[thebluebeast]

I have a m21 behind a small block. It started of with a centerforce clutch and a stock flywheel... after side stepping the clutch more than a few times :devil:, i noticed the clutch wouldn't fully disengage. thought it was the clutch going out, and replaced it with a zoom 3 finger clutch. bad choice. put everything back together and after a few days of driving, had the same problem, along with BAD clutch chatter. at the end of the day on my way home, the zbar snapped and the pedal stuck to the floor. mad it home by leaving it in 2nd and using the starter to take off. bad, but hey, it got me home.

after this, i decided the clutch was too stiff, and a buddy implied that maybe the stiff clutch put more stress on the linkage and z bar, causing it to break. i ordered a stock-style diaphragm clutch from zoom, along with a new z bar from classic industries, and a Hayes lightweight steel flywheel. after everything was installed, the clutch was nice and easy, but there was still a minor amount of clutch chatter!! The car shifted fine for a week (with me ignoring the infuriating sound of the clutch chatter), and now I have the same problem off and on!! one day it will shift fine, and the next its hard to shift, grinds into every gear, so i know its the clutch not fully disengaging.

Any ideas? everything in the clutch/tranny department is brand new. shifter, rebuilt tranny, flywheel, clutch throwout bearing, pilot bearing, linkage, z bar, all new.

the z bar mount on the frame side is somewhat bent, but still allows the z bar to move unhindered, and i dont think the minor change in geometry would make such a huge difference?

do i need a new z bar frame mount?
could the motor mounts be affecting the linkage geometry?
why is the problem off and on? is it temperature related?
im somewhat lost, the best thing i can come up with is to check the motor mounts, and either make or buy a new frame side z bar mount?
any help is greatly appreciated!!

 

[Nova 404]

Scatter shield or stock bell housing? Pilot bushing or roller bearing?

 

[6T6NOVA]

I had allot of problems with my stock clutch linkage. The new pressure plates are just too hard on the stock linkage. The Z-bar needs to have steel gussets welded to both of the arms. Make the strip long enough to wrap around the tube also. This will keep the arms from ripping off the tube. The Frame bracket also need some extra steel welded on to it. These have been known to rip apart. I also broke the threaded rod that goes into the Clutch fork. I bought a grade 8 bolt that was the right length. Cut the head off and milled the bolt down so it fit into the cup on the clutch fork.

After all of the mods I did, I never had any more clutch problems.

Hope this will give you some ideas.

Bryan

 

[the mechanic]

I have a m21 behind a small block. It started of with a centerforce clutch and a stock flywheel... after side stepping the clutch more than a few times :devil:, i noticed the clutch wouldn't fully disengage. thought it was the clutch going out, and replaced it with a zoom 3 finger clutch. bad choice. put everything back together and after a few days of driving, had the same problem, along with BAD clutch chatter. at the end of the day on my way home, the zbar snapped and the pedal stuck to the floor. mad it home by leaving it in 2nd and using the starter to take off. bad, but hey, it got me home.

after this, i decided the clutch was too stiff, and a buddy implied that maybe the stiff clutch put more stress on the linkage and z bar, causing it to break. i ordered a stock-style diaphragm clutch from zoom, along with a new z bar from classic industries, and a Hayes lightweight steel flywheel. after everything was installed, the clutch was nice and easy, but there was still a minor amount of clutch chatter!! The car shifted fine for a week (with me ignoring the infuriating sound of the clutch chatter), and now I have the same problem off and on!! one day it will shift fine, and the next its hard to shift, grinds into every gear, so i know its the clutch not fully disengaging.

Any ideas? everything in the clutch/tranny department is brand new. shifter, rebuilt tranny, flywheel, clutch throwout bearing, pilot bearing, linkage, z bar, all new.

the z bar mount on the frame side is somewhat bent, but still allows the z bar to move unhindered, and i dont think the minor change in geometry would make such a huge difference?

do i need a new z bar frame mount?
could the motor mounts be affecting the linkage geometry?
why is the problem off and on? is it temperature related?
im somewhat lost, the best thing i can come up with is to check the motor mounts, and either make or buy a new frame side z bar mount?
any help is greatly appreciated!!

If you could get a picture of the Z-bar and frame mount it might help....

The grinding into gear-hard to shift could be the tranny-have you checked the gear oil?-when you describe the problem being off and on thats what i think of....

the clutch chatter could probably be caused by the Z bar mount but im thinking not, how did the clutchs you took out look? what about the pressure plate?

When did you replace the throw-out bearing, was it new with each clutch?

 

[D-Man]

First off, I've never been a fan of the Zoom clutches!!:no: I've had a hell-of-a LOT better luck (and service) with SPEC clutches.:yes: The Stage 3 Plus I put in my Brother's late model T/A lasted over 65,000 miles and was abused frequently!! Oh yeah, it put right around 560 to the rear wheels on a DTS chassis dyno.:yes:

Check all of your shift linkage and z-bar bushings. ESPECIALLY on your shifter. I've seen quite a few people replace all of the shift linkage with solid threaded tubes and rod ends. There might even be a couple places selling kits for it now.

Replace your frame mount for the z-bar and possibly the drivers side motor mount. If it's the stock style RUBBER mount, a couple spirited shifts can separate or tear it apart. Even if not and it's just too spongy, it can still throw off the geometry enough to cause problems.

With a diaphragm style pressure plate, there SHOULDN'T be too much of a load on the z-bar but beefing it up with a couple gussets could NEVER hurt.

Have you had your flywheel surfaced? That could also be a cause of the chatter.

 

[tnblkc230wz]

How much torque are you making and what kind of tires are your running. That will determine the clutch you need.

 

[thebluebeast]

404-i have the stock bell housing on there, along with a new pilot BUSHIng.
and EVERYTHING is new.

6t6- I agree it would not be a bad idea to weld some gussets on the z bar, and i have heard more people say to "wrap the steel around the tube" what exactly do u mean by that? perhaps a picture would help me get the idea.

themechanic-the gear oil is full, and the tranny was completely rebuilt from synchros to seals about 2,000 miles ago, right after a brand new hurst shifter with steel bushings on the shift linkage. and the flywheel is brand new, along with the throwout bearing.

-dman-funny i was actually just checking out SPECs website..i am not a fan of zoom clutched either after this b.s.! i have the stock rubber mounts in there, and i looked at em today and i can see some cracks, so ill probly get some poly mounts.

from the responses, im gathering that i should do what i thought...replace the frame side z bar mount, and grab some new mounts. i will also weld some plate on the new mount and gusset the zbar. anyone know where to get the cheapest motor mounts? either polygraphite/urethane or hardedned rubber? dont really want to go with solid ones....
could the fact that i replaced the stock pilot bearing with a new BUSHING be the cause of any of this?
thanks for the help

 

[D-Man]

How much torque are you making and what kind of tires are your running. That will determine the clutch you need.

Don't forget vehicle weight.

could the fact that i replaced the stock pilot bearing with a new BUSHING be the cause of any of this?
thanks for the help

The ONLY way a new pilot bushing could be causing it would be if it was either too tight or the input shaft was binding on the bushing (depth wise) because the bushing wasn't pressed in deep enough of the input shaft was sitting too deep.
BUT....by now it should have "Self clearanced" and will be obvious upon inspection.:yes:

 

[veno]

Setting a clutch can be cumbersome.. but very straight forward... solid bushing or roller either will work equally well.. check the run out of the flywheel and check the centering.... runout .. you may have a slight bend in the flange....

hard shifting and grinding is a two fold... the blocker/syncros are not stoping the mass rotation.. or your disk is not releasing...

when the clutch pedal is fully depressed a .050" air gap should be present between the pressure plate and the clutch disk.. less and you will have shifting problems..... more and you will be over extending the release mechanism.


shifter linkage.. the nylon bushings in the shift rods are culpable...

Chatter is a condition of a couple of things..

a broken, damaged or worn Marcel spring,(side steeping the clutch)..... worn spring hub(side steeping the clutch) and high spots on either the flywheel or the pressure plate or both.. to much slippage or heaving riding of the clutch..


worn engine and trans mounts can exaggerate/exacerbate the conditions..


LAST THOUGHT.. check the crankshaft endplay..... you might be dealing with a thrust issue

 

[John65ss]

6t6- I agree it would not be a bad idea to weld some gussets on the z bar, and i have heard more people say to "wrap the steel around the tube" what exactly do u mean by that? perhaps a picture would help me get the idea.

I'd like to see a picture too.

 

[david68]

Check your bellhousing for cracks. I had this happen to me once. Nearly drove me crazy trying to figure out why new clutches, pilot bushings, TO bearings ect. would not fix the problem. Finally found the crack. This goes along with broken engine/trans mounts. Good Luck!

 

[thebluebeast]

well, i have decided to take on all the possibilities of this problem....i took a ride out to Nova Classics and bought a new frame side z bar mount, as well as a handy $10 nova assembly manual that explains exactly how GM adjusted clutches from the factory(along with a breakdown of the whole rest of the car).

after searching the internet for hours for some cheap poly mounts, and not wanting to bear the vibration of solids, i hit up the local autozone and got 2 new stock rubber mounts, along with a stock rubber tranny mount for about 16 bucks altogether(go taiwan! NOT) but hey, they came w a lifetime replacement warrantee. cant go wrong.

so this weekend i am going to pull the motor and trans, weld up some gussets on the z bar, as well as reinforce the new mount, regrease the z bar(just for good measure), pop in all the new mounts, check/inspect the tranny fluid, bellhousing, flywheel, pressure plate, throwout bearing, fork arm, pilot bushing and clutch. after putting it all back in, i will adjust the clutch to orig. gm specs.

HOPEFULLY all of this will take care of this bull**** clutch problem, but hey, you gotta pay to play. aint nothing left to do but do it.

wish me luck.

 

[thebluebeast]

So i got the new rubber mounts in yesterday, and welded up the zbar with some gnarly gussets as well as the frame side pivot bracket. it went fairly smoothly, and the test drive was a semi-success. the clutch engaged and disengaged smoothly, and unhindered. After a few trips around the block and getting the clutch adjusted just right, it was on the money. So the grinding and hard shifting is cured, but there is still a good amount of clutch chatter. So i am happy now that i can actually SHIFT the car and therefore drive it.
Time to cruise