84 944 Clutch Issues

[944cer]

My 84 944 developed clutch issues during the build process just before the race at MAM. The car will not go into gear while running but will go through the gears when off. I have checked the slave cylinder and it appears to have the required spec travel and no leaks. I did bleed the system.

Does anyone have any advice on anything else to check before I skip the race and start the major task of replacing the clutch assembly.

TIA

[Chuck T.]

So I was talking to Lee about this and I said ... "

 

Make sure the pressure plate bolts are tight and the rod that goes through the clutch fork is still in there... "

 

Thats all I know ? What do the experts say ?

[944-Spec#94]

Ok,

Couple things to check.

 

Car in the air neutral. Go to the tranny cover and get to the rear spline couper

 

Clutch pushed in = You should be able to rotate the shaft.

 

Clutch not pressed in = You should NOT be able to rotate the shaft.

 

 

If you can confirm it is not an issue with clutch master, clutch slave, or the fluid lines you will need to tear open the clutch to fix anything. I maybe any number of things and really the only thing you an mess with outside the bell housing is the clutch fork pin. Everything else requires the bell housing to be off.

[944cer]

Thanks, I assume by shaft you mean drive shaft.

[944cer]

I pulled the rubber boot on the front of the tranny to get to the spline. The spline/drive shaft would not turn by hand in either clutch position. With the car running it went into the forward gears just fine (axle turning) but did not want to go into reverse. It would go but had to jam it in.

Any thoughts?

Chuck. the pin and flywheel look fine.

[roberth944]

if you had the bell housing off it sounds like you missed the TO bearing fork alignment. The fork must slide into the to bearing groove on assembly. If you didn't have this apart at all then you most likely have a bad pressure plate assembly. the fact that you have a hard time spinning the drive shaft is that the cluch is not engaging at all.

[944-Spec#94]

... the fact that you have a hard time spinning the drive shaft is that the cluch is not engaging at all.

 

Correct!

 

Or more correctly stated the clutch is not DIS-engaging.

 

The way the system works is as follows. Most of this is probably obvious however.

 

Pressure plate is bolted to the flywheel with the clutch disk in between. Normally the pressure plate springs press on the clutch disk and in turn press on the flywheel. This the clutch disk which is rigidly attach to the torque tube drive shaft is squeezed between flyweel and pressure plate.

 

When clutch pedal is depressed it causes hydralic pressure to build in clutch master. This fluid pressure goes to the clutch slave and extends the piston.

 

The clutch slave piston pushes on the clutch fork arm. It actualy causes the clutch fork arm to pivot around the clutch fork pin. So movement of the slave piston torward the front of the car causes the other end of fork to move torward the rear of the car. The fork in turn pulls on the throw out bearing which pulls the finger springs of pressure plate away from the clutch. This the clutch disk is now free to spin relative to the engine.

 

Failure modes in the system are in the hydraulic controls.

Both clutch slave and master's can fail thus not translating pedal movement to the clutch fork. Air can get into the system as well.

 

The other failure mode is if the clutch fork does not pull back on the throwout bearing. Also the throw out bearing can be mis installed or damaged thus not pulling on pressure plate fingers.

[944cer]

Thanks Joe. It sounds like the prblem is in the TOB. Is it possible to tell from the view hole if there is proper functioning of the TOB? I can see the fork move appropriately but not much more. I'm also going to see if there is additional adjustment on the clutch peddle linkage to get more movement from the slave cylinder.

[Tim Meyer]

I had problems with a brand new SPEC stage 1 clutch disc coming apart immediately. SPEC replaced it with the kevlar clutch disc (stage 2?). The stage 1 disc came apart and lodged in a "double thickness" mode between the Flywheel & Pressure Plate. I am aware of 4 other 944s who had similar problems with the SPEC stage 1 clutch disc. What you've described is similar to the symptoms I experienced.

 

I'm looking for another clutch supplier besides SPEC. Any ideas out there?

 

Regards.................................Tim Meyer

[944-Spec#94]

II'm looking for another clutch supplier besides SPEC. Any ideas out there?

 

Regards.................................Tim Meyer

 

I have used a stock sachs spring centered clutch for years. I replaced the clutch the engine came with when doing an engine rebuilt in Jan 2003. 18 months any many many hard races I swapped motors and the clutch was perfect. In fact it showed virtually no wear. I am still using that clutch now.

 

I don't believe our cars put out enough hp for to and any kind of performance clutch at all. Stock street car replacments work great.

[Tim Comeau]

I'll second that. I used the same RUBBER CENTERED stock clutch for 2.5 seasons plus 5 enduros.

Stock is more than adequate because we don't have a lot of HP and we don't do standing starts.

[944cer]

Thanks for the help guys. The drivetrain comes apart this weekend to see what I find. Since the car hadn't moved while in the garage and the clutch went from working to not I wondered if something could have gotten wedged in there. I tried running it through the gears and some axle speed but nothing changed.

I'll let you know what I find.

[944cer]

Sorry for the late follow-up. The clutch disk was stuck to the flywheel. The only thing I can figure is that when I was splicing the heater core hoses some of the coolant dripped into the rear cover and interacted with the metal of the flywheel and the clutch disk material causing it to bond with the flywheel! Everything else looks fine. Sooo...I'm resurfacing the flywheel, replacing the clutch disk and reassembling.

At least I'll lose 2# of gunk after cleaning the tranny.