CAn I change only the final drive gears?

[fowljesse]

Thanks, Wytbishop!

[Yoda]

To swap the final drive, you need to change the pinion gear and the differential. The diff is easy, but I've been told that to take a gear of a shaft is a huge pain.

The gear is a shrink fit to the shaft. Where the gear is heated slipped onto the shaft then the final machining steps or completed. If you are going to change this gear you really should used the whole shaft otherwise the gear will probably become out of spec if it is heated and removed from the shaft and could micro fracture if removed cold creating all sorts of problems later. Also in certain cases I have seen were the gear and shaft were machined and one piece like in the trannys with the 4.588 final drive ratio

[wytbishop]

I wouldn't have thought that. Good thing to know. It would still be relatively simple to exchange the shaft with the pinion gear you wanted. You would have to completely disassemble the shafts and exchange all the gears and synchro hub but a meticulous person could manage it.

[tehbrookzorz]

You guys have got me nervous now with this talk about which diff ratio the Mazdaspeed LSD ring gear uses. I'd figured I was safe putting it in the MX-6 transaxle I picked up as a spare. I guess if I do have to swap the pinion shaft it makes sense to swap in the stronger newer generation mid-gears, but please clear this up for me.

[wytbishop]

OK...so I'm asking the guys at iMazda.com that actually did this and they say that yes, the MSP LSD is 4.11 and that yes the 95' PGT they were working on is 4.39 and that they didn't change anything. They just put it in there and it worked.

I physically counted the teeth on the two diffs. The one they took out had 79 teeth (4.39=79/18) and the one they put in had 78 teeth (4.105=78/19).

I am pretty sure that this means that the MSP LSD will work with the smaller 4.11 pinion gear (though I wouldn't have believed it) to give a final drive ratio of 4.33 (78/18).

I'm not sure what the deal was with Gro Harlem's tranny. He said he stuck the diff in and the shafts bound up and wouldn't turn. He also said he put ZX2 internals in his tranny at that time and I have found 1 reference HERE that says it has a 4.10 final drive ratio as well so that makes some sense. But why would it not work for his stock tranny and it did work in the iMazda 95' PGT stock tranny?

I don't know. But I am absolutely determined to find out.

[Nd4SpdSe]

Hmmm, I wouldn't be surprised if there was enough play in the teeth of the gears and the bearings that putting an MSP LSD into a 4.38 tranny may just work...but I wouldn't recommend it. You've even done the math yourself. My guess is that Gro got it right, while they guys on iMazda half-assed it and got lucky with just enough play to make it work.


Here's some related ProbeTalk links:
http://forums.probetalk.com/showthread. ... ht=msp+lsd" onclick="window.open(this.href);return false;
http://forums.probetalk.com/showthread. ... ht=msp+lsd" onclick="window.open(this.href);return false;

Here's the thread of Gro selling his LSD/ZX2 parts that I got:
http://www.mx-3.com/phpBB3/viewtopic.ph ... it=msp+lsd" onclick="window.open(this.href);return false;

And the thread of his setup:
http://www.mx-3.com/phpBB3/viewtopic.ph ... it=msp+lsd" onclick="window.open(this.href);return false;

[wytbishop]

In order for the 4.11 ring gear to mesh at all with the 4.39 pinion they have to have the same size and shape of tooth. Since they must have the same size and shape, the only way for the 4.11 to work is if it's slightly smaller in diameter. This wouldn't be clearly visible because the first gear secondary gear (which is large) is on top of the pinion gear so you would not see the diff mesh. What you would see is that the teeth don't fully engage. When two gears mesh perfectly their pitch circles intersect.



This would not be the case with a slightly smaller ring gear and the teeth of both gears would wear faster. It might work, but it would wear your ring gear out prematurely. That's what I think.

If you went the other way and tried to put a 4.39 ring gear into a 4.11 tranny, I don't think you'd even be able to put the secondary shaft in place. The larger ring gear would interfere with the pinion.

I'm going to find an MX-6 tranny and test this theory.

[Ryan]

I think anything besides using the correct mating parts is a VERY stupid idea. You don't want binding, or a loose fit. You want these gears to mesh exactly how they were meant to. This is your drivetrain. These parts are expensive. Why would you use it incorrectly?

-My 2 cents

[tehbrookzorz]

The problem is being 100% positive which gear ratio the Mazdaspeed LSD has, which we're trying to hash out.

[wytbishop]

Well every post I've ever read says it's 4.11 and the one in the iMazda thread has 78 teeth. I counted. 78/19=4.1052 so I'm pretty sure it's designed to mate with a 19 tooth pinion.

The one they took out had 79 teeth. I counted. 79/18=4.3888 so I'm pretty sure it's supposed to mate with an 18 tooth pinion.

The part that is tweekin my melon is that Gro said it wouldn't spin with his stock internals but the iMazda guy says he didn't change anything in the 95PGT tranny they put it in...which should be 4.39 like ours....and it worked just fine.

Maybe their PGT tranny wasn't 4.39 final drive. I've talked about it with my collegues and we all agree that it should not work with a 4.39 pinion gear.

[Daninski]

I love reviving old posts. I have a spare tranny and thought of doing some work on it so this thread is bang on. Now, who has these parts real cheap that I can buy? I really do need an LSD. Does anyone know if the LSD can be removed from the JDM MX-6 trans and installed in ours or do those twisty axel things have to go with it. I'll admit here and now I've done almost no reasearch here and am just starting to look into the LSD situation.

[Nd4SpdSe]

You can't. You'll encounter the same issue in reference to the MSP LSD. The Mx-6 trans should be a 4.11:1 final drive, thus the ring gear around the LSD is a 4.11:1 gear. It won't be compatible to work with the 4:38:1 pinion gear in the Mx-3 trans.

You could however technically drill out the rivets for the ring gear off the LSD, do the same on an Mx-3 diff and use the ring gear from that Mx-3's diff onto the LSD...it's basically the same thing required when using a Quaife LSD.

One thing though...I'm pretty sure that the Mx-6 LSD should have the right splines to work with our axles, but if it doesn't, it won't help you since the axles go into the LSD, so you'd have that same problem.

[Mooneggs]

I'm putting the MFactory LSD into my 626 tranny (4.11 gearing)... do you think I will have any issues? I kept reading through the imazda walkthrough and it looks ike a piece of cake but now I'm nervous...

[wytbishop]

You're golden Mark. You're going to have to take the ring gear from the stock diff anyway as the Mfactory diff doesn't have one. So you will have no compatibility issues at all.