DansYellow66

Can't always rely on new parts to be good I've rediscovered. Back in the 90s when I installed a new 30 lb Hays flywheel I stuck a dial indicator on the block, rotated the engine and found the flywheel was quite a bit out of flat - I ended up having to have it ground twice by two machine shops to get it flat enough to install.

Never thought to check a pressure plate but after installing a new one and having a bad shudder/chatter, I pulled it and laid it plate up, laid a metal straightedge across each set of opposing bolt holes and measured the distance from the straight edge to the disc with a stack of feeler gages. I measured at each of the 6 bolt holes



Rather than trust adding up all the feeler gage leafs I used a micrometer to measure the compressed stack.



Here is how my old clutch plate measured up and the defective new clutch plate. The new clutch was out over 5 times my old clutch.



I'm never going to put a clutch in again without checking this first.

Next, I noticed my clutch fork has quite a bit of play when installed on the TO bearing - maybe a tenth of an inch or little more. Any play and slop in the clutch linkage just takes up critical clutch pedal throw distance that's necessary for full clutch release for shifts.



That just creates extra free play at the top of the pedal for any given clearance of the bearing off of the clutch fingers that has to be taken up. It's just more slop in the linkage system. So I took a big screwdriver and tweaked the heavy spring teeth to where they ride closely in the TO bearing groove with just the slightest of play.



The other area of slop in the linkage that I've noticed is the lower rod pin in the Z-bar link. The hole in the Z-bar is quite a bit bigger. I haven't gotten to this yet but I'm going to see if possibly a steel shift rod bushing might fit in it and take up this area of play. I'll report back on that.

Jackfit

Hi, think about this , no slop, no anti rattle springs to take up slop

Frankie the Fink

That looks like the Speed Direct helm joint for GM, they also make a similar clutch pedal push rod..

MikeM

I would have to know if that was the correct way to measure PP height before I drew any conclusions. If you checked the plate at engagement height, might see different results?

GTOguy

I think this method is good enough to 'ballpark' check the run-out. Measured against the old PP, the new one is obviously crap. Back in the 1980's, I started noticing more and more defective brake rotors, brake drums, and pressure plates right out of the box. Some Ford rotors had a full .100" run-out brand new. Talk about a pulsating pedal! I returned anything with more than about .006 run-out, as I had to cut too much material off the offending part from the get-go to be comfortable with selling it as a new part.

4 Speed Dave

The measurement you did is not how you measure them. What you want to check is the ring height. Or in other words The distance from the top of the cover to the top of the pressure right on the pressure plate with the clutch and disc mounted to the flywheel all tightened down. In this ring height measurement you are checking to ensure that the distance is equal at each stand. Refer to the attached link for directions. This is for a Long style pressure plate but it might give you insight. The idea is to have equal pressure on the disc as it is installed. You are measuring the pressure plate in an unloaded form with the springs unloaded which is not yield good results it is the loaded measurements you should be looking at.

On my Nova I reset the ring height during the racing season as the disc wears.

The problem you face is that you have no idea what the ring height should be as this a diaphragm pressure plate I bet the MFG wouldn't even know the height.

http://www.ramclutches.com/pdf/FORM%...20clutches.pdf

DansYellow66

Yes, this is a diaphragm clutch - don't think I have any of the information or provisions on it to do any checks like that. I understand what you are saying about unloaded vs loaded condition but on an unadjustable diaphragm clutch I pretty much have to assume one condition is fairly representative of the other. I'm kind of leery about measuring from the top of the hat also - who's to say it's stamped to that close of tolerances? But I may be all wrong.

I could bolt it to the flywheel with a disc and place it in a press and engage the clutch and try to check the gap to the flywheel at the 3 points. Too late for now as I've sent the old one back.

The McLeod tech guy seemed good with my measurements (or as GTOguy said, at least good enough). He didn't ask that I try to check it any other way.

Thanks

DansYellow66

Jack - yeah, as long as those anti-rattle springs are strong enough to not be overpowered by the main clutch pedal return spring, the clearances should remain taken up in the sloppy pin fit. And that is probably the case although I'm not sure of it. If I can improve the fit without a bunch of effort I will. If not, I'll double check the anti-rattle springs keep everything together tight while the clutch is released.

Thanks

DansYellow66

Well, I'm back for round 3 or 4 or something of this clutch mess. I've been waiting on a custom pilot bushing to be machined by AutoGear to fit my crank and I now have a new replacement McLeod clutch and new disc. I bolted the new clutch down to my old flywheel and measured the plate distance to the flywheel.

Better than the old one by half - now it's only un-level by .013 inch side to side as compared to the last chattering SOB that was .026 inch un-level. My 15-year old McLeod pressure plate is a fraction of this. But I realize that this method of checking may not be accurate with the pressure plate fully relaxed and unsure what actually consists of a stop for the plate or diaphragm springsin this condition. So, unless someone can suggest a better approach I think I'm going to chuck the flywheel and pressure plate in my hydraulic press tomorrow and depress the clutch to a measured thickness of the disc thickness + .010 inch and then measure the how uniform the gap is between the pressure plate and the flywheel around the circumference of the pressure plate.

I don't want to put this thing back together until I'm pretty confident its going to work smoothly.

On a related issue - I sanded the surface of this brand new flywheel that literally has about 1 mile on it, with 80 grit sandpaper and a flat block and it looks better but I can still see some of the remains of the heat spots on it, although they are lighter. I thought they would probably sand out easily but that wasn't the case. This is the before condition - I haven't taken a picture after sanding yet.



Good enough or should I do a more aggressive sanding of the surface until I can't see any sign of the heat spots? I do not want any chatter from this thing.

GTOguy

Hit it with some brake cleaner and you're good to go. You don't want to sand waves into it by concentrating on the hot spots.

DansYellow66

Thanks GTOguy. Any thought on checking the clutch before nstallation? I've always had good luck with McLeod and in the past I would have just thrown all these new parts in and expected the best. Now, I'm a little paranoid. Don't know how many of these transmission pulls I still have left in me.

Kerrmudgeon

Just a note on my clutch experience.....when I was young and impressed by racing parts and their names I installed a Sheifer clutch in my 66. With about 5000 miles on it a spring broke out of the clutch plate and jammed up the whole thing. Junk....pure Junk!

I've used heavy duty GM clutches ever since and never had an issue. I used early z28 heavy duty and while they were heavy, they never did anything but BITE!

DansYellow66

I tested the flywheel in my hydraulic press this morning. The disc measured about .325 inch so I depressed the clutch fingers until I could get a stack of feeler gages measuring .335 to slip in. Since full release is typically considered about .050 inch clearance between the disc and the pressure plate, I figured this was somewhere around where the clutch would be starting to engage solidly. I purposely left the disc out as I figured it would just hinder getting measurements.





Then I measured at the other 5 positions around the pressure plate. I had a maximum variance of .005 inches. But then I released it and depressed it again and my narrowest area was now .003 inch wider than my starting point. So apparently this can kind of give you an idea if you have a problem but either it's going to vary a little each time you cycle the clutch, or to do this accurately every thing has to be set up perfectly centered, aligned on the exact same axis, etc. that beyond the capability of your average Harbor Freight hydraulic press in your garage. The other possibility is there just isn't any good way to test a diaphragm clutch in the field.

I also checked my flywheel for wobble and it was a max of .003 inch variance which I wish was better but is probably OK. Someone posted about using copper shim stock or HD aluminum foil to make washers out of to shim the low side. Not sure for my purposes if it's worthwhile to do so or not.
But, at least I can't see any big figure that should cause me trouble.

4 Speed Dave

You realize that your friction disc is not a fixed thickness. I am assuming you are using a standard disc with a marcel spring between each face and not a fixed backingplate hub. Thus allowing a softer engagement and disengagement. Thus your measurements are not really taking into account real life events on clutch disengagement and engagement as the marcel spring provides take up space.

This video shows it pretty well.

DansYellow66

Dave - yes, I do realize that and that's part of the reason I left the disc out of this whole check because it isn't completely consistent in thickness around the circumference due to it's construction. It's a dual friction type plate - organic on one side and some sort of triangular pads on the other but it's a street clutch (high perf) with a sprung hub and all.

Figuring I've already killed so much time on this already I went ahead and pulled the flywheel again and cut some washers out of .001 inch foil to put on the crank side in the low areas (bolt mounts). However, .001 inch was too much and I ended up with my low areas and high areas swapped side for side and still about .003 - ,004 out. I measured Saran Wrap and even it is about .001 inch thickness and I don't know what I could use that is about .0005 inch? So I guess I'm just going to clean things up good and install it as manufactured without any further effort on it. Time to put it all back together.

GTOguy

Just torque down the clutch cover cross-pattern and in stages, so it pulls in dead even. But you know that. I've had the same McCleod clutch in my '65 GTO since 1984. So yeah, they hold up well. And I used to drive that car hard.

DansYellow66

I was kind of surprised McLeod didn't ask how I tightened or loosened the bolts on the one I returned. if I had been them I probably would have. But I just go around in a circle after drawing the slack up out of the bolts and tighten each bolt 1/4 turn going around, and around, and around - takes me forever.

GTOguy

You never should go around in a circle. Go cross ways: 6 o'clock, then 12, then 3, then 9, then 2, then 7, etc.

DansYellow66

From where the pressure plate is just barely in contact with the disc I tighten the bolts a quarter turn (.015 inch) in a circular pattern, which takes about 15 trips around the clutch. That pulls the clutch down about as uniformly as is possible to avoid springing it. Then I torque in 3 increments in a criss-cross pattern to 35 ft-lb.