Ford 8.8 Axle Conversion
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: 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.
Here is a list of parts I gathered, some place between the start of the project and the time the axle got back from Off Road Unlimited where the locker and gears were installed.
Brake pads (P/N 6674, AutoZone)
Calipers (P/N's C576 &C577, AutoZone)
Guide pins (2 - H15068, AutoZone)
Banjo bolts (Ford P/N 385116-S2)
Hoses (2 - P/N 78738, AutoZone)
E-brake cables (Mopar P/N's 52008904 & 05)
"T" Hose (P/N 380889, NAPA)
2 - Hard Brake Lines (Checker Auto, 3/16" X 18" & 60")
Yoke Adapter (Spicer P/N 2-2-1379, NAPA)
Yoke bolts (Ford P/N N800594-S100)
The brake pads I used were Performance Friction. I have heard good things about these pads and they are reasonably priced. The calipers are rebuilts, which will work fine. If your axle comes with the brake assemblies you will not need the guide pins or the banjo bolts. The hoses are two right hand Explorer brake hoses. E-brake cables I thought were going to be a pain to adapt but, I looked at Stu's web site and noticed from the disc brake conversion he did on his D44 that the e-brakes on the 8.8 were similar, if not identical. So I went to the dealer and ordered 1995 Grand Cherokee e-brake cables, these worked great. The "T" hose I ordered to have the brakes completed and the axle ready to bolt up. This hose is not necessary to buy, it helps though. It is a stock TJ "T" hose. The hard lines I used were straight and needed to be bent to fit the axle housing. I bought these long in case of any mishaps. Last but not least the yoke adapter and bolts. The yoke adapter came from NAPA. You can buy these from MORE for $50 or NAPA, near me, charges $21. Hmmmm, which will you choose. The yoke bolts are 11mm coarse thread 12 point, this is definitely a dealer item, unless you know something I don't. Don't forget to get the rotors turned. I went down to the local Midas and talked to the manager, he said, the guys in the shop can turn then, just tip them, no charge other than that. On the other hand, the people at AutoZone said they couldn't turn the e-brake surface on the inside of the rotor. Go figure, at the point you are doing the inside it is just like a drum. Oh well, I would rather give my money directly to the working guy at Midas.
Now we have all the parts together and we get the axle back from the shop we can start a final assembly. I have to apologize at this point. When I got started putting things back together, all I could see is the "finish line" so pictures weren't on my mind.
Put the guide pins in the calipers, then install the pads in the calipers. Make sure to put the piston side pad in first, duh (like I said I could see the finish line). Do this on both calipers then attach the calipers to the axle. Then you can attach the brake hoses to the calipers with the banjo bolts. Use a 7/16-20 bolt to hold the "T" hose in place and attach the caliper hoses to the axle (using the nuts that we already welded to the housing). Now you can bend and cut your hard lines to fit.
On the passengers side of the axle I tack a little piece of strap metal to hold the brake line. I also ran zip ties through some holes in the pumpkin and around the brake line to hold it there. Here is a view from a different angle.
The drivers side was tricky because of the short length, not as much room to hide mistakes.
Again a picture from a different view.
Once all your brake lines are installed you will be ready to install the axle into the TJ. Remember to take the breather fitting off your old axle and replace the bolt you used to hold the "T" hose with it.
The yoke adapter will accept your existing u-joint, you will need some clips to hold the caps in place. Someone gave me the clips, since I didn't have any, out of their trail parts box. Your driveshaft should not need modified if you originally had a D35. If you originally had a D44 you will probably have to get the drive shaft lengthened by about 1-1/2".
The final install to the vehicle took four of us about 4 hours, start to finish. It probably could have taken less if I wouldn't have kept miss-placing things.
Bleed your brakes good after the install and then enjoy the strength and the stopping power this axle will offer.