Differential repair


Old 07-06-09, 09:18 PM
Thread Starter
Join Date: Jan 2009
Location: CANADA
Posts: 53
Differential repair

1989 GMC Van, 3/4 ton, 5.7 l (350 cu in) engine, conventional differential
Hi, I opened a differential because there was a whining noise when cruising at 80km/h. I found one of the pinion gears has a broken tooth and several others teeth are pitted. I took both pinion gears out, the other looks fine. I also checked the side gears (the ones driving the axels) they seems fine as well a crown gear. I phoned around and I was told by GMC dealer that they sell an o/h kit for $ 1,000.- but non is available across Canada! They suggested to ask an independent "rear end" supplier to get a pinion kit.
Do I have to replace all gears at once or is it ok to replace only the damaged one? Also do I have to adjust/shim some clearences? What to watch for?
Thanks for a reply! Danigo
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Old 07-07-09, 03:32 PM
Join Date: Jun 2008
Location: Eastern Georgia
Posts: 486
There is only one pinion gear in a standard differential, I suspect the gear you are looking at is a spider gear. The ring and pinion are the 2 biggest gears, then there are 2 axle gears, on the end of the axle, and the spider gears which mesh with the axle gears. You need to change 2 axle and 2 spider gears together as they have a wear pattern with each other. As for shims, if you put the existing ones back in the same place you will be fine. It is not very common for those gears to cause a whine as they do not turn when you are driving in a straight line, whining noise is usually caused by the ring and pinion set, and replacing these requires special tools and procedures, better to look for a used rear axle assembly in a scrap yard.
Old 07-08-09, 08:16 PM
Join Date: Jul 2009
Location: Washington State
Posts: 312

Twister nailed it If its whining at a steady speed and a broken tooth on the spider gear those parts had to go some place most likely threw the ring and pinion and bearings I'll bet there are grooves cut in both and the bearings are pitted as well.
As for a do it your self rear end job you will be better off getting a whole rear end from a wrecking yard. The special tools required are pricey and I'll bet it's a limited slip rear end also. I have aprox $900 USD tyed up in mine just to do the job [email protected] shop I know you could get a used rear end for cheeper than that. Just make sure the ratio is the same or you will be dealing speedo problems as well.But if you want to do it yourself you will need at least a torque wrench that goes to 300 ft lbs (Pinion nut gets from245 to280) A ball micrometer with a magnitic base(to set back lash) and a differential case spredder(The shims have to be that tight) and an inch pound torque wrench(to set bearing preload) You will have to take the componants to a shop to have both pinion and carrier bearings pressed on.Good Luck

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