Clutch adjustment
Thread Starter
Instructor
Joined: Aug 2017
Posts: 115
Likes: 15
From: Lebanon Ohio
Clutch adjustment
Just bought a very nice 71 with a slightly built 350, 4 speed. Original 270 hp block, original transmission. The transmission has been rebuilt and clutch, pressure plate, flywheel replaced. Everything feels good and works nice except there is no adjustment left to get the clutch petal up off the floor. It must be pressed firmly and fully to the floor to shift. The adjustment is all the way at the end of the pushrod. It seems as though the fork pivot ball is too short, but.... Also there isn't a feel of perceptible excessive free play at the top.
I don't understand why the stack up would have changed based on what I think I know about the replaced components.
Any ideas?
Many thanks.
I don't understand why the stack up would have changed based on what I think I know about the replaced components.
Any ideas?
Many thanks.
Team Owner
Joined: Sep 2006
Posts: 31,170
Likes: 4,245
From: Westminster Maryland
Hi Ns,
Welcome!
First Post!
And a 71, very nice.
Do you know about the GM Assembly Instruction Manual and the clutch adjustment procedure in it?
Perhaps in looking at that you'll spot something amiss.
Regards,
Alan
Welcome!
First Post!
And a 71, very nice.
Do you know about the GM Assembly Instruction Manual and the clutch adjustment procedure in it?
Perhaps in looking at that you'll spot something amiss.
Regards,
Alan
Thread Starter
Instructor
Joined: Aug 2017
Posts: 115
Likes: 15
From: Lebanon Ohio
Alan I really appreciate the quick reply. I'll go over all this and see if something reveals itself. Having been through several clutch projects over the years this one has me baffled at this point. It's really not 'car rocket science' if you know what I mean. Everything appears ok just from a visual perspective, except whereas your last photo shows several threads sticking out the pushrod shaft, mine has none!
Heel & Toe
Joined: Nov 2013
Posts: 17
Likes: 0
From: sharpsburg georgia
Great information. I'm having the same issue. Only mine grinds really bad going into reverse.
New clutch, Bearing, etc. 1st through 4th good, But pedal is pushed all the way in. When shifting into reverse Grinds bad.
New clutch, Bearing, etc. 1st through 4th good, But pedal is pushed all the way in. When shifting into reverse Grinds bad.
Pro
Joined: Jan 2001
Posts: 511
Likes: 66
From: Timnath, CO
https://www.corvetteforum.com/forums...and-specs.html
There was some good information in this thread about a potential cause for clutch adjustment problems. Not sure if I pasted the link correctly but if it does not work you can do a search for it.
There was some good information in this thread about a potential cause for clutch adjustment problems. Not sure if I pasted the link correctly but if it does not work you can do a search for it.
Le Mans Master
Joined: May 2008
Posts: 9,063
Likes: 2,736
2022 C3 of the Year Finalist - Modified
I found the AIM procedure did not work on my clutch. I simply had to adjust the clutch pedal in a position that worked, and it was nowhere near the position the AIM suggested. I have a SPEC clutch, and factory GM throwout bearing, arm, etc. I can't explain why.
Thread Starter
Instructor
Joined: Aug 2017
Posts: 115
Likes: 15
From: Lebanon Ohio
Sooo, - in poring through old receipts I learned it is a Hays clutch kit - pressure plate, clutch, and TO bearing. Flywheel was replaced too. The receipt makes no mention of changing the pivot ball or fork arm. And the previous owner was pretty **** about putting in the right part numbers etc.
However I read a cautionary note somewhere that it is easy to get the wrong throw out bearing and I'm kinda focusing now in that direction. It will be a few weeks before I can get the transmission out for closer looks. I'll try to find this thread and report what we find.
Thank you thank you Alan, and the others, for the input.
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Thread Starter
Instructor
Joined: Aug 2017
Posts: 115
Likes: 15
From: Lebanon Ohio
https://www.corvetteforum.com/forums...and-specs.html
There was some good information in this thread about a potential cause for clutch adjustment problems. Not sure if I pasted the link correctly but if it does not work you can do a search for it.
There was some good information in this thread about a potential cause for clutch adjustment problems. Not sure if I pasted the link correctly but if it does not work you can do a search for it.
Thread Starter
Instructor
Joined: Aug 2017
Posts: 115
Likes: 15
From: Lebanon Ohio
Ok got it all out. Overall height of the TO bearing is about 1.195". I have a manual that says it should be 1.250".
The fork pivot ball measures 1.375". All my parts catalogs seem to imply it should be 1.250". Would anyone have any thoughts on that?
The fork pivot ball measures 1.375". All my parts catalogs seem to imply it should be 1.250". Would anyone have any thoughts on that?
Thread Starter
Instructor
Joined: Aug 2017
Posts: 115
Likes: 15
From: Lebanon Ohio
Correction - pivot ball catalogs say 1.500", not 1.250. (Can't type)
Melting Slicks
Joined: May 2006
Posts: 2,364
Likes: 103
From: Centerville Louisiana
My 75 has the same Hays clutch in it the throw out bearing came with the clutch. I had to install a new GM fork as my spring busted. I measured what I had and the
new setup were almost identical. My adjustment is right at the end also. They make a extended adjustment arm. Just so you know your not alone.
new setup were almost identical. My adjustment is right at the end also. They make a extended adjustment arm. Just so you know your not alone.
Last edited by croaker; Oct 17, 2017 at 10:14 PM.
Safety Car
Joined: May 2008
Posts: 3,747
Likes: 713
From: Lafayette Louisiana
my experience,...
On my 68 with a 454, I was out of travel/threads to adjust the clutch rod any further, so I installed a C2 clutch rod which was a little longer and had plenty of length to get the clutch where it needed to be to disengage properly.
Who knows why
, 454 is obviously not original, maybe the location of everything was slightly off, maybe wrong clutch fork (but looked ok to me), but it works great now.
Great link, Lars always has great info and good to know about the "hump" and over travel. Hope this might help too if all else fails.
Who knows why
, 454 is obviously not original, maybe the location of everything was slightly off, maybe wrong clutch fork (but looked ok to me), but it works great now.Great link, Lars always has great info and good to know about the "hump" and over travel. Hope this might help too if all else fails.
Last edited by 20mercury; Oct 18, 2017 at 10:05 AM.
Thread Starter
Instructor
Joined: Aug 2017
Posts: 115
Likes: 15
From: Lebanon Ohio
Appreciate all the replies to this point. Part of my dilemma to be clear is that even with the adjustment fully out I have virtually no free play at the top. So now I’m beginning to think more about the Hayes pressure plate may require more travel than this vintage of Corvette can manage. (Re: Lars posting). I’m assuming when these cars were new they had good pedal travel, good free play at the top, and good release without having to cram your foot through the floor. I’m gonna figure this out!
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
The PO of my 69 had installed a Lakewood bell housing way, way before anyone had any idea about clutch pivot ball height. He used the factory pivot in the Lakewood. Clutch was fine, but there was very little room for adjustment. Spin forward 30 years- I built a new BB, that required a new flywheel that turned out to be a whole lot thinner than the factory one. Measured the ball height from the same sheet buns posted above. Set up the new pivot ball from those measurements and the clutch adjustment, (new Centerforce DF), moved the adjustment over halfway up the threads instead of it being within the last 1/2".
Thread Starter
Instructor
Joined: Aug 2017
Posts: 115
Likes: 15
From: Lebanon Ohio
One more question - the rod from the cross shaft to the clutch fork is worn oblong (which affects the overall adjustment, but not the total travel) which seems odd. Almost like that rod is too soft.
Can I just weld and repair the hole, or does somebody sell one that’s harder?
Can I just weld and repair the hole, or does somebody sell one that’s harder?
Race Director
Joined: May 2006
Posts: 18,660
Likes: 2,562
reverse
are you aware that the transmission is supposed to be shifted into a forward gear and then shifted into reverse due to the lack of synchros on reverse?
Safety Car
Joined: Apr 2006
Posts: 4,057
Likes: 421
From: BC
I had the same problem with my 69 427. The threaded rod was at the end of adjustment but the clutch worked just fine. When I had the engine out I replaced the clutch, flywheel, pressure plate and throw out bearing figuring it was just clutch wear. Nope, same thing... Rather than tearing everything apart I used a longer clutch fork pushrod from a 64 to 66 Corvette 327 that looks exactly the same right down to the spring holes for your stock anti-rattle springs but, it's 1.5 inches longer than the normal one on a C3. Overall length is 10.5 inches or about 10.0 inches center to center where the stock one is about 9 inches overall. It put the adjustment nuts right back in the center of the adjuster rod again. I attributed the problem to either an aftermarket clutch difference or throw out bearing difference but am not sure what the deal was. Both the old clutch system that was in the car and and new one were the same on lack of adjustment and rod position so it wasn't wear. Picture of the longer lower fork pushrod I used in the link below.
http://www.parts123.com/corvettecent...0050b&ukey=764
http://www.parts123.com/corvettecent...0050b&ukey=764
Last edited by CanadaGrant; Oct 19, 2017 at 03:02 PM.