I just picked-up a 9-bolt axle assembly out of a '88 GTA with 100K miles to replace the one in my IROC with 170K miles. My IROCs diff was making some serious growling noises due to what I believe is a bad pinion bearing.

When I removed the diff cover from the GTA axle, I saw something nobody ever wants to see... broken bolts swimming in the old gear lube at the bottom! Specifically, 2 of the case half bolts had broken. It looks like one of the bolts came completely loose and was bent and broken. Another bolt apparently broke as well and was bent, yet left some threads inside the case. I checked the ring gear and pinion gear for damage and there is none that I can see. All the teeth are intact and have no scars, pits, or burrs. The broken bolts appear to have been isolated from the gears, which prevented them from being damaged. The guy who sold me the axle assembly said the rear worked fine and produced no gear whine.

At this point I have 2 rear axle assemblies, both with damage that need repair. I am leaning toward fixing the one with the broken bolts since the bearings in it appear to be fine. It is a simpler job to remove the differential, fix the bolts, and put it back in than to redo all the bearings, etc. How concerned should I be about the fact that the diff had broken bolts in it? Is there anything else beside the ring and pinion gear that I should look at for damage?

Should I bit the bullet and rebuild my original rear end with the bad bearing instead?

Any comments or suggestions are greatly appreciated.

Thanks.

 

Do you mean the bolts that hold the caps on? If so, something bent them. I would be cautious of using anything in it.

 

I am talking about the small bolts that hold the 2 halves of the carrier case together.

 

He means these:



Someone probably worked on the diff and didn't tighten the bolts down in steps and in sequence so one of them must have been overtightened (the one with the broken threads) and the other maybe not tight enough?

 

Yep, those are the correct bolts. Twin_Turbo, what you are saying makes sense. One too tight, one not tight enough. I can use some of the bolts out of my other diff to replace the broken ones. It would be nice if I could just purchase some new bolts instead, and sell my old diff.

Is it OK to replace the bolts with any I can find in the same size, thread pattern, and torque rating?

Thanks!

 

I don't see why that would be a problem. Just torque the thing down in a star like pattern and make sure the case halves are seated properly before final torquing them down.

 

Ah, ok. I would still look around though. You said that the bolts were bent and broken. They would have had to grab something spinning to bend.

 

I'd like to replace some of the other bolts since they may have been over-torqued and weakened. The marking on the bolt head reads 12.9, indicating a metric bolt of 12.9 grade. Does anyone know the specs of these bolts and, most importantly, where I can but some new ones?

Thanks.