Clutch adjustment

[Timothy B.]

I request some advice from this wonderful forum on clutch adjustment on a 67 SB. I have read the archives and service manuals and still have a few questions.

There are two configurations of the clutch - quick and slow actuation. Which config is standard?? Which do most people use? With mine in the slow (less force required) configuration, the adjusting nut on the rod is at the extreme end of the rod, and even with it this way the disengagement/engagement point is very low to the floor. If I were to adjust the linkage as the manual says, it would probably barely disengage at all. I can't believe that GM wanted the clutch adjusted such that the release point was almost at max travel.

I am looking for comments regarding the two configurations of the clutch, which was the factory standard that corresponds with the AIM, where the engage/disengage position turned out to be in the pedal travel, general thoughts on the relative leg force with each, etc.

[John H.]

Re: Clutch adjustment

Tim -

67's didn't have the "quick-release" clutch feature in the clutch linkage - the bracket with the pushrod pin is welded solid to the clutch pedal, not bolted on (with two possible locations) as it was on earlier cars that had the feature. If your '67 has the feature, some parts have been swapped around.

[Joe L.]

Re: Clutch adjustment

Tim-----

I was not aware that mid year Corvettes had dual clutch linkage configurations; C3s which have a nearly identical clutch linkage do not. I assume that the different clutch positions must be effected at the bracket attached to the clutch pedal since that's about the only difference between a mid year and a C3 clutch set-up.

In any event, I feel quite certain that if there are dual configurations, then the PRODUCTION configuration would be the "slow" or "least effort" position. Usually, all PRODUCTION set-ups follow this "rule of thumb".

As far as adjustment is concerned, I can tell you that even when a Corvette clutch linkage set-up is PERFECT, the adjustment is VERY tricky. Getting the specified free play while having full disengagement when the clutch pedal is at full deflection is often impossible. Often, the best that can be achieved is less-than-specified free play if there is to be full disengagement with the pedal at full deflection. If the clutch starts to engage with the pedal just a "scoche" off the floor and this proves disconcerting, then the free play has to be reduced even more. You MUST maintain some amount of freeplay, though, regardless of how the pedal is at the other end.

One thing that you should do, though, is to check to be sure that your car has the correct clutch-related parts. These are as follows:

pedal push rod----19-3/16" OL (GM #3888213)

fork push rod-----8-37/64" OL (GM #3872960)

release bearing----1-1/4" front-to-rear (GM #15680264) or 1-7/32"

fork ball stud----- 1-1/2" (GM #3729000) OR 1-3/8"

cross shaft----GM #3888279 (unfortunately, this number is not found on the shaft)

If ANY of the above-referenced parts are incorrect, it will GREATLY compound the problem of clutch adjustment. Also, aftermarket clutches or excessively surfaced flywheels may complicate a proper clutch adjustment.

FOR A CORVETTE, EVERYTHING RELATED TO THE CLUTCH SYSTEM HAS TO BE PERFECT TO GET A SATISFACTORY ADJUSTMENT.

[Duke W.]

Re: Clutch adjustment

The 1963 Corvette Shop manual clutch section contains the instructions to change over to the "fast" clutch ratio, which reduces total pedal travel from the "standard" 6.5" to 5" if I recall correctly. All you need is some common hand tools.

The plant used the "standard" ratio for all production.

I'm not sure what year this feature was last available, but it couldn't
be any later than 1966.

Duke

[Timothy B.]

Re: Clutch adjustment

Interesting, and great response Joe! I will have to check and see for sure that my car has both clutch postions (car is not where I am right now). I think it does, but I am going from memory. Do you or anyone know typically where the adjustment link ends up on the pushrod when all the parts are correct? I do know that many years ago I replaced the fork pushrod with a new part from the GM parts counter, and I wonder if I got the right part. There is some interference between the fork and the pushrod where the two attach with a pin, where metal rubs at a certain angle - wonder if that is an indicator of a problem...

I wish there was a way to verify all parts with the tranny in place! :-) Of course if I decide to pull the tranny due to bearing noise (see other post), that would be my opportunity.

[Joe L.]

Re: Clutch adjustment

Tim-----

As John mentioned, the pedal rod pin mounting bracket on the 67 is welded to the clutch pedal shaft. So, it's not adjustable. As I mentioned earlier, a pin mounting bracket location change would be the only way I could see for mid-years to have "dual configuration". From what's been reported, apparently that's exactly how the 63-66 "dual configuration" was achieved; dual mounting pin bracket locations on the pedal shaft. I'd forgotten that the 67 was welded, but with the welded bracket there's no way to achieve a "dual configuration" on a 67. For 1968-81, the clevis pin for the clutch pedal push rod was attached directly to the pedal shaft through a hole with a tack weld. On these cars as well as 67's there's no way to change the pin position without doing a modification.

While you can't easily check the internal clutch parts from the list I provided, you can easily check the external ones like the 2 push rods. The clutch fork push rod is an item which, when replaced at some point in the car's life, is many times replaced with an incorrect part.

[Timothy B.]

Re: Clutch adjustment

Joe, thanks for the great info! This forum is wonderful! Do you or anyone happen to know if there is a fork pushrod that is slightly LONGER than standard but similar config that I could switch to? That would give me the extra adjustment potential on the pedal pushrod. If I have to pull the tranny to replace a bearing (see other post), then I can check these parts too, but that may be awhile...

[Joe L.]

Re: Clutch adjustment

Tim-----

The 1964-E1966 fork pushrod, GM #3844209, is 10-9/16" OL. However, I don't think that this rod will work with the 67 set-up. There are no other pushrods available from GM.

[Richard S.]

Re: Clutch adjustment

There are indeed two rod lengths.....check Long Island Corvette catalog...they carry both lengths I believe.