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What's wrong with my clutch, part 2

4K views 42 replies 13 participants last post by  Alan F 
#1 ·
Here was part 1 after having no clutch from changing the flywheel. https://www.chevelles.com/forums/33-transmission-driveline/1070644-clutch-release-arm.html
I just replaced my flywheel. Upon reassembly I have no clutch using a normal adjustment. I can over-tighten the push rod and get it to release but then it has constant pressure on the throw out bearing. I've got no more adjustment on the push rod.


I'm not sure what the problem is.

I'm also not sure why the problem showed up after replacing the flywheel. Here's a guess if it makes sense. The flywheel I took out was a billet flywheel and could have been thicker than the stock flywheel that replaced it.
This could cause the clutch to sit in a relatively rearward location.

Trying to figure out my next step.
Everything but the flywheel is the same. The clutch worked great before and doesn’t work now. I’m focused on what could have caused a problem based upon the known variables.

I’m sure I could make it work with a taller throw out bearing or longer (non-stock) push rod. But I really like to make things work as “The General” made them.

Thanks for the ideas. Still thinking.
The only thing that changed was the flywheel. After my last post I went and measured the differences between the flywheel flange to the face of the flywheels. The prior flywheel (billet) is .125” thicker than an OE replacement I had laying around. The actual replacement was also resurfaced before installation so add that to the difference. I’m guessing an easy .150” change.

The Zbar is original to the car when I got it but the release arm was a new replacement when the car was restored.
The problem is a function of how much pedal travel there is compared to release arm movement. It needs to move more to get the pressure plate adequately depressed.

Still thinking about it.
After much measuring and calculating, I ordered a new release arm, adjustable throwout bearing, adjustable pivot and pilot bushing. I will have everything I might need when I tear it down.

Thanks to all of you for your help.

Ps. I created a linkage calculator that measures the pedal rod stroke and converts it to release arm movement. It’s amazing how .150” can effect the operating range of the diaphragm. The only thing I’m missing is my actual flywheel deck height and clutch dimensions to verify my own situation.
There was 3.75" from the back of the block to the fingers on the pressure plate.
Using the ideal of alignment which is back of the throw out bearing in line with the ball on the release fork, the distance was 3.625". That means I needed .125" to bring the TOB towards the clutch fingers (using the stock short TOB). I had purchased the McLeod adjustable TOB that added .150" to the stock height (which is .025" more than needed). The clutch adjuster now is positioned to work correctly.

PS. The adjustable pivot ball was shorter than the stock one. That goes the wrong way for my problem.
The Lakewood HD clutch release fork I bought was about 1" longer than than the stocker and that would have also worked against my problem.

I sure learned a great deal about clutch geometry. Thanks to all who contributed.
After I put it all back together I had a bad knocking sound. It turns out the dust cover was hitting on the crankshaft. I took it back apart to fix that. I also added another spacer to the adjustable throwout bearing.

I still have no clutch. I had thought perhaps the pressure plate was stuck to the flywheel but it's all so new and clean. I don't know how that could be.

This video shows the throw out bearing fully engaging the pressure plate. It almost looks like it's pushing it too far now.

https://www.flickr.com/gp/164440338@N03/eq9171

I'm at my wits end with this. I could pull it apart again but have no idea what I'd be looking for.
 
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#2 ·
The approach to solving it this problem needs to be addressed one step at a time. For example, you don't need to put the transmission in the car, and hook everything up to check for clutch release. You should simply place the clutch in the car with the bell and fork and with an alignment tool ( or old input shaft ) hold the bearing against the pressure plate while someone else presses on the pedal. In fact you only need to hold the bell on with a few bolts. Press the pedal and manually see if you can move the disc.
Recently I had a flywheel not have enough clearance for the disc springs.

Other times I have seen the clutch hubs bottom out on the transmission input shaft, essentially once you place the transmission in the car the hub bottoms on the input spline and the clutch disc gets jammed up against the flywheel.

One step at a time.....
 
#3 ·
What do you mean by having no clutch it won't engage or it won't release. You say it all started when you changed the flywheel so you have to compare them both to see where they are different. Make sure your clutch disc springs are not hitting on the flywheel bolts.
 
#4 ·
Thanks for the feedback! The clutch will not release. It’s a stock cast flywheel with a clutch disk that was working on a billet flywheel before. Can’t say I KNOW there’s no interference between clutch disk and flywheel but it’s got to be something. I guess I’ll pull it apart again tomorrow. Keep you posted!
 
#5 ·
Your video shows what appears to be sufficient movement to release a stock clutch, about. .400, even if you add in an airgap between the fingers and throwout bearing. Something has to be binding up, pilot bearing to input shaft, input shaft to crank, disk to input shart splines, disk to crank bolts, springs to flywheel or bolts, disc in backwards, bell housing alignment........

Car is up on jacks, loosen the 4 trans bolts about a 1/4 inch and pry the trans back to the bolts, have someone step on the clutch while in gear, not running, and see if you can spin a wheel or driveshaft. Try this before loosening the bolts as a reference and to make sure it's locked up.

The trans went in easy right? You didn't have to pull it in with the bolts...she slid in like butter?

No luck with the above, then pull the trans. Get a input shaft or clutch installation tool and insert it, then have someone push the clutch while you hold the throwout bearing centered on the fingers and see if you can turn the disk. Disassemble and check at each step...process of elimination.

Maybe the pilot bearing tightened up upon installation? Might have to ream it out for proper clearance.

I can't tell the position of your clutch fork angle, I think I described that in your last thread. If you like or can, you can temporarily adjust your rod out further to preload the bearing and fingers and see if that releases the clutch. If it does, your clutch fork angle needs work. You mentioned over travel, well that's easily compensated during your testing by not pushing the clutch in as far.

Good luck.
 
#6 ·
I have an old input shaft I use as an alignment tool. I was very particular about the pilot bearing fit because I know what kind of problems that can induce. The fit was good on it. I will measure the thickness on it compared to the one in the trans and another trans to verify.

Yes, transmission went in like butter. I refuse to use bolts to pull it in. If I can’t get it seated by hand, I don’t put it together.

I think my clutch release arm angle was perfect before I added the last .150” shim to the throw out bearing. I’m going to remove it.

I did try limiting the clutch movement of the clutch pedal to compensate. It made no difference.

If this disk’s springs are hitting the flywheel I will just cry because then I for sure won’t know what to do.

Thanks for hanging with me. I’ll keep you posted.
 
#8 ·
Ok, took it apart this morning. Unbolted the shifter and kicked it in to neutral. Crawled under the car and went to remove the driveshaft and it wouldn't turn. WTH? I could not move the shifter levers under the car. I thought -AHA! The problem is with the shifter alignment. Spent time unhooking shifter trying to get it shifted to neutral so driveshaft would rotate. It was clearly in neutral and the driveshaft wouldn't spin (PS yesterday had it running in gear). Ended up removing the driveshaft and something in the rear is now locked up. {where's the emoticon with a gun to your forehead?} No problem with shifter or transmission.

After that waste of time, removed the transmission. Pics 1 & 2 are of the clutch immediately after transmission removal with TOB still hanging.

After I removed the transmission, I have an old input shaft and a input collar. Plugged that in to the clutch and had my helper depress the clutch. Try as I could the disk would not spin.

So, I'm on to removing the bellhousing. It's removed and pics 3, 4 and 5 are of the clutch to flywheel and the disk to flywheel clearance. There's nothing obvious to me.

So, I removed the pressure plate and disk. I held the disk up against the flywheel and spun it. There was no interference with the springs.

Pics 6-7 are of the flywheel. There are no friction burns. The turned finish is not disturbed anywhere.

Pic 8 is of the flywheel side of the disk. Note no marks on the springs.

I am absolutely stumped. I'm going to take the rest of the day off and think about it.
 

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#11 ·
Ok, took it apart this morning. . . . . . . . . .

Pics 6-7 are of the flywheel. There are no friction burns. The turned finish is not disturbed anywhere.

Pic 8 is of the flywheel side of the disk. Note no marks on the springs.

I am absolutely stumped. I'm going to take the rest of the day off and think about it.
FYI, pic 8 is the pressure plate side.
 
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#9 ·
That would have me freaking out because from here, I can't see the issue. Wish I could be there for you.

At this point, I would pull the flywheel, insert the flywheel bolts and install nuts on the back side to keep them tight. Put the disc against the flywheel and check to see if it can spin without contacting the bolts or recess. Then I would install the diaphragm and clutch disc on the flywheel and put the assembly on my press. I would check to see how much finger movement is required to achieve an Air gap between the clutch disc and flywheel. Airgap is the clearance between the clutch disc, flywheel, and pressure plate with the clutch released. A total air gap of .050 will measure .025 between each side of the disc. I've also seen this total number listed as .090, but .050 should result in full release and your disc should be free to spin.

If you can't achieve a free disc in this test, your diaphragm is highly suspect, your disc is bent or thicker than spec for that diaphragm, or there is mechanical interference somewhere in that combination of parts.

Again, good luck, and try not to pull your hair out or kick the dog.>:)
 
#10 ·
So you say with a old input shaft put into the disc with the pressure plate and disc still bolted to the flywheel and the clutch depressed you can't get the disc to turn. The only thing I can think of is the outside diameter of the disc is fitting tight in the I.D. of the Pressure Plate somewhere. Even though the pressure plate is coming away from the disc the O.D. of the disc is getting pinched somewhere. Does your center hub of the disc look concentric with the O.D. of the disc.
 
#15 ·
I'll confirm the direction of the disk but it will only go in one way. The thick side towards pressure plate and skinny side to flywheel. I'll add a pic of the other side if I got it wrong.
The car is at my home in the Houston area right now. My other home is southwest of Austin.

Right now I'm wondering if the pressure plate is broken somehow? However the fingers released as it was unbolted. Perhaps the surface job done on the flywheel is somehow holding it. I just don't know.

I have another project on the burner and went ahead and ordered another billet flywheel just to try something different.

I have worked with and made work the worst junk you've ever seen in the past. Get something nice and it's maddening not to have it work.
 
#16 ·
did you put the billit flywheel on it or was it there when you got the car?if so maybe the previous owner shortened the rod to compensate for the thicker flywheel.also looks like the lug on the end of the pushrod is offset to the front of the z bar.is it supposed to be like that or centered.been awhile since i messed with manuals.
 
#17 ·
Attached is a picture of the flywheel side of the clutch disk after removal. I received my 3rd billet flywheel today. It measures .885” from the crank flange to the clutch surface. I’m doing my ciphering one more time.

Anyone want measurements?
 

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#18 ·
You've got enough parts there that something HAS to work soon!
 
#19 ·
http://www.centerforce.com/images/store/midway-industries-inc/ctf-cf360310-i93gm002.pdf

.960 stock gm flywheel thickness
-.885 your flywheel thickness
=.075. the distance of the top of clutch fork ball, you need to move towards the engine.

4.750 stock gm pivot ball face to front face of bellhousing(engine mounting surface.)
-.075 difference between stock flywheel and your current flywheel.
=4 inches...new distance from pivotball face to engine mounting surface taking into consideration the thinner than stock flywheel.

Since you are short .075, this tells us your clutch fork angle will be well back of the preferred 5-7 degrees forward angle. That's not good and will result in less available throwout bearing movement to release your clutch. To fix this there are 2 options.

1. use an adjustable pivot ball and extend it out .075 towards the engine giving you a new front face of pivot ball to the front of bell housing engine surface of 4". With this set up you will use a stock height throwout bearing. Set it up this way then check your clutch fork angle for 5-7 degrees forward. If you don't have the proper forward angle, then adjust the pivot ball accordingly. once done, cut off the excess thread of pivot ball and red Locktite all threads on adj pivotball because they like to come loose.



2.use your current stock pivot ball and use an adjustable throwout bearing to achieve the 5-7 degrees forward clutch for angle.

Test your clutch disc to the flywheel then to the diaphragm. The disk should spin freely against both when held centered against each. Bolt up your flywheel and again, hold disc against the flywheel and make sure it spins freely against the flywheel.

Take that Lakewood clutch fork and throw it as far away as possible. It's longer than a stock unit and will decrease available throwout bearing movement due to the change in ratio.

Measure your installed pilot bearing vs the trans input shaft. You need .003 clearance. Also, measure from the step of the trans input shaft to the front of the trans mounting face. Then measure from the bell housing trans mount face to the face of the pilot bushing to ensure you have some clearance there. No clearance and that face will ride against the pilot bearing giving you symptoms of a nonreleasing clutch.

You can install all the pieces, then check for proper release by having someone press the clutch without installing the trans. Center your throwout bearing on the opening on the diaphragm. have someone apply pressure to hold it there then apply full clutch pedal while having a clutch alignment tool or spare trans shaft installed. With full clutch pedal, you should be able to spin the disc freely by spinning the tool.

.
 
#22 ·
4.750 stock gm pivot ball face to front face of bellhousing(engine mounting surface.)
-.075 difference between stock flywheel and your current flywheel.
=4 inches...new distance from pivotball face to engine mounting surface taking into consideration the thinner than stock flywheel.
This should be 4.750 - .075 which equals 4.675" not 4". :thumbsup:
 
#21 ·
I'm surprised that the back alley rebuilts I replaced replaced even worked at all.
Maybe those half as s rebuilders were better than what is now available new.
 
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#41 ·
Its funny you say that. I converted a 56 Chevy from a Powerglide to a 3-speed with all cast off parts from a bunch of different cars, and then using everything but the 56's bell housing and the 3-speed to convert a 62 Impala back to a 4-speed, again using parts from wrecking yards and friends. I never had any problems like this, and everything was just done in my Dad Driveway.
 
#24 ·
I'm going to assemble the clutch and flywheel on the bench. Then I'm going to bring it to my press and depress the fingers until I can spin the clutch disk before I assemble it again. I'll measure the movement required at the fingers so A. I know if it works and B. what it will take to make it work.

Is there anything else I should do?
 
#25 ·
Yes, check your bell housing alignment. It sucks, it's not fun. and nobody ever wants to do it.

You should check your "installed" pilot bushing clearance. I think I forgot to say installed in the above posts.

Note the corrected final distance as I choked in my subtraction.

I'm glad you will check it in your press.:thumbsup:
 
#26 ·
I had some time midday today. Took the flywheel and clutch assembly to the press to check the release. It took about 1/2” compression at the fingers to get release but it did release. When I was observing it through the release arm on the car I don’t think I had enough travel. I will be mocking it up again tomorrow. I’m slowly eliminating where this gremlin is hiding.

Some pics for discerning eyes. I used an old input shaft up through the bottom to check the release of the disk.
 

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#27 ·
Have you checked the pedal rubber bumper thickness like we have told you to do more than once. You have never commented that you have. The bumpers that they sell are much to thick and should be taken down to 1/4" to 5/16" max. When you do this your pedal comes up higher giving you more travel. You now reset your free travel from that point which in turn gives you more travel of the pedal to release the clutch disc. :thumbsup:
 
#29 ·
https://www.powerperformancenews.com/tech/clutch-and-release/ Give this a read with your morning coffee.

Your 1/2 inch travel to release a stock pressure plate is within spec. I watched your video 40 + times and it looks like you had that. Your pressure plate fingers should all be parallel to the bellhousing. (see above link for a picture)

"Most diaphragm style pressure plates require 0.500 inch of release arm travel to fully release the clutch. Given that most passenger car release arms use a 2:1 ratio, this means you will need a minimum of 1 inch of travel where the linkage hits the release arm.

A critical factor that will ensure the clutch releases properly is the position of the release arm (Cutch fork angle). The numbers for the amount of pressure plate release distance vary because of a number of factors such as the clutch disc thickness and the thickness of the marcel spring integrated in between the two friction surfaces on the clutch disc. Mild street clutches tend to have thicker discs than higher performance discs. Because of this variance, it is difficult to put a number of the amount of travel necessary for a disc to release. Our Centerforce clutch only requires 0.27 inch of pressure plate lever travel to create a 0.025-inch air gap of full release." (It's due to this reason and specification creep over the past 50 years that I start by using the measurement method described above, the double check this result with my clutch fork angle. )

"Other diaphragm pressure plates may require as much as 0.500 inch of lever travel to fully release the clutch. This means the release arm (between the pivot ball and the throw-out bearing) should be perpendicular to the input shaft at half release arm travel — 0.250 inch. This is important because the release arm travels in an arc the pivots around the clutch release ball in the bellhousing."

Don't forget to check your pedal stop thickness. That right there can buy you 1/2 inch in pedal travel.
 
#30 ·
Check the clutch fork for cracks or a break. Have seen that.
Also check all of the linkage pieces. I've seen broken clutch pedals, broken swing arms that look good until you put pressure on them. Just check so you know all is good.
 
#31 ·
After looking closely to your pictures, your bolts don't appear to be drawn tightly to the diaphragm. I think you are missing a cone washer and your bolts have a shoulder that is keeping the head from engaging the pressure plate.

Do I think this is your issue? Probably not at the moment as long as the pressure plate is tight against the flywheel and the threads are not bottomed out, but it could be in the future. YMMV.

https://www.jegs.com/i/ARP/070/130-2201/10002/-1#reviewTab
 
#32 ·
I noticed the same thing about the bolts. There are normally lock washers under the bolts which may have been omitted for the test. Actually you would think there would be space between the PP and flywheel. Also about the rubber stop. When I bought the ones for my car I thought they looked thicker than what I remembered them being. I was having the same problem with the clutch not seeming to be releasing enough. I started thinking what I need is more pedal travel. Now how am I going to get it. Light bulb goes off if I bring the rubber bumper down in thickness I gain more pedal travel. Now I need to convert that extra travel to the part of the travel that is actually used to release the clutch. Now you reset your pedal free travel at the top which in turn gives you more release travel.
 
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