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Old 01-16-2010, 03:52 PM   #1
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Default How to "backyard" build a Ford 7.5 Rear end

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.

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Old 01-16-2010, 03:53 PM   #2
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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.

Last edited by BogusSVO; 01-16-2010 at 03:58 PM..
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Old 01-16-2010, 04:37 PM   #3
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the thundercat 7.5 housing got wider in 86.5, apparently your housing is from a late 86 build.
the 8.8 housing stayed the same(hence your 88 TC axles being too short)

find an early 7.5 housing.

will this built rear be goin into the 85 TC mentioned in the first post?
i would take a second look at installing those poly bushing in the axle ears. they cause alot of bind in the rear suspension, and can lead to snap oversteer issues depending on the rest of your setup.

*edit again, this may help. it is posted on the tbird/cougar forum i am on.
based on jeremy's spreadsheet, a 93+ drivers side ranger axle shaft might work, or a 99-04 mustang axle shaft. the mustang axle shaft would widen the rear trackwidth and require shimming the caliper in some way. the ranger shaft may narrow it slightly.
gumby - beauty may fade, but stupid is forever!

past rangers: 97 XLT, 86 longbed turboranger, 03 EDGE, 02 XLT, 93 XLTurbo, 95 B2300T 4x4
current rangers: 04 B3000, 89 "S" RaceTruck

Last edited by gumby; 01-16-2010 at 05:01 PM..
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Old 01-16-2010, 05:29 PM   #4
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Nice tutorial, but I'm not seeing where you checked contact pattern or backlash.
'90 Ranger, 2.3L Turbo...96% stock
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Old 01-16-2010, 05:59 PM   #5
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gumby... the 88 axles would be fine, it is the difference in between the the end of the tube and the brake flage that is weleded to the tube

the ranger axl seems to be the same length as the 88 TC, just 5 lug not 4

Bossman.... no i did not set up or check that, the back lash feels fine, about .010 when it was clicked back and forth.

I will report back once I have it in and run it some and see what happens, But I have swapped parts around in this method on about 12-14 7.5 and 8.8 rears with out issue. Hence why I also labeled it a Back yard build.
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Old 01-20-2010, 07:31 PM   #6
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i'm lookin to do the same thing but swappin a 4.10 into a 3.45. how did you know that the stock shim pack was going to be okay for the distance? this is the only thing I'm worried about for my swap and was wondering if you can give some insight
Canada likes fast domestics too! hehe

-1993 ford ranger XL 2.3L
-minor N/A build on its way due to low budget.
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Old 01-20-2010, 07:45 PM   #7
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I would use your shims from yours and put them in the same places. I hated setting up rearend in auto class. the way i thought worked best to check is take a piece of paper run it through the pinion and ring gear. If it cuts the paper its too tight, and if it doesn't make a perfect pattern than its too loose.
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Old 08-22-2010, 09:55 PM   #8
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I race hobby grade rc and we check are pinion and spur gears the same way.
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Old 01-15-2015, 07:00 AM   #9
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Thats one thing I wont attempt myself
1988 ford ranger with a 87 turbo 2.3 and a t5. Mods to come a boport 1.5 cam, garrett t3 turbo, ported and polished head with bigger valves, header and fmic and 3 inch custom fabricated exhaust
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Old 01-15-2015, 07:29 AM   #10
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with the proper tools, or calibrated thumbs, it's not a difficult thing to do. My first experience messing with them I wasn't too involved with it, gumby did most of it. I watched and listened. Since then I've done over a dozen setups for other people. I do check backlash and bearing preload with proper tools, but you do get a sense of what it should feel like as well.
1996 - 2.5 CP Flattops, Billet Crower 5.2 rods, 12pt Head bolts, 1035 HG, Turbo VC, P&P BV Head, 2277 Cam, Jeff's Log/Tial MVS, HE351, FMIC, FLH2, ID1000s, HPX-E Blowthrough, Binary Editor, E85, 421whp/434wtq on 24# - SOLD. Coyote Transplant underway
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