A clutch that's truly slipping, for whatever reason, becomes first evident when the torque transmission requirements are toughest on it. This is in fourth gear. Lower gears demand less torque transmission through the clutch because the tranny MULTIPLIES the torque going to the rear end.

If you're experiencing a slippage in a lower gear, I'd be more suspicious of a slipping OD, which must transmit the torque to the differential. Remember that the tranny multiplies the torque going through it, so the OD must transmit higher torque in lower gears if you stomp on it.

On the other hand, if you never accelerate in fourth gear -- or never get the engine up to its "torquey" revs -- then the clutch might really be at fault. You'd need to perform several controlled experiments to more clearly point a finger.

But if it does not slip in fourth (OD out) while under heavy, torquey acceleration, then my bet is on the OD.
--
Don Foster (near Cape Cod, MA)

It should be most noticeable in 4th and OD where the tach will climb and the speedo will not if you step on it. Are you sure it is the clutch slipping?

Could be slipping from oil leak onto clutch. This happened to my car (83' 242Ti) with newish clutch (less than 20k, also rear main). I was merging onto the highway (boost up a notch, cold ⎪f] winter morning & new turbo & recently installed intercooler) with it floored (3rd gear 3500-5000rpm) and major clitch slip was taking place. Turns out to be random oil leaks caused by clogged PCV system "sprayed" back onto clutch somehow. Totally cleaned out the PVC system (while installing new intake manifold gasket), leaks discontinued and no more slip. BTW, I also had a MAJOR oil leak at or near this time (a year or so ago) involving a cracked brass "pipe" to the oil pressure sender (due to new alternator belt being to small and causing alternator to "lean" against sender). 60psi of oil caused one hellva mess under there, but it was taken care of with new "pipe" or adaptor, and longer alternator belts.

Isn't it crazy how chain reactions work, and the trouble they cause. Im currently trying to figure out why my windshield wipers dont work (brand new relay\motor), and why there is hesitation under load (likely fuel pump, or disconnected prepump hose). Also time for new brake line junction block (leaks at plastic warning sender) and mysterious vacuum\boost leak that causes a squeal (linear in loudness with boost amount) and hard starting that results in a few tries to get it started, except when cold (overnight).


Just so you know, if its the original clutch, yes it could be going, and so could the rear main seal, making it worse. The clutch in my car was replaced weeks before I bought it at 182k miles, and now I am pushing 210k. (previous owner was female with small children and used it as a family car. Current owner (me) is college student who drives it hard with the occasional offroad (rallycross), but babies it with synthetic fluids and regular maintience).

(PS: I had a few beers earlier tonight and it's 2:02am PDT, so my post is somewhat "off" compared to my regular posts. oh well.)

Good luck,


--
Zack Silver 83' 242Ti (208k)

seems early, but maybe if your clutch has had a rough life. Just did the 1st on my '84 at ~254k