Making JDM tranny work help.

[MoclovFlop]

Ok so As some of you know, me and STZYGT are working on getting everything in order for his swap. So i've got a couple questions about mating the tranny with the rear end.

First. I know the final drive on the JDM tranny is 4.44 and I know that we could swap out the rear diff with one from an auto 2.5rs since they had the same final drive.

Now instead of swapping out the rear end, can we simply swap out his center diff with one that is 4.11 (like one from a WRX since it's almost the same tranny) like his original rear end? Or is the center diff even relevant to what the final drive is?

Second: If we did swap rear diffs, I know he would need the matching axles, but what about drive shaft? Is there a length difference between subaru's rear diffs? or are they all the same with just different "pumpkins"?

Let me know what ideas you guys have as to how we should go about getting these things to work together.

[sheepdog]

Don't mess with cracking those transmissions open, just get the RS rear diff. You can use your legacy driveshaft, all rear diffs are the same length. In terms of axles, you might even be able to use the ones that are on there, so check before you buy replacement ones.

[MoclovFlop]

After doing a little more research, it looks like it would be hard to find a center diff with 4.44 anyway. So rear end switch it is.

What would be the differences between axles? Spline number? I know most Subaru's had the same drivetrain widths, so that wouldn't be a problem if we did end up using rear axles from the RS.....would it?

If for some reason we did end up having to use the rear axles off the RS, would that require a whole new hub assembly too (plus brakes and what not)?

[sheepdog]

It shouldn't, but I'm not sure. I think the RS axles will fit if you end up having to use them.

[mr_choung]

i think the wrx tranny is 3.9 but i could be wrong ;)

choung

[MoclovFlop]

Depends, It either 4.11 or 3.9 depending on year and wheter or not it's auto.

I found a 4.44 rear diff for pretty cheap, now i'm just trying to figure out how many splines are in the inlet for the axles. I'm getting conflicting research .

[Wiscon_Mark]

The WRX is a completely different deal. It's not the same thing as your standard 3.9 tranny - I believe the differential makes it 3.9 or something odd like that.

[rougeben83]

AFAIK, all auto trannies used on auto subbies have 4.44. You may want to dig around for a BD/BE Legacy auto tranny as well. The BE/BH GT/outbacks got LSD, so those would be my first choice. Get the rear axles for them just in case. IIRC there are differences in the axle connections.

[MoclovFlop]

Yea the WRX trannies were like 3.54 with a 1.1:1 so it came out 3.9.

And in terms of 4.44, I've found all the USDM Suby's that had a 4.44 rear end, and they are scarce. A couple specific foresters had them, and the auto version of the BE/BH models (the limiteds of the later years and the GT's had rear LSD) , and all auto 2.5 RS's had 4.44 as well; and 2000-2001 had LSD's. I know that sounds like a lot of models that had them, but it's hard finding one to get the rear end.

However, I was able to find a 2000 2.5 RS with a VLSD from an automatic, so that's damn good news. But I'm still having a hard time figuring out the spline count on everything, to see if his 98 GT axles will work with it.

From what I've found, it doesn't look like it because rear diffs with LSD's were 25 spline, and non-LSD ones were 22. But half shafts aren't too expensive, being around 40-60 at NAPA if worst comes to worst.

I'll keep you guys updated with what we end up useing.

[Huffer]

The USDM automatic BD's are 4.44 also - my GT has that ratio.
My GT wagon, being a 5spd, appears to have shorter gearing 4.11 as at the same MPH, my wagon runs a tad higher in the rpms.

[Sarra]

The WRX has a 1.1 drive ratio on the center diff. The front and rear diffs have different final drives... 3.54 rear and 3.9 front (IIRC)

Why go with a 4.444? That's a bit short, unless you've got a 6 speed. Sorry, I have no idea what your swap is involving...

Theoretically, you could run a different diff in the rear, however you would have to do some math, and run a different size tire front to rear. So, you'd have like 205 55r16 in front and 205 60r16 in the rear. Not worth it...

Is there a possibility of you moving up to a different axle? I have no clue about spline counts from an STi, but if you did hubs and axles from an STi, they would defiantly be stronger. NOt sure if that's relevant, again...

[MoclovFlop]

The reason he's sticking with the 4.44 is because the tranny is actually the STI-RA tranny (5-speed, non-DCCD), so it's really well built, and it came with the engine so it's some what worth it to keep the 4.44. It will suck greatly on the highway because of the gearing, but I've read a lot reviews from people saying it's a good match for the TT setup (yes he's still trying to keep that).

In terms of axles, we are a little worried about the strength of everything, because his axles probably aren't good for the power the engine is supposed to make (around 280+ hp) But it would be expensive to switch the whole assembly to something like STi because you'd also have to get the hubs... (but he could go STi brembos...... :twisted: )

We'll see what happens, in the future he may ditch the tranny and go for something 6 speed, or at least a better final drive.

[Wiscon_Mark]

WRX axles should be fine.

[MoclovFlop]

Would they have the same width as stock? And would he have to switch out his hub assembly for a WRX one?