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Pressure Plate Forces, What Are They?
Posted by: Max Roeder ()
Date: November 30, 2017 04:59AM

While I'm setting up my shop to put Snowball back together (correctly). I've been evaluting my flywheel/ pressure plate testing machine. I built this machine so as to confirm pressure plate force against the clutch plate. Also how much travel the pressure plate will be pushed in before release of clutch plate and if there are any uneven movement. I never thought about the advertised pressure plate diaphragm ratings much but always wondered what the value really meant.

After testing a couple 1500# and one 1800# wah-alh, the "pounds" are the engineering term Ks or pounds per inch. It only takes about 1/4" from first engagement to full peak load fall off, so the 1800# unit traveled about .21". That's not before clutch plate release, haven't incorporated that yet but plans are to be able to graph all three functions as test results.

After the first of the year I'll have most everything set up to make my flywheel assembly near perfect, even dynamic balancing. Long and winding road but what else am I'm going to do with my free time?

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Re: Pressure Plate Forces, What Are They?
Posted by: flat_six ()
Date: November 30, 2017 07:36AM

Here's a start:

Clarks Catalog

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Re: Pressure Plate Forces, What Are They?
Posted by: JamesD ()
Date: November 30, 2017 09:24AM

Are these guys a squad of the Pressure Plate forces?  It's the first image that popped into my mind.



James
'65 Corsa 4-speed, '65 Corsa V8                                                       Santa Clarita, CA.
“I may not always drive a car, but when I do, I prefer a Corvair.  Stay loose, my friends.”

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Re: Pressure Plate Forces, What Are They?
Posted by: Max Roeder ()
Date: November 30, 2017 09:27AM

flat_six Wrote:
-------------------------------------------------------
> Here's a start:
>
> Clarks Catalog


Start for what?

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Re: Pressure Plate Forces, What Are They?
Posted by: MattNall ()
Date: November 30, 2017 09:30AM

Bob helt will know for sure..

I've always heard the STD is 1200 psi and the Hi-perf / weighted is 1500 psi.

Most don't like the Hi-perf so the take a Standard and make it 1500?





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Re: Pressure Plate Forces, What Are They?
Posted by: flat_six ()
Date: November 30, 2017 09:32AM

Max Roeder Wrote:
-------------------------------------------------------
> flat_six Wrote:
> --------------------------------------------------
> -----
> > Here's a start:
> >
> > Clarks Catalog
>
>
> Start for what?


Per the subject of this topic, you are looking for pressure plate forces. The link has that data. Clear?

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Re: Pressure Plate Forces, What Are They?
Posted by: Max Roeder ()
Date: November 30, 2017 10:02AM

I guess I shot over some of your heads. I built a load cell based, hydraulically driven test machine to test the forces required to disengage pressure plates from clutch plates. The machine will (when finished) provide a graph showing how much force is required over what travel distance until a nominal thickness clutch plate is released.

My initial test were conducted on a 1800# and a 1500# Clark's pressure plate. The resulting data showed the 1800# and the 1500# values are in pounds per inch (Ks), theoretical only. The diaphragms will only travel about 1/4" before loosing pressure. The graph will look like a bell curve but the distance traveled will be only 1/4" or less, or maybe more. I don't have that many pressure plates to test but the 1800# peaked at 401#'s @ .210" of displacement. And that's about 10#'s per square inch of friction face on the pressure plate.

Because the diaphragms are more like a belleville washer the load increase over distance will not be linear and then fall off after a "break over center" type condition. I calculated the loads for both 1800# and 1500# and the results were the values published by Clark's and probably many more are a theoretical pounds of force per inch of deflection, just like all springs are rated #'s/in. (Ks).

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Re: Pressure Plate Forces, What Are They?
Posted by: BobV66Vair ()
Date: November 30, 2017 10:19AM

As I recall from my days working at Perfection American (Zoom) in the 70's, the rating was for clamping pressure, not release input pressure (pedal pressure). 1500# was the clamping pressure per sq" on the disc. The diaphragm spring was used because it required much less pedal pressure to release the clutch. GM used them. Ford and Chrysler use the common three finger pressure plates. Some odd vehicles used a "Long" type, that was a three finger but with counter weights on the outside of the fingers that increased pressure as RPM went up to clamp harder at higher RPM. Centrifugal force pulled the lever out and the anchor/fulcrum turned that into a downward pressure. I always like the diaphragm since I didn't work out my left leg much1

Bob Vinnacombe
Sandy, Oregon
1965 Corsa 140 stock
1966 Monza Soon to be race car
1968 Monza Parts for now

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Re: Pressure Plate Forces, What Are They?
Posted by: caroseiii ()
Date: November 30, 2017 10:48AM

According to GM literature "Corvair General" from 1962, "Effective plate load" range for the low horsepower is 900-1075 lbs. and for the heavy duty was 1050-1250 lbs. Its on page 99 of the download from GM Heritage.

Crawford Rose

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Re: Pressure Plate Forces, What Are They?
Posted by: flat_six ()
Date: November 30, 2017 02:19PM

Over some peoples heads, eh? Probably more an issue of communication skill.

So after six posts, some of us actually know what it is that you are doing.

Now, the only question that remains is: why?

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Re: Pressure Plate Forces, What Are They?
Posted by: Chilly Willy ()
Date: November 30, 2017 02:49PM

I use my left leg😁
it’s a good thing pressure decreases. otherwise, I’d have to get custom pants winking smiley.




The Corvair, Keeping Nader Notorious winking smiley


Will
Northern California

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Re: Pressure Plate Forces, What Are They?
Posted by: Max Roeder ()
Date: November 30, 2017 05:08PM

I shot over some of your heads means my explanation of the what and why was inadequate in detail. Not that you couldn't understand what I am doing.

When I rebuild a flywheel assembly the ability of the pressure plate to perform properly is a critical. The only way to confirm clamping force is to measure it. I do not believe the clamping forces are as great as some believe. Also if the pressure plate is too great that can affect throw out bearing life, and especially aftermarket clutch cables.

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Re: Pressure Plate Forces, What Are They?
Posted by: flat_six ()
Date: November 30, 2017 06:40PM

Ah. Got it!

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Re: Pressure Plate Forces, What Are They?
Posted by: vairmech ()
Date: November 30, 2017 06:41PM

The average pressure to push the clutch spring to release is 250-275 lbs on the throw out bearing. The average release point is right at the .21" that you came up with. Clamping pressures can be reasonably consistent in the advertised numbers but still all over the place depending on the tolerances.

The stock cables can take 350 lbs and live as that is what my dual disc clutch has in the race car and I run a cable. The cable in the race car is at least 25 years old and probably older and it lives. I can't say anything about the aftermarket cables, I haven't ever used one.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

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