FZJ80 4.10:1 in FJ60/62 Third?

[pappy]

I cross posted over in the FJ60 section too.

Will the 4.10:1 diff gears from a FZJ80 replace the 4.11:1 gears in a FJ60/62 diff?

Reason. I have a FZJ80 locker diff in the front which of course has the 4.10 gears, but I have a FJ62 diff in the rear with 4.11. I've been told not to worry about it. I've been told to worry about it. Several of you have re-geared your FZJ80s and have the 4.10 sitting in the garage, and Mike has offered me his set.

Will they fit? I visited the EPC and found several differences between the FJ60/62 diffs and the FZJ80, mostly in the bearings. Any thoughts?

 

[SteveLCetc]

I wouldn't worry about it.

Many older 4x4's were just a little bit off. Even now, the Dana 30 (front) has 4.10 and the Dana 35 (rear) has 4.11. (Not that we would take recommmendations on how Jeep does things, but as weak as those diffs are...)

It'll prolly increase your tire wear by a little when you run in 4 wheel drive on the highway. How much are you gonna do that?

It may be that the 4.10 gears (41/10?) are not as beefy as, and are quieter than, the 4.11 (37/9?) gears so since the 4.11's run all the time they need more meat.

 

[Beowulf]

IMHO the difference between the 4.10 and the 4.11 in a PT 4wd vehicle is nothing to be concerned about. You would get that much variance between worn and new tires and between different tire brands.

What was the rationale for those that said that you should be concerned?

-Mike-

 

[SteveLCetc]

Mike's correct. A half inch of wear on a 33" tire will change an effective 4.10:1 to a 4.23:1. The difference between 4.11 and 4.10 is effectively 1 millimeter of tread wear.

 

[pappy]

Ya, well ... I think this has now turned into a "gee-wiz" question about whether it can be done. One of those "it's good to know" trivia questions that probably has no real true value. One of those "I know, I know ..." kind of questions with some kid in the back of the class screaming with his hand up.

The carrier bearings are different between FZJ80 and FJ60/62. The carrier is not a problem because the FJ62 carrier would be retained and it's assumed the ring will bolt on (thickness issues?). I also double checked and the pinion bearings are the same between the two. I initially thought they were different.

Inquiring minds (mine) want to know. I have a boneyard FJ62 diff in the garage. Mike has the gears. I'm tempted to take the dang thing apart and find out ... right after I get da'40 done.

FJ62
Carrier Bearing: 90368-45066
Inner Pinion Bearing: 90366-40059
Outer Pinion Bearing: 90366-30038
Carrier: 41343-60030, 90368-50024

FZJ80
Carrier Bearing: 90368-50024
Inner Pinion Bearing: 90366-40059
Outer Pinion Bearing: 90366-30038
Carrier: 41311-60070