Rear Gear Question

If your car is stock, it has 28 spline axles. You can always pull one out and count the splines, too.

3.73 gears are probably your best bet if it's a stick car, 4.10s maybe for an AT. More or less depending on how adventurous you are and how you plan on using the car.

That install kit looks good, it would also be a good idea to put new axle bearings/seals in there while you have it apart.

I also recommend rebuilding your traction lok (FRPP offers a kit for that, too), and you'll need friction modifier and obviously rear end fluid.

If you've never had a rear end apart, that fluid is STINKY. Be ready, and avoid getting it on your skin and clothes, the smell is hard to wash off.

Iyzak said:

TY i think i'll go ahead and rebuild the traction lok as well , kits pretty cheap, and thanks for the tip about the rear end fluid

on the bearing and seals, is it Non-IRS or IRS???

Click to expand...

Independent Rear Suspension. If you have a stock Fox, you don't have IRS.

Not trying to give you a hard time or anything, just be aware that a gear swap is NOT for the novice grease monkey. I'm guessing you're new to this, based on how you didn't know what IRS was...?

I also think you are getting in over your head. Here's a link with a how to do it so you have some idea of what is involved: Back to the Homepage

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

Been there and done that! With success!

Auto trans 87-88 Tbird Turbo Coupes come with 3.73 gears and manual Turbo Coupes come with 3.55 gears.
Both rear ends are 8.8 units with traction lock.
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.

This tech note was written for 87-93 model 5.0 Mustangs, so if you have a 4 cylinder conversion or earlier model, there may be some other changes needed as well.. See 87-93 Mustang 5.0 Brake upgrade pages. Improve your 60-0 times! for more information.
You will need a several sets of fittings, I recommend that you get them from Matt90GT's website,
87-93 Mustang 5.0 Brake upgrade pages. Improve your 60-0 times!.
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.

You will need a proportioning valve, Summit has one for $42 + shipping. Wildwood 260-8419
You will need a kit (FMS makes the part) to gut the stock proportioning valve, Summit also
has that, about $18. Ford Racing M-2450-A

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.

You can use the stock 5.0 booster if it is in good working condition. No need to replace the booster.

Bleeding the brakes will require 2 people and some coordinated effort. I don’t recommend using your
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 how hard is it to bleed brakes? - Mustang Forums at StangNet
for details and pictures.

See Mustang Central.net FMS M2300K Brake Install 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.

The rear calipers have a funny self adjusting mechanism that requires the Ebrake to work correctly. The rear calipers also tend to seize up and not slide on the caliper mounts. You may want to use the old calipers for cores and get rebuilt ones.

Turbo Coupe parts list:
Rear axle
94-95 Mustang Master Cylinder with reservoir
Brake line Adapter fittings 87-93 Mustang 5.0 Brake upgrade pages. Improve your 60-0 times!
3 line to 2 line brake fitting kit 87-93 Mustang 5.0 Brake upgrade pages. Improve your 60-0 times!.
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
73 mm front calipers from a 91 Lincoln Mark 7 (two calipers) local auto parts
Emergency brake cable parts Summit or Jegs or .late model restoration
M-2809-A* Parking Brake Cable (need 2)
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.

Five lug Turbo Coupe conversion:
Use the 94-98 axles Mustang axles. Use 1990 Mazda MPV 3.0 V6 front rotors (10", 5 lug x 4.5" pattern, 2 7/16" offset ). While you are at the auto parts store, set a TC rear rotor side by side with the Mazda rotor and they are the same except for the offset.

The next step fixes the offset problem:
Use a Maximum MotorSports 1/8 spacer (MMWS6, Maximum Motorsports, the Latemodel Mustang Performance Suspension Leader! ) between the inside of the rotor and the axle flange. The spacers may need to have the OD machined to fit properly. The stock rotor offset is 2 5/16" and the Mazda rotors are 2 7/16" offset. The 1/8" spacer puts the rotor back dead center alignment with the calipers.

The Mazda rotors are under $30 each, and I have seen them for $20 each. The MM spacers are two for $30 + $9 shipping. So the entire package costs $99. That saves $41, which most of us could find a very good use for.