Geo

I'm getting ready to make a big push to finish my race car finally. I got the main hoop and front downtubes bent up over the weekend. The rest of the cage should be pretty easy from here on.

Anyway, I'm starting to look around for an LSD for my 84 944. My question relates to what is available (and perhaps where) and preference to type.

As I understand it, the available LSDs for the 944 are:

Clutch pack
ZF type
ATB (Torsen, Quaife, et al)

I've reread Carroll Smith's opinions in "Tune to Win." His assessment didn't help much (unusually). I wonder if the technology has changed much in the time since that book was published (certainly the Torsen is new since then). I imagine the clutch and ZF type LSDs have not changed much, although advances in friction materials may have dramatically improved the life of a clutch type LSD.

I don't necessarily expect to come away from this thread with a clear cut answer, but I'm trying to get more informed and with more contemporary data. I did a search of this section of the Rennlist forums and didn't really come up with anything valuable to me.

The issues I'm concerned about are:

reliability
driveability
availability

Preferences and opinions invited.

The ATB seems to be a love it or hate it thing.

The clutch type appears to be a concern for wear (according to Smith)

The ZF has some quirks in driveability (according to Smith).

Thanks. I know this is long winded, but I'm hoping to get this sorted out soon since I hope to drop the drivetrain in a month or two (as soon as the cage and interior are completely finished).

Untier

i got my torsion from powerhausII for my 951 and love it!
and had calif motorsports install/rebuild it.

Steve Weiner-Rennsport Systems

George:

You did a good job on your homework, might I simply add a few comments,......

Both types of LSD's are very reliable.

ZF LSD's, aka clutch-pack types, do something that no torque-sensing ones do,....these keep the drive wheels connecting during trailing throttle and this really stabilizes the car under braking and corner entry. Its a significant difference and I never use any Quaife/Torsen type LSD's in any race cars except dedicated AutoX'ers.

The handling differences alone are well worth the slight difference in maintenance between the two.

Any additional low-speed understeer from a clutch-pack type LSD can easily be accomodated by a set of adjustable swaybars that you likely have,....

Adam Richman

George, while my 944S is in the process of a motor transplant, I decided to go ahead and put in an Limited Slip (always wanted one in this car). We contacted the guy that builds the diffs for my IT car and low and behold he has been doing the 944s for a while (just not in a while). If its anything like the one in my IT car, I am already loving it. Its a clutch type and you can specify the friction material and rate (I believe its got a lifetime service policy on it). LAst year when I blew up my gearbox (racecar), every single thing was destroyed except the LSD - pretty much sold me right there (and 19 races later, still going strong). Shoot me an email if you are interested in details.

Adam

Geo

Steve, in Smith's book he describes a ZF as a cam and pawl arrangement and he discusses it separately from clutch pack LSDs. Is this a semantics thing or is there a real difference? I suppose I need to do a little more research on the ZF.

Thanks. Good to know. I'm coming into this out of FWD race cars and the ATB types rule those, at least for the Sentra SE-R we're running.

Steve Weiner-Rennsport Systems

Hi George:

Carroll mixed metaphors in that book and this was kinda confusing.

ZF builds nothing but clutch pack type LSD's, also known as Salisbury LSD's. These use symmetric and asymmetric ramps to tailor the behavoir of the unit. Further, these are available with 40% or 80% locking factors.

Indeed, FWD cars really work well with ATB LSD's as I can attest to that in all my VW's.

Geo

Steve, thank you so much. This is exactly the type of information I need. I had the opportunity to buy a ZF type about a month ago and passed because I wasn't sure it was the right thing to buy. Looks like it is.

I checked out your site and y'all are pretty 911 centric. Do you have these for the 944? I really appreciate the info.

I'm looking forward to dropping the drivetrain soon. Clutch, LSD, and engine freshening (assuming the insides are OK when I get there) all at once.

Steve Weiner-Rennsport Systems

Hi George:

LOL,..we stick to 911's as that is what we know best,....

I do indeed have these for 944's. I use the Guard Transmission 4340 chromemoly-cased ones which are bulletproof; something the German ZF ones are not.

If I can be of any assistance here, please do not hesitate to ask.

Jim @ EuroWerks

I'm sorry, Adam did you say something?

Bill L Seifert

Geo

Here's what I did. I found an old 83 944 trans with LSD. Don't know what type, but Jon Milledge says the 83-84 LSD is the second best type, behind the ones used in the Turbo Cup cars. They are cheap, especially if you find one in a bad transmission. Mine was free. I then bought a 1987 924S trans for $350. I did the work with the help of a friend, as I am a lousy mechanic. The 87-88 924S trans and the 88-89 n/a 944 transmissions have the .83 fifth gear, as opposed to the .73 in your transmission. I put the LSD from the 83 into the 924S trans, and it works great.

Trust me you need the .83 fifth gear, as the .73 is useless, especially on fast tracks. At Daytona, it adds over 15 mph to your top speed, and that is a lot. I would suspect on TWS, and that other infield course type track in Texas have a lot of top gear driving, though I have never been there. But it helps me at St. Louis, Rd Atlanta, and Sebring, and even a little at Memphis.

Good luck,

Bill

1983 944 Race Car
1987 944S Race car under Const.