clutch pedal collapsed

[kiwicobber]

Hi from New Zealand.

The clutch pedal has collapsed on my 77 911S while I was driving. I have checked the helper spring and the cable. The cable is intact but it had popped off the transmission end. I have put it back but the pedal still collapses back to the floor.

Does this sound like a broken pedal cluster roll pin or are we looking at a pressure plate? I appreciate it could be either but the clutch was OK until this happened and I just want to see if anyone else out there can guide me with their experience.

Also, in terms of getting the pedal cluster out, there are a couple of rods attached to the brake pedal and I can't see any of those in the technical advice about pedal cluster rebuild.

Thanks.

[slodave]

Clutch pedal shaft could have sheared...



Pedal cluster rebuild

[Walt Fricke]

I don't think your pressure plate has caused this. But it is possible for the clutch release arm inside the bellhousing - the one which engages the throwout bearing - to fail. I don't think that is common, but possible.

You can differentiate here with two sets of eyes/feet/hands: when you depress the clutch pedal, does the external clutch release arm move appropriatly. If it does, might be internal damage. If it does not, then the roll pin is exhibit A (since you are certain that your cable is OK, and the front end in the tunnel is still attached and moves with the pedal), Dave's picture is B, and I suppose some issue with the tunnel side of that shaft might be C.

You can deal with the roll pin without removing the cluster (though it might be easier all around if you pulled the cluster anyway). If it is a shaft issue the cluster has to come out.

Does your '77 have the brake booster, with it and the MC up high under the bonnet? If so, you are looking at specs for the earlier setup, with the MC immediately in front of, and bolted to, the pedal cluster. '77s came both ways (my early '77 Euro was not boosted).

But not to worry - there is a rod that transfers the pedal motion up to the MC, and another one that serves to reinforce things, with the boosted setup. Not really different. Simpler to remove, even. You'll figure that part out easily enough.

Walt

[euro911sc]

This happened to me once. Throwout bearing got stuck on the tube that sticks out of the transmission... Clutch cable was good, fork was good... 6 months later and multiple engine pulls it was finally found... this frustrating experience convinced me to do all my own work.

-Michael

[kiwicobber]

Hi everyone, thanks for your help here.

As an update, I got under the car this morning. The cable is still popping off the external clutch arm (?) under the tranmission. I can move the clutch arm back to its usual position. But when I reconnect the cable, and depress the clutch, it pops off again. The clutch is not enagaged.

The clutch cable is moving properly which makes me think it is not the roll pin in the pedal cluster. I have exposed the pedal cluster but not removed it yet and I can see the arm that the cable is connected to moving back and forth with the clutch pedal.

By the way, I checked the cable simply by trying to extract it from the transmission end. As I couldn't pull it through, I figured it was not broken?

[kiwicobber]

Oh, by the way, this car is a LHD import from the US

[kiwicobber]

Originally Posted by Walt Fricke

Does your '77 have the brake booster, with it and the MC up high under the bonnet? If so, you are looking at specs for the earlier setup, with the MC immediately in front of, and bolted to, the pedal cluster. '77s came both ways (my early '77 Euro was not boosted).


Walt

Hi, yes the brake booster and MC are in the bonnet area. Does this mean I don't need to remove the panel underneath the car and unbolt the MC from the pedal cluster?

[Mr9146]

May be a broken TO bearing fork inside the bell housing.

[kiwicobber]

OK, that'll mean motor out, right?

[Mr9146]

Originally Posted by kiwicobber

OK, that'll mean motor out, right?

You betcha.

[Walt Fricke]

Kiwi

If you need to remove the pedal cluster, you can leave the MC alone, which is good. However, you still need to remove the gravel/stone guard (or have very long arms), because the pedal cluster is bolted to the vertical part of the fire wall with two stud/bolts whose nuts are in that area, along with the two which hold it to the floor pan.

Before pulling the engine (and transmission, most likely) out, I'd do a bit more to isolate things.

1) Which of these two flavors of external clutch arm do you have:
a) A pretty straight arm, with a notch in the end. A sort of wedge shaped block with a hole in it fits in the notch, and the threaded cable end fits through this hole, with a not on the aft end for adjustment and so it doesn't pull through the hole?

b) A complicated system with a harp shaped helper spring, and a long and short arm, with the connection between long and short having an adjusting screw with lock nut? Ths one has a swedged on eye fitting on the end of the cable, which hooks into the end of the long arm.

I'm guessing a) because my '77 came with it, but I believe the '77s could come with either depending on market and date of manufacture.

2) Assuming a), how far can you move this arm by hand? You shouldn't be able to move it much - only as much as the play in the TOB groove times the mechanical advantage of the two combined arms. Again, not much.

If you can move it much by hand, unless you are Superman you probably have a broken internal TOB fork or something of the sort. With suitable lights, mirrors, and contortions, you should be able to look into the bell housing through the hole in the upper left side, and see if the internal fork is in the TOB groove. It sits vertically, so you would only see the top end of the fork. This isn't easy, but can be done. An alternative is to remove the starter - much better viewing from that side if you do this.

Your description of hooking up the cable, only to have it pop out when you step on the pedal, would fit with this scenario. If you can put the wedge shaped end back into the arm slot without removing or substantially loosening the , something is wrong or is not being done correctly.

b) is a bit trickier. If you can move the short arm (which is the one which is splined to the vertical shaft) any appreciable distance, something is probably bad inside (assuming all was well until it suddenly went sour). From clutch disengagement, the PP spring provides all the force which moves the short arm back to its rearward rest position.

3) Michael points out a problem I was happily ignorant of - TOB hanging up on the guide tube in the clutch disengaged position. Wow - would have to take a lot, one would think, to hold the diaphragm spring pressure back. One might think that the vibration of a running engine would eventually help move things back into engagement? After you have put things back together, then step on the clutch pedal and release it, what happens if you start the car in gear? Does it lurch forward? Or does the engine just rev as if the clutch were still depressed?

If the internal fork is broken, you cannot disengage the clutch no matter what you do. A guide tube issue ought to show up as a reluctance for the clutch to engage - the opposite condition.

4) Finally, if the arm is hard to move, but you can't disengage the clutch - I'd suggest pulling the cable to inspect it. You don't say what you have done by way of readjusting the cable. When a few strands of the cable break, typically the cable elongates. This can make disengagement impossible, though the cable might feel strong and intact. This is progressive - as more strands break, it gets longer yet. You are not stronger than even a single strand, though your pressure plate is.

In addition, a sheared roll pin can still exert a fair amount of friction on the cross rod. Without the cable being hooked up in the rear and adjusted, you can often move the pedal and see the cable and rod move up front. But if you hold the cable in the back (hooking to the cross arm, for instance), the pedal piece just slips farther around the rod.

Both of these can be insidious: clutch pedal release point keeps getting lower. You adjust, and all is well for a bit, then it happens again. Of course, it can go to hell in a handbasket all at once. My cable break was like that - no warning that I noticed until the pedal dropped to the floor. My break was back toward the rear, so I could pull the broken part right out of the housing. At least I didn't lose parts that way.

My thoughts

Walt

[carrera30]

I had what you've described. It was my throw out bearing fork. In my case, with all the other things I found while getting that fixed, it turned in to an engine rebuild. Just my woe's!

[Gunter]

kiwicobber,

Read Walts reply carefully.

Is the notch for the cable on the long lever worn to a point were it lets the cable slip off?

What direction or manual are you using to adjust the clutch?

[kiwicobber]

OK. there is a lot of play in the clutch cable. Basically it just slips off.

I could put the cable back without loosening anything and with a bit of leverage I can move the clutch lever back and forth.

[Gunter]

What direction or manual are you using to adjust the clutch?

Please, take a picture showing the whole assembly like this:

[Walt Fricke]

Kiwi

Were I forced to guess, I'd suspect the pedal roll pin first, and an incipient cable failure second. And I'd deal with both: remove the cable, and drive out the roll pin to see if it is in one piece, or three. You could also just try to pry the clutch pedal off of its cross shaft - if the roll pin is fractured, you might be able to do this, and without having to guess where the roll pin holes line up. If you can drive the pin out right off the bat, then (like the witche's dunking stool) it probably is in one piece and OK (unless the shaft fractured, like the picture showed).

Removing the cable allows you to inspect it, and the pin clip up front which holds it to the cross arm lever in the tunnel. And to take a look at that lever - there is a little plastic bushing in there, and it can squish, and play develop, and the hole in the lever can get elongated from wear, and even break through.

The work involved in a thorough inspection of the external linkage, compared to removing the engine and transmission (or just the engine), is small. So even if these are not the problem, you haven't wasted too much time or effort.

If you don't do that, and pull the engine/tranny, and find that everything is OK in there, then you really have wasted a lot of effort.

Another suggestion for you: pull the circlip off the bottom of the clutch vertical shaft, and pull the short arm off. Then put it back on a spline or two to the front (of the car) side of where it is. Then move it fore and aft with your hand. This is what will tell you how much free play there is up by the throwout bearing/release fork area. If it just moves a bit forward, and a bit back, all is probably OK up inside as you are feeling the normal play between fork and TOB slot.

Another possibility is that the clutch pedal side bushings in the pedal cluster have failed. The stock ones are plastic, and can break down. The effect of that is the same as lengthening the clutch cable. You could probably test this by seeing if you can move the end of the clutch pedal fore and aft. There should be minimal play there.

Dr. G: does it look like the center leaf of his harp spring is broken at about the 2/3ds mark? Could be an artifact of the grime, though. I'm thinking that a failed spring leads not only to increased pedal pressure, but more pressure on the roll pin, and thus more chances for it to fail.

Walt

[jcc911]

I had a problem simialr to this after I reinstalled my engine. For the life of me I could not figure out what had happened to my clutch/cable just form sitting unconnected for a few months.
After looking at the transmission, checking to make sure I properly matted the engine to the trans, roll pin, pedal assembly and the cable itself, every thing looked fine.
I crawled back under the car to look at the helper arm and spring.
Now, I like you, had everything adjusted properly, in fact I did not make any adjustments, all I did was take the cable off.
So I pulled that stuff apart again and put it back together, I check to make sure the helper and arm were in the right position and it was. Everything seemed to be right but the pedal still went to the floor.
One final check of the arm/spring and SNAP! The arm moved back to the rear of the car the 1/4 to 1/2" i needed to take up the slack in the cable and bringing the pedal back up.

So to make a long story short, I had not fully loaded the helper spring, and once I did, the arm was perpendicular to the trans and everything was fine.
Hope this helps. GL!!

[Gunter]

Walt,

Hard to say about the helper-spring; too much grime there.

Agree with a thorough inspection of the pedal cluster, especially the roll pin and lever/bushing on the other end that actuates the cable.

Shouldn't be too hard to determine if the problem is in the pedal cluster assembly or at worst a broken fork.

Still don't know what instructions he uses to adjust the clutch so the helper spring is working correctly along with the 1 mm gap etc..

[kiwicobber]

OK. I have not adjusted the clutch cable properly but armed with instructions from this website, I went to do so today.

I discovered that the U shaped fitting that the clutch cable adjustment nuts sit on either side of of is broken. It may be broken as a result of my attempt to adjust the nuts but I think it was cracked beforehand which will explain why the cable was just popping out. Replacement part ordered from Pelican already.

secondly, it is very possible the cable is stretched so I have ordered a new one.

Lastly, I can still love the clutch arm too and fro if I get some leverage on it. It does not move smoothly, it clunks from engaged to disengaged. I guess with the cable disconnnected, this is possible??

In terms of photos, I can't jack the car up high enough to get the perspective suggested but here's my latest attempt.

[Gunter]

Yep, that bracket can brake.

The long lever should move freely.
Remove the circlip on the bootom of the cross-shaft.
Remove the short lever. (Remember the position)
Remove the long lever (Some may have a dowel-pin).
Clean and lube the shaft.
Re-install the levers etc.

Install the new cable letting it stick out about 1/4"+ at the clevis-end (Pedal-cluster).
Make sure that the cable sits correctly in the tube at the transmission-end.

Inspect the pedal cluster for wear in the bushings.