Sad Discovery: GM 10 Bolt Fails

Ricko1966 · Mar 10, 2024

Buck69 said:
Hmm. It's probably been 30 years since I have been into an auto diff and only kind of remember playing with side shims. I do remember struggling with getting the crush sleeve to start to crush though.
Every diff since, including the one I am currently building for a 45T Volvo rock truck, have big nuts under the caps for adjusting carrier bearing preload and setting the backlash. My bad.

NBD at all man. I'm just to ease stress on the O.P. I've done a couple with the weird big nuts on GMC Yukon frt diff. Don't know if they are the same as Volvo. Pretty cool not needing 9000 shims for set up though, if they are the same as I'm thinking.

AZ Highlander · Mar 10, 2024

Thanks to @nvrenuf for the suggestion, I am also toying with the idea of pulling a 6 lug semi floater 14 bolts in the 88+ body style trucks from the junkyard here in town. I am going to put the cover back on the diff for now, fill it up with gear oil and only drive it short distances while I decide on what direction to go.
Keep commenting on what you would do. I really appreciate your suggestions

ChuckN · Mar 10, 2024

AZ Highlander said:
If it was your truck what would you do?
Look for another 10 bolt axle and check under the cover to ensure gears look decent? Search for something more durable? If so, what? Spend lots more for replacement parts installed?
Let me know why you would choose that choice too.

When I was looking for a truck, I was so excited to find one with a 12 bolt. Mostly because I was told that they were the cool ones when I was a kid.

Now that I own one, I’d almost rather have a 10 bolt 8.5. I see all kinds of offers on the Facespace Marketplace for 10 bolts. Stock take-offs, aftermarket stuff, you name it. Nothing for a 12 bolt.

I’d start there- if you can find one semi-local I’d go that route. If in good working order, it’ll me much cheaper than a 1500 dollar gear job (unless you have the skill to do it yourself).

Turbo4whl · Mar 10, 2024

AZ Highlander said:
Thanks to @nvrenuf for the suggestion, I am also toying with the idea of pulling a 6 lug semi floater 14 bolts in the 88+ body style trucks from the junkyard here in town. I am going to put the cover back on the diff for now, fill it up with gear oil and only drive it short distances while I decide on what direction to go.
Keep commenting on what you would do. I really appreciate your suggestions

Did you close this up and re-fill with oil yet? I would like to see a picture of the opposite side of the differential.

From what I can see, this differential has been apart before. Eaton makes the GM Govern lock. Eaton also sells a Govern lock, slightly different than the GM part.

Many second failures happen because all that metal can get in the axle tubes and they are overlooked when cleaning the housing. Right now the ring and pinion gears may be okay. If a larger chunk of the side gear or spider gear breaks off, it may trash the ring gear. Limit driving this if at all possible.

RaisedK5 · Mar 10, 2024

AZ Highlander said:
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Isn't that a gov lock? Can you get internals for those? Is it worth it? I'd probably rebuild it with an open carrier if you're not going to wheel it. Or a mild posi. But I wouldn't put money into a gov lock.

AZ Highlander · Mar 10, 2024

Turbo4whl said:
Did you close this up and re-fill with oil yet? I would like to see a picture of the opposite side of the differential.

From what I can see, this differential has been apart before. Eaton makes the GM Govern lock. Eaton also sells a Govern lock, slightly different than the GM part.

Many second failures happen because all that metal can get in the axle tubes and they are overlooked when cleaning the housing. Right now the ring and pinion gears may be okay. If a larger chunk of the side gear or spider gear breaks off, it may trash the ring gear. Limit driving this if at all possible.

Thanks @Turbo4whl
Will get a shot of the other side later, hopefully today when I Jack it up and turn a wheel. Yesterday was pure chaos and didn’t have time to button it up and refill yet. Must’ve been meant to be apparently. Having our first lambs of the season hit the ground yesterday made things even more interesting.

You must be registered for see images attach

mlparkey · Mar 11, 2024

I used to repair 1 or 2 differentials a week at the dealership. Most times, if the ring gear and drive pinion gear look okay and it's not making noise on straight ahead driving when accelerating, coasting and decelerating, the bearings should be fine and you should be able to get away with just replacing the spider gears. There's really no need to remove the carrier if you wash it out really well with some solvent.

AZ Highlander · Mar 11, 2024

@Turbo4whl
Here is 60 seconds showing the rotation two times.

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Craig Nedrow · Mar 11, 2024

That ring gear looks amazingly undamaged. Just to throw this out, a lunchbox locker replaces your spiders, and gives you a locker.

https://www.gmsquarebody.com/threads/1973-k20-350-to-454-swap.29840/page-3

This is a step by step method, this is a 14 FF, 12 bolt similar. Begins with post 38.

Blue Ox · Mar 11, 2024

Nothing wrong with that, if you want a locker.

I've regretted every locker I've owned except the Corvette. Sports cars, race cars, off-road,... all great. Most street applications, not so much.

Just be aware of what you're getting in to.

Turbo4whl · Mar 11, 2024

@AZ Highlander

Okay, very clear now. That is a Govern Lock differential where the locking (spinning) governor is missing. There would be a long pin with the locking part mounted where the two holes are inside the larger opening. One end of the pin has gear teeth that engage the small teeth on the side gear.

You must be registered for see images attach

All those parts are missing. That diff will no longer lock. Working as an open diff the smaller spider and side gears don't hold up well for high speed, one wheel spinning. (I didn't need to tell you that)

@Craig Nedrow Lunchbox locker's are to replace side and spider gears in the factory open diff. They will not fit this diff.

AZ Highlander · Mar 12, 2024

Turbo4whl said:
@AZ Highlander

Okay, very clear now. That is a Govern Lock differential where the locking (spinning) governor is missing. There would be a long pin with the locking part mounted where the two holes are inside the larger opening. One end of the pin has gear teeth that engage the small teeth on the side gear.

You must be registered for see images attach

All those parts are missing. That diff will no longer lock. Working as an open diff the smaller spider and side gears don't hold up well for high speed, one wheel spinning. (I didn't need to tell you that)

@Craig Nedrow Lunchbox locker's are to replace side and spider gears in the factory open diff. They will not fit this diff.

Thanks. That helps. What would you do now that we know that? Look for a complete new rear end? If so, avoid another 10 bolt?

Turbo4whl · Mar 12, 2024

AZ Highlander said:
Thanks. That helps. What would you do now that we know that? Look for a complete new rear end? If so, avoid another 10 bolt?

You don't need a new rear. You need a new differential. Buying used rear end could be cheaper, but what do you get? Another butched up potential problem?

If the gear set is okay, buy a diff. Buy new side bearings. I would also want to check and clean the pinion bearings, so at least a new seal and crush collar.

Check the backlash before you take it apart. Pull the axles out completely and clean the axle tubes. Clean and check the axle bearings, and where they ride on the axle.

Clean everything first, then buy parts. If you buy a used axle, you need to match the ratio to the front axle. Used axle, you probably need u bolts, how would the brakes be? Are they the same size? These trucks are old. Used parts are old or even older?

AZ Highlander · Mar 12, 2024

Turbo4whl said:
You don't need a new rear. You need a new differential. Buying used rear end could be cheaper, but what do you get? Another butched up potential problem?

If the gear set is okay, buy a diff. Buy new side bearings. I would also want to check and clean the pinion bearings, so at least a new seal and crush collar.

Check the backlash before you take it apart. Pull the axles out completely and clean the axle tubes. Clean and check the axle bearings, and where they ride on the axle.

Clean everything first, then buy parts. If you buy a used axle, you need to match the ratio to the front axle. Used axle, you probably need u bolts, how would the brakes be? Are they the same size? These trucks are old. Used parts are old or even older?

Thanks Wayne. Yes, that was what I was wondering. A “new to me” rear would be potentially worse than what I currently have. Also, I just completely rebuilt the brake system and got new tires. Would be nice to use those. It’s a 3.73. Got any recommendations for a new diff? Looks like it is time to start budgeting, measuring backlash, pulling it apart, cleaning, and then shopping. Would be nice to know what to budget for and how long it takes to save up while I’m working on disassembly.

gmbellew · Mar 12, 2024

GM85-TTGBK-GM 8.5" 10 Bolt / Eaton Detroit Truetrac Pos

www.quickperformance.com

This is what I had installed when my rear end went out.

Sad Discovery: GM 10 Bolt Fails

Ricko1966

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GM85-TTGBK-GM 8.5" 10 Bolt / Eaton Detroit Truetrac Pos

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