Ford 8.8 broken shims

[Junkhead]

I just pulled the cover on my 8.8 for a fluid change and found a couple broken shims on the driver side. Any ideas what would have caused them to fail? And how would I go about fixing the problem?

 

[Mach2nh]

Looks like someone didn't use the shim pack holder thingy. Instead just put the shims in lose. So when the bearings break in and the tension is taken off the shims fall out like what you have.

 

[Junkhead]

Is it possible to just pull the shaft and replace the bad shim pack without tearing the whole thing apart? Everything else in there is tight and looks great and the fluid that came out wasn't too bad either.

 

[Truckedup]

Hmmm....At this point you MAY want to to pull the caps,remove the carrier without mixing the shims and have a look at the bearing races. Then if ok put it back together with the same size new shims on the left side and check backlash and gear pattern.
Or just replace the shims and call it good ...

 

[Junkhead]

I'm still stumped as to how they came to be like that. I was able to pull them out and they all have two clean breaks and missing a little less than 1/4 of the circumference. They were all still wedged in there pretty good and I don't think the backlash was off by much so I'm not going to pull the races. I'm not positive on the miles but based off everything else I've seen on the rig I don't think theres more than 10k miles on the rear end after it was rebuilt and regeared. Whoever put the rig together wasn't very skilled and the next owner was a little clueless so the simple issues it had kept it off the road.

Now that I think about it what are the chances someone was extremely challenged and cut the shims to fit past the shaft instead of doing it the right way? There really shouldn't be any shearing force on these shims at all and they aren't brittle. In fact the only failures I've found are from people getting too aggressive with a hammer while installing.

 

[RWKHausSupply]

There are three different kind of shims for that.
Stock - Where they are one solid shim and $$$

Super Shims - like the below reg shims but stepped so individual cant fall out separetly

and then just shims -

Those you have there are just reg shims. Nothing wrong with them, but the preload was way loose and allowed them to slide out, but the axle in side is still holding them in a bit...

 

[RWKHausSupply]

Oh and the splines on the shaft likely ground away the shim(s) and why they are missing in areas...

 

[Junkhead]

Thanks for the info on the shims and the likely cause. Theres a trans/diff shop maybe 3 miles down the road and I'm going to go see what they recommend as far as fixing it. Do you guys think it would be safe to refill and drive it that far if they offer to fix it for a reasonable price?

Heres a picture of the shims that I pulled out for reference.

 

[Truckedup]

Looks like someone didn't use the shim pack holder thingy. Instead just put the shims in lose. So when the bearings break in and the tension is taken off the shims fall out like what you have.

I do differential work on Dana and GM but never a Ford 8.8.....The carrier pre load isn't supposed to go away when the bearings break in. And roller bearings don't have a break in that I know of. In fact the bearings of differentials with years of use with still have a decent preload when disassembled for gear changes. GM rears have the shims on the outside like that Ford and when they spit out it's because of bearing failure or improper assembly.

Don't drive it until it's fixed.

 

[Junkhead]

Well I decided to let the shop pull it apart and fix it the right way. I don't know differentials enough to monkey with it, and it would take me days just to get parts in anyways. They quoted me 4 hours labor + parts which isn't too terrible as I think I caught the problem before it became something major. Best part is they think they'll get it in and done tomorrow. Also $50 for a 3 mile tow, but thats a whole lot cheaper than trashing a carrier trying to drive it there.

No fun having to spend a bunch of money, but it could be worse right.


Edit: There wasn't any noise coming from the rear end so I'm going to assume it was improper assembly, but we'll see when they pull it apart if the bearings are bad. I had a 99 WJ and lost a carrier bearing while doing 50 mph and it trashed the entire rear end. I'm glad I caught this before that happened again.

 

[Junkhead]

I stopped by the shop today and got some good and bad news. They said it looked like poor installation and new bearings and shims should be all I need. But he also was concerned by the number of shims they had installed on both sides so he's getting a second opinion from a mustang guy. He seems to think maybe the wrong carrier was used but it should be the one that was in there from the factory. Also the ring gear teeth were ground a little so the pinion shaft would fit, whats up with that?

Oh and they informed me that I only have one shock on the rear, I didn't even notice.

Edit: According to Google theres only one carrier for the 8.8 and the larger gears use a stepped pinion shaft to clear the teeth, but grinding the inside corner is an acceptable way to make the normal shaft fit.

 

[RedHeep]

The ground cross pin is weaker, which is why people grind the inside of the tooth to make the solid one fit. That's normal when you install gears in an 8.8.

If my mechanic shop was surfing the mustang forums to figure out how to put gears in an axle, I'd find another shop.

 

[Junkhead]

He was just going to get a second opinion from a friend of his since he admittedly didn't know everything about that rear end. I'm also just assuming his friend is a Mustang guy, since the 8.8 is what those guys run. And the rear end was regeared and the LSD rebuilt by someone before I got it, whether it was a reputable shop or backyard mechanic is anyones guess. These guys are just making sure everything is right before they put it back together and I have no problem with them seeking outside advice.

 

[jeeperjohn]

It sounds like what RWKhaus said, the rear was put together with too little carrier bearing preload. An 8.8 should be done with a case spreader to ensure proper carrier preload. Or it should be done with the spendy one piece shims that have to be driven in with a mallet.

 

[Junkhead]

I'll be picking it up later today and getting more details about shim thickness and backlash. They replaced the carrier bearings and were able to get a good pattern without having to mess with the pinion shims so thats a good sign. He did say the tubes were full of metal so he cleaned them out but I need to get more details on that as well.

 

[jeeperjohn]

Make sure you put a super magnet on the inside of the diff cover to pick up any remaining metal debris.

 

[Thehowler]

One on the outside cover works just as good.

 

[Junkhead]

The fill plug has a nice big magnet on it already but good idea to stick one on the outside. I'll be changing in a heavier oil and inspecting the guts again in the spring just to be sure everything is good and get ready for summer. I currently have no leaks and my breather is routed way up above the fuel tank so if theres no water in there by then, I'm going to put in some fancy expensive lube and not crack it again for a while. It'll also give me an excuse to order up a heavy duty cover since the stock one is extremely thin.

 

[Locked98GC]

When I rebuilt (2) 8.8's they had a shim about 1/4" thick on each side and then used the thin shims for adjustment.

 

[RedHeep]

The fill plug has a nice big magnet on it already but good idea to stick one on the outside. I'll be changing in a heavier oil and inspecting the guts again in the spring just to be sure everything is good and get ready for summer. I currently have no leaks and my breather is routed way up above the fuel tank so if theres no water in there by then, I'm going to put in some fancy expensive lube and not crack it again for a while. It'll also give me an excuse to order up a heavy duty cover since the stock one is extremely thin.

Ruffstuff's cover is the best.