QuarterMaster 7.25" clutch spring measurement

[Gary_T]

Hey everyone,

I'm hoping to put the engine/trans back in my Swift SE-1 shortly. I have a couple of clutch options, both QuarterMaster, one V-drive, one older (pro?). Of course, the spring colour codes have worn off.

The QuarterMaster catalog lists a process for measuring them.

https://www.quartermasterusa.com/wp-...16-Catalog.pdf Page 70.

Using a press with a 5,000-10,000 psi max. pressure gauge and .560" diameter hydraulic piston, measure the maximum gauge pressure needed to compress the spring over center and compare to the available ranges listed above. All measurements are taken with the spring in a free standing state using a standard 7.25", 2-3/8" bearing on a pressure plate with a 6.250" diameter pivot.

Unfortunately, this doesn't make much sense, right? A .560" diameter piston would give a piston area (pi * radius^2) of 0.24 sq-in. If they meant a piston radius of .560" (diameter of 1 1/8"), it would be a piston area of 1 sq-in. That would let me read the gauge pressure (pounds per square inch) directly as pounds. I'm pretty certain this is just a typo.

Next, a 2-3/8" bearing? that's a 60mm release bearing, on a 7.25" clutch? If that's correct, our typical 44mm release bearing requires 73% of the force listed below.



I've tried contacting QuarterMaster, and they just want me to send the clutches in for them to measure for me. Time dictates I'd rather not go this route.

Has anyone measure these themselves? What parts did you use? What's wrong with my reasoning above?

Thanks!

[Bob L.]

Seems like with release forces being listed...you could just forego all that pressure/setup stuff.

Assuming that release load listed is actual load AT the PP (not over on some pushrod/lever), then...

Take one of your load cells (scales, many pads can do 1000#/ea.), put it on hydraulic shop press, set clutch on top and centered. Put old T/O brg or similar dia piece on fingers... start pressing? Watching for "release" as described in write up, record the load when reached...

If nothing else, shouldn't hurt anything and give you some idea of spring used.

Don't forget to compensate for disk thickness, or the .100 step usually seen on flywheel for friction face.......again, assuming numbers are "as installed"...not something else..

Just thinking....

As far as piston areas....10,000 psi ram, with 1/4 sq. in, allows 2500 lbf max test range for release...should cover the max force listed (850 lbf) for all listed springs...so, don't see issue there... using smaller area, gives more sensitivity (bigger changes in values) to readings than a larger bore......on that pressure gauge (we don't usually, have...?)

Bob L.

[Gary_T]

Thanks Bob,

I have a press and a variety of gauges, but putting the scale underneath as a double check is a good idea.

Good point on the .100 step as well.

[Steve Demeter]

If you have a gage on your press and do not have scales that could be a rough reading. my 2 cents nothing more.

I am sure you already know that the wrong diameter release bearing can really mess up a clutch but just in case I am feeling knowledgeable tonight