Clutch cable advice required

[Neilnaz]

Hi everyone - I have a snapped clutch cable - luckily it happened 100yds from home when leaving for a morning drive - just changing into 2nd gear and foot to floor. My wife and a helpful neighbour helped me push the car home and up the driveway and into the garage.

Well, having checked things out, the pedal has no connection to anything else. This may explain why the bite point had been noticeably lower recently. I imagine that the cable was stretching and has now broken. Full diagnosis will follow when I get the car in the air to inspect.

The thing is my car is a 1971 T with the original engine but a later 915 (non-Omega spring) gearbox which was changed prior to my ownership. What I was interested in is whether I need a clutch cable for my car year or whether I need one for the Gearbox year or whether I need some special adaptation to a 1971 cable to fit with the later gearbox. Or something else. What is currently in place seems to have a piece welded onto the end of the cable - photos to follow....

Now I suppose no one can answer the question until I have provided some more information - Gearbox number and a photo or two - would that be all I need to get some expert advice? I imagine that the Gearbox and the cable attachment changed over the years?

Thanks in advance

Neil

[DanS911]

Best to take it out and check, measure to be sure what you got there.

[Neilnaz]

Thanks Dan - will do. I will know more tomorrow when I get under the car and reveal the cable and the pedal cluster. I will take some pictures and record the Gearbox number as I actually know very little about the Gearbox. I have a feeling that the current (snapped) clutch cable has been cobbled together to mate the pedal to the gearbox.

Cheers, Neil

[javadog]

A '71 had a different clutch release mechanism to to all of the cars that had a 915 gearbox, so I'd start with the cable appropriate for the gearbox you have. You might want to compare part numbers on the clutch pedal shaft, also.

JR

[Neilnaz]

Thanks Javadog. I have had an initial look and the cable is intact but the 'Clevis pin' is broken. I will order a new one from our hosts. Everything else looks fine. I imagine that it is just one of the those things. I checked the cable runs fine in the inner OK and all seems to be in order.

Cheers, Neil

[Neilnaz]

Well I had to get both floorboards out the gear lever out and disconnect the accelerator linkage so that I could get to the clevis and the clutch cable. I didn't have a spare clevis pin so decided to use an M6 bolt and Nyloc nut to get me by until I can replace with the correct part. I will get a few other parts while I am at it.

I had to release the clutch cable at the Gearbox end but marked the position of the lock nuts beforehand so that, when reconnecting it, I would have a good idea how tight the cable needed to be.

I put things back together adjusted the cable to where I thought it had been plus an additional turn for good luck and went for a test drive.

Result - perfection - good bite point and a reliable gear change with good feel.

I am a happy guy!

Cheers, Neil

[javadog]

I'd suggest that you look up the correct procedure for adjusting the cable on whatever year transmission you have and make sure the free play is correct and you have enough travel.
JR

[Jeff Burger]

Did you take a good look at the lever arm from the pedal assembly when you replaced the clevis with the bolt?. Given the wear on the clevis there may be corresponding wear on the arm. There isn't a lot of meat around it and I have seen the hole break out leaving the clutch inoperable.

[Neilnaz]

Thanks Javadog and Jeff. I did read the adjustment procedure. I don't have an Omega spring so the adjustment is straightforward. The result is a bite point reasonably high up which is easily adjustable. Everything feels fine.

I will be replacing the clevis and clevis pin with new items although I didn't notice any elongation of the hole through the clevis. The Clevis pin had sheared and there was still parts of the pin lodged in both of the holes either side which were tricky to remove.

I drove the car to work this morning and it is as good as new.

I am just about to place an order with Pelican for the clevis and clevis pin and a number of other un-associated items. Thanks for your words of advice.

It is always helpful to get some assistance even with these relatively mundane issues because you never know you may miss something obvious (to others) and make mistakes or forget something quite important.

Cheers, Neil

[Neilnaz]

Jeff, I will check the lever arm when I replace the clevis and clevis pin (I missed your point when I first read it - sorry). I hope there isn't an issue there as the pedal cluster was a reconditioned one - but it is definitely worth checking.

Cheers, Neil

[javadog]

The clutch pedal shaft changed from 1971 to 1972. I don't recall what the change was. It changed several times over the years; it seems like some changes changed the effective length of the arm, others changed the lateral offset of the arm.

On the later 915 transmissions, the clutch cable travel needs to be around 25mm at the transmission. Early cars were adjusted a little more crudely. I'd probably start with measuring the cable travel to see what you have.

JR

[Neilnaz]

Javadog thanks very much for your helpful advice. As I said I have mentioned I put in an M6 bolt as a temporary fix which seems to work a treat. I adjusted the clutch to get a good bite point. If anything the bite point is a little high so I may revisit it.

I am looking for advice on the following guide for adjusting the clutch copied from the tech section. It mentions adjusting for free play to begin with then adjusting to ensure that the clutch definitely releases (doesn't goring when going into reverse) and doesn't slip.

Am I OK if I am sure that it fully engages and fully disengages?

I cannot find any sort of 'free play' by pulling the clutch pedal forward it has pressure from the clutch release arm constantly. How important is it to have some free play?

Maybe adjusting and dropping the bite point slightly will give me a little free play....

Cheers, Neil

911 (1965-76)

The early 911s had a relatively simple clutch adjustment mechanism. Despite the fact that there were four different clutch adjustment mechanisms during this period, the procedure is very similar for all of them. To adjust the clutch, release the adjuster nut near the underside of the transmission until the clutch pedal free play at the pedal is about one inch. The free play is measured by pulling back on the clutch pedal from inside the car. The pedal should travel about one inch when you pull it towards you.

Now, tighten up the locknut underneath the transmission. Start the car and with it at idle, press in the clutch and wait about 10 seconds. Then select reverse with the shifter. If the transmission grinds going into reverse, then you will need readjust the cable at the release fork end, underneath the transmission. The grinding indicates that the clutch is not disengaging all the way when you press in the clutch pedal. You use reverse to check the gears grinding because the reverse mechanism doesn't have any synchros that will disguise poor adjustment in your clutch.

When the clutch pedal is pressed completely to the floor, the travel on the throw out release fork should be about 0.6 in (15mm). Of course, this distance is highly dependent upon the condition of your clutch components. Worn clutches may require more movement, new clutches may require less. If the release fork doesn't move enough to disengage the clutch, then you will need to adjust the cable again, or check the other end of the cable that is attached to the pedal cluster. If you need to tighten the cable more than the amount that you can at the transmission, then you will have to adjust the trunion and pin on the clutch cable that attaches to the pedal cluster. See Project 9 for more details on gaining access to the trunion end.

Depending upon the wear in your clutch disc and pressure plate, you may have to play with these adjustments quite a bit until you get the right feel. Unfortunately, there is no exact science for adjusting the clutch on these early cars. The rule of thumb to follow is that you tighten the cable underneath the car if the transmission grinds into gear, and you loosen the cable if you cannot engage the clutch to the drivetrain (the clutch slips). Adjust the nut only three to four turns at a time. The clutch is quite sensitive to changes in the cable length, and once you get into the ballpark, only minute changes in the cable are necessary to dial in the clutch to your preferences.

[javadog]

Free play is good, so that all of the clamping force from the pressure plate gets applied to the disc. No free play means less clamping force, depending on just how tight it really is. Not enough cable travel results in insufficient movement of the release arm, which may mean the clutch doesn't completely release, which will ruin your transmission synchros in short order.

I'm more familiar with the design of the later style release mechanism, and I've never measured the clutch cable travel on that design you have, so I can't give you much advice as to how much of either is enough.

JR