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clutch pivot ball height check

14K views 49 replies 9 participants last post by  RAIDER SS 
#1 ·
At the risk of sounding like an idiot - I'd like an opinion for those of you who have adjusted your clutch pivot ball distance in order to get it right. It's kinda throwing me a curve to get the right number, but I'm pretty sure I've got it figured out. I just need someone else to verify my work, because this is over my wife's pay grade.

Given; Original GM flywheel thickness - .960". Original GM pivot ball distance to mounting flange - 4.750"

My new Hayes flywheel measures 1.010" thick.

What should the new dimension be for the pivot ball distance to mounting flange?
 
#2 · (Edited)
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I could be wrong, but most Hays flywheels have a measured deck height that is less than the stock flywheel thickness. This leads to the requirement to have a longer pivot ball to retain the 4.75 distance. You could also use an adjustable throwout bearing, but then you must use the eyeball method to achieve a proper 5-7 degree forward angle of the clutch fork. If you decide to use an adjustable pivot ball, it must retain least 3/4 thread depth in the bell housing bushing and be red loctited into position. Longer pivot balls are available if needed. Failure here, and you might be posting of how you got into an accident because of pivot ball failure or you keep loosing clutch adjustment.

I cued this video to the point where flywheel deck height is measured correctly.



Once you double-check your numbers, bring them back and I'll check them for you.
 

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#3 ·
Hello Al. Thank you for taking the time to show me how to do this step. I respect that you wanted to teach me how to do this rather than just give me the number. :thumbsup:
Of course you didn't know this, but I have already watched this video and I also have the instruction sheet that Centerforce graciously provides us.

As it turns out, I happen to have 2 new Hayes (same part number) flywheels, and both of them measure exactly the same at .050" thicker than GM's .960" dimension. The confusing part for me was to see in my brain that my pivot ball height measurement needed to be a larger number than what GM required on their stock setup pivot ball. I eventually realized that since my new flywheel is .050" thicker; then in actuality all I should have to do is move my pivot ball back into the bellhousing .050" to compensate for the extra flywheel thickness.

I did that by keeping (bonus) the factory pivot ball, only I made a .050" steel spacer washer that fits entirely under the head of the threaded factory pivot ball, so when I tighten down the pivot ball with this spacer washer under it - It now resides at the correct height for that flywheel. And the head of the pivot ball (as seen from the outside of the bellhousing) is still slightly lower than the transmission mounting surface, so I'm good to go at that end, too. I was asking for this new pivot ball height dimension to reinforce to me that I am correct in my thinking of this situation.

Of course I still used a straight edge to make the measurement to prove that I moved the pivot ball the correct distance. I am using a corvette clutch fork, and it is the design where as soon as the fork exits out the side of the bellhousing - it makes a sharp turn towards the front of the motor. This makes it very hard (and not very reliable) to get a good visual as to the angle of the clutch fork (the motor is in the car while I'm doing this work)..... hence my desire to get an accurate measurement of this geometry before I installed everything onto the motor.
 
#4 · (Edited)
Your new pivot ball height should be 4.800. 4.750 + .050. You installed a thicker Hayes flywheel which moves the clutch fingers out from the flywheel which increases your clutch fork angle. By shortening your pivot ball by the additional thickness of the flywheel, you have restored the clutch fork angle to stock specs. Take a look at the first attachment and it will help you visualize what occurs when you increase your flywheel thickness. Even after using the measurement method, I double check my clutch fork angle visually before I stab the trans. This is difficult to teach or explain over the net.

As for the Corvette clutch fork, it should work as long as the lever length is the same. The Chevelle clutch for pre 73 measures from tip of bearing end to the center of the pushrod pocket is 9 3/4", overall length is 10 1/4". The difference in the distance between the pushrod pocket and bellcrank lever caused by the increased forward bend can be adjusted to fit by the pushrod length. The bell crank may need to be modified to be in line with the end of the Corvette pushrod mount. If the lever length is different, then you may have issues with too much or not enough throw to get a proper release.

Put your clutch fork down on a table and take a measurement from the rod pocket to the inside tip of the bearing end. If longer than the Chevelle clutch fork you'll be handicapped in throw. If shorter you'll get more throw at the cost of more force required to actuate the clutch. The excessive throw could over actuate the pressure plate fingers. I think they will be the same, but I have never measured a corvette clutch fork. So this is new to me.
 

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#7 ·
As for the Corvette clutch fork, it should work as long as the lever length is the same.

Put your clutch fork down on a table and take a measurement from the rod pocket to the inside tip of the bearing end. If longer than the Chevelle clutch fork you'll be handicapped in throw. If shorter you'll get more throw at the cost of more force required to actuate the clutch. I think they will be the same, but I have never measured a corvette clutch fork. So this is new to me.
Turns out the corvette clutch fork is not going to work out well because it is 5/8" longer from pivot ball to clutch fork push rod mounting location. As Al stated, this handicapped the throw and my clutch will not release. There's just not enough travel on the linkage to disengage the clutch.

In an effort to correct this; I modified my z-bar to gain more travel, and even thought I did gain a little more travel - it still wasn't enough to disengage. So instead of spending more time trying more mods to the z-bar; I'm going to go with the factory Chevelle clutch fork setup with all stock components.

At least I went through the exercise of getting the clutch pivot ball at the correct height for the new thicker flywheel. :thumbsup:
 
#5 ·
Great info., Al - thank you.

I will measure this corvette clutch fork and compare it to your provided numbers. I understand what you are stating, and it's good to know.

I do know that this fork aligns perfectly inline with the z-bar and clutch adjustment rod, so I took that to mean the fork endpoint was very close to a stock Chevelle fork, but now that I have your numbers; I'll check!
 
#6 ·
https://www.chevelles.com/forums/33-transmission-driveline/1077240-clutch-fork-angle-check.html

The above thread shows a Corvette fork with what appears to be the correct5 5-7 degree forward clutch fork angle in a sfi bell housing. This is with the throwout bearing held against the fingers. It will get a little more forward as you adjust your throwout bearing airgap.

I wish I would have seen a picture looking straight down the fork from the side, but that did not materialize.
 
#10 ·
You'll want part #3892632

https://www.4speedconversions.com/3892632.html

Avoid anything that has GM part #14066235, says Lakewood, which is a rebranded 14066235, or HD, OR TRUCK. All listed are easily identified by the wings and are about 1 inch longer than the stock pre 73 Chevelle/Camaro clutch fork (pictured on right).

The attachment shows the difference in the 2 forks. Avoid the wings.;)
 

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#11 ·
You'll want part #3892632

https://www.4speedconversions.com/3892632.html

The attachment shows the difference in the 2 forks. Avoid the wings.;)
Yes - 4speedconversions is where I ordered my new clutch fork from. They do a great job of providing correct parts at good pricing IMHO. Their website is full of good info. too! :thumbsup:

Funny you showed these 2 forks, because I went over to my buds house yesterday to compare clutch forks and he had both the correct fork and this truck fork in his inventory. Using the info. provided on 4speedconversions website we were able to come to this conclusion that he had the truck fork as well as the correct Chevelle fork.

I ordered my new clutch fork and clutch fork push rod kit from 4speedconversions yesterday, and this morning I received my shipment notice with tracking number. Looks like I'll be busy again in a couple of days!

Thank you for your help Al (and from Russ at 4speedconversions), and I'm sure this info will help others using the search function :thumbsup:
 
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#12 ·
Man, this clutch is kickin’ my butt!

I bought a new GM Chevelle fork, a new clutch fork push rod kit, and a new repo z-bar from 4speedconversions. I also have 4speedconversions upper rod (to the pedal). Everything was bought for the Chevelle 1st design z-bar setup. After installing all these pieces; everything is looking great. Sure looks like about a 7 degree or so angle to the clutch fork in the at-rest position. Pedal feels right, and I can adjust end play for the pedal. Problem is; the new Hayes clutch wont disengage. (remember I have new Hayes flywheel too, and a new non-magnetic pilot bushing.)

So I check bellhousing concentricity and the bell is about .016” lower than needed. (Yup – my block was line bored). Ordered the .007” offset dowels – install and check – bingo. Now at about 006” total (under the .010” max). Parallel @ .001” after I removed all paint and stoned block to bell mating surfaces. I also removed paint off tranny mount side of bell with thinner and went over it with scotchbrite pad.

Installed drivetrain today (tranny easily entered pilot bushing) – fired it up and….. clutch still won’t disengage. I adjusted ALL the freeplay out to where the throwout is contacting the diaphragm fingers all the time. Still wont disengage. I can’t get close to entering reverse when idling. I managed to get it into first, but that was way too hard on the syncros.

Did I mention this clutch is kickin’ my butt!
 
#13 ·
Did you check the inside diameter of your pilot bushing after it was installed??? Installed inside diameter should be .593. The pilot axel on your input shaft should be .590.

Did you test fit the clutch disc against the mounted flywheel and see that it would spin freely and not contact the flywheel bolts??? The flattest section of the marcel is mounted towards the flywheel and the tallest section faces the trans.

Did you use the measurement method to set your pivot ball depth??? Your measurement of the Hays flywheel concerns me a bit because every Hays I have seen has always had a thinner deck height than am OEM flywheel. Revisit your measurement. The flywheel clutch surface should be face down on a flat surface and the measurement taken from the flat surface to the flywheel/crank mounting surface. Are we good here?

I usually need to run an adjustable pivot ball or a Mcleod adjustable throwout bearing with 2 spacers to get the proper forward clutch fork angle of 5-7 degrees with a Hays flywheel and clutch. Typically I use the measurement method first and set my pivot ball height. Then I'll check my collection of pivot balls to see if one has the correct height. If not, I'll use the Mcloud adjustable throwout bearing and set the spacers to match the clutch fork angle notes with the adjustable pivot ball. I have no issue with using an adjustable pivot ball as long as 3/4 of the adjusting threads are still in the adapter nut. I red lock tight all threaded portions of the pivot ball. If threads are lacking, a longer pivot ball is available and will likely need to cut the excess threads to length. But it's expensive.

Can you supply any pictures of your clutch fork angle with the throwout bearing touching the fingers and the fork hole boot removed? A picture of the clearance to the front of the hole helps, but better is one shot from the frame towards and inline with the pivot ball level with the clutch fork. Tough to do, but a phone camera shot and aimed blindly can get a shot. The more the better.
ng
How thick is your clutch pedal bumper? If it's thicker than 3/16, you can cut it down and gain some travel. The repop pedal bumpers are based on the truck bumper which is a little thicker than 1/2 inch.
 
#15 ·
Great thought, Al, but yes - I have my TOB installed correctly. :thumbsup:

To me it just seems like there is not enough stroke.

BTW - I do have the correct '66 pedal assembly from a donor car, too.
 
#16 ·
Where is your clutch pedal now compared to the brake pedal height?

Typically the clutch pedal sits about 2 inches higher than the brake pedal at rest. You can cheat in a little more throw by shortening the pedal to the bellcrank rod with an adjustable rod if there is still clearance at the firewall. This will result in an even higher pedal location when at rest.
 
#17 ·
I knew the clutch pedal is supposed to be higher than the brake pedal, but I didn't know how much - so I went out and measured mine to be sure. Yup - it's about 1.5" higher.
The brake pedal and the clutch pedal are both up against their rubber bump stops at rest.

I thought about a shorter pedal to bellcrank rod, but that would result in the pedal end of the bellcrank closer to the firewall - which in turn would move the other bellcrank arm (adjustable clutch rod arm) end farther away from the fork..... of which then I would lengthen the adjustable push rod to make up the extra distance to maintain the TOB at the proper distance off the PP.

My mind isn't seeing how this would result in more clutch fork travel. I can see it resulting only in where the bellcrank arms are at their starting points (at rest). What am I not seeing?
 
#18 ·
I attempting to see if I have enough travel in my clutch linkage compared to what other 66 BBC Chevelle's have.
In these 2 pictures - I'm holding a ruler up against a hard stop in order to get a reading of where the outside end of my clutch fork is at rest versus where it resides when the clutch pedal is fully depressed.

(It doesn't matter where the mentioned hard stop is as long as the ruler is held up against it in the same position for both pictures. In my pictures; I put a big magnet on the floor of the car to act as a hard stop for the end of the ruler.)

So in the "at rest" position - the 7" ruler mark is aligned with the edge of the fork. In the full pedal depressed position - the same edge of the clutch fork is aligned with the 5 5/8" positioned, which gives me a travel distance of 1 3/8".

Trouble is - I have nothing to compare this travel distance to. Can anyone please provide me the same distance measurement on your '66 BBC clutch fork?
 

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#19 ·
I can tell by looking at just those 2 pictures and tell you that you don't have enough forward clutch fork angle so you are not going to get a full clutch release. Remove the spacer you put in the pivot ball and see if you get a full clutch release. You don't need to stab the trans to check the clutch release. You can make your adjustments, use an old input shaft(works best) or clutch alignment tool, hold the throwout bearing centered on the finger hole and have someone push on the clutch fully. Watch your fingers keep them out of pinch points. When fully depresses, try to turn the input shaft. It should be completely disengaged. If using an alignment tool, use pliers to keep your fingers clear.

Just by looking at the pushrod cup, I can tell it is still back of 5-7 degrees forward. With the proper CF angle, your pushrod cup will be nearly perpendicular, or slightly forward, to the car centerline. The front of the CF will also be very close to the front of the CF hole in the bell housing. The pushrod will sit nearly 90 degrees to the cup.

I think you will need an adjustable pivot ball or throwout bearing. Looks like your clutch fork needs to go forward about 1/2 inch just by judging by the pushrod pocket on the CF. I don't think you will get there by removing just the spacer you installed on the stock pivot ball.
 

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#22 ·
I have the throwout bearing that came from Hays in the clutch kit. It measures 1 3/16" overall thickness.

Is this the long bearing or the short one?

And is this the one I should be using?
 
#26 ·
If you can repeat the measurements from the pictures in your earlier post that may help you confirm that to have moved your CF to get a full release. Just move your clutch fork forward by as much as you added to the pushrod length and you should be good.

You might take a Sharpie and run a line from the throwout bearing finger through the pivot point of the pivot ball to help visualize the CF angle. Some CF's have a stamping mark you can see, others don't.

pictures show you original picture from the previous post and the best view to check CF angle and also show the proper 5-7 degree forward angle of the CF with the throwout bearing held against the pressure plate fingers. Picture credit to Jody's Transmissions.

If you use an adjustable pivot ball, make sure to red loctite all pieces in place and that you still have sufficient thread engagement.
 

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#27 ·
PS, I ended up using that same McCloed bearing. Had one heckuva time with the adj pivot ball. I ended up with two shims in the TO for a nice angle, the 1.5" setting. PS: its a wee bit noisy.
 
#28 ·
Good suggestion, Al. Thank you. I'm hoping to achieve proper travel without using an adjustable pivot ball, but we'll see...

I'm working on a way to possibly measure this angle. I'll report on my progress, but I do have a question:

I've read where the optimum scenario would be +5* forward angle at rest, and -5* rearward angle with clutch pedal at floor. It makes sense to me, but is this really true? I believe at this setting I would end up with the least amount a force required to depress clutch pedal as a bonus.

Gene - thanx for the heads up on the noise!
 
#29 · (Edited)
Good suggestion, Al. Thank you. I'm hoping to achieve proper travel without using an adjustable pivot ball, but we'll see...

I'm working on a way to possibly measure this angle. I'll report on my progress, but I do have a question:

I've read where the optimum scenario would be +5* forward angle at rest, and -5* rearward angle with clutch pedal at floor. It makes sense to me, but is this really true? I believe at this setting I would end up with the least amount a force required to depress clutch pedal as a bonus.
You'll be able to get your angles using the Mcleod adjustable throwout bearing. I think you'll need one spacer to get the job done with a stock bell housing and Hays flywheel. If you are running an SFI bell housing with a block saver plate normally We use 2 spacers. YMMV.

It's true. At 90 degrees tour lever has it's highest mechanical leverage making for the least force required for the task. As the lever moves off of 90 degrees it moves in a circular arch which effectively shortens the lever and you lose leverage. Don't ask me to prove it. As you move off of 90 degrees, you start losing throw. We only have so much to work with to get the job done and still have an airgap.

You say at rest, but at rest, your forward angle will be greater than 5-7 degrees because of the airgap required from the throwout bearing. Your 5-7 degree forward angle is checked and set with the throwout bearing touching the pressure plate fingers.

There is one other adjustable throwout bearing available. It's the Novac and it is infinitely adjustable. I have one in my car now going strong for about 4 years now. It has threads that adjust the length and pins to hold the adjustment. I red lock tite the threads because the pins looked weak. I put that **** on everything.:grin2:

You might give this Novak clutch bible a read if you have time. The Novak Guide to Clutches, Linkages & Bellhousings for Jeep® Conversions
 
#30 ·
Thank you, Al. Great Novak article and website!
I've been tied up with other things so no more work has been done on my clutch. I'll let you know when I do.
 
#31 ·
Did I mention that this clutch is kickin' my a$$!

(BTW - I have my pivot ball installed without any spacer shims under it, so it is at "factory" height).

So today I installed the McLeod adjustable TOB with 1 spacer shim in it. This one spacer in the TOB moved the fork so far forward that it is ~almost~ touching the bellhousing opening up front. (So far forward that I don't think I could even try to install the TOB with 2 shims). I thought to myself this was too far forward to the point where I wouldn't be able to get any freeplay at the top of the pedal, and that maybe I should put a shim back under the pivot ball..... but I didn't. I said; what the hell - go for maximum movement, leave it like this. Well, turned out I was able to adjust to get a little freeplay on the clutch pedal, albeit with the fork ~almost~ in contact with the bell opening.

Started the car and still not disengaging! When under the car and over stroked the clutch adjustment by a 1/4 inch longer than "stock" setting. This forced the TOB into the PP fingers with the clutch pedal at rest, therefore partially holding the fingers inward all the time. Now the clutch will disengage. No problem getting into reverse. Appears I am still not getting enough stroke out of my stock Chevelle components...
 
#32 ·
If your clutch for angle is forward of 7 degrees then it's just as bad as being back too far. Your clutch fork at 90 degrees should be real close to the half way point of your available pushrod travel. If I remenber correctly the typical clutch needs about a half inch of travel at the fingers to disengage. Your clutch fork is a 2:1 ratio, so you need an inch of movement from finger engagement to release the clutch. Clutch finger movement to completely disengage a clutch may vary between pressure plates.

Which bellcrank did you go with?

Many repops have the levers off by 10 degrees or have incorrect hole spacing or lever lengths. All of which can affect the available throw. I prefer stock or rebuilt stock bellcranks to the repops for this reason.

I'll double check measurements of the clutch bellcrank in my 70 in the am. The 67 actually had 3 different available bellcranks. One for small block and a 1st design, which is the same as 66 and a later design mid year. I think the difference in the 1st and second designs was only in the shape of the upper arm bend and the way it was attached. I think the actual functional geometry was the same.

Did you ever check the thickness of the clutch pedal stop? 3/16" is what you want and this does put the clutch pedal higher than the brake pedal which is how they came out of the factory. If you see a stop that is 3/4 inch thick, it's a repop from a Chevy truck stop which is what many of the repops were modeled from.

Before you rip into it, duplicate your measurements as in post 21 and 26 and we'll see where you ended up. Pictures of your clutch fork angle during the process might help.
 
#33 ·
Let me jump in here and say that I am the Corvette guy that Al referenced in the earlier thread. With Al’s help I got it perfect. My fork is almost touching my Lakewood as well. Now since you are using the Corvette fork, I don’t know if this could be an issue for you, but in C2 and C3 Corvettes, if a clutch doesn’t release in .550 of an inch, it won’t release as that is how limited the travel is. There is a guy over at Corvetteforum who has tested a bunch of off the shelf clutches on a press, and found many don’t release within this range of travel. I know this was mentioned in that thread, but wanted to bring up this subject again. I had tried the McLeod adjustable bearing and found even at its shortest length was too long. I am using the stock for Corvette 1.25 inch throw out bearing and McLeod adjustable pivot ball. I know how frustrating these problems can be.

Bill
 
#34 ·
Hi Bill, glad to hear that your clutch is working well. David is using the correct #3892632 Clutch Fork for his Chevelle. He wisely decided not to run the Corvette clutch fork which would have cheated him out of even more available throw as the effective lever length is longer than on the Chevelle fork.

Your Corvette crowd that needs more throw might benefit from relocating the pushrod hole on the clutch fork inboard by 1/2 to 5/8 of an inch and elongating the pushrod clearance slot. No free lunch though. This would decrease the leverage ratio and result in a stiffer pedal.
 
#35 ·
David, I took a look at my 70 and the measurements are the same as these listed at https://www.4speedconversions.com/3920615.html. I cannot at the moment measure the angles of the Zbar, I can't find my protractor or angle finder. Probably in my work toolbox. When I get the tools I'll check the angles.

Check your clutch fork angle. 5-7 degrees is the target. Too far ahead or too far behind and you'll lose throw.

Since I don't know what Z bar you have, I'll post up some info so maybe you can figure out where the issue lies. There are also 2 pedal rod lengths available for 67. Read to the bottom of the comments section on the 4 speed site pages.

https://www.4speedconversions.com/67_chevelle_linkage.html

https://www.4speedconversions.com/3920615.html

https://www.4speedconversions.com/3872895_r1.html

And also a thread on the 67 z bars and pedal pushrods in the sticky section on this site:

https://www.chevelles.com/forums/33...e/363707-67-z-bars-clutch-rods-oem-repop.html
 
#37 ·
So I pulled the tranny and removed the TOB in order to measure clutch fork travel at the TOB end. My wife operated the pedal while I measured with the clutch pedal fully up and fully to the floor. Measured again and again, and got the same result; the TOB end of the clutch fork moves ~.700~! Holy crap - that's more than I expected based on what I've been reading. Mathematically that should be enough to get clutch disengagement..... but not on my clutch.

So I removed the bellhousing, placed it perfectly level (used a bubble level) on a flat table with the engine mounting side facing up, and kept the fork installed on the pivot ball, but no TOB. Then I used a small level across where the TOB would reside to keep the fork level, and I used a magnetic angle gage on the top of the fork - located on the inboard side of the fork; over the pivot ball area. This was as close of a area that I could find to get a reading of what angle the fork would reside. Then I tilted the fork upwards toward the engine mounting side of the bell and measured the outermost end of the fork. At +5* - the fork was 2.375" down from the engine mounting surface of the bellhousing. Next I tilted the fork back to a negative 5*, where I now have a measurement of 3.75" down from the mounting surface. (so a total of 10 degrees travel).

3.75" minus 2.375" equals 1.375" of travel. Since our forks provide a 2:1 ratio in movement - this 1.375" of travel divided by 2 equals .6875" travel at the TOB, which is as good as my previous eyeball physical measurement of .700" travel!

Now what?.....Did I mention that this clutch disengagement issue is kickin' my a$$?
 
#39 ·
Now what?.....Did I mention that this clutch disengagement issue is kickin' my a$$?
Mine too. I'm hoping someone will jump in here and shine some light on what I'm missing here.

The clutch disc came with the pressure plate?

I would probably pull the flywheel and mount the disc and pressure plate. Then put the unit in a press to see how much throw is required to get a complete release. I think you already did this and came up with .580. So keep digging.

Something is not adding up here, I'm not seeing it and it's buggin me. Check to make sure the Marcel on the disc is not bent and all the fingers on the diaphragm are at the same level, none out of place or bent.

From your earlier measurements, I figured you would have about .625 at the throwout bearing. I saw 1.25 throw at the pushrod end divided by 2. This should be just enough to get the job done and still have a minimal airgap.

I wonder if you're losing actual throw through deflection of any of the components. The numbers you are seeing are unloaded numbers. I remember Hays had a memo or instructions out to gusset the bell crank at one time..........Just brain storming out loud....
 
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