-78 rear end troubles - carrier bearing spun??

[Nut124]

Has anyone else seen this or fixed it?

I have blown two rear ends. They both failed the same way at hard launch with sticky tires. The carrier bearing journal shears off on the ring gear side.

Upon examining the damage I have found that the outer races of the carrier bearings had spun to the point where there is grooving wear on the outside of the race. I'm not sure if the spun bearings contributed to the failure or if some of the spinning happened after the failure while towing with tons of metal debris in the oil.





Nut124

[Nut124]

OK, this is what I did - let me know if you think this is crazy.

I used a cutting wheel to cut v-shaped grooves to the outer races. Then drilled and tapped a set screw hole in the bearing caps. Installed a tapered tip set screw. The groove in the race was aligned with the holes but the screw was not installed until after gear lash and bearing preload were set.

If this rear end blows, it will a different failure moe than the two previous ones.

Thoughts?

Nut124

[Sparky]

That does seem pretty crazy. First, there's no way you should be transferring enough torque to the outer race unless something has gone horribly wrong with the bearing.
Second, if you do want to keep it in place, I'd use a slip fit loctite retaining compound rather than creating future fracture points. I'd probably go with loctite 609.

[DieselSpider]

One would think that it would have to be the inner race spinning to cause the failure shown in the picture if that was indeed the root cause. Are you certain that the ring and pinion are being set in the correct relationship to one another or that the axle shafts themselves are not askew?

[gm404]

One would think that it would have to be the inner race spinning to cause the failure shown in the picture if that was indeed the root cause. Are you certain that the ring and pinion are being set in the correct relationship to one another or that the axle shafts themselves are not askew?

Yes, this is the inner race.
How do you, OP, set the preload of the side bearings?
BTW I see you have a Russian 10/43 gear set
The fine gap between the main gears is one thing, but parallel to that the preload of the carrier is to be set.
I am sure you know that is measured by the "widening" of the two bearing housings by 0.16-0.20mm. If the bearing caps are too firm, the bearings can overheat and rollers "glue" to the race instead of rolling.
Original tool can report both values at the same time.


Low tech method is to use a caliper, preferably not a manual, as on the pic, but a digital one to zero it in position w unloaded bearing covers.


It is also too indefinite to use the raw cast surface for the caliper. I use the calipers only on the head of the temporarily fixed clamp screws (just the screws) Either with one corner or a flat edge pointing to the side. That gives repeatable readings and can be sure of the correct value at the end.
Also it is generally a good idea to have the one and two legged clamps in proper quantity (2-2 from each) so that you don't need to overtighten the bearing cap nuts just for the sake of being able to fix them.

[Odoyle]

I can't speak on whether or not your repair will suffice, but what you can do is make sure; your lubricant is "SAE 80W/90 EP (extreme pressure) gear oil 1.4 quarts". One of easiest way to mess up a diff is with wrong lubricant.

[Nut124]

Hello gm404,

I do have the factory manual but not the original tool. I used the 2nd method exactly like you you described, slide caliper on the bolt heads. I worked on it pretty hard and I am comfortable with the bearing preload - we'll see if that is warranted.

When you talk about the bearing caps being too "firm", do you mean too much pre-load or are you implying that the ID of the split outer journal bore could be too small?

Yes, I ordered a complete pumpkin on eBay - may be yours? And the LSD from Russia.

Do you think the russian gears will hold up? My car has ~130+HP and is driven hard.

Nut124

[gm404]

Hello gm404,
When you talk about the bearing caps being too "firm", do you mean too much pre-load or are you implying that the ID of the split outer journal bore could be too small?

I have though on too much preload. It can develop tremendous heat and act and eat up metal like no oil on it at all.

Yes, I ordered a complete pumpkin on eBay - may be yours? And the LSD from Russia.
Do you think the russian gears will hold up? My car has ~130+HP and is driven hard.

Recently one rebuilt pumpkin with Torsen LSD went to PA another one to CA. It is possible you are one of the two guys.
I am sure the gears will hold up. I insisted the maker to send me the enforced type.

And here one curious russian animal I saw so far only on picture and video. A locker type called DAK, that cycles a ton of bearing balls in a closed loop and has no preload at all.

[Nut124]

Recently one rebuilt pumpkin with Torsen LSD went to PA another one to CA. It is possible you are one of the two guys.
I am sure the gears will hold up. I insisted the maker to send me the enforced type.

This one was a plain 10/43 pumpkin ordered in May 2016 from gm404 on ebay.

The LSD I ordered separately.

I may take an another look at the preload and make sure it is not at the high end of the range.

Do you do the yoke spin torque test? I did but cannot recall the results other that they were in the acceptable range.

[gm404]

Recently one rebuilt pumpkin with Torsen LSD went to PA another one to CA. It is possible you are one of the two guys.
I am sure the gears will hold up. I insisted the maker to send me the enforced type.

This one was a plain 10/43 pumpkin ordered in May 2016 from gm404 on ebay.

The LSD I ordered separately.

I may take an another look at the preload and make sure it is not at the high end of the range.

Do you do the yoke spin torque test? I did but cannot recall the results other that they were in the acceptable range.

OK, that was me
The spin torque tool I don't have yet, but I could fabricate one with a piece of iron and a spring load fish scale.
https://www.enasco.com/prod/images/prod ... 09797l.jpg
So far I trust instead on my hands. I have checked how much twisting force that prescribed preload on new bearings would mean. It is like wringing out a thick wet piece of cloth or a towel. On used bearings (those ran more than 30km) the value drops significantly, to one fifth as memory serves. On rare occasions I rebuild diffs with used bearings, and set them accordingly with less preload on the pinion gear.
Btw. I have about 5 complete sets of used but perfectly good bearings, taken from renewed diffs. I would use them on my own car, but I build diffs for sale and promise people all bearings, and these just remain on me. They are too good for the trash, so I intend to make 1USD ebay auctions with them, as an advertising measure.