BigNNasty

Better to not dump the clutch at all!

billthe3

Well yeah, thats obvious. But if you're going to, might as well do it somewhere with crappy traction.

H2

I have to get my rocks off occasionally. I hated to do it but I couldn't find any good mud.

Harvey

H2

That's a GOOD point. I'll crawl under the car with a magnifying glass and look at the bolt heads on the trans and see if there's any wrench marks indicating they've ever been touched. I'm hoping somene fixed the pinon and added LSD.

H2

ninefiveone

This may help clarify things, or not at all.

Technically the term LSD referes only to clutch pack differentials with break away torque specs like 40% lockup, etc.

Torsen is a gear based differential that "torque senses" and sends torque to whichever wheel has the most grip. It is infinitely variable.

Under 95% of conditions, both will do the same thing. Deliver power to both wheels under power instead of only one like a normal differential.

What will cause problems for a torsen diff is if one tire is not on the ground at all. This is more torque split than a torsen can handle and it'll send all power to the wheel in the air. That sucks but really, how often is one wheel not in contact with the ground for any substantial period of time? It happens but for most drivers, it'll never be an issue. I've heard of, but not experienced, torsens having difficulty in icy conditions.

LSD diffs tend to be grabby in tight cornering situations (parking lot maneuvers). If you've ever driven a 4wd jeep with the diffs locked, you'll know what I mean. Torsens are much more street friendly in this case.

Most torsens that I've seen will spin the tires in opposite directions when tested in the air. Just like a normal open diff.

Based on the symptoms you describe, it sounds like you have a torsen diff.

Dave in Chicago

And, as pointed out above... the 220 option was ZF-type or Torsion-type, depending on the specific time during the 968 production run. As an aftermarket add-on (during a pinion bearing fix), either may be added.

Sounds to me like you have a Torsion-type diff now. Could be factory or aftermarket such as Quaife. Either way, sounds like a nice little surprise for you.

Robby

Finally- thank you ninefiveone & Dave... How have you been Hugh? Long time no see... I can't comment on the direction the wheels will spin- my Turbo S has a ZF (clutch type, like all 951/944's, etc) & the wheels spin the same direction when both off the ground- I was always led to believe that if they spun the opposite direction, then it hasd no form of LSD, but I can't say for certain... I HAVE been in a 951 w/out LSD & you can EASILY tell coming hard out of a corner as the rear end will not oversteer under power the same way- it just sort of spins the inside tire & keeps going fairly straight... No crazy powerslides w/out LSD...

As Dave said, the 968 had BOTH types of LSD (IF you can call a Torsen that?) in 1992 & it was the only 944 style car that ever offered both- but for 1993, they dropped the ZF & went to Torsen only- T-o-r-s-e-n- it's actually not Torsion- stands for TORque SENsing as already stated... I'm pretty sure that this is just like a Quaiffe- an autmatic torque biasing differential...

I've often wondered which one to go to in the event of a possible rebuild of my factory ZF- btw- forgot what ZF stands for, but... ZF has to be rebuilt but Torsens supposedly do not- Danno told me once that when he went from a ZF to a Torsen at WSIR that he saved a full second per lap & he felt that more than half of that was due to one corner- it was some sort of switch-back (can't comment- never been to the track- wrong side of country)- Garrity Repta used to tell me he liked ZF's better for road racing. But most people seem to prefer Torsens- smoother, etc...

Fishey

My 993 spins opposite directions and its LSD (I have been inside the gearbox so I am 100% sure its got LSD)


Its also a 1995 G50/21 (I think)

Jfrahm

Not true. On pavement, some one-leggers will leave two marks if both tires have nearly equal traction at launch.

It's pretty hard to tell if a car has a Torsen or not. There needs to be some drag on the opposite wheel or it will act like an open diff.

One way to tell: If the right rear tire spins in a hard RH corner exit, no LSD.

-Joel.

ninefiveone

Hey Robby. Long time no see, indeed. I've been well, thanks! What is the latest thing you're chasing these days?

I've never seen a clutchpack LSD spin tires in opposite directions in the off the ground test unless very worn but Fishey's experience suggests otherwise. On 951's and 944's in particular, I see a lot of very worn LSD's.

Torsens do spin in opposite directions off the ground. It's just the nature of a gear based posi diff. Quaiffes are all torsens.

Many people prefer clutchpack LSD's for road racing because they're what are called 2 way diffs. They provide limited slip under both acceleration and braking. This has a tendency to stabilize the rear end under heavy braking. A torsen diff will not do that.

For 90% of the population, a torsen diff is the way to go. Quaiffe, Guard Transmission, whomever.

For a dedicated track car that's competitively racing, I'd go clutchpack.

If you're somewhere inbetween, chances are a torsen will satisfy most of your needs without the need for rebuilds somewhere down the road.

TRWright

I don't like how Porsche used the 220 code for both LSD and the torsen. . .

Dave in Chicago

Yes, it is odd. I thought I read that it was changed at a specific point in the production life span of the car, but cannot seem to find it now. They refer to the two diffs as 40% Torsen and 40% ZF. The Torsen unit appears to have a number of 928 part number internals while the ZF seems to have a number of 917 part number internals.

Hmm... how cool would that be to know that 917 parts are in your transaxle?

thingo

[QUOTE=Dave Swanson

Hmm... how cool would that be to know that 917 parts are in your transaxle?[/QUOTE]

The discs in the 951 lsd are 917 parts

Dave in Chicago

COOL!

Robby

Hugh- excellent info- thanks a lot! The only times I've ever done an off-the-ground test, like w/my car, etc, the wheels have gone the same direction w/LSD, but I've only done a handful of cars that way at most- I had heard that when a clutch type was worn out, that it could spin opposite, like an OD... I remember that now about the clutchpacks stabilizing under braking- had forgotten that benefit... I'll send you a PM in a few minutes about my latest stuff, although it's much more mainstream than some of my eariler projects...