu

Shop

Garage

Cart

Account

Products to Compare (max of 3)
X
Compare These Parts

Replacing a G-Body 7.5" Bolt Rear End

4/3/2020
Add Article To List
Tags: Tech, Street, Street

I’m currently in the middle of doing an LS swap in my 1981 Buick Regal. The G-body platform, for the most part, came from the factory with lackluster power. These cars from the factory were producing between 110-180hp. The exception to that would be the Buick Grand National, which was the fastest production car of 1987 and came from the factory producing 245hp from a Turbocharged V6.

With that being said, GM put 7.5” 10 bolt rear end in the G-body platform and everything, except for the '84-'87 Buick Turbo Regals (Grand Nationals) and the '84-'87 Olds Cutlass 442. These came with an 8.5” 10 bolt rear end. The issue with the 7.5” 10 bolt rear end is that it isn’t made to withstand the power of a 300hp+ motor. I’ve seen many videos of people putting a high hp motor in their G-body while ignoring the rear end. The result is usually a broken axle with the wheel still connected rolling by you down the street.

Knowing that I’m going to be pushing 400hp+, I knew the first upgrade I needed to do was replace the rear end in my car. There are a few different options while doing this. A great option is to order a Ford 9” from Speedway Motors with the correct metric brackets, or some people have been swapping Ford 8.8” into their cars. A 3rd option would be to find an 8.5” 10 bolt from an '84-'87 Olds Cutlass 442 or an '84-'87 Turbo Regal (Grand National).

The going rate for the 8.5” rear end used is usually between $800 - $1200, depending on if it’s an open differential or a posi differential. The 8.5” are becoming harder to find and typically sell fast when someone posts them for sale. If you are fortunate enough, you can find one in a junkyard, which is how I came about mine. I found an '85 Olds 442 in the junkyard and the car still had the rear end in it.

To this day, this rear end is probably the best score I have ever found in the junkyard. The rear end was an 8.5" posi with 3.73 gears. I knew that before I swapped it into my car, I would want to open the cover, change the fluid, put a new gasket on the cover, and make sure everything looked good before I put it into my car.

When I got the rear end home, I set it on jack stands. I set a drain pan under the differential. I loosened the ten bolts holding the cover. I took 9 of them out, leaving one to hold the cover on while the gear oil was draining. There was some old silicone holding the cover on, so I just pried a little till the fluid started draining. After the fluid stopped draining, I took off the cover completely.

After inspecting the gears and posi unit, everything looked pretty good to me, so I was ready to move forward with replacing the gasket with Mr. Gasket 84B Rear End Differential Gasket, putting new gear oil in it. I chose to use Valvoline VV975 Synpower 75W90 Gear Oil.

The first step was to remove the old gasket, silicone off the old cover, and housing. I just used a gasket scraper to do this. When I got all the old stuff off, I used brake cleaner to clean the surfaces. I was ready to reinstall the cover with the new gasket. First, I put some RTV silicone on the outside of the cover. This silicone prevents leaks in case the cover isn’t 100% flat. Next, I sat the gasket on the cover lining up the holes on the gasket and the cover. I put a bolt through the cover to make sure that the cover and gasket lined up correctly. Once I got the gasket lined up on the cover, I bolted the cover to the rear end. I didn’t put RTV on housing, just because it’s already on and machined surface.

With the cover in place, I was now ready to add the fluid. There is a set screw on the side of the housing. With the housing level, I removed the set screw and poured the fluid in. When I purchased the fluid, I got 3 quarts. The capacity is approximately 2 quarts, possibly a little more. I filled the rear end until oil started flowing out of the oil fill screw. After the fluid ran out (telling me that the rear end was full) I put the screw back in. You can also replace the gasket and fluid while the rear end is in the car, I just chose to do it before I installed it into the car.

Products Featured in this Article

Related Articles

How Big of Tires Can I Fit - Plus Sizing Guide
by Mark Houlahan - Posted in Tech
3/7/2023
Changing your tire’s profile, be it width, height, or both, can provide increased traction, braking, and handling. Learn more in our guide.
Mopar Flexplate Identification Guide
by Mark Houlahan - Posted in Tech
1/25/2023
Determining the correct flexplate for your V8 Mopar-powered project takes a little understanding of how these engines were balanced. Our Mopar flexplate buyer’s guide will help.
Ford Flexplate Identification Guide
by Mark Houlahan - Posted in Tech
1/13/2023
Ford’s small block and big block engine families have their share of flexplate differences. We’ll show you what to look for in this buyer’s guide.
LS Engine Flexplate Fitment Guide
by Mark Houlahan - Posted in Videos
1/11/2023
The LS swap is no doubt still going strong, but if you’re planning to run an automatic behind your 4.8, 5.3, or 6.0L LS-powered ride, you’ll need to pay attention to a few items we discuss in this buyer’s guide.
Small Block and Big Block Chevy Engine Flexplate Guide
by Mark Houlahan - Posted in Tech
1/11/2023
Over several generations of small block Chevy (and big block Chevy) engines there have been several changes that dictate what flexplate works with them. We’ll help you determine the correct flexplate for your Chevy engine in this buyer’s guide.
Why Convert to A One Wire Alternator
by Mark Houlahan - Posted in Tech
12/29/2022
Learn how to hook up a 1-wire alternator on your vehicle. 1-wire alternators are perfect for engine swaps or just keeping things simple for your project.
What You Need to Know About Flexplates
by Mark Houlahan - Posted in Tech
12/27/2022
The engine’s flexplate is a critical part to transferring power to your drivetrain. Using the correct part is imperative to engine longevity and proper drivetrain assembly.
Ammeter vs Voltmeter: How They Work, and Which One Is Right for Your Car
by Mark Houlahan - Posted in Tech
12/21/2022
Ammeters and voltmeters are two very different ways of monitoring your vehicle’s charging system. Both are better than an “idiot light” but which one is right for your build?
1967-1972 Chevy C10 Pickup Lowering Guide
by Mark Houlahan - Posted in Tech
12/19/2022
From a mild leveling to slammed and “in the weeds” there are several options to lowering a C10. We discuss the options in our ’67-’72 C10 lowering guide.
What Is Positraction and Do You Need It?
by Mark Houlahan - Posted in Tech
11/10/2022
Posi, limited slip, Traction-Lok, or whatever your favorite brand calls it is how your rear axle provide equal traction to both tires, and trust us, you’ll need it! So, read all about posi units and their benefits here in our guide.
Error
X
Note
X
Ok