TJ/Ford 8.8 Conversion
By: J.E. Towle
AzVJC, Chandler, AZ
Page 1
The Ford 8.8 conversion for my TJ was a good choice. I had a D35c with and ARB and 3.73 gears. I wanted to be able to go to 35" tires with out breaking any axles and I knew I was limited with my D35c at the 33" tires I was running.
Note: There are some items in the parts list that you may not need or want. I did this conversion knowing my Jeep, a daily driver, could not be down over night. (There is a complete parts list at the end of this write up).
First the axle housing donor, I did a search on: http://car-part.com/ . The search was for a 1996 Ford Explorer rear axle. The one I was looking for had to have 3.73 gears so I wouldn't need to buy new gears. If you use this search engine look at the results. For some reason when I did the search an Explorer rear axle was about $700 where as the same year Mercury Mountaineer was half that. A Mercury Mountaineer is Mercury's version of the Explorer, there is also a Mazda version of the Explorer, I am not sure of the model. This being said, my donor came from a 1999 Mercury Mountaineer.
The axle didn't come with calipers although the e-brakes were in good shape. Most places want around $50 each for cores on the calipers. Luckily the AutoZone near my house said, they didn't care what core calipers I turned in, as long as I had some calipers. I found some old Chevy calipers that I used for cores. Along this same line, there were no guide pins or banjo bolts with this axle, so finding one with calipers/brakes could save you as much as $125 or more.
Next I order the bracketry. RE sells a kit (P/N RE9969) that has all the brackets needed for a TJ rear axle. These kits are made for a D35c & D44. The axle tube diameter on these axles is 2.63" and the tube diameter on the 8.8 is 3.25" so some modifications to the brackets will be needed.
I tore a part the axle housing cleaning out the rust and junk left in it from sitting in the junk yard. I was also inspecting it to make sure there was no major damage that would prevent me from rebuilding this unit. I later had my inspections confirmed by the installers at Off Road Unlimited to absolutely make sure everything was okay before I did any bracket welding on the housing.
With everything looking good and torn apart I started on the axle housing modifications. My tools of choice for this was a cutting torch and an angle grinder. I cut off the existing brackets and then grinded the tubes smooth.
I also, later, took a wire wheel and cleaned off any other rust/paint to give me a fresh start.
With the brackets in hand I was ready to start the modifications to the brackets. The brackets, as I have said, need to be modified to fit a 3.25" tube. The inside of a Tuna can is about perfect. I marked all the brackets and started grinding with my 4.5" angle grinder. The hardest bracket to do is the trac bar bracket. It is made out of 1/4" thick steel and rides on the down side of the rear radius of the axle tube. I believe I used a cutting wheel to get the majority of the metal off and then ground to fit. Along the way, of grinding, you can check the brackets to see if they are beginning to fit. The bracket grinding took me about 2 hours.
Once the brackets are ground down you can begin to weld them to the housing. My pinion angle on my existing D35c was perfect. I checked the pinion angle it was 19 degrees. I set the housing behind the Jeep on jack stands and lifted the pinion angle until it was correct. I used a dial type angle finder that measures everything off horizontal, you can get one of these at Home Depot. You will need to check this angle periodically to make sure it stays where you put it. I marked the center of the donor axle housing as a reference and decided work from the outside of the axle to inside would be best. The first brackets to be tacked into place were the spring perches. Since I want the perches to be level at rest this is easy. Measure center-to-center of the existing spring perches and set the angle to 0 degrees, perch-to-perch should be about 39-7/16". On all the brackets, after tacking, measure from the outside of the housing to some point on the bracket and make sure the brackets are the same distance in from each side.
The lower control arm brackets are next, these are the worst brackets to locate. The top of the lower control arm brackets need to sit at 0 degrees. For me this meant grinding a bit more off one corner of the bracket because it interfered with the spring perches. To get a measurement for these brackets, center-to-center, is a pain. Take your time and do it correct then check the brackets on the donor axle and make sure they are centered. There is no quick way I can tell you to set these.
Next the sway bar brackets need to go into place. Even if you do not plan of hooking your sway bar up, I strongly recommend you putting these brackets in place (the reason will be clear). Measure center-to-center for these brackets, mine were 26-1/2". Tack the new brackets into place, fat end up and with the face of the brackets being 90 degrees off horizontal (perpendicular). The upper control arm brackets fit on the housing with the sway bar brackets in the middle of them, thus, the location is easy. The leading edge of these brackets also needs to be 90 degree off horizontal, or parallel to the face of the sway bar brackets.
Before we go any further it is time to think a bit. The breather outlet on the axle is right where the drivers side upper brackets are being placed. I filled the breather with weld and ground smooth. Get good penetration on this weld without letting too much weld drip on the inside of the housing. We will drill and tap a new location later.
Now the track bar bracket, the inside front edge of it wraps around the driver's side upper control arm bracket. Therefore it is easy to locate. Last but not least is the shock mounts. The easiest way I found to do this is by getting the center-to-center measurement, holding the bracket up to your existing axle, measure from the ground up to the existing shock mounts, now hold the new bracket up to your existing axle and make it the same measurement from the ground up, you can tilt it rearward about a 1/4" because the axle tube will be bigger. Holding the shock bracket in that place measure an angle off the front of the bracket. Duplicate this angle measurement on new axle housing with the center-to-center location correct and tack in place.
All the brackets should be tacked on. Have at least one other person check all the angle and the distances center-to-center. Then you go back and check everything. This is the crucial part of this, no turning back, lots of money could be lost here, etc., etc..
If everything is good it's time to weld complete. Weld about one inch at a time making sure to weld at one side of the tube then the other. Let the housing cool down in between welds as much as possible, heat kills and warps. Also it is a good time to tack the axle tubes to the housing. In the above picture you can see I did this before tacking the brackets. I just did it for safety and peace of mind. Make all weld good because your life could and does depend on them. After you are done scrape off all the weld splatter.
This is a good time to re-drill for the breather fitting. The thread size is a 7/16"-20, so you will need a 25/64" drill bit and a tap. If you have the pinion angle still set you can measure half way between the driver's side upper control arm bracket and the pumpkin on the top side of the axle tube and then go a bit rearward and drill a pilot hole, the pilot hole will make the drilling the bigger hole easier. After the required hole is drilled tap it, this is done.
This
is also a good time to modify the spring perches. TJ's are really good about
bending shock cans when the can is down, so I cut away part of the spring
perches to give more clearance for the shock cans.
You have to cut part of the pumpkin now. The sway bar hits the bigger pumpkin on the 8.8. If you mount the sway bar on the axle, or attempt to, you can see exactly where it will hit. Put a cutting wheel on a grinder and notch the passenger's side of the pumpkin until there is no more problems. You can barely make out this cut in the picture.
As
long as we are finishing up we can weld some nuts to the tubes to hold the brake
hoses. If we use two right Ford Explorer brake lines, it needs a 5/16" bolt
and nut to hold the hoses to the tubes. I checked the distance from the end of
the axle tube by using the original brake lines for a template and putting the
hoses as close as I dared to the spring perches. I also tacked a 7/16" nut
next to the 5/16" nut to help prevent it from rotating, by using the
locating pin on the hose. Then I cut off the top of the 7/16" nut flush
with the top of the 5/16" nut. I used a fine thread 5/16" to give me
more thread grip. This picture shows the driver's side after completed.
Wipe down the outside of the housing with lacquer thinner to get it ready for painting. I taped off the ends of the housing to prevent paint from getting in and also the pinion hole. Paint as desired.
After
the painting it is time to start a partial reassembly. Put the backing plates
& brackets back on and assemble the e-brakes. Here is a picture I took of
the e-brake assembly before I removed them. This picture helped me to remember
where everything went at assembly. Before reinstalling the e-brakes, I took a
piece of sand paper and removed all the surface rust and cleanup off the brake
shoes. On top of the picture, there was already some blue paint on the parts to
mark where things went or what parts went with which assembly.
The housing, for me, is already to be returned to Off Road Unlimited for inside cleanup, gear, locker and new bearing/seal install.