Carrier Scarred by Thrust Washer--Help

[Hugh G.]

[Joe L.]

Re: Carrier Scared by Thrust Washer--Help

New to NCRS but a long time Vette owner. Could not find information on my particular situation. I’m rebuilding my 1968 BB-390 differential. Three things popped out: 1-pinion bearing had excees play (~1/32); 2-pinion bearing shot (this and two dry u-joints probably accounts for the noise(s)) and 3-one of the trust washers has been turning marking the Carrier case seat!
Searched the internet and have not found shims for this situation. A vendor told me that if I was not planning to drive my Vette under severe conditions to clean up the marks on the case seat, install a new thrust washer and not worry about it. Other wise buy a new posi housing! First, I’m hoping the Vendor is correct, second is there such a thing as shims for improper fitting thrush washers? I'm one of those 500 miles (on this car) a year guys. Hugh

Hugh------


Gary Ramadei, a frequent contributor to this board, is going to be the best source of advice for you on this question. Hopefully, he'll see this and respond.

[Gary R.]

Re: Carrier Scarred by Thrust Washer--Help

Hi Hugh, Joe
Can you post or send me some pictures? Wear on the posi case pinion seat is not common, the older diff's used a brass thrust washer but by 68 they were steel. The sizes vary only a little on new washers and I think that is just from metal used vs having a selection available. I used to measure all the new washers when them came in so I could keep the same size in the case. I found they were only off 001-002"

Was there a washer in place when you disassembled it?

If the case seat is chewed up then your only option would be to replace the case but again it is rare. When I build a posi I don't use the springs and plates. As a result the lash is -0- in the spiders and the pinion and sides gears are tight in the housing and I have never seen an issue with the side or pinion gears including the thrust washers.

Now if it's not too bad and since you don't really drive it much you probably can rebuild it but I would like to see it first.

As far as the diff, other then the stamping and the "HD" axles there is no difference inside the diff between a SB diff. I often see diff's list as HD BB as if there were special parts used in them. Your 390 gear would either be a GM counter part or Richmond aftermarket set. You can tell by looking at the stamping on the OD of the gear the mfg,ratio, and date.

[Steve G.]

Re: Carrier Scarred by Thrust Washer--Help

Very difficult to measure the scoring, so what you want to do is look at the amount of play/lash in the spider/axle gears. That is really the only consequence of the wear. If the housing hasn't been gouged to the point that the lash between these gears is excessive, don't worry about it. Replacing all of the thrust washers will reduce total lash in assembly, which is all you care about.

I doubt very much that the carrier has worn to the point of being a problem.

Steve

[Hugh G.]

Re: Carrier Scarred by Thrust Washer--Help

Hi Hugh, Joe
Can you post or send me some pictures? Wear on the posi case pinion seat is not common, the older diff's used a brass thrust washer but by 68 they were steel. The sizes vary only a little on new washers and I think that is just from metal used vs having a selection available. I used to measure all the new washers when them came in so I could keep the same size in the case. I found they were only off 001-002"

Was there a washer in place when you disassembled it?

If the case seat is chewed up then your only option would be to replace the case but again it is rare. When I build a posi I don't use the springs and plates. As a result the lash is -0- in the spiders and the pinion and sides gears are tight in the housing and I have never seen an issue with the side or pinion gears including the thrust washers.

Now if it's not too bad and since you don't really drive it much you probably can rebuild it but I would like to see it first.

As far as the diff, other then the stamping and the "HD" axles there is no difference inside the diff between a SB diff. I often see diff's list as HD BB as if there were special parts used in them. Your 390 gear would either be a GM counter part or Richmond aftermarket set. You can tell by looking at the stamping on the OD of the gear the mfg,ratio, and date.

I will not be able to get pictures until next Wed. The unit is at my friends who is helping my with this project, doing it alone is above my pay grade. The grooving is on the housing and thrust washer, one side only. The car sat for 15 years (mostly in AZ) and I only drove it around the block since getting to run and drive. Are you referring to the spring that hold the spider gears and the plate the posi clutch plates? Thank you for your quick response. Hugh