Can someone ELI5 the clutch arms on a 915 and why there are two??

[ADDvanced]

Why does the 915 have a big clutch arm, with a smaller one?



I guess I'm just not understanding it. I had my 1976/77 Magnesium 915 rebuilt by Accumoto $$$ and the engine and trans are now in the car, but I can't really push my clutch pedal in. I have not adjusted the clutch pedal cable yet, because I was assuming it would be similar to how it was setup when I took it out, but right now I can maybe push the clutch pedal an inch before it feels like what is a hard stop.

I have a Sachs Power Clutch kit (aluminum) w stock flywheel, and I know for SURE the clutch fork is engaged to the throw out bearing properly. Maybe I'm not getting something. What is the function of part #18?

[fanaudical]

Take a look at the pics in this thread:

Omega Spring Tension?

The clutch cable pulls on the big arm (13); screw 16 sets the gap between the big arm and the little arm (18). The omega spring (21) provides an assist in moving the big arm. Adjustment of the gap and cable is the key to making this work correctly.

Have you verified that your pedal cluster is in good condition? Having the clutch arm at the pedal cluster come loose on the shaft will mess things up.

[OSC911]

I assume you have the later clutch arm assembly with the omega spring? I have a ‘76 with a mag case and have the lever #6 on the schematic - non omega spring. I just did a clutch with new Sachs power kit with aluminium pressure plate. I did the clutch shaft bushes and In doing so, missed the orientation by one spline. My pedal was like yours as the arm was fouling on the bell housing when the pedal was depressed. I moved it around a spline and now perfect after the cable adjusted.

[David Inc.]

I know what it does but I guess I couldn't say why they designed it like that. Maybe it was the best way they found to have an arm that could be pre-loaded while free to move independently of the actual clutch arm? If the helper and clutch arm were one you could never pop the omega spring loose to remove the assembly.

[fanaudical]

My interpretation of the design evolution:

- Two-piece lever allows the cable to be tight for immediate pedal response and allows a small gap between the arms to make sure the throw-out bearing is not constantly loaded.

- Omega spring helps lighten the driver effort on the pedal allowing faster actuation of the clutch.

[fetus]

The Omega spring makes the clutch feel like an on and off switch versus slow engagement of the throw-out bearing to release the clutch.

[proporsche]

add.to help you better take a picture of the bottom clutch arm and let us see the setup you have..
Ivan

[porschedude996]

I just went through a rebuild and problems on my 1983 SC. Maybe you can extract something.

1983 911SC Clutch Mechanism Rebuild

[ADDvanced]

Originally Posted by proporsche

add.to help you better take a picture of the bottom clutch arm and let us see the setup you have..
Ivan

To clarify, the big arm doesn't do anything, just swings around, UNTIL it hits the little arm? Mine never does. Maybe I need to adjust it? Pretty confused.

Also, threw a scope in the hole at the top of the trans to verify the clutch fork was engaged, and found this, lots of metal shavings???? Why?

[fanaudical]

Correct - Big arm makes contact with the little arm. The gap between the adjuster bolt and the small arms seems excessive. Will try to find a good post with the adjustment procedure and link it here. General procedure is to get the cable tight, verify cable travel, and then adjust the gap to 1.0-1.1mm.

I'm not sure this pic represents current assembled state of your clutch linkage or if was just the first pic you had ready to go: There is a circlip missing in your photo. Should be a circlip on the shaft under the little arm. Something else - cable anchor is not tight.

Not sure why you have metal shavings in the second pic - almost looks like specks of lithium grease?

[ADDvanced]

Yeah, I haven't tightened the cable or put in the circlip because it doesn't feel right yet.