changing final drive

svynx

Forum Member
Joined
Sep 11, 2014
Messages
28
Location
Dover, pa
Car Year
looking around
Car Model
unsure on what
Transmission
i want to lift
I just purchased a 2003 Impreza TS wagon. It already is lifted on 04 FXT struts and springs. Rear trailing arm bracket switched to recenter the wheels. It currently has 15" wheels, with a no name brand tire (extremely loud, even at 25mph). Still stock size overall, so no issues driving. I've driven a similar setup that had the same gearing, but 215/70/16 tires. Needless to say, low end torque disappeared, and acceleration was non existent. So, after some research, I found that the TS has a 3.9 final drive. If I were to swap out the ring and pinion gear with that of a 4.44 (and the rear diff), increase the tire size to something in the 27" diameter range, the feel of the car will be back to normal.

I don't know if this is possible or not. I would switch to a FXT transmission, but the clutch type is wrong. Anyone try something like this?
 
But isn't increasing the tyre size going the opposite way to lowering the diff ratio? One will negate the other.
 
Gidday SV

I agree with guzzla, it's a bit more complicated than that.

You do really need to work out what you want to achieve first, otherwise you are just going to flush a whole lot of cash down the gurgler ... :(.

From my Batphone
 
Increasing tyre size will lower your gearing. So yes you can change to 4.44 and it should be very similar (maybe a little slower).
What motor do you have? Over here our bas model imoreza's only had a 2.0l n/a or 2.0l turbo or the RS has the 2.5.
 
Thanks for the replies. Our TS has the 2.5l. I think my wording was off, and could be causing confusion, but I think you guys understood what I was going for. I will be increasing the tire size, and I would like the gearing to change so that the speed vs rpm would be as close to stock as possible.
 
Ok. Seems like I'm thinking along the right line. I guess I need to make a decision on if I'll modify the transmission I have or convert the clutch type from a push to a pull style so I can run a 04-08 forester XT transmission. Cost wise might be close either way.
 
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Dual range gearbox?? Or Loyal Part Time 4WD gearbox?
Id personally go that route if I lived in the US as you never got the AWD MT dual range boxes.
 
Wish I could, but finding one is near impossible. The stock trans in our TS is identical to the 04-08 FXT trans, minus clutch type, and a 3.9 final drive (vs the FXT's 4.44). My options are:
- change the ring/pinion gears to get the 4.44 final. This allows me to use the stock clutch that is there (and fairly new). I would need a different rear diff to match the new final drive.
- swap to a FXT 5 speed. I would need a new clutch and slave master. Again, a different rear diff to match.

Cost difference will determine what direction I go. That and how hard it will be to find a FXT trans.
 
If you want those tyres, I'd go the 4.44 diffs. Easiest way would be to swap in a FXT box, better would be to split your box & swap in the 4.44 crown wheel & while you're there a front LSD...makes a huge difference!

For your rear diff, I would try to find a complete 4.44 LSD with matching axles, plated if you can
 
With cost being a factor in this endeavor, I have decided to go a slightly different route. The 97-04 n/a forester has a 4.11 final drive, and they are really easily found. I actually know where to get one, vs the FXT trans (which seems to be made of gold and can only be found on the 6th friday of the month). I did some calculations, and as long as I stay below the 27" diameter tire dimension, the drivablility will stay about stock. And, I won't have to do anything to the internals of the trans itself. So, for $200, I can toss this in and save for a while for the 4.44 conversion of the factory trans that comes out (that is if I feel the 4.11 isn't enough).
If any of you are looking to figure out gearing, and what happens when you change tire size/gearing/final drive, here is a great site to visit.

https://www.teammfactory.com/gearcalculator.php#
 
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