FJ40 Diff Swap Front to back?

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Borrego

Borrego

10 Year
Joined
Apr 29, 2015
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29
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443
Location
Coeur d' Alene, ID
I've searched but can't find a solid answer... If this has been covered please point me in the right direction... I have a 71 and the rear diff is welded. (bought this way). I drive it 75% on road, and 25% on logging roads. It works great, but I'm tired of the squealing and tough to turn corners from the welded diff. I'm on a budget, so I was thinking, is it possible to swap the front and rear diff? I've looked for the last couple of weeks on CL and can't find a local diff that doesn't need to be completely overhauled or isn't fully rusted out. Some on here say they will ship me their spare diff for cheap, but shipping is still a lot due to the weight. What do you guys think about my idea to swap front to back? I'm fairly mechanically inclined, and I know the front diff will be some work to get it out, but will they bolt right in? I've read a little about the front being a full float and the rear being a semi float. I don't have a lot of experience with that. Would I need to swap anything internally on the diffs to make them work? Any pics would be great!

(also, I know the dangers of breaking axles, etc... This 40 rarely sees difficult terrain, and if it does, I will be very easy on the throttle)

Thanks
Eric
 
Depending on what's welded might be easist to just grind the welds and replace those parts. Depending on how they welded it may need to do that to get it out. Spider gears and side gears can be replaced without pulling the diff. On the front the inner axle have to be pulled to get the diff out. A lot more work than the rear.
 
Front and rear diffs are the same, assuming no one has done an axle swap or swapped in a different gear ratio. So, swapping front to rear is as easy as pulling the axles and swapping the 3rds. As LITP said, a lot of times, people just weld the spider gears. If that's the case, you can just buy the spider gears and swap those out. That would be a lot cheaper on shipping. But, in the mean time, swapping front to rear works.

On a side note, you are correct about the front being full float and the rear being semi-float (on most US axles), but the diffs are the same.

:cheers:
 
Hope you have power steering and like shifting the 4wd shifter a lot off road. Turning will be a bitch in 4wd with a welded diff.

Do it right once. Owning a 40 isn't cheap.
 
Swapping out the sider gears for new or used is by far the cheapest route for you. Anyone who has installed a locker has them filling up a box somewhere.
 
all US LC 9.5 diffs thru fj62 are swappable front to rear as long as the spacer block is moved from the rear diff to the front diff when the front diff is being put in the rear housing...9.5 diffs also swap with FJ80 and FZJ80 rear thirds thru 97? I think...HTH
 
anyone who has a box filling up with spider gears and washers should keep me in mind as an option to throwing them away, or hoarding them...
 
Thanks for all the insight! Never thought about just swapping spider gears. I have some time off over Thanksgiving and plan to work on it then. I'll post what I decided to do.
Thanks again! Keep on keepin' on.
Eric
 
Good Luck pulling the welded spider gears out. I bet it will be like one of those twisted nail puzzles.

Dyno
 
Dynosoar said:
Good Luck pulling the welded spider gears out. I bet it will be like one of those twisted nail puzzles.

Dyno
Click to expand...

^^^ This! A few that I have seen had neatly welded teeth, so they came apart, most were a welded mass, not coming out.
 
Hi all,

Borrego, where are you located? I have some misc. spare diff parts, we may be able to repair that rear diff.

Regards,

Alan


Borrego said:
Thanks for all the insight! Never thought about just swapping spider gears. I have some time off over Thanksgiving and plan to work on it then. I'll post what I decided to do.
Thanks again! Keep on keepin' on.
Eric
Click to expand...
 
Hi all,

Borrego, the first step would be determining which differential parts were affected by the welding.

Can you take the rig off the road for a few days?

If so, drain the rear diff then remove the access cover. Wipe the gear oil from the diff parts, then take some photos and post them in this thread.

Regards,

Alan
 
In my younger days, I would take a piece of .25" plate and weld it between the spider gears. Then for good measure, I would weld the spider gears to the case. Unless this was a really crappy weld job, the only way too deal with this is to swap the carrier to something like an ARB locker.

...or just swap in a different diff. Someone should be able to help you out. If you were close to me, I'd trade you labor- swap my 4.10 diffs for my new 3.70 diffs and you could take the 4.10 diff home.
 
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