Does the 4 speed behave normally when Diff ratio changed to 3.9? - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

DansEdgli · 05-10-2004, 07:28

JUst a quick question about my 6 cyl EB, I know that the speedo will be out when going from a 3.27 single spinner to a 3.9 LSD but will the trans still shift gears at the correct revs and kickdown like it normally would?
Being electronic would the different revs for a given speed mess with how it functions?
I want better acceleration but the turbo project will take too long to gather all the parts so I figure Ill need LSD anyway so I may as well make it quicker while im at it.
HAs anyone done this change? Was it worth it?how much quicker was it with takeoff?

Thanks guys,
Dan

Walkinshaw · 05-10-2004, 07:56

IM VERY intrested in the outcome of this. Ive heard stories of the 4speed craping istelf as the transcomputer/ecu has the diff ratio in its calculations as it uses road speed to judge kickdowns etc, and changing the diff ratio mucks up the shift and kickdown patterns.

Not to deviate, but with 2500/2800 stalls, does this give the computer a similar headache.

EBXR · 05-10-2004, 17:58

What about upgrading to the AOD box from the states? No computer required, and you get the 4sp auto.

OED666 · 05-10-2004, 18:33

well, DansEdgli, you know how mine crapped itself with 3.9's. Kickdowns were all over the shop.

I spoke to an auto place in brisbane, and they said the diff shouldnt effect the way the car behaves?!?!?.....

I would love to see an "good" condition auto with 3.9's

Walkinshaw · 05-10-2004, 21:04

what do you mean by all over the shop?

OED666 · 05-11-2004, 01:12

it just wouldnt shift right. but then again, i also could put that down to a dying gearbox. if anyone in brisbane with an auto wants to swap diffs with me for a trial (less than 2 hours), contact me... i cant live with out 3.9's now!!!

DansEdgli · 05-11-2004, 01:23

If I lived in brisbane I would be at your doorstep right now.

I dont want an AOD mainly due to the cost factor involved in the conversion.
It will take me at least 2 months to gather all the parts for my turbo conversion.
Then if the auto doesnt satisfy me after the turbo was on then I was going to make it a manual. I dont want to change trannies 3 times if I dont have to.

I have some cash saved up now that I was going to buy the manifold with but I really crave something that can get the arse out on corners and on take off like my XF did.

Will 3.9's in the diff acheive this?

Hopefully someone can give the answers.

OED666 · 05-11-2004, 01:45

well, i know that 3.9's went hard in first gear, and thats about all i could tell. it would be a MASSIVE stuff around to swap the diffs for the experiment, but may be worth it for the rest of everyone else.

I had a run with UNR8D back from the coast from a set of lights, and i beat him to 60k's, buy a fair bit of a margin, but then that was it for me, and all i saw then was the back of the Fairlane in the distance...

DansEdgli · 05-11-2004, 01:50

Was that loss due to your stuffed auto?
I really should just convert it to manual but then the trans wont hold when its turbo. Its so annoying.

OED666 · 05-11-2004, 03:35

yea, i would say its cuz of the auto being stuffed. on the way home, a couple of k's down the road, it wouldnt stay in 4th.

how much power are you looking out of your car with the turbo???