1991 GMC Suburban Rear Dif Trouble

Old 10-02-04, 09:13 PM
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1991 GMC Suburban Rear Dif Trouble

I own a 1991 4X4 GMC half ton Suburban and this weekend I went to change my rear wheel bearings. I removed the rear dif cover and took out the rear pinon set screw. Here is where I found the problem the previous owner had snapped off the pinon set screw inside the rear pinon. I mean all of the threaded portion of the pinon set screw is in one piece except maybe the last piece of the thread. Now this set screw is wedged inside the pinon and I have found no way to get it out. Can anyone think of a way to get this out? I tried to use an EZout with negative results. So now I have no way to release the rear axles to change out the seals and bearings (and one of them is way shot). I am running out of time and am in dire need of help before I have to take the beast to a shop. Any help would be greatly appreciated. Thanks,

Old 10-03-04, 06:34 AM
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Matt try these ideas on your broken stud


I will be honest, I searched the net for a diagram of the Pinion Set Screw for my own education and was unsuccessful so the following is based on the fact that you can access this broken stud. (You have said that you tried an Ezy Out, which suggests you are able to get to the stud).
Mail a jpg or diagram if the following does not help.

Try the following and hopefully I am on the right track -

1 - Broken Studs can sometimes be shocked and loosened if you use a punch
and give the stud several sharp hits with a hammer, this can loosen the bond between the threads.
Loctite recommend this procedure if you are undoing a Loctited Bolt or Nut, it literally shatters the Loctite. Then try your Ezy Out again.

2 - If this fails you can try (Arc Mig) Welding. Find a suitable nut and weld this onto the end of the broken stud, the heat from the welder usually causes the stud to expand and then contract as it cools down which lets you undo the stud with the nut you have welded on.

In some cases you have to build up weld on the broken stud and then knock your nut on and weld it as it can be tricky getting a good weld initially.

Please Note

- Disconnect your battery before welding. (Obvious)

- Place your earth as CLOSE to the broken stud as possible as earth current can run through your driveline, Engine etc and leave Hotspots on Bearings, Gears etc so you eliminate this danger by placing earth at the stud.

- Have a Fire Extinguisher or Garden Hose ready and with you in case of Fire.(Obvious)

- You need to keep your Diff and Housing as clean as possible so, wet rags, and pack them into the housing to prevent Welding Slag etc from covering your diff. Wash out your housing after your finished just to be on the safe side.

3 - If this fails you may have to resort to drlling the stud out, if you are very careful, use a drill that is just under the size of the Studs shank, so you dont damage the thread in the hole but you will remove the bulk of the stud allowing you to clean out the stud hole and thread using a Tap or picking the thread out with a sharp pointy instrument.

Make sure that your initial pilot hole is Centered as if you drill off centre you will damage the threaded hole. I realise that you have already drilled.

Hope you Win

Old 10-03-04, 11:34 AM
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when ive encountered this problem I was able to use a small pick and continue to twist the locking bolt out after tapping on the center pin slightly one direction or the other to get the locking bolt out of a bind.
hopefully you didnt mess up anything when you drilled the bolt for an attempt at using a very small easy out.
alot of parts stores carry a replacement locking bolt for gm differentials if they carry motormite or help brand products they will likely have one.

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