Clutch Cable Stretched Beyond Limits?

[Guardsred911]

I recently went through the shifter linkage, omega and seal on the '77 911S, and with those things, and new Kendall oil, eliminated a lot of the crunchy grindy noises!

It sat for a few months.... and, I went to drive it today, and while I can shift just fine with the engine off, when I try to shift with engine on, it wont go into gear (and grinds).

I checked the 1.0 mm measurement on throw-out arm and helper, all good there.

Clutch travel was about 22 MM, so 3mm short (I just used a 24MM wrench - ghetto, I know!)

I pulled the front floor board, and looked at the clutch cable to see if I could adjust it, and I have no more threads available. in looking at the Tech articles, I saw this picture and there are about 10 threads visible...
https://cdn4.pelicanparts.com/techarticles/911_clutch_replace/pic28.JPG

Guessing the cable is just stretched and needs replaced?

[juanbenae]

the cables do stretch over time and if it's original it has to be long by now. the new omega spring and adjustments have exacerbated the issue.

[DRACO A5OG]

+1 on Cable Stretch on an old cable.

Clutch travel should be 25.0MM +/- .5MM. Adjust the floor board travel limiter plate until you get close to 25MM.

If that does not fix it then it could also be your fork bending ready to snap, was it replaced on the last clutch job? Have a helper press the clutch pedal while you feel thru the top inspection hole.

With cable off of the helper spring, you should read 1.20MM with cable on 1.00MM

[fanaudical]

You might also check the pedal/shaft/arm at the pedal cluster and make sure there is no extra rotation between the pedal/arm. A little slop there will lose lots of clutch travel.

[Uwon]

You sure you don’t have any more adjustment at the front clevis ? First I would adjust the plate on the floor board to give you 25 mm travel at the trani. If that lets you shift, then try a couple more mms but no more. Readjust gap at trani per specs. You may also have too much play in your pedal shaft which will require new bushings.
Hope this helps.
Johan

[billybek]

My old cable (old being the key word here) would not hold adjustment and stretched to the point of failure while on a drive. Of course I was 40 miles out of town at the time. Couldn't have happened down the block from the house. Noooo. Stupid cable... (said in my best Homer Simpson voice.)
Replace the cable and see if your issues go away.

[Guardsred911]

Thanks for all that! I did check the clutch stop, and I could adjust a bit there.

I was able to snap a picture of the clevis. Take a look at the remaining threads... Also, bushings on that seem like they were replaced recently... not be me, but no slop there.




Also, I found this "thing" in the box behind the gear lever.... it's a white plastic box that maybe attaches to a mic that's behind a plastic fascia... very professionally installed... maybe factory? I had to move it to get to the clevis... Any ideas what it is? not hooked up to anything, so going away....

[DRACO A5OG]

The Clevis is in the proper position, 1/8" or 3 threads from bottom.

Sorry, that device is not factory, strange place to put a speaker

[Uwon]

By your pic, it appears that you can still shorten the cable by screwing into the clevis. The “manual” says that you should loosen the lock nut at the clevis, unhinge that stupid lock for the clevis pin, pull out the pin and screw in the clevis. I just loosened the nut and then screwed in the cable from underneath and voila! Remember to retighten the lock nut. Yeah, a pain to put everything back and remeasure to get to 25mm, set your preload gap and load gap.
Johan

[Flat6pac]

Why even use the locknut. It has to be removed to run the old cable out. The front clevis is locked from turning and the rear of the cable is locked on the levers. So, I ask how would it loosen?
With out the nut you can turn the cable from the back to make a better adjustment on the Bowden cable by running a few more turns into the clevis.
Bruce

[Uwon]

Originally Posted by Uwon

..... I just loosened the nut and then screwed in the cable from underneath and voila! Remember to retighten the lock nut. Yeah, a pain to put everything back and remeasure to get to 25mm, set your preload gap and load gap.
Johan

What I said.
Johan

[Jonny042]

This is a little OT perhaps, but anybody figure an easy way to measure the cable travel without a helper?

Also, heathen that I am, I just installed my cable and tightened it until it felt good at the pedal - a barely perceptible amount of free play (a smidge. maybe a smidge and a half) and it seems to work fine.

Am I missing something about the importance of this 25mm travel? Plus or minus .5mm seems to be pretty close tolerance for something that you don't really have much control over besides the pedal stop which isn't particularly robust?

[DRACO A5OG]

When my helper is not around, I use my trusty old 2x4, and a thick rag to press against the seat bottom and pedal. Measure then release and measure and do a little math.

As far as significance of the 25MM, it may be a bit over board by the PAG engineers but it is safe:

If too long of a throw you could damage the pressure plate and or the fork. Too short of a throw you may not be releasing completely off of the fly wheel and cause premature wear on your clutch pad. The idea is to have engagement and release at middle of the throw so you can modulate your clutch play. Someone more experienced will chime in hopefully.

I am guilty of shortening the throw so I can feel engagement a bit sooner but since have put it back to spec after my 915 rebuild.

[Guardsred911]

a bit of an update.....

The clevis pin has a LOT of wear on it, so much so that it's out of round. I'll be replacing that for sure as this probably contributes to at least 1 MM of decreased throw.

The clevis fork has no wear, but will still be replacing

I did see some wear on the hole of the clutch shaft where the clevis pin goes it such that the hole is out of round. I imagine this contributes to losing another MM of throw at least.

Was considering putting a bronze clevis bushing in and seeing what that does before I replace the clutch shaft. Thoughts?

[Guardsred911]

Following up on this, and sharing what I found. Hopefully it helps someone else...

In my work, I did discover an OG speaker... not sure if it was an alarm or something else...

I replaced the clevis, pin, and bushing. The clutch lever where the pin connects was dished out a little bit, so I replaced the bushing with the bronze bushing from the host. I had to think about how to press it in while the pedal cluster was installed, and I used a bolt with a couple washers and a nut to press it in, no issues.



After I installed this, I used a 25mm wrench instead of calipers to measure the throw, and got that pretty dialed in, all adjusted.

But still no luck!

Reading more about this, seems like a lot of the symptoms were the clutch stuck to the flywheel (not driven for a long time, sitting in a damp environment, etc.)

I put it in reverse, started the car in gear and got out to the drive. Once I put it in 3rd and started, it broke the bond from the clutch to the flywheel. Ran and shifted the same! Put some miles on it to get rid of the rust.

I have to go through and adjust the gears and replace the cups, etc., but at least working well now. Thanks for the help from those who've posted their issues and solutions.

[DRACO A5OG]

Good Job!

[Uwon]

Well done! I was resisting suggesting another possible cause for your issue and I’m glad I did. Now that yours is solved I can post what happened to me just after I finished my build a couple of years ago, and yes, one crack is all it takes......



Johan

[Guardsred911]

Wow! That's Terrible!

[DRACO A5OG]

Did Uwon ever figure out why this occurred, maybe too long of a throw beyond 25MM?

Originally Posted by Uwon

Well done! I was resisting suggesting another possible cause for your issue and I’m glad I did. Now that yours is solved I can post what happened to me just after I finished my build a couple of years ago, and yes, one crack is all it takes......



Johan

[Uwon]

Originally Posted by DRACO A5OG

Did Uwon ever figure out why this occurred, maybe too long of a throw beyond 25MM?

Good question. Don’t really know, except that when I contacted the manufacturer, Kennedy Clutches, they wanted the whole unit back for research, so they kindly replaced it free and even paid for shipping.
If you look at the pic, you will see a clean scrape where the fork hit the finger which was likely the result of me tightening the cable well past the 25mm setting (in a last ditch effort to get the clutch to release) to the point where the fork will hit the fingers. I would presume that because the crack is the weakest point, the clutch plate will release from the flywheel face earlier all the while pushing/ dragging on the flywheel at the opposite side. All it likely takes is a fraction of a mm clutch plate wobble on the input shaft to screw thing up. My layman’s analysis.