krazik

What exactly is different with your new Diff, vs the stock one?

The Reverend

Quite a bit, actually.

The stock diff is a Torsen Type II gear type differential. It's actually not a true limited slip differential, but really an automatic torque biasing differential. It consists of two side gears and eight planetary gears. The side gears have splines on the inside where the axle hubs go into. The side gears are connected to each other via four pairs of planetary gears. When not accelerating or decelerating, the planetary gears allow for the side gears to freely move in opposite directions (like an open diff). When accelerating, the planetary gears bind on the casing and act to limit slip to some degree. The advantage of this is that it is quiet and transparent in operation. The disadvantages are that it does not allow full lock up and 50/50 power distribution. Also, if one wheel comes off the ground in a turn or a pothole or whatever, when it hits the ground again, you can strip the gears of the differential to hell. Not to mention, the Torsen units they put in our cars are poorly cast. You only need to take on look at one to see what I mean.

http://www.torsen.com/T-2.htm


The differential I installed is a forged Kaaz 1.5 way LSD. It is a clutch type LSD, so it works more like an open differential, except it has a sort of cam mechanism that pushes the side gears outwards under acceleration (half as much under deceleration). When pushed outwards, the side gears are pressed against the clutch plates and slip is limited effectively. This type of unit is anything but transparent in operation. When you drive a car with such a differential, there is never any question in your mind when it is limiting slip and when it is not. You can feel it very easily as the car responds immediately to changes in throttle. There is a small amount of chatter and noise in low speed turning situations like parking lots. This is hardly an issue after the break in procedure and about a week's use, however if you do not use Kaaz gear oil (which is unfortunately about $40/bottle) the noise and chatter becomes quite severe. The reason I used this differential is simply because I have never heard of anyone breaking one and I've already broken two of Honda's torsen units on my S2000 so far. I didn't want to break another (especially since I was particularly gentle with the second torsen unit and it still broke). However, now that I have it, I consider it one of the best mods I have done to the car. The car just cuts through corners amazingly well.

Here's a small pictures of how a Kaaz LSD works (I used to have a bigger picture, but I don't remember where it is):


The interesting thing about the torsen unit I took out of my car is that it was obviously not functioning properly as per the test provided in the service manual. It was binding and not turning freely. When we took the rear end apart, we expected the problem to be something obvious - a thrown bearing, an adjustment way out of spec, or some stripped gears. However, all adjustments were only a little out of spec, and not enough to cause such noticable malfunction. When we opened up the diff, we expected to find the real problem. Well, we did - kind of... The torsen unit at first was binding and would not budge. We took it apart, dropped a couple planetary gears in and found that about one out of four times we dropped the planetary gears into the casing, they bound up and wouldn't budge. There just wasn't any reason. They all looked beautiful, but it seems that the differential will work fine, then you shake it around a little and it doesn't. Shake it around some more and it does. Not exactly the kind of engineering I would hope for in such a car.

2kturkey

TR, can I ask what was causing your diff to break when there seems to be little history on this forum of others having the same problem. Were you doing something specific (and unusual) or is this a problem we can all expect to encounter some day?

Mugen

as i just got my s2k I was just wondering how much that diff. cost? and does anyone know of any problems dropping the clutch at say 7500rpm or even 9000rpm? i've seen plenty of other owners do it with no APPARENT problems,

The Reverend

Well dropping the clutch at 7500+ RPMS is definitely a good way to ruin your rear end and just about everything in your drivetrain. As for any special circumstances - I was fairly hard on the first rear end I had since I figured this was a sports car and should be able to take sporty driving. After a very short time, it started to make clunking noises while turning at parking lot speeds (it was binding when it shouldn't be). After Honda replaced that rear end, I made sure to be extra careful with the new rear end to make sure nothing else would break. Well, 6 months later the same thing happened again. This time Honda did not agree to fix it under warranty. I wont get into it too much as I do plan to take legal action on the matter, but I will say that if you have a lot of problems with your car, you have my prayers as Honda will not back up their product (at least not in my case). Quite to the contrary, I have found them confrontational and insulting. I will never own another Honda or Acura.

Anyway, back to the subject, the cost... well it's not cheap. I replaced all bearings and seals and the differential itself. I get a 20% discount from the parts department out here because they know me. Anyway, even with the discount, I spent around $1400 in parts. About $250-$350 of that was just on some of the special Honda tools that we didnt already have and needed for this job. I did all labor myself with a friend helping. We videotaped pretty much the whole process for legal reasons. It was a 20+ hour job as I was pretty sick and we were being very careful not to screw anything up. You need standard tools, the special Honda tools mentioned in the Service manual, a dial gauge, a hydrolic press, and a fish scale (or a push pull gauge if you've got one).

krazik

Rev,
Thanks for the lengthy and detailed post. ~19k miles on my stock diff right now and it seems to be hold up. (I drive pretty hard)

But I have been told, by a couple of my friends that race, that you can get much better performance from an aftermarket diff.

I'll hit you up in a couple months and see how it's working for you.

How many miles did you have on the car, and on the first and second OEM diffs?

Thanks!
-k