Grimace5.0

Transmission
Ford Mustang 1989-1993 Repair Guide

Fluid Recommendations

Both the automatic and manual transmissions covered by this information use Mercon® automatic transmission fluid for lubrication. DO NOT use improper fluids such as Dexron® or gear oil. Use of improper fluids could lead to leaks or transmission damage.


EDIT to add:
I just found this info:
Manual Transmission
Ford Mustang/Capri 1979-1988 Repair Guide


FLUID RECOMMENDATIONS

All 4-speed and 5-speed manual transmissions except for the T5OD - SAE 85W/90 gear oil

T5OD 5-sp - Dexron®II or Mercon®ATF

SAE 85W/90 gear oil may be used in the T5OD transmission in very warm climates or if gear/bearing noise is excessive. Conversely, Dexron®II or Mercon®ATF may be used in the ET 4-speed in very cold climates, or if hard shifting is a continuing problem.


Your guess is as good as mine. I have a 85 and use ATF.

silver91gt

I use mobil 1 synthetic ATF for my T-5 tranny and for my rear end I have royal purple synthetic 80w90 gear oil, it has additives in it already, but my auburn chatters still, I will change it back to regular 80w90 oil with some good smelling ford limited slip additive.

SpooledupRacing

ok so for this weekends task.. I need to use ATF in my 5spd trandmission..

btw does anyone know how many qts to use?

Dave

Grimace5.0

Per the chart I posted above: 5.6 pints.

SpooledupRacing

so just under 3 qts thx.. I bought synthetic Dex/mercon 3




Dave

Bad Karma

That's like saying..

"There's no point in changing your engine oil unless you are doing a rebuild."

Do you think that the rear gears are exempt from heat? How about pressure? Stress? Dirt? Moisture?

It needs to be changed every 30k at least. Knowing most of how the guys run their cars, I would change it every time I came back from the track or ran it hard. What's it cost to change out the fluid? $15 in parts? $40 to take it somewhere?

I put more $ in gas and don't think that it takes care of my car like Gear fluid would so....?..

-Ivan

PRO50SC

Royal Purple in the tranny and w/e my buddy put in for the rear. He works for Ford so that should tell ya something.

SpooledupRacing

I will be doing my diff next (after tranny and exhaust go on tomorrow)

I wont be using royal purple.. but the dex in the back (like above) next is diff fluid

Dave

5Liter Import Eater

i have never changed my tranny fluid and i dont think when the shop put in my clutch that they changed the fluid either, do u think that could be why after i drive my car a while, it becomes really hard to shift?

Bad Karma

I seriously doubt that the shop replaced your trans fluid without some kind of charge. It's not normal to include this with a clutch job. The reason that it's hard to shift could be due to several things...yes the fluid could be going south, but that usually wouldn't make it any harder.

I would second guess the Syncros in a heartbeat. Ususally a failed Syncro is from failure to replace fluids or powershifting like a madman.

Let us know what you find,
Ivan