2G Evo 2 Transmission with Front LSD

[Greeno]

I have a few questions which arise from one major problem. I bought a 6bolt swapped 98 AWD DSM which had an Evo 2 transmission installed without changing the ring and pinion gears to correct the drive ratio. Once I figured out what was wrong, I sourced the correct gears, pulled the tranny, swapped the gears and reassembled it. I did not pull apart the center differential.

This unit has the clutch type front LSD. From what I remember, I had access to a factory service manual that provided the torque specs I needed. Unfortunately I can't seem to find this manual anymore, and I forget many specific details, as this swap was done approximately 13 or 14 years ago.

What I do know is, after assembly, the front differential didn't seem to have any slip. Tires squealing on corners, and turning was more difficult than it should be.

So, I'm planning on pulling the tranny out again to see if I can figure out what I did wrong the first time with the front diff, and to inspect/replace/rebuild the center differential as required.

I have 2 different W5M33s from 1992 models which should be able to donate a center diff/VC. And I will double check that I have the correct pairing of ring gear and T-case ratios.

I plan to be quite a bit slower and more deliberate this time, solder test, setting preloads, etc. As I'm hoping this will be the last time I need to disassemble the transmission for a while.

Is there anything else I should do/check while I have this thing on the bench?

And does anyone here have a FSM for the Evo 2 that would include assembly instructions and torque specs for the front differential clutch type LSD?

 

[Canadian_CD9A]

Torque specs will be the same as DSM. The Evo FSM is in Japanese and it's quicker to just go to the DSM book. For the specs on the aftermarket diff itself, usually good-n-tight on the screws is fully sufficient, but I can probably point you to the JDM specs if you show me what diff you actually have. Anyway, count the teeth on your front crown wheel. I assume the 63/64 tooth Evo crown wheel is out and a 57/58 tooth DSM crown wheel is in. Are you sure you installed the matching pinion gear? Evo and DSM pinions have the same number of teeth but don't work with the opposite's crown wheel. If it's correct, make sure you match your DSM front crown wheel to the proper transfer case. A 91-96 58-tooth crown wheel needs the 1.090 ratio transfer case and the 97-99 58-tooth crown wheel needs the 1.074 transfer case.

If that's all correct, check if your center diff is welded, which would also create some angry tire noises driving around. Driving around with mismatched ratios may also nuke the viscous coupling, center diff or transfer case, so those are all in play. Ensure whatever center diff you put in has the correct pitch - a 92-99 diff would work, but 91 and earlier won't. If that's correct and working properly, then it seems your LSD may be something aggressive like the Cusco MZ, which makes it sound like things are breaking when it's working properly. Some friction modifier can tame it down. If that still doesn't satisfy you, you may want to consider swapping the front LSD out to something more reasonable, like the Cusco RS or Kaaz, or a Quaife.

 

[DSMPT]

I bought a 6bolt swapped 98 AWD DSM which had an Evo 2 transmission installed without changing the ring and pinion gears to correct the drive ratio. Once I figured out what was wrong, I sourced the correct gears, pulled the tranny, swapped the gears and reassembled it. I did not pull apart the center differential.

What rear ratio do you have? You should confirm it first before swapping the front ring gear and the pinion. Maybe the previous owner has replaced the rear ring gear and the pinion with the early EVO's instead of the front ring gear and the pinion gear to match the ratio. Maybe that's why tires squealing?

 

[Greeno]

Torque specs will be the same as DSM. The Evo FSM is in Japanese and it's quicker to just go to the DSM book. For the specs on the aftermarket diff itself, usually good-n-tight on the screws is fully sufficient, but I can probably point you to the JDM specs if you show me what diff you actually have. Anyway, count the teeth on your front crown wheel. I assume the 63/64 tooth Evo crown wheel is out and a 57/58 tooth DSM crown wheel is in. Are you sure you installed the matching pinion gear? Evo and DSM pinions have the same number of teeth but don't work with the opposite's crown wheel. If it's correct, make sure you match your DSM front crown wheel to the proper transfer case. A 91-96 58-tooth crown wheel needs the 1.090 ratio transfer case and the 97-99 58-tooth crown wheel needs the 1.074 transfer case.

If that's all correct, check if your center diff is welded, which would also create some angry tire noises driving around. Driving around with mismatched ratios may also nuke the viscous coupling, center diff or transfer case, so those are all in play. Ensure whatever center diff you put in has the correct pitch - a 92-99 diff would work, but 91 and earlier won't. If that's correct and working properly, then it seems your LSD may be something aggressive like the Cusco MZ, which makes it sound like things are breaking when it's working properly. Some friction modifier can tame it down. If that still doesn't satisfy you, you may want to consider swapping the front LSD out to something more reasonable, like the Cusco RS or Kaaz, or a Quaife.

Yes, the 63/64 tooth is out and the 57/58 in. I'm 99% sure that the pinion gear was changed to the matching DSM version when I did the swap. I'm 90% sure that I did check that I have the correct T-case for whichever gearset I swapped in, but I'll definitely reconfirm that when I do the teardown.

I don't believe it's an aftermarket front differential, I think it's the factory upgrade option that was available in Evo 2s, that's why I'm hoping to find a FSM with the diagrams and torque specs for it. I could be completely wrong here, but nothing else about this car was upgraded to the point where an aftermarket front LSD or a welded center diff seem appropriate. It is not fast or powerful, and the seller didn't even know that the transmission was an Evo 2 model (or if he did, he didn't tell me/use it as a selling feature). I believe they were dumping it on the cheap because they couldn't figure out why it would ”lock up" and make horrible noises after a moderate amount of driving.

The trouble with the front tires chirping on turns only showed up after I did the 58 tooth swap, which is why I'm assuming I did something wrong when reassembling the front differential.

What rear ratio do you have? You should confirm it first before swapping the front ring gear and the pinion. Maybe the previous owner has replaced the rear ring gear and the pinion with the early EVO's instead of the front ring gear and the pinion gear to match the ratio. Maybe that's why tires squealing?

I have no idea tbh, the ring and pinion gear swap is done, though it could be undone, if necessary. Based on the issues I had when I first purchased the car, there was almost certainly a ratio mismatch between front and rear wheels which caused some pretty awful noise/behaviour after about 40km of highway driving.
I think it's highly unlikely that PO swapped the internals on the rear end, but it's definitely a possibility that I hadn't considered. I will figure out the different ratios that exist between DSM/Evo and figure out which one I have. If anyone knows them off hand and wants to drop the numbers here, that would be appreciated, but I'm sure I can find them relatively easy here.

Thanks for making me consider an angle to this that I hadn't thought of before!

 

[Canadian_CD9A]

Yes, the 63/64 tooth is out and the 57/58 in. I'm 99% sure that the pinion gear was changed to the matching DSM version when I did the swap. I'm
90% sure that I did check that I have the correct T-case for whichever gearset I swapped in, but I'll definitely reconfirm that when I do the teardown.

I don't believe it's an aftermarket front differential, I think it's the factory upgrade option that was available in Evo 2s, that's why I'm hoping to find a FSM with the diagrams and torque specs for it. I could be completely wrong here, but nothing else about this car was upgraded to the point where an aftermarket front LSD or a welded center diff seem appropriate. It is not fast or powerful, and the seller didn't even know that the transmission was an Evo 2 model(or if he did, he didn't tell me/use it as a selling feature). I believe they were dumping it on the cheap because they couldn't figure out why it would ”lock up" and make horrible noises after a moderate amount of driving.

The trouble with the front tires chirping on turns only showed up after I did the 58 tooth swap, which is why I'm assuming I did something wrong when reassembling the front differential.

I have no idea tbh, the ring and pinion gear swap is done, though it could be undone, if necessary. Based on the issues I had when I first purchased the car, there was almost certainly a ratio mismatch between front and rear wheels which caused some pretty awful noise/behaviour after about 40km of highway driving.
I think it's highly unlikely that PO swapped the internals on the rear end, but it's definitely a possibility that I hadn't considered. I will figure out the different ratios that exist between DSM/Evo and figure out which one I have. If anyone knows them off hand and wants to drop the numbers here, that would be appreciated, but I'm sure I can find them relatively easy here.
Thanks for making me consider an angle to this that I hadn't thought of before!

The only factory LSD in Evos was a viscous unit that usually doesn't give any trouble. If you were able to swap a DSM crown wheel onto it, it's definitely not that factory viscous LSD, which has a unique crown wheel that doesn't interchange. So, if you can see straight through the front diff with the axles out, you have an aftermarket LSD in there. Japanese people LOVED swapping aftermarket LSDs into these things. It was common to see a totally stock appearing car scrapped and half-cut, but that car might have all 3 diffs swapped when the driveline was dissected. This doesn't rule out a transfer case mismatch. Do a full tooth count on the front diff, the transfer case, and the rear diff. That's step 1.

 

[Greeno]

The only factory LSD in Evos was a viscous unit that usually doesn't give any trouble. If you were able to swap a DSM crown wheel onto it, it's definitely not that factory viscous LSD, which has a unique crown wheel that doesn't interchange. So, if you can see straight through the front diff with the axles out, you have an aftermarket LSD in there. Japanese people LOVED swapping aftermarket LSDs into these things. It was common to see a totally stock appearing car scrapped and half-cut, but that car might have all 3 diffs swapped when the driveline was dissected. This doesn't rule out a transfer case mismatch. Do a full tooth count on the front diff, the transfer case, and the rear diff. That's step 1.

I'm definitely not an expert on these things, I'm basing this off what Tim has said in other posts about these transmissions, for example:

All Evo 1/2/3 transmissions had options of either an open front differential or a clutch-type LSD front differential, or the rare case of a viscous lsd front diff that had a unique right CV joint spline length, and a unique front diff ring gear to fit on the viscous front differential. All Evo 1/2/3 transmissions came with a standard 2-spider viscous center differential.

 

[Canadian_CD9A]

The clutch type 'option' he's referring to is actually a Ralliart over-the-counter item that was so commonly purchased and installed that it could have been mistaken for a factory option. It swaps right in like the open diff with the same ring gear and axles (just like any other LSD other than the viscous). It's super easy to identify - it's got a machined cast housing that isn't seen on any of the other front LSDs. This one is a kitty cat, quite mild and docile like a factory option would be. It doesn't have much preload and as such, won't chirp the tires much - or maybe not at all. I really doubt you'd have this one installed if you have excess locking.

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My guess is that you're going to see the one on the right, the Cusco MZ, if every part is correct in the car and if nothing is broken. The milder Cusco RS (left) looks the exact same except it will have tiny coil springs visible through the windows. I've had two people reach out to me and ask what's broken in their transmissions, turns out they had an MZ that was just doing its job. It absolutely goes clunk-chirp-bang when step up normally. You can detune preload and mess with friction modifiers to make it livable, but it wasn't really made for that. These do sometimes break the bearing posts off or crack the housing under heavy abuse, which would definitely cause odd behavior.

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Here's a video of one in action:

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And another:

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And a Kaaz front LSD in a later Evo, same idea. Preload likely jacked up.

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[Greeno]

The clutch type 'option' he's referring to is actually a Ralliart over-the-counter item that was so commonly purchased and installed that it could have been mistaken for a factory option. It's super easy to identify - it's got a machined cast housing that isn't seen on any of the other front LSDs. This one is a kitty cat, quite mild and docile like a factory option would be. It doesn't have much preload and as such, won't chirp the tires much - or maybe not at all. I really doubt you'd have this one installed if you have excess locking.



My guess is that you're going to see this thing, the Cusco MZ, if every part is correct in the car and if nothing is broken. The milder Cusco RS looks the exact same except it will have tiny coil springs visible through the windows. I've had people reach out to me and ask what's broken in their transmissions, turns out this thing is just doing its job. It absolutely goes clunk-chirp-bang when step up normally. You can detune preload and mess with friction modifiers to make it livable, but it wasn't really made for that. These do sometimes break the bearing posts off or crack the housing under heavy abuse, which would definitely cause odd behavior.

That's really cool, thanks for the explanation! I guess I've got to get this transmission apart so I can figure out what this diff is, and then do some decision making. Based off my (questionable) memory, the Cusco certainly looks more familiar than the first one.

 

[Greeno]

My guess is that you're going to see the one on the right, the Cusco MZ, if every part is correct in the car and if nothing is broken. The milder Cusco RS (left) looks the exact same except it will have tiny coil springs visible through the windows. I've had two people reach out to me and ask what's broken in their transmissions, turns out they had an MZ that was just doing its job. It absolutely goes clunk-chirp-bang when step up normally. You can detune preload and mess with friction modifiers to make it livable, but it wasn't really made for that.
And another:

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And a Kaaz front LSD in a later Evo, same idea. Preload likely jacked up.

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One question from watching those videos, mine doesn't "clunk" like that, the tires would just scream while turning. Is that significant? I saw another post here where someone complained about tire screech while turning that was solved by replacing the VC. I have to imagine that since my unit has a front LSD and a high likelihood of a destroyed VC, it's probably tough to differentiate between the two.

I've spent some time looking into these LSDs, reading more posts about center diffs and VCs, and I think I've got a new plan. (I'm working away from home right now, and won't be able to get my hands on the car for at least 2 weeks)

I assume you're right about the Cusco, I was looking at their reference materials, and I remember stressing about how to reassemble those clutch plates. As you said, I could tune the setup to make it more liveable for a street car, but that doesn't seem like a good use of an expensive performance component.

So I'm thinking I'll confirm the rear diff ratio, pull the transmission from the 98 and one of the 92s, inspect the 98 center diff for damage, pull the Cusco out and transplant the front diff/VC from the donor tranny into the Evo. At this point I can rebuild/replace the center diff and T-case as necessary. I suppose I should look into the 4 spider diff upgrade while I'm doing this, right?

I believe that would leave me with an OEM+ setup that is more appropriate for my ultimate goal of having an AWD street car that's "fast" and fun to drive. Is there anything else I should consider here?