[CCF5000]

Hey guys, I have a 1991 Mustang GT with a little bit of work done to it. It's got a FRPP 8.8 Rear end with 3.73s and a FRPP Superduty T5 transmission. Should i just use regular dexron 3 atf for the transmission and what weight for the rear end? Someone told me 75w90 would it be ok to use mobile 1s synthetic in the rear end along with ford's limited slip additive? both have about 5000 miles on them not worried about it yet but gonna change both of them out at 10,000 miles.

[Young_Buck]

What oil or lubrication is currently in the transmission and the rear differential? I sincerely hope that it's not Gear Lube in that Transmission...

If they were rebuilt recently (as in that 5,000 miles ago) it might be within your best interest to change out that oil NOW. If the transmission and the gears were brand new, they were coated with a type of additive that is meant to keep things from locking up when you first installed them and prevent them from rusting or oxidizing while they sat on the storage shelves. As a result, that additive is now floating around in the current lubrication that you've got in both the transmission and the differential. Unless, you know for a fact that a "Break-In" was completed with the Transmission and the Differential and the oil has been changed out of both after that period, in which case you won't need to change it for quite some time. If, as stated, you haven't done a break in then fluid change, you want to change out that oil.

To answer your question on what oil to use? Use basic Dexron 3 ATF (Try to stray away from the Synthetic stuff with this, it's known to hurt the transmission more than help it) for the transmission and the Rear Differential takes 75w90 with a bottle of Limited Slip Additive in it. You can go synthetic with the Rear Differential without causing much problem. Also, seeing as how your Rear Differential fluid is changed out (I believe...) every 75,000 miles, or so, why not go with the good stuff? Royal Purple 75w90 Synthetic Oil. That's what I went with in my Rear Differential and I've never been happier!

-YB

[CCF5000]

Well see i bought the vehicle from a guy who was selling it with receipts for everything. The guy was fairly knowledgeable and did most of the work himself. The car has 102,000 on the body.
It has a 5.0 rebuilt with GT40 Iron heads 62cc, GT40 E intake manifold, 65 mm throttle body, 75mm mass airflow sensor, fenderwell cold air, TFS stage 1 cam, BBK Headers, Off Road H pipe, Flowmaster mufflers, i have the stock h pipe with cats for inspection purposes. FRPP Superduty T5 transmission, FRPP 8.8 Rear end with 3.73 gears, alluminum driveshaft and new u joints, and i think that's all i may have forgotten something. About 4000 miles on the entire driveline so it runs like a champ but i'll probably follow ur advice and change it out next week. Also is it ok to jack the vehicle up by the motor K member and rear end? That's how i worked on my 240 i wasn't sure i've never worked on a stang before so it actually should be easier. Thanks man I love the car its so much fun.

[CCF5000]

http://a452.ac-images.myspacecdn.com...41b97702d3.jpg
There's a pic of it i paid 3800$ for the car