swapping of final drives

[smagg26]

got a 91 fwd manual trans. was wondering if you can swap the final drive to a higher one like the 4.11 and if there would be anything else I would need to swap over as well. I'm looking to get shorter gears for faster accel.
I know that it will lower my top speed and change my shift points (in mph).

[cj91legss]

You can swap transmissions and diffs. I am happier now that I converted to 4.11 over 3.90. Only way I would go back to 3.90 is if I got a 6 speed.

What you have to swap over depends on the type of transmission you get. cable push, hydrolic push, or hydrolic pull.

[Alphius]

Cable push and hydraulic push are interchangeable. The trans case has provisions for both types of clutch fork.

As a side note CJ, I found out the other day that the 3.90 USDM STI transmission has almost exactly the same final gear ratio in 1-5 gears as a JDM v.5-6 STI RA DCCD 4.44 5mt. Those gears are super short.

[mike-tracy]

Why does the tranny case clutch actuation style have anything to do with the ring and pinion setting the final drive? I'm genuinely confused. He's trying to change the ring and pinion in his FWD tranny.

[Alphius]

Oops, I didn't catch that, I just replied to CJ's trans swap postulation.

Yes, the front ring and pinion can be changed if you take the trans out and split the case. Im not sure if the AWD and FWD pinion gears are interchangeable, so even though it is technically "possible" the parts may not exist to actually do the swap. There's lots of shims and adjustments necessary to set proper tooth engagement on the front diff which a transmission shop may be able to help with. It's a very involved swap.

There's a website focused on VW swaps that has the parts necessary to convert an AWD 5mt to FWD as well, that may be an option as the AWD 5mts could be had in 3.90 or 4.11 fairly easily and the FWD 5mt as I said before may not work with AWD ring and pinion sets. The site is subarugears.com. They also have procedures for doing the conversion yourself on there without buying parts, which is useful since they are in Australia.

[smagg26]

I've been weighing out the things I want to do, swap over to an AWD set up or swap the ring and pinon. either way I will have to rebuild the trans because syncros are going out on 1 and 2. so if it gets rebuilt why not throw in a high final drive for better accel?

[cj91legss]

I didn't pay attention this morning, my apologies.

[Legacy777]

The simple answer is that you can't really do this "easily" if at all.

On the AWD transmission the pinion gear shaft goes through the center of a driven shaft. The FWD transmissions do not have this and just have a larger pinion gear shaft. The diagram below shows the AWD pinion gear shaft.

http://main.experiencetherave.com/subar ... n_assy.jpg

[Legacy777]

As a side note CJ, I found out the other day that the 3.90 USDM STI transmission has almost exactly the same final gear ratio in 1-5 gears as a JDM v.5-6 STI RA DCCD 4.44 5mt. Those gears are super short.

I can attest to that the 3.9 USDM STi trans has pretty short gears. My freeway revs were actually lower just by a little bit with my 5spd 3.90 turbo legacy transmission in 5th gear compared to the STi's 6th gear.