Oh, boy, more problems - Rear Differential

[Matt Wilson]

Here I am posting again. This time I'm having differential problems.

I removed the rear differential to replace the gasket, which was leaking. When I got the diff out, I found one of the ring gear bolts had broken, head popped off. Amazingly, no other damage was done. I got lucky.

Has anyone else ever seen this happen? My biggest concern is what may have caused it. Sure, I could replace the failed bolt, but I'm worried it may happen again, and possibly with worse consequences.

[DavidGB]

Matt,
My guess would be that someone had previously been at it and over tightened that bolt. The leaking gasket further suggests this. You may wish to replace the rest of the bolts and torque to specification. I am no expert on differentials but have pulled many out over the years and have seen a number of ruined ones but none with that type of failure.
DavidGB

[W_A_Watson_II]

I've found the same broken bolts, multiple in the same differential, with others loose. So in my case, I'd say they were not properly torqued, and the locking plates not properly used. I had damage from either them or the carrier pin that were also out.

Good luck,
Will

[Gordon Maney]

Usually in an instance of a broken ring gear bolt it is the result of numerous bolts first loosening, then the ring gear getting worked against the loose bolts. There is a first one to break. Continued use then shears more. You are fortunate you found it when you did. Ultimately there is a catastrophic failure.

[Charles Talbert]

Gordon has the correct answer

It's bolts that have worked loose that break. Several reasons why this happens and it is fairly common.

First off, these original bolts are ungraded and should never be reused. They stretch, threads pull and strip, etc, etc. If old bolts and nuts are reused, you are absolutely setting yourself up for heartache.

I strongly suggest replacing the bolts with new grade 8 fasteners, and center locking grade 8 nuts. Torque the nuts evenly to 38 ft. lbs., and no more. Use RED lock-tite on the threads.

One thing that is often over looked is that once bolts get loose and are run for a while that way. The bolt holes in the carrier flange become deformed (enlarged) and out of round. The bolt holes in the ring gear are not affected very often (maybe in severe cases) since the gear material is hardened and is much tougher than the carrier material. Once the holes are out of round and the bolts no longer can retain the snug fit that was intended, the possibility of some movement occuring between ring gear and flange during normal operation still exist, even with new hardware, as a result of the loss of a good bolt fit. This will allow the possibility of bolts being sheared off if the movement is enough, or it will certainly promote the loss of bolt torque starting the original process all over again. This situation calls for replacement of the carrier assembly as there is really not a good way to repair the worn holes. If new gearing is installed on a flange with worn bolt holes, chances are the same issue will come up again; and unfortunately there is a huge possibility that it may go undetected until a major failure is realized. And trust me; if this happens, it will very likely be major in both damage and $$.

My best advice is to check the flange bolt holes very carefully for oversize and out of round condition if you have found the broken bolt issue. Replace with new grade 8, 3/8" fine thread hardware even if you see no signs of this or problems with the original bolts. NEVER reuse old ring gear bolts and nuts!!

[Gordon Maney]

It's bolts that have worked loose that break. Several reasons why this happens and it is fairly common.

First off, these original bolts are ungraded and should never be reused. They stretch, threads pull and strip, etc, etc. If old bolts and nuts are reused, you are absolutely setting yourself up for heartache.

I strongly suggest replacing the bolts with new grade 8 fasteners, and center locking grade 8 nuts. Torque the nuts evenly to 38 ft. lbs., and no more. Use RED lock-tite on the threads.

One thing that is often over looked is that once bolts get loose and are run for a while that way. The bolt holes in the carrier flange become deformed (enlarged) and out of round. The bolt holes in the ring gear are not affected very often (maybe in severe cases) since the gear material is hardened and is much tougher than the carrier material. Once the holes are out of round and the bolts no longer can retain the snug fit that was intended, the possibility of some movement occuring between ring gear and flange during normal operation still exist, even with new hardware, as a result of the loss of a good bolt fit. This will allow the possibility of bolts being sheared off if the movement is enough, or it will certainly promote the loss of bolt torque starting the original process all over again. This situation calls for replacement of the carrier assembly as there is really not a good way to repair the worn holes. If new gearing is installed on a flange with worn bolt holes, chances are the same issue will come up again; and unfortunately there is a huge possibility that it may go undetected until a major failure is realized. And trust me; if this happens, it will very likely be major in both damage and $$.

My best advice is to check the flange bolt holes very carefully for oversize and out of round condition if you have found the broken bolt issue. Replace with new grade 8, 3/8" fine thread hardware even if you see no signs of this or problems with the original bolts. NEVER reuse old ring gear bolts and nuts!!

Charles, what do you mean by center locking nuts ?

[Charles Talbert]

There are 3 common types of self locking nuts. The cone shaped crush type nut which must have at least a thread or 2 protruding past the nut for it to work properly, the ny-lock type which uses the nylon insert on 1 end of the nut to provide the interference fit, also requires protruding threads, and the center lock type. This type looks exactly like a common hex nut, but is crushed slightly in the center of the nut. Since the interference area that does the locking is in the center area of the nut, flush thread engagement is acceptable without protruding threads. This is by far the best for the ring gear mounting application. Protruding bolt length is not good here. We have used this set up for years without a single issue to date, so I feel confident with it. I have had issues when original bolts were reused, not a pretty picture.

[Matt Wilson]

Wow, I did not realize the original bolts were ungraded. I can't believe Dodge didn't use something a little better. Not disputing what you said, Charles, just expressing my surprise and disappointment.

Folks on Joe's forum made the same recommendation to use Grade 8, fine thread bolts and nuts. I will do so, and I will look for the center locking nuts. Hopefully I can find the nuts at Home Depot or Lowes, but if not, I will go to a fastener retailer. Do you recommend I cut off part of the head of each bolt in order to somewhat replicate the "half-round" head configuration of the original fasteners? That may be the only choice if there is not enough room for the full head.

Last night, I looked more closely at the bolt hole in the ring gear and in the hole on the diff case, and they are in perfect condition, like new, but there is a visible misalignment. It could be, like Charles and Gordon suggested, that the other bolts are loose and the gear was beginning to work its way around, or it could be the they were misaligned when the gear was installed. I installed the new ring and pinion (4.89) nearly 20 years ago, and I would like to think I would have noticed and corrected any misalignment, but maybe not. But more than likely I probably did re-use the same bolts, not knowing any better.

I learned something here, and fortunately, so far it seems that I may have not had to learn it the hard way, although I still have the remaining bolt holes to examine before I will know for sure if I'm getting off easy or not.

By the way, when I installed the ring & pinion so many years ago, I used red Loctite and it appears I used a center locking nut. How difficult will it be for me to get the nuts off the remaining bolts? Red Loctite is supposed to require special tools or heat, or both, isn't it?

Thanks once again....

[Charles Talbert]

Forget the big box store for the center locking nuts. McMaster-Carr has them or other specialty fastener outlets. Don't go for imports, get top quality US made nuts and bolts. Yes one side of the bolt will have to be machined off, we do that with an end mill. Don't remove any more head material than is absolutely necessary, as you want all the possible strength remaining in the fastener you can get..

[Cheyenne Dave]

The "center locking nut" also goes by the term "prevailing torque nut". Our Cheyenne NAPA keeps them on the shelf.

CD

[Matt Wilson]

Thanks, I will be getting these fasteners - after I verify (hopefully) no damage to the other holes in the gear and differential case.

I will also be replacing all ring gear bolts in the front differential.

[Charles Talbert]

Thanks, I will be getting these fasteners - after I verify (hopefully) no damage to the other holes in the gear and differential case.

I will also be replacing all ring gear bolts in the front differential.

That is a smart move.

[Matt Wilson]

Charles, I looked at the McMaster-Carr website and found that any 3/8" bolts shorter than 1-1/2" length are fully threaded (no shank). Is this what you use? I would prefer to use bolts that have a smooth shank at the interface between the ring gear and the diff case. Although it shouldn't matter in theory, since the bolted interface relies on friction rather than shear resistance of the bolts to prevent the slippage between the two parts.

I guess I could buy longer bolts and cut them down.

[Charles Talbert]

Charles, I looked at the McMaster-Carr website and found that any 3/8" bolts shorter than 1-1/2" length are fully threaded (no shank). Is this what you use? I would prefer to use bolts that have a smooth shank at the interface between the ring gear and the diff case. Although it shouldn't matter in theory, since the bolted interface relies on friction rather than shear resistance of the bolts to prevent the slippage between the two parts.

I guess I could buy longer bolts and cut them down.

If I recall correctly, I think the bolts we use are 1 1/4" long. They are "Lake Erie" grade 8, fine thread. The Lake Erie style has a heavier head than the common standard grade 8. The head is marked LE along with the six marks that are typical to grade 8 fasteners. You typically see this type of bolt used on CAT heavy equipment.

I looked into having original bolts duplicated in grade 8 stock several years ago. Would have had to buy thousands before the folks would even consider making a run, and the cost would have been off the charts expensive, so we looked at other alternatives. We have had 0 problems using these, they are a definite improvement over the ungraded originals.

[Frank Irons]

Charles, I looked at the McMaster-Carr website and found that any 3/8" bolts shorter than 1-1/2" length are fully threaded (no shank). Is this what you use? I would prefer to use bolts that have a smooth shank at the interface between the ring gear and the diff case. Although it shouldn't matter in theory, since the bolted interface relies on friction rather than shear resistance of the bolts to prevent the slippage between the two parts.

I guess I could buy longer bolts and cut them down.

Matt,

Check with Mopar for bolts for the 9 1/4 ring gear axle. Paul Caudell was putting together axle rebuild kits for the Power Wagon and I remember him saying that he got the bolts from Dodge. I would try to find actual ring gear bolts instead of hardware store bolts. You could also check with Spicer to see if there is a similar sized ring gear bolt.


Frank