8.8 rear end swap

Walt Jaquith

YJ Enthusiast
Supporting Member
Joined
Apr 12, 2020
Messages
111
Location
Lafayette, OR
So begins the saga of the 8.8 rear diff swap. The donor is an early 80s axle from a Ford Explorer. It came with limited slip and 3.73 gears. During early tuning of my 4.3 I'd figured I would need to regear from my current 3.55 , and so when this one came up for sale reasonably, I snapped it up. Now I know that I want to stay with the 3:55 gear ratio, which is fine; it just means I don't have to touch my front axle. I picked up a good used 3:55 ring and pinion for the 8.8, and started working on it this weekend. I got everything torn apart, the old spring and shock brackets cut off, and the housing de-rusted.

I plan to fit disk brakes to the rear end, upgrade the yj master cylinder and install a slip yoke eliminator on the transfer case as part of this project. The Jeep's still on the road; I won't actually tear into it until the weather turns.

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When I did mine I found an 8.8 explorer that came with OE disc brakes, before install I put new clutch discs in the limited slip & shined them a little tighter than recommended, works good as a locker but doesn't squeal tires when turning on asphalt, I used the original yj master cylinder & propositioning valve & it worked great, also with a little modification was able to use the factory cable for the 8.8 park brake, make sure to get spring perches at the correct angle so you wont need shims, very easy swap, I did it by myself in one day.
 
So begins the saga of the 8.8 rear diff swap. The donor is an early 80s axle from a Ford Explorer. It came with limited slip and 3.73 gears. During early tuning of my 4.3 I'd figured I would need to regear from my current 3.55 , and so when this one came up for sale reasonably, I snapped it up. Now I know that I want to stay with the 3:55 gear ratio, which is fine; it just means I don't have to touch my front axle. I picked up a good used 3:55 ring and pinion for the 8.8, and started working on it this weekend. I got everything torn apart, the old spring and shock brackets cut off, and the housing de-rusted.

I plan to fit disk brakes to the rear end, upgrade the yj master cylinder and install a slip yoke eliminator on the transfer case as part of this project. The Jeep's still on the road; I won't actually tear into it until the weather turns.

View attachment 116203
View attachment 116204
You have got that sucker very clean. And the clean tubes are equally impressive.
 
This project has been on hold for a long time, but it has a new urgency. When I swapped in the 4.3, I put the T-case back exactly where the old one was. I've never loved the driveline angle, but it was working before, so I figured I could live with it. Nope. I've picked up the dreaded vibration. So back to the axle...

I got the guts buttoned up, and did a wrecking yard run for brake parts. Disk brakes from a 2000 Explorer bolted right on to the early 80's axle housing. I love it when auto makers don't fix stuff that aint broke.

Also ordered a JB Conversions ultra-short slip yoke eliminator. The plan is to match the pinion and T-case angles (since I'll be welding on the spring saddles), and then have a CV driveshaft made. I don't want any weak links in the drivetrain.
 
This project has been on hold for a long time, but it has a new urgency. When I swapped in the 4.3, I put the T-case back exactly where the old one was. I've never loved the driveline angle, but it was working before, so I figured I could live with it. Nope. I've picked up the dreaded vibration. So back to the axle...

I got the guts buttoned up, and did a wrecking yard run for brake parts. Disk brakes from a 2000 Explorer bolted right on to the early 80's axle housing. I love it when auto makers don't fix stuff that aint broke.

Also ordered a JB Conversions ultra-short slip yoke eliminator. The plan is to match the pinion and T-case angles (since I'll be welding on the spring saddles), and then have a CV driveshaft made. I don't want any weak links in the drivetrain.
Just bought a couple from Tom Woods Custom Driveshaft.
They have an immense amount of information there and Very in formative videos.

I believe the correct pinion angle for a CV is actually the angle of the drive Shaft with the vehicle sitting on the ground.
And matching angles are for regular Non-CV shafts, but I could be wrong.
 
I believe the correct pinion angle for a CV is actually the angle of the drive Shaft with the vehicle sitting on the ground.
And matching angles are for regular Non-CV shafts, but I could be wrong.
It depends. With a single cardan (regular u-joint at each end) shaft, I need the t-case and Pinion flanges to be parallel. But that probably won't work for the angle I'm running, so I'll go double cardan at the T-case, meaning the pinion needs to match the driveshaft angle. A complicating factor, the 8.8 is offset a few inches to one side. bottom line, I'm going to talk to some experts before I weld anything up for sure, and go with what they recommend.
 
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It depends. With a single cardan (regular u-joint at each end) shaft, I need the t-case and Pinion flanges to be parallel. But that probably won't work for the angle I'm running, so I'll go double cardan at the T-case, meaning the pinion needs to match the driveshaft angle. A complicating factor, the 8.8 is offset a few inches to one side. bottom line, I'm going to talk to some experts before I weld anything up for sure, and go with what they recommend.
Talk to the guys at Tom's, man they're good. They will have answers.
 
Quote from the OP: "The donor is an early 80s axle from a Ford Explorer. "

This 8.8 axle has to be from the early 1990's, (1991-1994) if it has factory drums as the first Ford Explorers came out late 1990 as a YM 1991 vehicle.

Yes it is nice the disc brake assemblies from a 1995 YM to 2001 YM Ford Explorer will swap over to the 1991-1994 Explorer axle and are basically dimensionally the same units but with drums instead of disc brakes. I have seen them as little as $25 on half price day in some salvage yards too. You can't even buy one new disc rotor for that price at a parts store much less get the whole enchilada for that!

I've installed an 8.8 axle in my CJ, in YJ's, TJ's an XJ and even had a friend who put one in his V8 5.9L ZJ Grand. Another friend of his put one in the later 2nd gen WJ Grand. They are excellent choices when you don't need 1-ton weight or strength requirements. They will easily handle tire sizes up to 37" without much trouble provided you use low hydrogen nickel rod and stitch weld the axle tubes to the center section.

The axle tubes aren't super thick but they don't bend easily since bending moment is a function of tubing diameter and not just the tubes thickness. The larger diameter the tube, the stiffer it becomes within reason and at 3.25" for all but the neck down at the very ends, it is stout enough for even serious off-roading.

I've personally had powerful Chevy V8 strokers or LSx engines in front of them no issues.

Ford Aerostar minivans have the companion flange adapter for the U joint in both 1310 or 1330 sizes. You'll have to look under the van to see which U joint it has but I've robbed several off of them at junk yards to make the 8.8 fit with an existing driveshaft if the length is correct. It's a great low budget way to fit the axle in your Jeep.

BTW, I just left the tone ring sensor screwed into the top of the center section and left it unplugged to keep from leaking. No reason to weld up the hole or grind the protector ears off of the housing unless you want to go through all that extra trouble.

Great budget cost effective choice @Walt Jaquith !

RR
 
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The slip yoke eliminator is in, and the 8.8 is fitted. I'll order the driveline today. Final driveline angle was 8.8 degrees at ride height, accounting for the offset of the 8.8. The E-brake cables from the 94 Grand Cherokee (installed when I converted the old axle to disk brakes) fit the Ford emergency brakes perfectly. I have rubber brake lines, new calipers and various little parts coming this week.

I'm going to redo the lower shock mounts, and probably replace the shock absorbers. The ones on there were leftover from my son's JKU lift, and they're a bit stiff for my much lighter yj. They're also a little long, which hasn't been a problem since I don't wheel this rig much, but I can get shocks with the right travel and valving and be done with it.
 

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Quote from the OP: "The donor is an early 80s axle from a Ford Explorer. "

This 8.8 axle has to be from the early 1990's, (1991-1994) if it has factory drums as the first Ford Explorers came out late 1990 as a YM 1991 vehicle.

Yes it is nice the disc brake assemblies from a 1995 YM to 2001 YM Ford Explorer will swap over to the 1991-1994 Explorer axle and are basically dimensionally the same units but with drums instead of disc brakes. I have seen them as little as $25 on half price day in some salvage yards too. You can't even buy one new disc rotor for that price at a parts store much less get the whole enchilada for that!

I've installed an 8.8 axle in my CJ, in YJ's, TJ's an XJ and even had a friend who put one in his V8 5.9L ZJ Grand. Another friend of his put one in the later 2nd gen WJ Grand. They are excellent choices when you don't need 1-ton weight or strength requirements. They will easily handle tire sizes up to 37" without much trouble provided you use low hydrogen nickel rod and stitch weld the axle tubes to the center section.

The axle tubes aren't super thick but they don't bend easily since bending moment is a function of tubing diameter and not just the tubes thickness. The larger diameter the tube, the stiffer it becomes within reason and at 3.25" for all but the neck down at the very ends, it is stout enough for even serious off-roading.

I've personally had powerful Chevy V8 strokers or LSx engines in front of them no issues.

Ford Aerostar minivans have the companion flange adapter for the U joint in both 1310 or 1330 sizes. You'll have to look under the van to see which U joint it has but I've robbed several off of them at junk yards to make the 8.8 fit with an existing driveshaft if the length is correct. It's a great low budget way to fit the axle in your Jeep.

BTW, I just left the tone ring sensor screwed into the top of the center section and left it unplugged to keep from leaking. No reason to weld up the hole or grind the protector ears off of the housing unless you want to go through all that extra trouble.

Great budget cost effective choice @Walt Jaquith !

RR
Wondering — do you suggest any mods to the master cylinder after doing an 8.8 swap on a YJ. I just did the swap and now have rear disc brakes but my brake pedal is feeling spongy …
 
Wondering — do you suggest any mods to the master cylinder after doing an 8.8 swap on a YJ. I just did the swap and now have rear disc brakes but my brake pedal is feeling spongy …
Mine firmed up quite a bit when I put the 8.8 in there. Even with the disks on the Dana 35 that I had before the pedal was weak, but the 8.8 helped a lot. I don't know if I just got more air out when I bled them, or what, but the braking on my rig feels much better now.
 
I didn't do anything but changed the master cylinder when the front axle was changed to a D44 with full size discs. Never pulled the O ring or anything, ran stock until the front axle swap, that's where I had to use the Econoline van master cylinder.
If your front axle is stock, I just ran the same factory didn't change anything. On the YJ and TJ's. In my CJ, I still have the stock master until the swap time the D44 also.

RR
 
If you read my post on "The Diesel Jeep Build" I am re-doing my front axle again this time installing the full-size knuckles out treatment. That includes full-size 1/2 or 3/4-ton modine single piston calipers, full size F-150 rotors and all the components that go with that.

On YJ wranglers that I've done this in the past to, I changed the MASTER CYLINDER ONLY to a mid 1970's to early 1980's Econoline E250 3/4-ton master cylinder ONLY when going to full size front brakes and Explorer or ZJ Grand rears together.

This firmed up the brakes and made everything work as it should with the Explorer 8.8 rear disc brakes out back. I could stand on the brakes and lock all four 35" or even 37" tires up on the highway in a hard panic stomp on the pedal.

Prior to changing the fronts out from the original CJ or YJ discs, I left everything the same with the original master from Jeep and the brakes all worked fine. Didn't bother removing "O" rings or anything in the proportioning valve. Only on one of the conversions we did for a friend that I went and snagged a ZJ Grand proportioning valve from a 4-wheel disc 1995+ ZJ. IT DIDN'T MAKE ANY DIFFERENCE that I could notice except for maybe decrease some rear residual pressure off the back calipers for the first 100 feet of driving after being at a stop or so. Not really noticeable difference at all. Didn't affect rear heat or fuel economy so everyone figured it was a waste of time to do that.

Finding the E250 van master for use in the 1995 power brakes YJ Wrangler took LOTS of trial and error with a parts house I worked with. We tried Corvette, F150, Cadillacs and all kinds of master cylinders until I found the Econoline van E250 master cylinder from a 1978 to 1986 E series van worked perfectly without any aftermarket pressure adjusters or "O" ring fiddly things etc.

It was a friends shop who had a good working relationship with his parts house that allowed us swapping some 15 different master cylinders until we found the correct combination on 4-wheel disc brakes (Explorer or ZJ Grand rears with full size GM, Ford or Jeep SJ front discs). We did the math on piston sizes and volume of fluid moved, we used caliper brake line pressure gauges and everything that sound engineering practice would expect. After all, this is your life and the lives of others around you on a safety item like brakes so it absolutely HAD to work correctly. No mickey-mouse playing around with safety!

With the Explorer or ZJ Grand rear discs and the stock YJ or CJ front brakes, the factory master worked just fine up to 35's and the factory power brake booster. Over 35's we start thinking of a hydro-boost system because the small calipers have a limit to clamping force against the larger diameter wheel. It's a physics thing at that point. You know, larger lever, more surface area required etc.....

RR