How to "backyard" build a Ford 7.5 Rear end January 19, 2010, 06:11:23 PM How to backyard Build a Ford 7.5 Rear End This will also work on a ford 8.8I have a pile of assorted Ford rear ends, and decided my car could stand a freshened up rear. The car is a 1985 Ford Thunderbird Turbo Coupe with a factory installed 3.45:1 gear set with a Limited slip differential.I will be installing a Ford Motor Sport Limited slip with a 3.73:1 gear setThe rear brakes will be upgraded from a 9 inch drum set up to a 9.250 rear disk brake set upThis is a “backyard” build up, In the sense that most of the parts are used, and come from several different rear ends. To start I disassembled one rear end for a case. The first step is to drain out the old fluid. Next remove the cover Now rotate the diff over till you find the cross pin lock bolt (8mm)Now remove the cross pin lock bolt. Now slide the cross pin up and out of the way. *Note* with some ring sets the cross pin can not be fully removed.with the cross pin out of the way, push in on the end of the axle Now remove the “C” clips now with the old drums off, and the “C”clips removed the axles will now slide right out. Now unbolt the drum brake backing plate, remember to unhook the wheel cylinder line. Now remove the bearing caps, by removing the 4 bolts *Note the caps have to go back on the exact same way they come off, side and facing direction. Reach in and lift out the differential Now the case can be rolled over and the pinion nut can be removed, followed by the pinion seal. With a copper/brass hammer lightly tap the pinion to unseat the outer bearing. Be ready to catch the pinion, or have a soft landing place for it under the case.The cups that match the differential bearings came out. But the press fit cups that are in the case for the inner and outer pinion bearings stayed with the case. Now the case is ready to be cleaned for reassembly.I cleaned mine with a wire brush, followed by a chemical soak, then a pressure wash. Now with the case clean and painted it is ready to be built I start off with removing the old 3.45 ring gear from the FMS differential Unbolt the ring gear then tap with a copper/brass hammer The ring gear has a bit of a press fit. Now I can bolt up the good used 3.73 ring gear.I used 4 of the ring gear bolts to align and seat the gear. The bolts were removed and cleaned. Blue loctite was applied to the threads Then torque to 77ft/lbs Now the 3.73 pinion can be installed into the case. Now the differential can be installed, I used the shim package that was factory installed. The spec I found/used was .008 to .015 for backlash. Next I torqued the differential bearing caps to 80 ft/lbs Next I rolled over the case and installed the crush sleeve, outer pinion bearing, splash shield Sliding the outer bearing and splash shield onto the pinionI knocked in a new pinion seal Since I was doing seals I installed new wheel bearing seals too Removing the old one.Installing the new one.Next I bolted on the disc brake mounting plates. At this point I came across the glitch of this build, I cleaned up the wrong pair of axles, The ones I had ready to use were for a drum brake set up, NOT a disc brake set up. Also I came across a different pinion I want to use. This rear end is being built using parts from several different Ford 7.5 and 8.8 rear ends3.73:1 gear set from a 1985 Ranger 7.5Disc Brake set up is from a 1988 Thunderbird Turbo Coupe 8.8Pinion is from 2001 Mustang GT 8.8Ford MotorSport Differential was found in a 1987 Mustang 7.5Axles are from a 1988 Thunderbird Turbo CoupeCase is from a 1986 Thunderbird Turbo CoupeUPDATES10/14/2009Heres an update..... I am having issues with axle lengths, both sets that I have are too short, apparently the 7.5 rear w/ drum brakes is a 55 inch case from to and the 8.8 is 54,w/disc brakes, so trying to find the right axles seems to have me a hold for now.12/24/2009*Update* I have been looking for a pair of axles that are .500 longer than the ones I have so I could go to disk brakes, Yes I know I can order some aftermarket ones, But this was to be done on the cheap, It looks Like I will end up with some 10 inch drum brakes, I have a pair of FMS drum brakes I will use. Quote Selected
How to "backyard" build a Ford 7.5 Rear end Reply #1 – January 19, 2010, 08:18:17 PM What you had is one of the wider 85.5-88 7.5 housings that were used in the Tbirds/Cougars. The 8.8's used in the 87-88 TC's used the narrower "Mustang"-style housing. The axle (track) width is the same between the two though. We've covered this A LOT on this forum.Axles that *might* work are from an SVO or an earlier Mk7 with the 11.5" rear disks. They are 1/2" longer than the ones used in the Tbirds. However, they are 5 lug and no guarantees that the bearing surfaces will be in the right place.You're most likely going to need to go with the drum brakes unless you have custom axles made. Quote Selected
How to "backyard" build a Ford 7.5 Rear end Reply #2 – January 19, 2010, 08:48:22 PM Quote from: Chuck W;307039What you had is one of the wider 85.5-88 7.5 housings that were used in the Tbirds/Cougars. The 8.8's used in the 87-88 TC's used the narrower "Mustang"-style housing. The axle (track) width is the same between the two though. We've covered this A LOT on this forum.sounds familiar. ;)i was off a year, i guess.....thought the half year was 86.5 not 85.5 Quote Selected
How to "backyard" build a Ford 7.5 Rear end Reply #3 – January 19, 2010, 09:04:29 PM Quote from: gumby;307044sounds familiar. i was off a year, i guess.....thought the half year was 86.5 not 85.5Well, we've stumbled across a handful of 85's with the wider housing, so it's best just to measure. Quote Selected
How to "backyard" build a Ford 7.5 Rear end Reply #4 – January 20, 2010, 03:01:45 AM Other than the axle lenght, good writeup, at least for someone who's never done a diff swap. I'll refer to this when I do mine soon.Thanks man :D Quote Selected
How to "backyard" build a Ford 7.5 Rear end Reply #5 – January 20, 2010, 09:19:04 AM nice post. can you, or someone, please explain the whole backlash / shim thing? (the picture installing the diff where the caption refers to measurments of .008 and .015). Quote Selected
How to "backyard" build a Ford 7.5 Rear end Reply #6 – January 20, 2010, 10:33:30 AM the backlash is the clearance between the ring and pinion, I call it the clunk to clunk, basicly measure the movement of the ring movement, turn the ring grear counter clockwise till it just touches the pinion, zero the dial indacator, then turin the ring clockwise till it touches the pinion, and see what the movement is.since this was a no money/budget build.. I just "hand" checked it.. It felt right to me so I did not break out the inacator. Quote Selected
How to "backyard" build a Ford 7.5 Rear end Reply #7 – January 20, 2010, 12:03:48 PM I've hand checked many ring and pinions but I highly don't recommend it. Carbon paper, lipstick, dial indicator all the way. Quote Selected
How to "backyard" build a Ford 7.5 Rear end Reply #8 – January 20, 2010, 02:30:56 PM whats with the carbon paper and lipstick? Quote Selected
How to "backyard" build a Ford 7.5 Rear end Reply #9 – January 20, 2010, 02:47:04 PM Quote from: mattg;307165whats with the carbon paper and lipstick?He likes to look pretty when setting backlash. Quote Selected
How to "backyard" build a Ford 7.5 Rear end Reply #10 – January 20, 2010, 05:14:08 PM One thing missing, heat the bolt that hold the cross shaft to break the lock tight. Seen to many bolts snapped off by not doing that. Just a heads up. Quote Selected
How to "backyard" build a Ford 7.5 Rear end Reply #11 – January 22, 2010, 10:01:09 AM can someone describe the procedure with lipstick and carbon paper? Quote Selected
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