Jfrahm

Best thing to do, if you are looking for a clutch-type LSD, is to jack up one wheel and check the breakaway torque. Easier than jacking up the whole back end and you learn how tight the LSD is, if fitted. The option tag or trans tag might be wrong after all these years.

-Joel.

Imo000

Lift up the trunk carpet and look for option code 220, trans code is another way. Also if you lift the tow rear tires to check for LSD you need to have the auto trans out of Park or else the tires will spin the opposite way (regardless of having a LSD).

Some open differentials will have both tires spinning in a straight line. You need to come out of a turn and see if both tires are spinning to know if it has LSD.

Imo000

The option code is stamped into the case. So if it was never openned it should have everything in there.

Vilhuer

PSD was stock on all 928 '90-95. Its combination of LSD friction disks and electronicly controlled clutch mechanism which compresses friction disks together for desired locking percentage. There are many more steps than 10 and selected lock amount is based on several different parameters.

http://www.youtube.com/watch?v=_PoocIsiV2c

mark kibort

you will have to video that event for us

If you dump the clutch, you will only spin one wheel. It is extremely unusual to spin both without LSD , unless you do a slight turn, then both spin and leave two black marks. I have video of some bat turns and U turns burning rubber where the black marks are from both tires. (on my old 84 on the street)

mk

dr bob

The "breakaway torque" test method is certainly the most reliable way to tell if you have LSD -and- that it's actually working. Use the wrong lubricant or too much graphite additive, and you can reduce your LSD effectiveness to nothing.

With gearbox in neutral and parking brake released, raise one rear wheel. Use your standard lug-nut torque wrench setup to determinw how much torque is needed to get the raised rear wheel to turn. If it turns easily even before the wrench goes on, likely no limited slip. The torque wrench is the definitive tool to determine how tight/effective the LSD is. Minimum breakaway torques might be in the 25 lbs/ft range (SWAG), and tracked cars might want to set up tighter. Too much friction means possible chatter in low-speed corners, and can actually interfere with good low-speed handling on slick surfaces. Too little increases the risk of spinning a wheel when accelerating on uneven surfaces.

For most drivers most of the time, having or not having LSD is simply not an issue. In all but situations with uneven traction while accelerating hard, it's more a liability than an asset. For instance, I wash the car in the garage, and on the smooth epoxy floor the LSD in the rear makes steering in the front impossible; the car always goes straight no matter which way the front wheels are pointing.

mark kibort

This isnt a good test either, as on a loose surface from a standing start, my loose wheel will spin madly. in fact, i can get stuck going up driveways with my cage stiffening up the chassis. once one wheel leaves the ground, im stuck

the limited slip of the S4 is pretty weak. good enough for racing. I think its force is under 20ftlbs

mk

Andre Hedrick

I saw one car at Devek Days with a true locker, does anyone make one?

Meaning I heard the springs and teeth pop in a sharp turn and the rubber chirp on a weak turn.

fabric

What *you* did isn't a good test. Pulling off the side of the road just off the shoulder into a bit of dry dirt is just fine - you should be able to tell if the one wheel spins, but not get yourself complete stuck.

icsmike

Thanks all, good info.

Richard S

That was Dennis Kao. I don't think it lasted very long before he broke it. But he can break anything

Rich

mark kibort

one wheel in the dirt will spin the dirt wheel madly! It is kind of a characteristic of a mild LSD as we have with the S4. of course, it spins even easier with out LSD

mk

Jim bailey - 928 International

Mark the limited slip friction discs wear out over time they are a normal replacement item. Your transmission PROBABLY had the Euro style 1983-84 slip which is shimable to about 80 % lock up. The Holbert car was built to run on the salt flat where wheel spin is a MAJOR ISSUE it is all " dirt".

mark kibort

actually, the holbert car came with an open diff. hard to say whether the trasmission was the original, as it looks like it might have been.
I bought the LSD from you guys at 928intl when i converted the car to a race car. maybe thats why Holbert couldnt break 180mph like the car did at Nardo. too much wheel spin due to an open diff.

Mark was talking me into doing the early euro style 80% locker, but the stock stuff has been so good, i didnt want the car doing anything different out of some of the slow turns. (althought there is one where i do have single wheel spin that could be helped by more limited slip force) however, i wouldnt want to induce more slip on some of the critical turns at the higher speeds.

mk

Bill51sdr

Agreed! My Miata will lay 2 black stripes... as long as the car is pointed straight. It has an open diff.