I am baffled!

[maggie8264]

My front left hub was leaking at the input seal. But when I went to change, the bolt holding the half shaft in the hub was tight and rounded off. I wasn’t able to remove, so I took it to a local shop. They got it out and replaced the seal and discovered the two boots on the half shaft were torn. I bought a new half shaft which they installed. However they called me today and said the bolt holding the half shaft in the hub would back out when in reverse. Said everything was installed according to specs. I am baffled as to why.

 

[Mogman]

That is really strange, there is no twisting or turning of that bolt under normal conditions, it simply prevents the shaft from backing out
UNLESS you bought a 10K shaft and are trying to install it in a 12K hub, IS THAT POSSIBLE???
What model truck do you have and where did you get the shaft and what was the part number??

 

[maggie8264]

I have a 1989 M998. Part #12342974-3

 

[Mogman]

I suppose it is possible someone swapped the hub, it was driving before yes?
Did you buy it from GP or an individual?
Can you post a picture of the inside CV joint of the old shaft??

 

[Mogman]

That would be the correct part number for a 1989 M998, having a 12K hub is the only thing that makes sense given what the shop is reporting...
It is possible if you have 10k hubs that the splines are worn out but that would be obvious when you tried to drive it.

 

[maggie8264]

I suppose it is possible someone swapped the hub, it was driving before yes?
Did you buy it from GP or an individual?
Can you post a picture of the inside CV joint of the old shaft??

It drove fine before. Bought from eBay. Truck is still at the shop.

 

[Mogman]

Heck it might not even be a M998, data plates get swapped all the time, does it have V belts or a serpentine fan belt?

 

[maggie8264]

Heck it might not even be a M998, data plates get swapped all the time, does it have V belts or a serpentine fan belt?

It has v belts.

 

[Mogman]

Well the next thing to do is to compare the splines of the old shaft to the new shaft, at least that is all I can think of.
Also the inside CV joints look quite different between the 10K and the 12K shafts, you can look at those without having to pull the new shaft.

 

[maggie8264]

Well the next thing to do is to compare the splines of the old shaft to the new shaft, at least that is all I can think of.
Also the inside CV joints look quite different between the 10K and the 12K shafts, you can look at those without having to pull the new shaft.

Thanks, mechanic said shafts look identical, splines are the same. I am going to stop in there tomorrow. Will let you know what I find.

 

[Mogman]

Please do as that is just plain weird!

 

[86humv]

3 different shafts....

 

[Dieselmeister]

Check the washer that the bolt goes through to hold the shaft in the gear. If its deformed (or the wrong washer), and binds against the housing, it could cause the bolt to back out when reversing. Also check the distance between the bolt head, and the hole plug. Compare the left and right side. The washer should only make contact with the shaft and the gear.

 

[TOBASH]

Use blue Locktite! Some might even use red.

 

[maggie8264]

Update, after visiting the shop, the spline on the half shaft will turn inside the drive gear. Does that mean it is a 12K hub? The part number on the hub is 5574615-R, I think that is a 10K hub. Could a 12K drive gear be installed in a 10K hub? Attached pic of passenger half shaft and left hub number.

 

[Mogman]

The hub housings are the same, the only difference is the "input" pinion gear.
Do you have a picture of the old left side halfshaft?

 

[Mogman]

Have them inspect the splines on the input gear, also have them pull the magnetic drain plug, if that is a 10K gear and the splines are gone then there would very likely be allot of metal on the drain plug.
The picture you posted is a 10K or 7K half shaft, same thing basically.

 

[maggie8264]

Have them inspect the splines on the input gear, also have them pull the magnetic drain plug, if that is a 10K gear and the splines are gone then there would very likely be allot of metal on the drain plug.
The picture you posted is a 10K or 7K half shaft, same thing basically.

The splines on the input gear appear to be fine. So, I'm thinking I must have a 12K input gear in my 10K hub. Will a 12K half shot bolt in?
First two pics are the old shaft, last one is the new one. Both of these shafts are too small to fit the input gear.

 

[Mogman]

Yes if you have a 12K hub an A2 half shaft will bolt up, I have not seen that particular half shaft, the inside CV joint is usually ether perfectly round or triangle shaped, that one is a little different, comparing the splines should tell you, the 12K has a larger dia. splined shaft.
I doubt the casting number is a valid way to say you have a 10K hub, as they all used the same housing, at least the basic (what your truck is) the A1 and the A2 (12K) hubs all use the same housing, not sure about the REV trucks etc.
But again comparing the splined shafts should reveal if you have a 12K hub or not

 

[biscuitwhistler37]

Maybe @Retiredwarhorses can shed some light on this, if anyone aside from everyone already on this thread is going to know or have experience with an oddball HMMWV issue like this I think it'd be him. I would try the washer thing mentioned earlier myself, seems the simplest place to start.