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Need some help with gear pattern

Posted: Mon Feb 29, 2016 11:54 pm
by Ravensbud
Hi Jim - I'm in the midst of my first rear end rebuild. I've got a 1967 BOP 8.2 with 2.93 posi. Its original to my 1967 GS400. I'm just putting in the new bearings/races I bought from you and reinstalling the original carrier, ring and pinion but I'm having trouble with my pattern. I've increased pinion shim width 4 times now (by a lot!) and think I'm headed in right direction but figured I'd post some pics for confirmation....I didn't think it would be this difficult to reinstall my factory gears in original housing.

Here is a set of pics after the last shim addition (backspace and pinion shim width on pic). Each pattern was obtained with 12-15 in-lbs pinion preload and very snug carrier preload. I oiled all bearings with gear oil but not the ring and pinion teeth. I'm turning ring gear by hand and there's quite a bit of resistance so it should yield an accurate pattern.
I started with the factory .032 pinion shim and barely caught the edges of the teeth. I kept backlash at .007-.008 while adding pinion shim depth to increase gear mesh. I'm up to .065 and its getting better but I'm still not there! I thought a few thousandths would be all I needed. Am I on the right track here? (There are more pics over on V8Buick: ... ar-pattern)

I checked all the new bearings/races against the old ones before installation and everything checked out. I'm using the old pinion bearings for initial set up.

Any advice or insight would be greatly appreciated.


Re: Need some help with gear pattern

Posted: Tue Mar 01, 2016 7:27 am
by monzaz
Ok, So these gears were ORIGINALLY in this housing? Did you check the backlash before they were removed and it was a good running rear when you removed the gears . This .032 was the original shim with these gears in this housing?

NO rear had .065...So you need to take everything apart and start over.
Increase the backlash to about .010 until you can find the correct depth WHICH should be the original shim that was in there.

The pattern does appear to be too shallow...BUT other stuff can trick that pattern...
IS the carrier seated all the way in the bearing saddles? Install the carrier caps and run the bolts to tight ...They do not need to be torqued just install all the way down.
Do not over worry the pinion preload and do not use a crush sleeve YET. No seal yet either.... concentrate on the pattern that is all .

The coast side should get a good swipe and will be the best side to determine if you are in the correct place. drive side will usually look a bit deep if there is wear on the gear.

Make sure the carrier saddles are clean from debris and oil -

IF this truly was in the housing and running correctly you should only need to put bearings and races in use the original shim and make the backlash back to .008 .009 .010 at the most.

Re: Need some help with gear pattern

Posted: Tue Mar 01, 2016 7:29 am
by monzaz
would like to see the .032 pictures if you have them... Jim

Re: Need some help with gear pattern

Posted: Tue Mar 01, 2016 9:14 am
by Ravensbud
Yes these gears are original and it was running fine. .032 was original shim. Backlash was 0.0115 prior to disassembly. I'm not using a crush sleeve or seal yet.

I believe carrier is seated all the way in the saddles and yes I'm snugging up carrier caps before running pattern. I think carrier preload is ok as I'm having to tap the last shim in pretty hard and I really have to work to get the carrier back out by hand. Carrier shim on the ring side is .198 and OEM shim was .200. Housing was spotless inside prior to assembly.

All the pics are in that link on V8Buick, but here are the .032 pics:
As you can see I was barely catching the edge of the drive side and the lower corner on the coast side. Thanks for the help...I feel like it must be something simple I'm missing.

Re: Need some help with gear pattern

Posted: Tue Mar 01, 2016 10:37 am
by monzaz
Do you have a set-up bearing?

MAN that is WAY too weird.... NO rear sets up with .065 from GM.... Just crazy... well I am totally stumped :( There has to be something wrong...

Be absolutely sure your carrier is snug in the housing. YOU should not be able to pull it out by hand at all. J bar pry bar should be used. If the carrier tips even a little it will trow your pattern off...

I would say try a different set-up bearing and see what happens...???

Did you see what the pattern looked like before removal...will run a pattern before removing gear to be sure if we are reselling them they are good pattern runner it the rear was a junk yard not out of running car find.

After that run the .080 and see if that get the pattern in all the way...??? TOTALLY weird. ??? @*($&$#(@) Geez

Re: Need some help with gear pattern

Posted: Tue Mar 01, 2016 10:39 am
by monzaz
to me this still seems like a case of the carrier bearings not seating all the way in the carrier saddles...we get this with 12 bolt chevy rears all the time.

try to torque the bolts to spec too and see if the caps are seated to the case and your sure you did not mix the carrier caps from left to right..??? this is all just shooting in the dark questions...

Re: Need some help with gear pattern

Posted: Tue Mar 01, 2016 10:10 pm
by Ravensbud
By set-up bearing I assume you mean the old pinion bearings? Yes, I sanded those just enough that they slide on and off with some persuading. I don't have another bearing to try but I can't imagine why the old one wouldn't be sufficient...its in great shape.

I just snugged the caps to spec (60 ft/lbs) and the carrier bearings appear to fit the saddles perfectly. I marked the caps with a punch prior to disassembly so they're impossible to confuse. The new races also measure exactly the same diameter as the old ones.

Tomorrow I guess I'll start again at the beginning with a fresh eye, increase carrier preload so its pry bar tight, increase backlash to 0.010 and see where its at. I'm at a loss too.