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All of the 4/5 speeds I’ve owned had one quality that was consistent. When pressing on the clutch pedal, after the initial 1 inch of free play and the pressure of the throw out bearing pushing the pressure plate diaphragm fingers back, there is a relief of that pressure. Which makes it easy to hold the clutch pedal to the floor.
I have a bad feeling about my latest clutch/transmission install.
I installed a new clutch disc/ PP/TOB kit for a 1963/ with a rebuilt Muncie M20. While at it I rebuilt the Zbar and checked the clutch rod and clutch fork. Both ok condition. But my car was modified by the previous owner which opens a big can of worms for me. My biggest challenge is not to rebuild his mistakes if you follow me.
Clutch fork is not an original to the 1963. Clutch rod the same. I’m checking on the quick clutch release option up behind the dash tonite.
When depressing the clutch there is constant pressure all the way to the floor. Something is not right but I just can’t put my finger on what that might be. Car is on the lift and I haven’t tried starting her up and going through the gears yet. Hoping it’s a problem solved by pedal to clutch linkage/geometry. Has anyone had this experience or understand what is happening with this setup?
Just shooting from the hip here, but there are 2 different clutch forks for C1 and C2. They look the same but there is a different angle where the push rod hooks up.
Yes I saw that but wasn’t sure which one to go with so I used the fork that came with the car. It did not work well before I tore into everything but there was so much wrong with the previous owners setup (Z bar slop, pins loose, etc) that I couldn’t isolate what was working and what wasn’t. After rebuilding the Zbar and tightening/replacing loose pins that aspect is solid and smooth as it was from the factory. And that is where I’m at.
I’m narrowing it down to possibly the clutch fork design/angle being wrong and possibly the wrong throw out bearing?
And this is why I don’t want to get the car down off the lift. Right now I can easily pull the transmission back out and rectify any error. I’m hoping someone’s got a good insight into what’s happening here.
Right now I can easily pull the transmission back out and rectify any error. I’m hoping someone’s got a good insight into what’s happening here.
It does not look easy to me.
I am in the process of pulling my trans out because There is something wrong in the bellhousing, I think the throw out bearing is wrong. (previous owner)
I only want to do this once in my life time, so I am following what you discover in yours,
Mine makes a weird vibrating sound (sometimes) like something is hitting the pressure plate and the peddle feel stays the same from top to bottom there is no over the top feel at the bottom and when engine is up to temp its hard to get it into 1st gear
Last edited by walleyfisher; 03-25-2024 at 03:08 PM.
I guess there are potentially 4 possibilities here:
clutch fork pivot ball wrong size/length
clutch fork incorrect
incorrect throw out bearing
z bar and linkage incorrect
clutch disc and pressure plate could be defective but on inspection looked good and I didn’t see any shipping damage.
your description of the pedal feel was identical to my experience
Because of my recent clutch crisis I have done a fair amount of research, both on the forum and off, into clutch geometry and applications specific to mid-year Corvettes.
I have heard it suggested by a quite a few folks that I may have the wrong throwout bearing. It would appear that all 63-67 Corvettes used the same bearing (the short one, which is the one I have installed) so I cannot see how that could be an issue. Others have suggested perhaps using the longer bearing as a solution.
Harking back to my high school geometry class (disclaimer: that was a long time ago!), I cannot see how that would make a difference, since that wouldn't appear to change the total amount of pedal travel - all it would do is change the point of release to a different position on the pedal travel arc, as opposed to actually reducing the amount that the pedal must travel from fully engaged to fully released...?
Sorry for the semi-technical explanation, but am I missing something?
Just curious. Thanks. Wow, More and more folks are having problems in this area. I to have spent a lot of time with this one so let me lay out first the different parts out there for use in all 63-7 cars. I do not see where you mention the year on yours.
1) there are two different length pushrods from the pedal bracket to x-shaft. 63-5 and 66-7
2) There are two different brackets available that bolt to the pedal that the push rod attaches to, one is for all 63-66 small blocks and 396, one is for 66 BB. Each has two different mounting possibilitys, one for standard street use, and one for "faster shifting driving" this of course would also equate to increased pedal effort alone. I think the only place this was described was in the service manual.
3) there are a total of 4 different x-shafts, one was 63 only and was never serviced, one was 64-65 sb and 396, one was 66 sb, one was 66 bb and 67 all, this is the one that most commonly although incorrectly finds its way into cars it was not meant for, as this was the only one used from 67 all the way to 82 in all applications.
To make it real complicated, NONE of them ever had a part number on them, and with the exception of the original 63 unit, they are all quite different in orientation of the two levers. The 63 unit is very similar to the 64-5 one and is quite acceptable if the original is gone.
4) There are a total of three different lower push rods, one, 63 only (must be used with 63 only fork), one is 64-5 sb, and one is 65 BB and66-7 all
5) There was two different length ball studs if memory serves correctly, There was a long one used on the sb cars and on the BB cars 66-7 and then all the way to 82 there was a shorter one, currently only one is available and thats been the case for some time. It is a compromise in length between the two.
6) There was only two clutch forks available from 63-82, one was 63 only and needs two be used with the 63 only lower push rod, the other for ALL applications.
Lets stop here for a moment and look at this list of GM only available parts, it should be easy to see that with all those different parts, its VERY easy to mix parts up that all look very similar and not one of them has a part # on it, Only a tag if its an over the counter part, also remember as time went on GM would offer in the way of replacement parts for service a part that would function, it may not function the same but it would function.
All those different parts were generated and changes in geometry made for one reason, to keep the "rollover center arc" at about mid pedal travel. That was changed do to clutch design and size changes and customer feedback for pedal effort required. In a car with correct geometry once you "go over center" and the pedal is on the floor it takes very little effort to keep it there and should engage smoothly just as you are reaching the "over center" on the way back up and have the required free pedal play at rest ( here is another potential problem, bent pedal stop and/or missing bumper stops.
Now with that behind us add all the variables created by all the different type and styles of clutches installed in 45 years and the number of aftermarket flywheels of uncertain geometry, original flywheels cut and resurfaced many times, ball studs replaced that have all sorts of lengths and we will not even let in after market bellhousings or scattershields.
The only way to know what you have in a car you have purchased used is to start with the first part in the chain and go thru them one at a time to ensure you have the correct parts in the first place.
Once you do that its easy to determine whats wrong. Remember when they left the factory they were all the same as far as pedal effort and free play, now just about every car you get in has different feel, so, something is different.
Lewgar
Very nice post that explains a lot of the confusion over the parts that we may or may not have.
Is your info based on experience Or are you an old Chevy parts man.
I wonder if your clutch is fully disengaged when you depress the clutch pedal toward the floor? You may have a pressure plate that will not disengage with the short travel in a Corvette. See the attached article: https://www.corvetteforum.com/forums...vel-range.html
You describe how it SHOULD feel perfectly. The trick is to integrate all as listed above into the mix. First is determining the pressure plate being used. Many 'higher perf" styles are "raised diaphragm" style vs flat style. That changes the geometry if wrong bearing,stud, fork are used.
My buddy's '65 had that "perfect" feel...but recently he replaced the clutch after 10-15 years of torture on it (he drives hard and powershifts well). He had flywheel resurfaced .060" and that amount has made it feel much different acting. He's going back in there to change the pivot stud length to compensate.
Years ago, there were 3 stud lengths as well as 3 bearing lengths. Now you can onlyget two usually. The adjustable studs are very helpful to dial it in and my buddy has always had one. He'll just re-adjust it. In addition, McLeod makes a really cool bearing with a removable bearing from the collar. It comes with 3 shims to allow you to create that "mid" length version when needed.
I always set it up with the fork as far forward as possible (at rest) without contacting the pressure plate or bellhousing opening. That really helps get that "feel" and make it easier to push.
On my '67 that I race....when I was using mechanical linkage I actually swapped the arms on the cross-shaft to create a much faster acting setup where a toe tap would release it. Made it a little harder to push....but with real "race" clutches..pedal effort is very low anyway.
I'm not sure if these pictures posted on the forum quite some time ago are useful for this discussion but thought it might be helpful to have them in this thread.
Gary
Looks like you have the 66-67 lower rod. I would ensure all four parts are 64-65 so they match. Please post a picture of the clutch adjustment. Its position my provide additional clues.
I ordered and received a new lower clutch fork rod #28. Not correct but longer. Thought this would push the fork a little further past the arc. While putting all this back together I noticed there was a lot of slop in all the connections starting from the clutch pedal bracket to upper clutch rod. The adjusting nut that fits into the arm on the Z bar was very loose. The lower clutch for rod where it inserts into the clutch fork needed a bushing also. After addressing all these points I felt sure that the result would be some improvement but it did not help at all. The clutch pedal still feels very stiff all the way to the floor board.
‘I can’t proceed further until this gets figured out so my next step is to change the clutch fork to a circa 1963 correct fork with a correct length lower fork rod.
I don’t believe this will solve the issue but I need to replace all the incorrect parts one at a time until I get the right combination.
‘my gut tells me it’s the new clutch. It’s the only culprit left. But the po installed an 11” clutch with 621 bell housing flywheel etc.
‘If after the original clutch fork is installed and there is no improvement I’ll look into replacing the clutch.
‘I’ve heard good reviews of Luk. Should it come to this Can anyone recommend them and a specific item # that is 11” that I could use? Or do I have to decommission the entire 11” flywheel/bellhousing/ in favor of one that supports the original 10.5? In other words revert everything completely back to the stock drivetrain between engine and Muncie.
quite a chore this is turning out to be.
The clutch pressure stays constant and not becoming easier when fully depressed. I don't believe that you have a problem. If you have free play and the clutch isn't dragging you should be good to go. Back in the day I had a 3000 lb three finger pressure plate in the Vette, was loads of fun holding the clutch in.
Rink, I wrestled with this thought last night. I was sitting in the car pushing down on the clutch pedal. With about 3/4-1” of pedal freeplay, i felt a consistent pressure all the way to about 1-2 inches above the floorboard. This is difficult to describe, but at that point, the pedal stops feeling smooth and there is a feeling of resistance just before the final end of the clutch pedal travel. Sort of like metal rubbing very briefly on metal. There is no “arc” where the pedal pressure increases, clutch disc disengages and the pedal goes to the floor with minimal effort. That’s what I’m used to. This continuous pressure all the way to the floorboard seems foreign and I’ve never driven a manual vehicle that had this characteristic. But as you said, there may not be any problem with this. It just might work regardless.
My suspicion is that when I get the car down and start it up, there will not be enough disengagement of the pressure plate to allow an easy shift into gear. That particular problem has been gone over many times here on the forum. It takes very little movement on the throw out bearing to disengage the pressure plate from the clutch disc. But there is a lot of movement prior that happens to get that to take place. A combination of too short a z bar shaft, loose or sloppy pins, wrong angle on the clutch fork, short throw out bearing when it should be long etc is all playing into this. The previous owner was not able to solve this problem. That and other issues I believe had a hand in him selling the vehicle.
I've only used a short bearing. I don't believe that you could put the trans in with a long bearing without forcing the issue. The front bearing retainer is in good shape? I've seen them worn where the throw out bearing slides. I would figure out a way to start the car in natural and slowly disengage the clutch. If it seems ok then try a gear. Even with the lead exhaust pipe off, you won't be running it that long.
Last edited by Rink; 04-03-2024 at 10:37 AM.
Reason: misspelling
03-25-2024, 12:10 PM
New clutch install into a 1963 question
