7.5 to 8.8 swap

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Dec 23, 2003
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foxchassis.com
#2
1985 Turbo T-bird did not have 8.8. Only 1987 and 1988 did.

A 1987-88 8.8 TurboCoupe rear it will "bolt up" but unless you change and adjust a bunch of other stuff (wheels, rear brake lines/hoses, master cylinder, proportioning valve) it will not fit and work right. That's because it has disc brakes, which makes it wider flange-to-flange, and the front-to-rear brake bias must be adjusted. The easiest thing to do is re-use the axles and brakes from your 7.5 in the TC rear, but you will have to cut the caliper brackets off the housing.
 
Last edited:

jrichker

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#4
1985 Turbo T-bird did not have 8.8. Only 1987 and 1988 did.

A 1987-88 8.8 TurboCoupe rear it will "bolt up" but unless you change and adjust a bunch of other stuff (wheels, rear brake lines/hoses, master cylinder, proportioning valve) it will not fit and work right. That's because it has disc brakes, which makes it wider flange-to-flange, and the front-to-rear brake bias must be adjusted. The easiest thing to do is re-use the axles and brakes from your 7.5 in the TC rear, but you will have to cut the caliper brackets off the housing.
@Thebigwhopp

Wrong answer, I have actually done just that...

Been there and done that! With success! :nice:

Do the 87-88 T-Bird Turbo Coupe rear end swap!

Auto trans 87-88 Tbird Turbo Coupes come with 3.73 gears and manual Turbo Coupes come with 3.55 gears. Cost is $125-$300 for the rear axle. Add another $100-$200 or so to complete the brake upgrade.

I choose 3.55 since I do more highway driving. Both ratios have 10 5/16" disk brakes with vented rotors as standard equipment.

It takes 2 guys the first day to get the old rear end out and the new one bolted in place. It takes 1 guy another whole day to do the brakes.

You will need a several sets of fittings, I recommend that you get them from Matt90GT's website, http://home.comcast.net/~mjbobbitt/mustang/page5.html. Read Matt's instructions thoroughly, everything you need to know about the brakes is all there. You need to be patient and follow all the internal links, and there are many of them. You will need 2 fittings in the rear to adapt your old brake tubing to the TC disk brakes. The fittings go between the steel tube and the caliper brake hose. You will need another set of fittings to make a 2 port to 3 port adapter. To make life simpler, just buy the kits from Matt. You could piece them together, but it's not worth the time unless you work at an auto parts store with all the fittings ever made.

You will need to drill the quad shock mounting holes 2” below the holes drilled for the Turbo Coupe mounting points. The bolts are metric, so don’t loose them or the nuts. A 15/32” drill should be about the right size unless you have access to metric sized drill bits. Going without quad shocks is not an option.
When you install the axle assembly you will need to leave the bolts for the control arms only finger tight. Once the axle and all the control arms are in place, put jackstands under the rear axle and under the front A arms. Level the car as best you can while it is on the jackstands. Then and only then tighten down the control arm nuts and bolts to the factory specs. This assures that there is no preload to position the axle up or down, it is preloaded to normal driving height.

You will need a proportioning valve, Summit has one for $40 + shipping.
You will need a kit (FMS makes the part) to gut the stock proportioning valve, Summit also has that, about $10.


You will need a new master cylinder, see Matt's site and make you choice. I used a 94-95 Mustang master cylinder. Note that rebuilt 94-95 Mustang master cylinders do not come with a reservoir. That means a trip to the junkyard and some more money spent.

Your brake pedal may be very hard and almost impossible to lock up the brakes. I had to replace the front calipers with 73 mm calipers from a 91 Lincoln Mark 7 to get the braking performance up to par.

Bleeding the brakes will require 2 people and some coordinated effort. I don’t recommend using you wife or girlfriend to pump the pedal – they get offended when you yell at them. I used a homemade power brake bleeder constructed from a garden sprayer and some fittings from Home Depot. It cost about $25 and was worth every penny. See http://forums.stangnet.com/showthread.php?p=6143048 for details and pictures.

See http://www.mustangcentral.net/tech/brake.html for help with the emergency brake. The red words link to some very useful photos on how to modify the handle. The stock setup tends to lock up and not release properly.
All in all I have been very pleased with the results.

Turbo Coupe axle swap parts list:
87-88 T-Bird Turbo Coupe Rear axle
94-95 Mustang Master Cylinder with reservoir
Brake line Adapter fittings http://home.comcast.net/~mjbobbitt/mustang/page5.html.
3 line to 2 line brake fitting kit http://home.comcast.net/~mjbobbitt/mustang/page5.html..
Proportioning valve, Wildwood 260-8419 Summit or Jegs
Kit to gut the stock proportioning valve Ford Racing M-2450-A Summit or Jegs
Reuse stock brake booster – no changes needed with the parts in this list
73 mm front calipers from a 91 Lincoln Mark 7 (two calipers) local auto parts store
Emergency brake cable parts: Summit or Jegs or Late Model Restoration
79-92 Mustangs use: M-2809-A* Parking Brake Cable (need 2)
93 Mustangs: use 93 Cobra Ebrake cables.
All years use: M-2810-A* Parking Brake Cable (short cable that attaches to the parking brake handle)

I recommend that you use reman calipers and use the calipers from the Turbo Coupe axle for cores to return. The parking brake mechanism and the caliper slides tend to lockup and freeze

Identifying a Turbo Coupe rear axle:
1.) Measure the rotors - a TC disk brake uses 10 5/16" vented rotors.
2.) Measure the length of the quad shock mount arm and compare it to the mount on your existing stock axle. The TC quad shock mount arm is about 8" long if I remember correctly.
3.) Measure the distance between the axle flanges and compare it to stock. The TC rear axle assembly is 3/4" wider per side, or 1 1/2" wider for both sides.
Fixing the added axle length problem:
If the extra width is a problem for your wheel and tire combination, North Racecars makes some rather expensive brackets ($160 +) which allow you to use the stock axles. See http://northracecars.com/Brakes.html


Five lug Turbo Coupe conversion:

Copied from @Mustang 5L5;

But 87-88 TC and 1993 Cobra use the 45mm rear caliper.

1993 Cobra R also uses a 45mm rear caliper, but it's off the 91-92 Lincoln Mark 7 platform and not very well known. 5-lug, 10.5" VENTED rotors. 91-92 Saleens also got this setup. (may be an exact 1 for 1 match except that the Lincoln are 5 lug).

Not a whole lot of Mustang'ers even know about this rare setup.
Use the 94-98 axles Mustang axles.
 
Feb 19, 2018
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#5
Also. Some earlier 7.5 Thunderbird rears will bolt into a fox perfectly, and are the correct width. I found one with a 2.73 posi. It had longer axles with some funky brake drums that fit the axles and put the working part of the drum inboard over the brakes. Swapped in with Mustang axles and it works fine.