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109 Posts
Discussion Starter #1
How to backyard Build a Ford 7.5 Rear End

This will also work on a ford 8.8

I 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 set

The rear brakes will be upgraded from a 9 inch drum set up to a 9.250 rear disk brake set up

This 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 flange 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 flange 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 pinion

I 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 flange I want to use.

This rear end is being built using parts from several different Ford 7.5 and 8.8 rear ends

3.73:1 gear set from a 1985 Ranger 7.5
Disc Brake set up is from a 1988 Thunderbird Turbo Coupe 8.8
Pinion Flange is from 2001 Mustang GT 8.8
Ford MotorSport Differential was found in a 1987 Mustang 7.5
Axles are from a 1988 Thunderbird Turbo Coupe
Case is from a 1986 Thunderbird Turbo Coupe

Heres 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 flange to flange and the 8.8 is 54,w/disc brakes, so trying to find the right axles seems to have me a hold for now.
*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.

3,902 Posts
Awesome! I like the color :D I am going to be rebuilding mine soon with all new bearings and gears. I also opted to get a solid pinion spacer(shim-able) instead of a crush sleeve. I used it on a ford 9" and whoa it seemed like much less headaches. I know the pain of an over-crushed crush sleeve plus I think it also makes pinion depth measurements more accurate. ;) I didnt know that the drum/disc axles were different, but I suppose it makes some sense. Good luck on finding those axles.

109 Posts
Discussion Starter #3
glad you like the color, on my bird everything I have pulled/replace on the underside has been cleaned and painted ford dark blue. makes it a bit easier to remember what all i have food

109 Posts
Discussion Starter #5
95badbird... this is true... the package i bought had 2 in it, for around $9.00 from O'Reilly Auto Parts.

*note* If told they do not have them for a 7.5... ask for the ones for a 8.8 they are the same.
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