GM 10 Bolt 8.5" Rear End Rebuild Thread

[EscapeRacing]

I had all this posted previously, but am resurrecting to add to the new content. I decided to take out the stock rear end from my 1979 Trans Am which was a 2.41 posi and switch it to a 3.23 posi. This was a huge learning experience and hoping it helps some future builders.

I am not a professional - this is all being done in my garage by myself. I am also listing all the parts and costs for reference - you could probably do this cheaper professionally, but i wanted to give it a shot myself.

One important thing I learned early was there are two different carriers - a Series 2 and Series 3. The Series 2 takes ratios up to about 2.73 and if you want to go higher (3.08, 3.23, 3.73, etc) you need to switch to a Series 3 carrier (or use an adaptor which is not highly recommended).

Here's my journey in pics and explanations. I am breaking this into a few posts in case something goes wrong...

I started by buying a complete 10 bolt on Craigslist for $150 with a 3.08 (thus 3 series carrier) so that I could build the new rear end and still drive the car until i was ready to swap it out.

[EscapeRacing]

I started by opening up the rear end and taking it apart. I replaced all the races, bearings, seals, axles, brake lines, brake hardware, etc. When taking apart the rear end, its is critically important to mark everything. For example, the carrier brackets have to go back on the same side they were removed from. So make sure you punch a dot on one side, bag and mark it, or whatever you need to get things back where they came from. You will need a good set of tools to do the job right. I will show what I purchased for this project in a moment. Here a pics of the tear down.

FYI - the number cast on the carrier can be used to tell if its a Series 2 or Series 3

[EscapeRacing]

Okay, here are the tools and parts i have used to get this done. Obviously this does not include the normal hand tools and wrenches. This is the specialized stuff. It was not too expensive and glad I have them at my disposal going forward.

The hydraulic press was quite possibly the best tool I have bought in a long time. Dont know I how i managed without this in the past!

PARTS
Yukon Gear & Axle (YDGGM8.5-3-28-1) Duragrip Differential for GM 8.5 with 28 Spline Axle ($300)
JD Race - NEW 3.23 GEARS YUKON ($195)
JD Race - NEW REBUILD KIT COMPLETE ($95)
JD Race - NEW MEGA KIT (AXLE BEARINGS & SEALS) ($35)
Motive Gear SS10 - Motive Gear Differential Carrier Shim Kits ($15)
TEN FACTORY MG22101 - Motive Gear Ten Factory Axle Shafts ($262)
Ratech 9024 - Ratech Carrier Bearings ($37)
Spicer U-Joints Line: SPI | Part # 53147X ($47 for 2)
BrakeBest Brake Cables Line: BHH | Part # BC92680 ($40 for 2)
BRC-608 1967-1981 Drum Brake Backing Plate Mounting Hardware Set ($14)
BRC-609 1967-1981 Wheel Cylinder Mounting Bolts ($5)
CCB76R2 1976-81 Camaro Z28 Firebird TA Rear Drum Axle Brake Line Kit, 2pc OE ($22)
H767 1976-81 GM F-Body Rear Rubber Brake Hose ($10)
INLS7068 1964-77 F-Body, 68-74 X-Body Rear Drum Spring Kit, Does Both Sides ($10)
WCN024 1967-77 GM F-Body Rear Drum Wheel Cylinder 7/8" Bore 1pc ($30)
Prothane 7-1709-BL Black Rear Upper and Lower Multi Leaf Spring Pad Kit ($30)
Dorman HELP! 81057 Pinion Bearing Spacer ($3 - needed a couple of these)
Yukon Gear & Axle (YSPPN-018) Pinion Nut ($13 - needed a couple of these)
Allstar ALL72148 Differential Pinion Seal for GM 8.5" 10-Bolt Pinion ($11)
Yukon Gear & Axle (OK 3-QRT-Conv-A) 80W90 Gear Oil with Positraction Additive - 3 Quart ($40)
Rust-Oleum 248903 12-Ounce 2000 Degree, Flat Black Automotive High Heat Spray Paint ($5)
Summit Racing SUM-720203 - Summit Racing® Sway Bars (OPTIONAL - $160)


TOOLS
YOTOO Bearing Pullers Set 5 Ton Capacity, Bearing Separator Kit ($42)
Loctite 209741 Heavy Duty Threadlocker, 0.2 oz, Red 271, 0.2 ($6)
CARTMAN 10pc Axle Bushing Bearing Race & Seal Removal/Install Driver Master Tool Set ($15)
ARES 70213-1/4-inch Drive Beam Torque Wrench - 0-80 Inch/Pounds ($22)
All Industrial Tool Supply TR72020 Dial Indicator Magnetic Base & Point Precision Inspection Set ($46)
Powerbuilt 940376 Transmission Stop-Off Tool ($9)
Digital Micrometer ($15)
Hydraulic Press ($50 used)

[EscapeRacing]

Here are some of the new parts with notes

Its good to save the inner pinion bearing from your old pinion and hone it out a bit to use as a test fit bearing for your new pinion before you press on the new inner pinion bearing. You are going to need to do this a few times when getting the pinion depth and mesh pattern correct.

Getting the ring gear on the new carrier can be a bit tough as well. Some folks heat it up in the oven and freeze the carrier to get it to slide on. I was lucky enough to get a few threads of the ring gear bolts started and took my time using the bolts to "pull" the ring gear and carrier together. Ring gear bolts are reverse thread so righty is loosy. Once you have the two married up, you need to go back and thread lock the ring gear bolts. Good practice is to mark the ones you have thread sealed with a marker so you dont forget half way through the process.

You will need to remove the old carrier bearings if you are using a used carrier and press on the new ones. You can do this right away as you dont need to test fit those bearings and wont need to remove them later. Also, use the micrometer to measure the carrier shims (carefully noting left and right sides) as that will be a good starting point for your new shims.

Side note, always keep your bearings and races matched. Dont mix those up.

[EscapeRacing]

Setting the gear mesh is a very time consuming process that takes lots of patience. There are tons of resources out there on how to do this properly and great youtube videos so i wont go into all that here but happy to share my experience if you want. Just DM me. Also, not a huge Facebook or twitter guy, but I did post pics on Instagram along the journey.

Pinion wise, measure the shim that was on the original pinion and start there. This is were the honed out test bearing will be useful. You will need to install the inner and outer pinion races (drive them in) as well as the outer pinion bearing and seal so that you can put your new pinion in and tighten it up using the yoke. Dont use a crush sleeve at this point - you are only trying to get a good pattern.

Then drop in your carrier using the shims talked about earlier. THis can be pretty tight - preload is good on the carrier. Make sure you put on the proper left and right side carrier brackets. You need to measure your backlash here and get that right by adjusting the carrier shims.

Then paint your ring gear and look at the pattern. Again, lots of resources online on how to get this done but it will take multiple tries and adjustments of the pinion shims and carrier shims.

Once all is good, then you take out the pinion, replace the test bearing with teh new one and press it on. Finally you can install your crush sleeve and tighten the pinion nut. Note, this part sucks. If you crush the sleeve just a bit too much, you have to start over with a new one. And you should try to use a new pinion nut as well. All the preload specs are online for various applications, but you will need that inch pound torque wrench here.

You cannot take enough notes here on your shims and measurements.

[EscapeRacing]

Might as well change the u joints at this time as well. Just mark everything and be careful with reassembly to ensure no pins drop out or get damaged.

Look at where the fitting goes - make sure you face it out or it will be hard to add grease. Use tape to keep the u joint caps on until you press them in.

[EscapeRacing]

Last update for today - i used a harbor freight transmission jack to drop the old rear end and lift the new one.

[FormTA]

Great write up! Having done a few of these, I know what is involved.  Good job!

[highway star]

Great price on the Yukon differential!  I paid a lil over 500 for an Eaton Posi. I dig your cleanliness!
Just a heads up, on your new axles, check the fitment of the drum's inner hole to the outer pilot on the axle.
I ran into an issue with drums on Moser Street Axles, the axle pilot was smaller than the oem's axles, not allowing the drums to
snug on squarely, in other words, the drums would slide on but would drop down just a bit. and therefore induced a vibration.
I tried the oem drums and new drums. Moser would not rectify the problem, just said they would cut a pilot any diameter I wanted for the price of new axles! My temp fix was to wrap aluminum tape around the axle pilot until the drums squared up, no more vibration but will be reinstalling the oem axles.

[langss]

Great Write Up. Thanks For Putting This Up.

[EscapeRacing]

Thanks, for taking a look. More pics tomorrow. Managed to get the new rear end mounted and attached the driveshaft tonight.

[EscapeRacing]

Update!

The new rear end is officially installed and I went for a drive. I mentioned this in the "Today I..." thread but wanted to keep this thread in tact. As a reminder, this project was to build a new rear end and swap to 3.23 gears from 2.41.

I let it sit overnight before driving with all the brake fluid and gear oil filled to see if I would spring any leaks - all good there!

As far as the test drive, it felt really smooth and there is definitely a seat of the pants difference in the gearing. I really didn't get on the gas much, but it still barked going into second gear (TH350) and it never did that with the 2.41 gears.

Unfortunately, I still have some tweaking to do. The gears are "humming / wooooooing" on coast / deceleration so I have to adjust the backlash, pinion spacing, or pinon preload. Guarantee I will be starting with the easiest things first - backlash.

Also unfortunately, I used the yoke that came with the replacement rear end without checking to see if it fit my u-joints and, of course, it didn't. So, I had to remove that yoke after installing the rear end and put on my original yoke. That means removing the pinion nut which removes taking pressure off the crush sleeve. I didn't replace the crush sleeve when I put on the new yoke but I did use a new pinion nut and got the preload to about 20 inch pounds again but I realize I probably need to take out the pinion and do another crush sleeve which is a total pain.

Lesson learned a few times during this build - check everything before assembly. I had to go back and redo things a few times that I could have avoided with more patience.