1971 911T with 911/00 Trans - Clutch Cable Adjustment Questions

[misterjalopy]

I am new to 911s, so please forgive my ignorance and incorrect nomenclature.

I have a 1971 911T. The trans is marked 911/00.

From my research on Pelican, I see mentions of eccentricities on transmissions/clutches of this era.

Question 1: Bowden Cable Hanger/Guide

In the attached picture, the guide for Bowden cable is a U, not a through hole. Is this correct i.e. not broken?

When I got the car, it had two zipties anchoring the Bowden cable to the guide. Naturally, that isn't spec, but is it necessary/make sense to anchor the cable to the guide?




Question 2: Adjustment of Clutch

Background: I have adjusted the clutch pedal free play according to spec with the nut/lock nut. It was much better i.e. not chattering/grinding into gear, but it is still grinding sometimes. If I hold the pedal for a little longer, it seems to disengage.

Do I adjust the indicated nut clockwise to until get better disengagement and ceasing to chatter/grind?



Thanks very much!

[Flat6pac]

I recognize the worn guide tube, it's a guide for the Bowden cable as that is the item that moves to engage the clutch. The second picture, I don't recall the block but there is supposed to be a wedge that fits into the clutch actuator lever.
It's been 4 years since doing a 70/71 for reference.
Bruce

[steve911T]

The Bowden tube, as Bruce says should be in a circular hole that keeps it in place. Without being kept in place, the Bowden tube will have unrestricted movement and not operate the clutch. I guess that is why the zip ties were there. Search for Bowden tube and clutch adjustment in PParts. The two nuts above the arrow saying clockwise are the ones that adjust the clutch. I think that you are looking at less than an inch of free play at the clutch pedal for the correct clutch adjustment. Good luck.
Steve

[silver356]

Not to hijack this thread, but this is the setup I have on my 70t. Its different for sure from the pictures in 101 Projects for your 911. I am having problems with the clutch not disengaging all of the way, or so it seems, with crashing gears, especially if not at road speeds. According to the 101 book, the rule of thumb is to tighten the clutch cable to reduce crashing, and loosen the cable if its not engaging. My question is, is tightening the cable moving the inner nut of the two nuts( the lock nut being the outer nut) towards the rectangular actuator block in the picture, or away from it?
Thanks for your help,
David

[steve911T]

David, it is all in the free play at the clutch pedal. Pull the clutch pedal out to get the free play, it should be around 3/4". Set it there, at 3/4" and try to put it into reverse, no grinding good to go. Did you replace anything else? My guess about the lock nut is that to get the clutch to engage farther from the floor, tighten it more, in other words turn the nut counter clockwise. That seems to make no sense but by loosening the locknut, you are actually tightening the cable. Remember. in the 70-71, Rube Goldberg was the designer. There some other great posts on the board that if you search by Bowden tube or clutch adjustment, they really tell you what you need to know. Steve

[911T70]

I have a 70 T and have been struggling with the clutch since I got it two years ago. It's a very strange design and it took a while before I could wrap my brain around it. Here's a very good explanation of the concept and the adjustment by Grady Clay, a true early 911 guru.

clutch cable for 70-71 901

I'm curious: do you have the guide bracket on the differential cover pictured on the above post? My car doesn't have it and I'm wondering how critical it is? My clutch has recently become very stiff with a lot of chattering noises - anyone know what can cause that?

Hope the info in the link is useful - good luck with your clutch!

[steve911T]

911T70, I am assuming that you mean the hole in which the Bowden tube goes through? I would think that it was very important because that helps guide the Bowden tube (clutch cable outer tube)and helps pulls the Bowden tube away from the motor which then causes the clutch fork to push the release bearing on the PP to release the clutch. Without that, using the clutch might be tricky. There are posts where people have custom made bolt ons to guide the tube. I would visually watch the clutch in action and see if it is working correctly and then, again, pull the clutch pedal forward and make sure there is >1" of freeplay. If you do not have the U shaped guide on the transmission, it should still work. That, I guess is to gauge the correct position of the cable (lots of fun to replace the cable), and to keep it in line with the guide hole and keep other cables, etc, from interfering.
Good luck. Steve (just spent 6 months working on clutch, cable, Bowden this and that?.

[911T70]

Thanks, Steve. I meant the U-shaped guide. My clutch cable is new and it continuously needs adjustment. The clutch is so stiff I guess it's probably stretching with use. I'm grasping at straws trying to find the cause of the stiff clutch and was hoping the missing bracket was responsible, even if I knew it was unlikely. My last attempt before surrendering to clutch repair work will be lubricating the cable.

Didn't mean to hi-jack misterjalopy's thread - hopefully this info will be useful to him.

[steve911T]

911T70. The main thing with the U bracket is that it allows you to correctly adjust the cable when replacing it with a new one. One of the posts above has Grady Clay's link which shows you how high the cable should be over the bottom of the U bracket. It should be about 1-1.5" above the bottom of the U bracket. Believe it or not, it is kind of critical. How much free play do you have at the clutch pedal? No free play, means it is way too tight. I did find that when I replaced the clutch cable (used one) I had to readjust it again as it settled into its new home. But it got a bit looser, pedal engaged near the floor. Grinding slightly going into reverse was the symptom. Did you replace the clutch? Also, go on PP part sales and advertise for the bracket on the trans. Probably less than $40 with shipping. Easy to install. Steve

[911T70]

Thanks again, Steve - I really appreciate your help!

I adjust the clutch cable in order to get a bit less than 1 inch of free-play when I pull back the clutch pedal. The car shifts well in every gear but, as I said, the clutch is super stiff. Following your advice, I'll measure the amount of travel at the location where the bracket should be when the clutch is depressed. If it doesn't move by the right amount, I'll adjust the clevis at the front of the cable and re-adjust the free-play. My teenage daughter is getting fed-up with actuating the clutch as I fiddle with the cable under the car!

I haven't done anything to the clutch, yet. I will look for a used U-bracket.

[steve911T]

Good luck. The only thing that I can think of is that the clutch fork is having a problem moving correctly. I replaced every thing from the Pivot bolt that holds the fork in place to the flywheel. I am assuming that you have removed the clutch cable and replaced it, so, did the clutch fork have a lot of play or was it somewhat tight? It should be kind of tight but not rigid. If the trans has not been off for a few decades, you will find the answer when you pull the motor. It is always something on these cars. Steve

[frosty2]

911T70 I have much the same set up and not sure if this is your problem or not but my clutch got very stiff and I had to keep adjusting it which seemed strange so I put it on jack stands and found that the little coupling on the end of the cable ass'y that fits over the nipple were the cable enters the tunnel had slipped off and allowed the the cable to bend up at that point and was binding on the nipple.
I put the little coupling back on the nipple which kept the cable going straight into the tunnel and problem solved.
Hope this is of some help.
Thanks
Mike

[911T70]

Thanks, Mike! I'll have a look at that next weekend. It'd be great if it was as simple as that!

[911T70]

Originally Posted by steve911T

Good luck. The only thing that I can think of is that the clutch fork is having a problem moving correctly. I replaced every thing from the Pivot bolt that holds the fork in place to the flywheel. I am assuming that you have removed the clutch cable and replaced it, so, did the clutch fork have a lot of play or was it somewhat tight? It should be kind of tight but not rigid. If the trans has not been off for a few decades, you will find the answer when you pull the motor. It is always something on these cars. Steve

The cable looks brand new but I did disconnect it from both ends when looking for the source of the friction. I checked the clutch fork and it was very tight, which gave me relief because I was afraid that the pivot bolt was broken. How much force should be necessary to move it? I clamped on a pair of vise-grips for extra leverage and could not move the clutch.

I'm still hopeful that a more precise adjustment will help. It's a lot easier to operate after each of the many crude adjustments I've made.

Thanks again for your help!

[silver356]

I see we have a couple of different thread lines going here, but all about the same issues, so I wanted to conclude my saga, but also ask a question. Steve911T, you asked what else I had changed, and the answer is nothing. This is a car I purchased a couple of years ago, but have spent the time since doing body work and paint, etc, and only now am I getting around to making it a driver. The motor is was running pretty well, but had some carb issues, so I tackled that first, and its better, but when I would test drive the car, the tranny would crunch a bit. At first I thought it was synchros, but more reading led me to decide it might be clutch adjustment, which led me here.

After doing more reading here, and finding Grady Clays great diagrams and descriptions, I tackled the adjustment. The two adjustment nuts move toward the actuating block to reduce pedal free play, and away from it to increase it. My Bowden tube is dead center in the U-guide. I reduced the free play to about 3/4". and jumped in to test it out. Fired up the motor, pushed in the clutch, got about 2/3rds the way down, there was a grinding noise and chatter, and the motor went dead. Started it back up, and carefully tried again, same thing. So back under the car, and I decided to add more free play back in.

Long and short of it, I ended up with about 1 1/4" of free paly. Any less, chatter and grinding(tranny in neutral), any more, crashing in reverse. The difference is about 2 turns of the nut.

Can anyone help me understand why not enough free play kills the motor, and what is grinding?

David

[911T70]

Originally Posted by silver356

I see we have a couple of different thread lines going here, but all about the same issues, so I wanted to conclude my saga, but also ask a question. Steve911T, you asked what else I had changed, and the answer is nothing. This is a car I purchased a couple of years ago, but have spent the time since doing body work and paint, etc, and only now am I getting around to making it a driver. The motor is was running pretty well, but had some carb issues, so I tackled that first, and its better, but when I would test drive the car, the tranny would crunch a bit. At first I thought it was synchros, but more reading led me to decide it might be clutch adjustment, which led me here.

After doing more reading here, and finding Grady Clays great diagrams and descriptions, I tackled the adjustment. The two adjustment nuts move toward the actuating block to reduce pedal free play, and away from it to increase it. My Bowden tube is dead center in the U-guide. I reduced the free play to about 3/4". and jumped in to test it out. Fired up the motor, pushed in the clutch, got about 2/3rds the way down, there was a grinding noise and chatter, and the motor went dead. Started it back up, and carefully tried again, same thing. So back under the car, and I decided to add more free play back in.

Long and short of it, I ended up with about 1 1/4" of free paly. Any less, chatter and grinding(tranny in neutral), any more, crashing in reverse. The difference is about 2 turns of the nut.

Can anyone help me understand why not enough free play kills the motor, and what is grinding?

David

Hi David,

Looks like we're on parallel paths, but going opposite directions! I too have owned my 911 for a couple of years; my carburetors need tuning, but I want to get my clutch working properly before I tackle that intimidating task.

The design of this system is very strange and I can see why they changed it in '72 or so. Sure seems sensitive to minute adjustments. Your problem is very strange and I wish I could help you. Sounds like there's something wrong with your clutch and it's being engaged when it shouldn't. Have you tried moving the lever the Bowden tube pushes manually when the cable is disconnected? Is it loose/tight - is there noise/grinding?

Being very frustrated with mine, I've been searching the web for all the information I can find and came across a great YouTube channel by Peter Morgan, and early 911 expert. In this video, he shows how to re-assemble a clutch/transmission. It helped me understand how it all works and gave me confidence in tackling this job in the future if I can't resolve my clutch problem with cable adjustments. Maybe you'll find it useful:

https://www.youtube.com/watch?v=Bltyb0y-PWw

Good luck - keep us updated on your progress.

[911T70]

Well it looks like my clutch dilemma is over! Last Friday night I pulled the clutch cable out and inspected it. I tied a string at the clevis end so that I could easily pull in back through the tunnel. The cable was in perfect condition, looking brand new. I lubricated it with a wax-based lubricant I had from my cycling days. It doesn't attract dust and it won't harm the plastic/vinyl of the Bowden tube. I re-installed it and adjusted it following Grady Clay's post (posted above in this thread). After going back and forth a few times, I was able to get about 1" of free-play at the pedal and the right amount of curvature of the Bowden tube so that it would come down by about 1 1/2" with the pedal depressed.

Saturday morning I took it out for a test drive and couldn't believe how silky smooth the clutch felt and how well the transmission shifted. The car has never shifted so well - gone is the friction and chattering in the clutch pedal and so is the grinding when changing gears. I was very surprised, and relieved because I was convinced something was wrong with the clutch. I had even purchased an ATV jack in preparation for my first engine/transmission drop!

So what I've learned is that it's important to fully understand how this strange design works and that proper adjustment is critical. There seems to be a sweet-spot in the adjustment range where it works beautifully but will make you believe there is something terribly wrong if elsewhere.

[silver356]

Well, Michel, I'm glad you have found the sweet spot in your clutch adjustment! I have not been able to road test mine, after I was able to eliminate the chattering on one side, and the gear grinding on the other, but your post gives me hope. I will try and road test it this week. I am hopeful I will have similar results.

I would still love to understand what I am missing- why does the clutch grind and chatter, and stop the motor, if there is not enough free play? I sense you had similar issues, as we are using similar words to describe the sounds and sensations, but I'm still stumped.

I realize this is very basic, and I apologize in advance for the stupidity, but it would seem like the opposite of grinding gears, (the clutch not separating the engine from the transmission), would be the clutch never engaging at all, so the engine never turns the transmission. That's what I get from the description in the Pelican Tech article on clutch adjustment, even though its not specific to the 70 clutch arrangement. Any thoughts?

BTW, Michel, you should definitely attack your carb issue. If you do them one at a time, and take your time, its really quite easy and doable. Alfa1750 on ebay has all of the parts you need, whether its Zeniths or Webers, and there are tons of articles here on the bird.

Cheers!

[gamin]

I am the original owner of my 70T. The only adjustments that I have made over the years to the clutch have been free pedal 3/4" done at the 2 nuts and pulling the pedal rearward and clutch pedal stop done at the floor board. Never any problems. And there have been very few readjustments. Recently changed the clutch package and cable only because engine and trans were out of the car and I "was in there". I think a lot of people forget the pedal stop adjustment in the floorboard under the carpet. Could be cause of grinding gears.

[911T70]

Originally Posted by silver356

Well, Michel, I'm glad you have found the sweet spot in your clutch adjustment! I have not been able to road test mine, after I was able to eliminate the chattering on one side, and the gear grinding on the other, but your post gives me hope. I will try and road test it this week. I am hopeful I will have similar results.

I would still love to understand what I am missing- why does the clutch grind and chatter, and stop the motor, if there is not enough free play? I sense you had similar issues, as we are using similar words to describe the sounds and sensations, but I'm still stumped.

I realize this is very basic, and I apologize in advance for the stupidity, but it would seem like the opposite of grinding gears, (the clutch not separating the engine from the transmission), would be the clutch never engaging at all, so the engine never turns the transmission. That's what I get from the description in the Pelican Tech article on clutch adjustment, even though its not specific to the 70 clutch arrangement. Any thoughts?

BTW, Michel, you should definitely attack your carb issue. If you do them one at a time, and take your time, its really quite easy and doable. Alfa1750 on ebay has all of the parts you need, whether its Zeniths or Webers, and there are tons of articles here on the bird.

Cheers!

Hi silver356,

If your clutch stops the motor, it's because it's not releasing, isn't it? I would check the amount of travel at the arm to see if it's within specs. Sounds like it's not enough or not in the range where it should be, completely out of adjustment. What solved the problem for me was the adjustment at the clevis end. It's difficult to reach at the pedal cluster but once disconnected by unclipping it, it can be pulled out of the tunnel through the top opening and adjusted. With the right amount of free-play at the pedal, the right bow in the Bowden tube and the right amount of travel of the arm, it should work properly. Like Grady Clay wrote in another thread: 'That tube needs to have a slight bow to it to accommodate the slight fore-aft movement of the engine/trans. Otherwise the clutch is very chattery –grabby and difficult to engage. Don’t feel bad if it takes you several tries to get this right.'

Thank you for the carb advice. I've found lots of good information on this forum, bought books, an airflow meter and float level gauge; basically been in 'analysis paralysis' for months. Now that my clutch problem is resolved, I have no excuse to procrastinate - I'm attacking those carbs next weekend!

Good luck with your clutch - keep us updated!