Just opened up my differential to see if I should rebuild before putting back togeather. It is obvious by the wear on the posi case that at one time it was hitting on the pinion gear. However there is no wear on the pinion gear (not shiney at all, just looks like it from the flash). I also put some grease on the posi case and rotated it and it is not making contact. It also appears that the unit was built at one time because of the single dot on the left hand cap and the 2 dots on the right cap. This is not how it came from the factory as I understand it. I hate to spend money rebuilding a unit that has already been gone through and is good to go. The clutches also look like they are in great shape. Any opinions or recommendations as far as what else to check to make a good decision? Checked my side yoke play and it seems good.

 

Just looked at my side yoke bearings and they are torringtons, anyone know if they are the stock bearings?

 

GTR1999 is the guy to ask. Do a search for his paper on re-building these diffs. He will probably chime in at some point, but I know first hand, he knows his stuff!!!

 

That 'shiny' area you show in the photos is not wear from the pinion...that is some "clean-up" machining of the rough castings that is done to assure clearance from interference of rotating parts. Obviously, you can't tell a lot about the condition of a differential from a few photos, but I don't see anything in the photos to be concerned about. More important would be the amount of 'play' in bearings/yokes and the running pattern of the teeth on 'coast' and 'drive' side of the pinion and ring gears. Someone with experience in evaluating these gearsets will have to touch & feel the hardware to make that assessment. My recommendation is to find someone in your local area that is qualified to make such an assessment and pay them a fee to check it out properly. That may be all it needs, if that unit has been serviced regularly and not abused during its life.

 

In the last picture it looks like the axle stub is gone. It looks like it is mushroomed over and needs to be replaced. Does it move in and out?All this metal is now floating around in the posi case and bearings. Yes a tear down is needed. You could probably get away with replacing the stub axle and flushing the unit but I would at least tear it down and clean all the debris out.

 

In the last picture I actually had one of the shafts out. Neither one is mushroom and both came out fine. I really think that this unit has been rebuilt at one point since the caps are marked and since I have had no real problems. I think I will put new gaskets and seals and run it. I had it in my car running low 13s behind a big block with no problems. I have read the threads on how to rebuild the differential but cant seem to find anything on what I need to check for before I put it back togeather. Anyone know what I need to check for other than cracks, wear and side yoke end play?

 

Oh yea. Looks much better with my glasses on. I should have put them on before posting this. Refill it with clean fluid and have at it.

 

Looks like a typical stock rebuild, which isn't saying much. someone was in there before as you noted the witness marks.
Can't see much from what you show but I didn't see any posi case marks from the pinion. The Torrington yoke bearings are correct,should be full complement no cage bearings.The yokes appear good, if there is no center drill hole in the face they are rebuilt yokes, most likely from Lonestar. The posi case is rough cast with the stock springs and plates.
The cheapest upgrade you can do now is to replace the hex head bolts in the cap with socket heads. Look at the shims under the caps, if it was a good rebuild you'll see steel shims, otherwise if you see solid cast shims those are factory. If they were tight,as they should be, they will break hammering in unless a spreader was used.
You can check the lash and pattern now. Look for uniform pattern and between 005-008 lash. Look at the side of the ring gear, if original you'll see GM, the tooth count,and date code on the side. If Richmond a doube DD, if US or Toms' a G logo,no logo- imported.
Good luck with it, use GM additive, lucas 85-140 oil and watch it if you continue to abuse it in that setup, it will break given enough abuse. I replaced many broken ones with engine HP under 400 but a lot of abuse and shock loading.

 

Had to go ahead and tear the whole unit apart. Did not like the noise I was hearing from one of the sides and turns out I had a bad bearing. No damage to the yoke or housing. Now it is time to be honest with myself and need some advice. I plan on putting a 496 with about 550 HP at the crank with a 125HP nitrous shot on this car.
3 questions:
1. What should I do now that I have had to take it apart to support these numbers?
2. Any suggestions if I need to replace the ring and pinion as to what ratio? Plan on using a TKO 600 with .64 overdrive. Current ratio is 3.55.
3. How do you get the bearings off the sides of the posi unit. Just broke my 2 jaw puller and the bad bearing still did not come off?

 

1. With 675 to 700 HP at the crank you will need some serious upgrades. The stock unit is just not up to repeated abuse with this kind of power.

2.With the TKO 600 I would stick right at or around a 3.55 ratio. That seems to work very well with the TKO transmissions.

3. Puller or press is the best way to get the bearings off.

Refer to Garys GTR1999 last 2 sentences. You are going to put a lot of stress on the rear with these power levels.

 

And the diffy is not the only area in the rear suspension that will need significant upgrades to operate reliably under that level of stress.