Hello everyone, Hoping for a little insight on a clutch installation that I just finished. It’s nothing fancy, just a Summit Racing clutch that is supposed to be rated for about 400 hp. Here is a link to the clutch kit: https://www.summitracing.com/parts/sum-700806/year/1972/make/buick/model/skylark I replaced the flywheel with a freshly resurfaced one that I bought from a fellow member on the forum here. Rebuilt the 3 speed Saginaw transmission with new bearings and synchros, and ditched the crappy unbranded floor shifter for a Hurst Mastershift. It’s a typical case of a project creeping into something significantly larger. After changing out all of this, the clutch engagement seems very gradual and lacks the “positive” feel that I expected from a new clutch. Had to fabricate a new pushrod for the connection between the z bar and the clutch fork. The original one was too short, so I made a longer one. That helped. Followed the shop manual instructions a second time for linkage adjustment, and got it a little bit better. But it still seems kind of mushy and soft, like it might not be engaging and releasing correctly. Any thoughts on what might be going on?
Did you have any issues with the clutch system before? Check all the points in the linkage with someone else actuating the clutch (not running). Look to see if anything is flexing, bending or "going sideways" (loosing linear compression), as well as any places along the way with "play" or lash, as it is cumulative. Check and measure the full travel of the bearing as well as the air gap at rest. And check the fork travel and working angle (since you changed transmission, clutch assembly, it may have effected travel of the clutch assembly/and the bearing's throw). Trying to "diagnose" things like this without being able to put eyes or hand on, is a bit of a challenge, but doing the above may reveal an obvious issue to you.
Thanks for the response. The clutch linkage seemed OK before taking everything apart, but the clutch itself was slipping badly and had to be replaced. Reused the original clutch fork and Z bar assembly. I'll get back under there and have my son work the clutch pedal. Maybe I can see something awry as he actuates the clutch. That's a good idea and worth a try for sure. I'm not sure how to measure the bearing travel with everything put together. Or the air gap for that matter. How do I go about doing that? I agree that trying to "diagnose" things like this through a forum and not firsthand is challenging. Just attempting to clearly describe the symptoms is a little tough. It's partly why I've been messing with it for a week before posting to the board. Thank you for the ideas, I'll get back under it and see if there are visible problems as it is actuated.
Have you tightened the clutch cover bolts little by little diagonally? Not doing so might result in a run out of the diaphragm spring right at the tips touching the release bearing. Did you test the clutch function with the motor running? Any strange noises, vibrations at the clutch pedal (pulsing)? Is this a flat, or a potted flywheel? In some cases resurfacing can cause problems as the geometrie is screwed up and the clutch cover, even with a brand new disk is in "worn out position".
Yes, the clutch cover was tightened in a crossing pattern, a few turns at a time. The clutch engagement issues are observations from driving it after installation. The flywheel is basically a flat design. I'm unclear what a "potted" flywheel is. When engaging the clutch, is wants to shudder a little bit. It was doing this before the clutch replacement as well. Would the external linkage be implicated in shuddering?
It is possible the clutch springs are contacting the flywheel bolts. That can sound like/cause "shuddering". (had that happen over 40 years ago). The things that causes shudder is contaminated surfaces, hot spots and /or "weak engagement". What is happening is "slip/grab/slip/grab" very rapidly and the clutch disc springs compressing and releasing as well. If prolonged, you risk burning/hot spotting the flywheel and pressure plate, and/or "glazing" the disc facing material. Was there any "hot spots" on the flywheel before it was resurfaced? And do you know how much was cut? Hot spots are a result of localized heating to the point the metal crystallizes and becomes hardened. Those spots will be slightly raised and can create chatter, shudder, slipping, and grabbing. With the pedal at rest, you should have about 1/8 minimum "air gap" from the face of the bearing, to the fingers on the pressure plate. With the car off, and the pedal pressed fully, see if you can get feeler gauge(s) in between the clutch disc and the pressure plate, as well as between the disc and flywheel. You should have about .010 to .040. (just ballpark numbers to see how much release you get, as well as how much gap the bearing has). The pivot for the fork may be out of adjustment, since you have changed the clutch assembly and the transmission, and where things were before you started. And trying to get a "baseline", before you start adjusting things, to see if anything was obvious.
I don't know how much was cut off of the flywheel that I've just installed. The flywheel that came out was badly hot spotted and required 40 thousands to be cut off before it was clean again. That flywheel is going on the 350 engine I'm building using the new TA aluminum heads. Since shuddering is still an issue, and the pedal feel seems off, I think you are onto something with the weak engagement. I'll be focusing on that to start with. I'm guessing that I might be able to get feeler gauges up by the bearing and fingers once the inspection plate is off? With a stamped steel clutch fork and a pivot ball threaded in place on the bellhousing, I'm unclear how that would go out of adjustment. How would that happen? How would I correct it?
The adjustment to the fork/pivot, since the clutch disk, flywheel, pressure plate and throw-out bearing all together make up and take away from the stack up of components. That can affect angle of the fork in three points. The rod end the articulates the fork, the pivot of the fork, and the fingers that hold the bearing. You would be surprised at how little can have a big effect on the mechanical lever in play. The pivot has an internal hex head that you turn with an allen wrench, but you may have loosen the transmission and slide it back to get to it. So leave it to later, and focus on seeing what the measurements are. Do you have a manual that lists the specs, adjustments for your car? If not, I can try and locate them. As for the air gap, you can take a dowel and whittle the end, get it smooth, then insert the point and push enough to make an imprint. It will not be precise, but should give you a close idea of the throw. I improvise "on the fly" in a lot of odd ways, but I get the job done. Learned a lot of ways to solve a problem from military and other things in life. If you can get a video of the bearing, input shaft and the pressure plate fingers while someone is pressing and releasing the clutch, it might help to see the results. Even pictures of it at rest and depressed. (Engaged/disengaged)
Yes, it is currently adjusted with about 1/8 of an inch lash between the pushrod and the clutch fork socket. This is the best setting so far, so maybe a little more slack would help.
Its been a while since updating this thread. Followed all the helpful advice and verified that clearances were within target. Adjusted the lash to the 1/8 inch specification. With pedal pressed in fully, measured about 0.032 clearance with feeler gauges. My son was under the car checking my adjustments and discovered that the post on the threaded block wasn't round anymore. Years of use had ovalized it, creating intermittent and variable lash. Used a couple of washers to shim the Z-bar connection outward to the non-ovalized part of the connection post and all of a sudden, the whole linkage started working a whole lot better. Seems obvious, but I learned yet again (umpteenth time?) that all old parts need to be thoroughly checked for wear.
