I have a 69 GTO with a Muncie 4 spd that uses a z-bar clutch linkage. On multiple occasions, I have pulled up to a red light or had to stop and sat with the clutch engaged while waiting to go. All of a sudden, the car started taking off even though I had not let off the clutch. After taking off, the clutch went back to working properly but then the same thing happened again latter. The clutch itself does not seem bad. It does not slip or do anything unusual when driving. Everything is new since the car has been restored. What can cause the clutch to disengage when the pedal is on the floor? Why is it sporadic?
There are a few things to look at: Check the play in the clutch linkage. Sometimes new stuff will change dramatically after break in. See if there is excessive play and check the play at the clutch arm where it contacts the linkage.
Even if the pressure plate is new, there is the pssibility that a finger broke. Is it a 3 or 4 finger pressure plate or is it a diapraghm type, (where there are fingers all the way around)?
Are the motor mounts new?
Is there any change to the vehicle that is different than its original setup, such as: changed motor from small block to big block, different type of tranny, heavy duty or multi-plate clutch, etc?
Let me kow and I will keep this post on my list. I will get back with you ASAP and see if I can help you out.
November, 9, 2010 AT 10:29 AM
Reviewed the clutch linkage, from the pedal all the way to the clutch fork (arm) while depressing and releasing the clutch pedal and everything seems fine. No flexing, sway or slop. The clutch and pressure plate are from Centerforce (CF2). Motor mounts are new and it's the original engine rebuilt. The car was originally an automatic and was converted to a 4 spd with a rebuilt M20 Muncie. Throw out bearing is the recommended CF part number. Car has less than 500 miles on it since getting it back so it's not a wear issue due to many miles. Any help is greatly appreciated. Thx
November, 9, 2010 AT 3:03 PM
There is an adjustment for free play in the pedal. This is generall as tight as you can get the linkage without it dis-engaging the clutch without the pedal being pressed.
I adjust mine at the arm that sits on the throwout bearing. It is really the most accurate way to get the most dis-engagement when the pedal is pressed. I tighten the linkage until there is just a little bit of free play without the throwout bearing riding the pressure plate. This way when you press the pedal it will move the throut bearing as much as possible without the clutch risking not being fully dis-engaged when the pedal is releaed.
Also, with a custom job from A/T to M/T the linkage alignment can be critical depending on the setup. If the linkage is mounted strictly on the motor and tranny the alignment is less of an issue as opposed to the linkage being mounted on the chassis.
If you had to weld linkage in place somewhere on the chassis or custom fabricate something, I would try to get measurements form a stock setup oir maybe call the tech line at Center Force.
Let me kow how it goes.
There are also some good links on this site for diagnosing the issue. But, I don't think there is anything that will have specs or measurements as that would be found in a factory service manual. The Mitchel ! Online maual offered on this site is a great deal because you get service manuals for essentially any car that you own or ever will own.
I will check back to see how it is going.
December, 23, 2010 AT 2:58 AM
Couple of things tocheck here. Take a bar and with the engine off, push the harmonic balanecer forward. If it moves more than a couple of thousands then you have a worn crank thrust bearing and when you push the clutch in it is actually pushing the crank forward. It can also be a broken crank at the back two journals. It can also be a bent release arm. It's going to be one of those assuming your clutch is ok.
January, 7, 2011 AT 3:35 PM
Sorry I was out the month of December.
Hmac brings up excellent points to check that could be the cause.
I think he mnay be on the right track as your clutch is new and as long as you installed it correctly. Centerforce is a good clutch and it is unlikely that something is wrong but not impossible.
Thanks to hmac300 for covering during my absence.
We aim to please!
I am back in action and I am sure both hmac and I will keep an eye on the outcome and help any way we can.