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Discussion Starter #1
Going to be buying a 98 5MT SF very soon for a winter car. I know of a Automatic WRX rear diff for sale near by fo $80. It's a 4.11 diff.
Just want to know if this would be a good upgrade compared to the stock diff in the SF. I believe that the SF is an S model.
 

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Upgrade in what respect?

2.5 5MT SF are 4.44:1 so you would have a mismatch with a 4.11 rear, so not a straight swap.

Simon
 

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Discussion Starter #3
There might be a 4.44 on the turbo but I'm pretty certain there isn't one on the S. The only Subaru's that come with 4.44 are Type R STi's, 04/05 XT's and NA automatics.
I just wanted to know if the WRX would have a better LSD.
 

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SF Forester MT is 4.11. But as far as I remember, only Foresters and 2.5 Imprezas had compatible diffs, all WRX had lower ratios (I might be wrong, but I did search some 2 years ago when I was replacing my diff).

BTW, if you're getting later years diff (2000+ ?), the axle connections are slightly different. They fit and latch just fine, but the "toothed" parts are offset a bit, so you lose about ~1/3 of the strength (should still be strong enough; or change axles along with the diff).
 

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Discussion Starter #7
SF Forester MT is 4.11. But as far as I remember, only Foresters and 2.5 Imprezas had compatible diffs, all WRX had lower ratios (I might be wrong, but I did search some 2 years ago when I was replacing my diff).

BTW, if you're getting later years diff (2000+ ?), the axle connections are slightly different. They fit and latch just fine, but the "toothed" parts are offset a bit, so you lose about ~1/3 of the strength (should still be strong enough; or change axles along with the diff).
The diff is from an automatic WRX though.
 

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I'll have spare shafts from my XT when I do my R180 swap.
So then you're have the diff, too. Really, for $80 (plan on new axle seals) you can try it (make sure of the gear ratio), otherwise just wait. If you really get stuck, that vLSD is not going to help.

P.S. Early-2000 Outbacks have the compatible diffs, too. Few have vLSD though.
 

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N/A 5mt SFs are 4.111, swapping in that diff from the WRX will be adding an LSD.
OK thanks, the parts ref site I used said 4.44 for a US 2.5NA so imperfect then I guess!

Simon
 

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I just wanted to know if the WRX would have a better LSD.
If you're doing this for the LSD, then I would save yourself the time and effort as the LSD really doesn't work all that well off road. Below is a video showing my rear tires just spinning, and the LSD not doing anything to help. It may help on the street, but not off-road in my experiences....and using the handbrake or regular brakes to "trick" the LSD doesn't work either....(at least, not for me in the few situations I've been in)

YouTube - More Forester Offroading
 

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Actually, the video shows that it does work - were it not for vLSD you'd likely not be able to back out on that first try.

But yeah, it's weak, not for off-roading, no doubt there. Still, it helps a little bit in many situations, such as starting on ice, hill climbing, or getting the rear end out for a power slide (on loose gravel or snow/ice, not on dry pavement).
 

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The OEM vlsd isn't worth the bother of "upgrading". It does barely anything as said above and the diff isn't any stronger or anything. Just weld up the stock diff!
 

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What part do you weld? Does anybody have a link to more info on this?
Wasn't entirely serious. But if you want traction and its not going to be driven on pavement much, its a cheap option. Basically you make it so the 2 sides are always locked together, although it will hop a bit on dry pavement.

If you're only going to be using it in the snow, you could even weld up the center diff like many rally cars have done.

However this isn't something I would do if you want a smooth daily driver. Just a cheap way to get good offroad traction.

Just don't do this:

 
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