legacycentral bbs

I know there's been some threads that deal with this but I just wanted to ask so that I have the most current knowledge.

If I swap a 5mt tranny from a WRX into my '93, do I need to get a different rear diff? What do I do about the speed sensor?

The following is based on memory of reading other posts, not based on personal experience:

You do need to do something about the differential ratios. There are a couple of options:

1) Use a WRX rear differential. This would also require WRX rear axles. You'd end up with an LSD.

2) Swap your stock center differential into the WRX transmission. Then you should be able to use your current rear differential.

3) Swap in an SVX rear differential. I think this will work with your stock rear axles and give you the right gear ratio. This is an LSD, I think. You should be able to tell by all the "I think"s that I'm the least certain about this option.

The speed sensor shouldn't be an issue. You should be able to thread your stock speedometer cable into the WRX transmission and all will be well.

Scott - For you, yes, you need the WRX rear differential.

Since you have an automatic, you can't use your current stock center diff.

You could source a transmission from a 5-MT Legacy and steal the center diff and entire rear-half of the transmission and bolt it on there.

It should bolt right up though, without much issue.

vrg3 wrote:3) Swap in an SVX rear differential. I think this will work with your stock rear axles and give you the right gear ratio. This is an LSD, I think. You should be able to tell by all the "I think"s that I'm the least certain about this option.

SVX gear ratios eat 4EAT's alive.

I don't think that's the reason they fail, since every 4eat (including SVX) I've ever seen specs on has the same gear ratios. There's plenty of speculation as to what causes the death, one of which is the final drive ratio being too low which makes the oil pump turn too slowly. Again, that's speculation.

You really don't need to swap the center diff, only the rear transfer reduction gears.

I'm trying to get away from the 4eat, that's what I'm swapping out.

ive heard that the old legacys na or turbo have stronger trannys than the wrx's because of rally car usage.

anything to support this.

azn2nr wrote:ive heard that the old legacys na or turbo have stronger trannys than the wrx's because of rally car usage.

anything to support this.

There have been a TON of revisions to the design over the years. We have a really archaic, but more durable synchro setup. The newer boxes have a less reliable, but MUCH smoother synchro setup. The downside, is the synchro will, simply put, break. The teeth will shear off and instead of the synchro slowing the gear to allow the shift collar to slide over the engagement teeth, it... won't do that... and the gear won't slow down, and you will have trouble getting into gear, or grinding gears. Under normal driving circumstances, there is absolutely NO reason that the WRX transmission would fail you, unless you abuse it. The gears aren't strong enough, even for the stock power of a WRX, but driven "normally" you shouldn't have problems. Some people NEVER have problems. It's all about style and how it works. I see ALL WRX's as being potentially transmission-less.

Our synchro setups are more durable, but not nearly as efficient. Or that's the folklore. The newer boxes SHOULD be more durable, but simply put, the WRX is driven harder, i'm sure, than FHI had originally intended. That's why the 2003.5 and newer transmissions have been further beefed up.

I doubt it's got anything to do with rally car usage, but simply advances in design and technology.

Josh - I don't believe you can JUST swap the gears. I think you actually need to replace the center diff, and the diff housing as well as the gears and such. I think it all needs to be replaced with your original stuff.

Aren't the SVX rear axles setup differently? I remember something about one having a long stub and the other having a short stub. Its been a while though, so I'm not totally sure.

I'd say that if you're getting the tranny and rear diff, it shouldn't be too hard to get the axles also. That's what I did when I put a WRX tranny in my 92.

Josh - I don't believe you can JUST swap the gears. I think you actually need to replace the center diff, and the diff housing as well as the gears and such. I think it all needs to be replaced with your original stuff.

From the diagrams I've seen, they look the same, and I don't see why they would be different. However I haven't done it, so I can't say for sure.

Aren't the gears machined onto the shafts, or at least welded? I seem to remember them being so. While the "idler" side (the side that rolls on bearing in a race in the housing) should fit right in, the other shaft is splined for the center diff.

I think the splines are different between OUR center diffs, and the WRX center diff, and that's why you can't swap just the gears (I think).

Yeah I would assume the gears are permanently mounted to the shafts.

Yeah I don't know about the splines being different or the same....so your guess is as good as mine. It might have the info in the FSM's, but I haven't looked.

which clutch and fly wheel do you use when doing this swap???

WRX or your stock clutch