T56 swap, can't get enough throw on f body master cylinder - Pontiac GTO Forum
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post #1 of 4 (permalink) Old 11-17-2017, 07:20 PM Thread Starter
 
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T56 swap, can't get enough throw on f body master cylinder

So I have the speedway or amp? Booster adapter plate for using the stock f body master cylinder. I'm using 67 pedals in a 66 and I can't seem to get enough throw to release the clutch. Well I CAN but I had to cut and thread the pushrod and add about an inch to the length. Now my clutch pedal sits WAY above the brake pedal and even then I have to push it almost to the floor to get the clutch forks to release. What would some of you recommend? Right now the pushrod is almost dead center in the bore and pedal effort feels right. Not sure how much I can move the rod up or down. I've heard some people have had problems with the brackets but mine all fit in correctly, I just don't know if the angle is off. Thanks
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post #2 of 4 (permalink) Old 11-17-2017, 08:27 PM
 
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Three things come to mind. FIRST, wrong throw-out bearing for your clutch assembly, wrong clutch fork, or you need to purchase an adjustable pivot ball which is located inside the bellhousing and is what the clutch fork pivots on.

Most often, the problem is in the throw-out bearing. It seems the short Chevy throw-out bearing is handed out as a piece that fits and then it does not. There are three various lengths of throw-out bearings. They are determined by their length, - short, medium, and long. Put in the short one, and you will not get the clutch to successfully disengage. You lengthen the pushrod at the clutch fork thinking this will solve the problem, but it improves it but you still cannot get a clean release. Bear in mind that you are creating quite an angle on the clutch fork as fitted on the collar on the throw-out bearing and you can break the collar and if it goes into the pressure plate/clutch at any high speeds - you take out the pressure plate and clutch. Ask me how I know. LOL As I recall, a flat finger diaphragm pressure plate will take a long and the raised finger diaphragm a
medium, or possibly the short, length depending on how raised the fingers are.

There is a "generic" clutch fork sold to fit a host of GM applications to include the Pontiac. It does not. I has an incorrect angle to it and you cannot get enough throw into it to push in the throw-out bearing. This could be a possible problem, or adding to it. The Pontiac parts suppliers usually off the correct Pontiac clutch fork, not the generic one if you have replaced yours with an aftermarket piece.

Third, the factory pivot ball is fixed and cannot be adjusted. Lengthening the pivot ball changes the geometry/fulcrum as it moves the clutch fork closer to the pressure plate. By lengthening the pivot ball, you will get a better throw on the throw-out bearing which will release the clutch as needed.

The clutch fork arm that sticks out of the bellhousing, with the correct throw-out bearing, should be forward of the hole centerline it sticks out of, but not so much as to have the clutch fork arm hitting the opening's edge from being too far forward. If you have the incorrect short throw-out bearing, the arm on the clutch fork will be positioned past the centerline of the opening giving you little space for movement of the clutch fork arm.

Now one last possibility is the wrong cross shaft. You could have a geometry issue when you depress the clutch pedal. If you have a factory piece, you are probably good. if you have an aftermarket piece, it is possible the arms might not be welded in the needed position to give you the leverage throw needed to push in the clutch - but this would be one of the last things I would check.

Read this post, with pictures, as it may help: https://www.gtoforum.com/f154/68-gto-...problem-83201/

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post #3 of 4 (permalink) Old 11-17-2017, 10:47 PM Thread Starter
 
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Hey Jim thanks for your response but it seems like you are talking about a factory style manual transmission setup. I have a T56 swap from a 2002 Camaro and it has a hydraulic throwout bearing. Sorry if I wasn't clear enough
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post #4 of 4 (permalink) Old 11-18-2017, 09:34 AM
 
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Quote:
Originally Posted by Dealer369 View Post
Hey Jim thanks for your response but it seems like you are talking about a factory style manual transmission setup. I have a T56 swap from a 2002 Camaro and it has a hydraulic throwout bearing. Sorry if I wasn't clear enough

AND HERE IS WHERE WE NEED PICTURES.

"Well I CAN but I had to cut and thread the pushrod and add about an inch to the length. Now my clutch pedal sits WAY above the brake pedal and even then I have to push it almost to the floor to get the clutch forks to release. "


OK, this description is what is often done when the throwout bearing is too short on a standard style clutch set-up.

Why the clutch fork? I thought the hydraulic throwout bearing sits on the trans input shaft collar and operates off the hydraulic pressure from the slave cylinder at the pedal? So I am a little confused, but no experience with the stuff.

Never messed with or had an hydraulic clutch set-up. However, it should not be too hard to diagnose. As long as you know you have no air in the system and have bled it, and the master matches the throwout, and these are both correct with the pressure plate/clutch set-up, then it has to be geometry. You are most likely not getting enough throw at either the pedal or the Z-bar. You are combining modern components with older components.

I would consider two things to look at. The fulcrum at the clutch pedal may be different than the Camaro donor. You need to measure from the pivot point on the Camaro pedal to the attachment point for the slave cylinder rod and then do the same thing for the '67 pedal. These need to be the same. If the '67 pedal pivot point is longer, you will not get the correct movement as the pedal swings though its arc. If longer, you would have to move the pedal much further to get the needed clutch rod travel - and may be why you had to extend the clutch pedal rod at the pedal end of things?

The second thing is the Z-bar. Are you using a Z-bar? If so, then same thing - geometry. Locating one of the attachment holes on the arm closer to the crossover shaft will change the arc producing a larger reaction (throw) on the opposite arm.

Again, big guess here without pics. But, my guess is getting the correct geometry on things if all components are matched.
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