I think the tranny is screwed

jjrowe · 10-19-2004, 05:58 PM

I was driving north on the 15 to work this morning. When I put the clutch in on the offramp I felt a little pop in the pedal and the clutch went to the floor. I figured it was a clutch cable so I drove it home very carefully (without clutch) and got a look underneath. I took the cable off at the pedal cluster and then went to the tranny. The fork on the tranny seems to be stuck in the clutch engaged position. I was able to take off the cable at the tranny and the fork is still in the same spot. What am I facing here?

Jesse
76 911S

Jack Olsen · 10-19-2004, 06:20 PM

Broken arm on the clutch fork? That happened to me, once.

Jim Sims · 10-19-2004, 06:25 PM

Most likely a broken or bent release bearing fork (inside the bell housing); maybe a release bearing failure but not likely. The engine at least will have to come out to access the clutch parts. If there are many miles on the clutch parts then it's a good time time for a clutch job plus an easy time to replace known oil leaker parts and seals on the back (part facing towards the front of the car) of the engine. Jim

Tyson Schmidt · 10-19-2004, 06:25 PM

Yep, broken clutch fork.

john walker's workshop · 10-19-2004, 06:27 PM

the bearing can get pulled out of the p/plate, but that's usually preceded by several days of squeeling noises.

Joeaksa · 10-19-2004, 06:27 PM

Same here, was driving it to the shop to get my clutch changed and pop, and the pedal was on the floor.

Joe

dhoward · dhoward's Garage

Quote:

Originally posted by john walker's workshop
... but that's usually preceded by several days of squeeling noises.

Uh oh....How many is several?

Jim Sims · 10-19-2004, 06:36 PM

http://www.pelicanparts.com/911/911_Parts/1974-75/3-1.JPG

Part 1 is the release bearing fork

Part 9 is the release bearing (AKA throw out bearing)

jjrowe · 10-19-2004, 07:08 PM

Thanks guys. The clutch(new) and tranny(full rebuild) have around 30k on them so they shouldn't be too worn. The engine/tranny has always made a scraping noise at low RPMs for instance when accelerating in too high of a gear. Not sure if that is related. Looks like I will be doing my first engine drop here in the next few days. I will post pics when I get it apart.

Jesse
76 911S

jjrowe · 10-20-2004, 06:03 PM

I got the engine dropped and it looks like the fork is OK. I noticed that it will spring back now. There are some rings that appear to have sheared off of something on the engine side. Ideas?

Jesse
76 911S

Jim Sims · 10-20-2004, 07:13 PM

Release bearing circlip failure (that and one of the thrust washers are what one sees inside the diaphragm spring of the pressure plate (1st image of clutch parts posted). Was the release bearing replaced last clutch job? Circlip likely wasn't seated properly and worked it's way loose. If no damage to driven plate and pressure plate then you may only have to replace release bearing. Pressure plate will have to come off to install new release bearing. Loosen and retighten pressure plate mounting screws evenly (not one side all at once) to avoid warping diaphragm spring. You'll also need a clutch pilot tool. Jim

jjrowe · 10-21-2004, 08:31 AM

thanks Jim, on a side note. What keeps the release bearing away from the pressure plate when the clutch is not engaged so that it doesn't spin all the time?

Gunter · Gunter's Garage

What keeps the release bearing away from the pressure plate when the clutch is not engaged so that it doesn't spin all the time?
Proper adjustment of "Free play" and, not having your foot on the clutch pedal as a rest position.

jjrowe · 10-21-2004, 09:00 AM

What I am asking is how does the clutch spring back? I can feel if I push the fork forward that it springs back. What makes it spring back so that the release bearing is no longer in contact with the pressure plate?

Gunter · Gunter's Garage

The pressure plate has a circle of segmented springs; each single one looks like a pie slice (Wedge) Together, they have a fulcrum, usually a steel ring mounted within the pressure plate. The position of this fulcrum determines the amount of pressure needed to move the segments. When you press the clutch pedal, the fork forces the release bearing against the segments in the PP, which opens the clamping force holding the disk against the flywheel. The return spring on the clutch release lever takes the slack out of the release components like fork, cable and pedal. (Freeplay) With proper freeplay, the fork, which sits in the groove of the release bearing, moves the RB away from the PP. Without freeplay, the RB rests agains the PP and rotates all the time. Cheers.

jjrowe · 10-22-2004, 08:58 AM

Thank you for explaining that. Where is my return spring on the clutch release lever? I do not have the helper spring on the fork arm under that transmission, I think this is normal for my year.

Jesse

Gunter · Gunter's Garage

It's an ordinary spring similar to P-116-614-02 in Pelicans catalog. You don't have the "C" spring, (which has nothing to do with freeplay) but there should be a spring from the release lever to the transm. case holding back the lever. Ask some '74-'76 owners what it looks like. Cheers.

jjrowe · 10-22-2004, 10:27 AM

Ok, thanks. One last question. My clutch failure appears to be due to the throw out bearing getting stuck on the Throw Out Bearing Guide Tube. The inside of the bearing is caked with muck and the guide tube is also dirty. Is this normal for this to get that dirty?

Gunter · Gunter's Garage

Well, some dirt/muck will accumulate. Check the bell housing for oil coming from the transm. or engine main seals. Also, the disk lining will shed material. But maybe the parts were not properly cleaned and lubed on the last clutch job. Clean, check for wear, and lube the parts as required. Replace worn parts and look at the disk lining. Is it still good enough? Cross shaft bushings? Transmission input shaft splines, and RB guide tube, and cross shaft bushings get a moly-type grease.

Jim Sims · 10-22-2004, 10:54 AM

On a '76 there is not a spring on the lever on the bottom of the transmission; there are only the diaphragm spring in the pressure plate and the clutch pedal return spring up front at the pedal cluster.

No, the guide tube shouldn't have a bunch of debris and muck on it; the workmanship of the most recent clutch job is coming into question. It should have been cleaned, inspected for excessive wear and a light coat of grease applied on the outside running surface (where the release bearing slides). Over time the grease will collect some debris in the form of clutch friction material dust and a small amount of dust that enters from the outside through the vent openings in the top of the bell housing but this shouldn't be the cause of your problem. I suspect the guide tube wasn't cleaned before and it also may be excessively worn. Fortunately this is an easy item to replace on a '76 915 transmission (do not forget the new o-ring seal). Also make sure your pilot bearing is greased. Jim