clutch pivot ball height check - Chevelle Tech
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post #1 of 50 (permalink) Old Jan 25th, 20, 4:08 PM Thread Starter
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clutch pivot ball height check

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?


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post #2 of 50 (permalink) Old Jan 25th, 20, 5:05 PM
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Re: clutch pivot ball height check

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Originally Posted by RAIDER SS View Post
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?
]

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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post #3 of 50 (permalink) Old Jan 25th, 20, 10:36 PM Thread Starter
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Re: clutch pivot ball height check

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.
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.


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post #4 of 50 (permalink) Old Jan 26th, 20, 12:01 AM
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Re: clutch pivot ball height check

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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post #5 of 50 (permalink) Old Jan 26th, 20, 12:45 PM Thread Starter
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Re: clutch pivot ball height check

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!


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post #6 of 50 (permalink) Old Jan 26th, 20, 3:12 PM
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Re: clutch pivot ball height check

https://www.chevelles.com/forums/33-...gle-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.
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post #7 of 50 (permalink) Old Jan 28th, 20, 10:11 PM Thread Starter
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Re: clutch pivot ball height check

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Originally Posted by DUTCH MAX HEADWORK View Post
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.
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post #8 of 50 (permalink) Old Jan 28th, 20, 10:34 PM
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Re: clutch pivot ball height check

Quote:
Originally Posted by RAIDER SS View Post
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.
I wonder if you could drill a hole 5/8" inboard of the existing rod hole and extend the notch. The throw distance would be the same as the Chevelle fork so you will still have the same ratio. Any movement fore or aft can be made up by the pushrod length.

I learned what you learned the hard way too. The pre 73 Chevelle and Camaro bell cranks only offer so much throw and it works with the stock length clutch fork. Changing any part of the equation has consequences. The Truck fork with wings, the Lakewood HD and later HD clutch forks are longer than the stock Chevelle fork. This will cost you throw. Either you won't get a good/full clutch release, or your throwout bearing won't have an appropriate air gap and will run continuously. If you move the connection point on the bell crank to give enough throw, you radically increase pedal effort for the same clutch. If you move the location of the lever on the bell crank, it will burn you somewhere else. Stock Chevelle fork for the win.

There is one cheat, you can remove or trim down the clutch pedal stop and gain a little throw. Some of the repops were giving guys problems because the repop was based on a truck bumper and was 1/2" thick. The Chevelle bumper is about 3/16" thick. The price you pay here is the pedal will sit up a little higher than stock height if you cheat with a thinner pedal stop.

Stock OEM 64-81 Corvette clutch fork below.
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post #9 of 50 (permalink) Old Jan 28th, 20, 11:06 PM Thread Starter
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Re: clutch pivot ball height check

Quote:
Originally Posted by DUTCH MAX HEADWORK View Post
I wonder if you could drill a hole 5/8" inboard of the existing rod hole and extend the notch. The throw distance would be the same as the Chevelle fork so you will still have the same ratio. Any movement fore or aft can be made up by the pushrod length.

There is one cheat, you can remove or trim down the clutch pedal stop and gain a little throw. Some of the repops were giving guys problems because the repop was based on a truck bumper and was 1/2" thick. The Chevelle bumper is about 3/16" thick. The price you pay here is the pedal will sit up a little higher than stock height if you cheat with a thinner pedal stop.

Stock Chevelle fork for the win.
Yes, I agree there still may be ways to cheat and make it work...… but I'm done with making mods in an effort to make the Corvette fork work in my Chevelle.

Stock Chevelle fork for the win.
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post #10 of 50 (permalink) Old Jan 29th, 20, 12:55 AM
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Re: clutch pivot ball height check

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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post #11 of 50 (permalink) Old Jan 29th, 20, 10:07 AM Thread Starter
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Re: clutch pivot ball height check

Quote:
Originally Posted by DUTCH MAX HEADWORK View Post
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!

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
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post #12 of 50 (permalink) Old Feb 15th, 20, 10:09 PM Thread Starter
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Re: clutch pivot ball height check

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!


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post #13 of 50 (permalink) Old Feb 16th, 20, 1:13 AM
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Re: clutch pivot ball height check

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.
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post #14 of 50 (permalink) Old Feb 16th, 20, 1:38 AM
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Re: clutch pivot ball height check

Please forgive me for going over stuff you probably know or rehashing things we have covered.

Proper throwout earing installation.

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post #15 of 50 (permalink) Old Feb 16th, 20, 7:51 AM Thread Starter
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Re: clutch pivot ball height check

Great thought, Al, but yes - I have my TOB installed correctly.

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.


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