ZZ4 Clutch problem with smaller 327 size flywheel.

[loup68]

Has anyone else had a problem with their clutch when using the smaller GMPP 153 tooth flywheel on a ZZ4 ? I had a 68 L-79 and I wanted to keep the stock, one year only starter. Everything is stock, bellhousing, 10 1/2 " clutch,bell housing ball stud. When I tried to adjust the stock type diaphram clutch, The adjustment was off the end of the clutch rod. I ended up getting a thicker "racing" throw out bearing to compensate, from summit. At first I thought I had put the fork on wrong and was kicking my self. But it was correct. Has anyone else had this problem? The only thing that I can think of is that the flywheel thickness has to be different than the normal 350 164 tooth flywheel.

 

[tracksnblades1]

I have seen this before but usually on trucks. More specific Chevy/GMC gen1 trucks. Some heavier GMC's had beefier throw out bearing assemblys. I'm a little puzzled about your 164 tooth flywheel. I hope it's just a typo. I remember the 12.5 inch flywheel with 153 teeth and the 14 inch flywheel with 168 teeth. Watch out for the RARE 400sbc and 454bbc flywheels. These flywheels bolt right on too, but have external balancing and require the correct dampeners and applications. Shake shake shake if you get the wrong combo.
AGE QUOD AGIS
Do what you do, Well

 

[Hib Halverson]

If you had to use a longer TO bearing then the flywheel got "thinner" not thicker. That's not likely.

You mention a "stock-type diaphragm" clutch, but wasn't clear in your post if you replaced the clutch or just transferred an existing clutch to the new flywheel.

If you installed a new clutch, did you verify that the finger height was the same?

 

[loup68]

Yes that was a typo,I ment 168 tooth. Hib, I installed the ZZ4 about 6 years ago. I had a borg and beck 3 finger clutch. It needed too much pedal travel, so I went back to the stock Hay's 10 1/2" diaphram clutch with the change to the ZZ4. I never changed the clutch ball stud but I did get a new stock fork from Zip. I am almost sure that it is the same size as the old one. I think I really goofed by not getting an 11" clutch & bellhousing. I'm pissed at chevy for not putting the 350 in the 68. They delayed the 68 vette a year , introduced the 350 in the 67 camaro but could not put it in the flagship vette in 68? I wanted to retain my starter to be able to go to a store and still say I need a 68 starter.

 

[Hib Halverson]

Yes that was a typo,I ment 168 tooth. Hib, I installed the ZZ4 about 6 years ago. I had a borg and beck 3 finger clutch. It needed too much pedal travel, so I went back to the stock Hay's 10 1/2" diaphram clutch with the change to the ZZ4. I never changed the clutch ball stud but I did get a new stock fork from Zip. I am almost sure that it is the same size as the old one. I think I really goofed by not getting an 11" clutch & bellhousing. I'm pissed at chevy for not putting the 350 in the 68. They delayed the 68 vette a year , introduced the 350 in the 67 camaro but could not put it in the flagship vette in 68? I wanted to retain my starter to be able to go to a store and still say I need a 68 starter.

About all I can offer at this point without seeing the parts myself is that the clutch fork height and the release bearing position have to be matched to the clutch finger height. There were three fork ball studs of different lengths, as I recall. Also, there are vendors which sell adjustable height studs. Regardless of what aftermarket clutch you have, you need to have the right fork height and the release bearing length correct or the clutch linkage geometry will be incorrect.

Often is the case that with aftermarket clutches with other than stock pressure plate designs or finger heights, you have to mock-up all the parts before engine installation to visually inspect geometry. I would not assume the Hays 10.5 is "stock" as far as finger height unless the Hays people tell you that or you measure it. You might contact Hays' tech support and ask them if they know the proper ball stud, bearing combination to work with their clutch.

Keep in mind that the best clutch linkage geometry starts with the right ball stud height and while the release bearing length can compensate for the wrong stud to a certain extent, both parts need to be right for best results.

Good luck.

 

[JohnZ]

For reference, with stock GM parts, there were two setups, only one of which was ever used on Corvettes. Corvettes used "bent-finger" diaphragm clutches (in both 10.5" and 11" sizes), with the "short" (1-1/4" overall) throwout bearing. Most passenger cars and trucks used "flat-finger" diaphragm clutches, with the "long" (1-3/4") throwout bearing.

As Hib noted, not all "bent-finger" diaphragm clutches from different manufacturers have exactly the same finger height, although they should if they're designed specifically for the Corvette application; if the adjuster swivel is off the end of the pedal pushrod and the rest of the linkage is stock, either the finger height is WAY low to spec or you have a "flat-finger" clutch. I've used LuK bent-finger diaphragm replacement clutches and "short" throwout bearings in many Corvettes over the years, and have never had any adjustment issues.