Optimising your clutch Flattening the diaphragm

[rolesyboy]

Has https://www.youtube.com/watch?v=C3c5EcpYiP8&t=415s

This HRE guy does some really interesting videos and knows how to get stuck in. I have been experimenting with this idea of optimising my clutch flywheel set up
Reduced the horn height of the backplate until the diaphragm is parallel which should make for an nicer clutch pedal, takes load of the thrust bearings etc.
However because the contact point for the thrust release bearing moves toward the centre of the engine it means that the throw for the clutch arm increases significantly. In turn this means when you depress the clutch pedal it overthrows the slave cylinder seals and all the clutch arm adjustment (20 thou) and throw out stop goes tits up.
Has anybody on here optimised (?) there clutch set up in this way and if so how did you overcome this problem? I guess I could make up a spacer to sit between the thrust bearing and the clutch release centre plate but its an odd shape and has to accommodate the retaining spring. Longer pushrod maybe?? Wish I was an engineer and not an enthusiast sometimes

Scroll to about 7 minutes on the video for a better explanation

Cheers

[imack]

I played around with this 'clutch optimisation' lark with my current engine build. I found that if you set the diaphragm flat you actually ended up with less clamping force. My KAD flywheel and back plate with an old style orange diaphragm and new AP organic clutch plate required 140 lbs ft torque before slippage occurred as I set it up. Slipped at 110 lbs ft if diaphragm was set up flat.
Currently have engine out of car and flywheel removed so I might retest it later to see how it performs now it's all bedded in.

[rolesyboy]

Cheers. I'm glad somebody else has experimented with this. I struggled to get my head around it too.
Not having a machine shop makes the whole experimentation part a bit of a drag but but I liked the idea and thought, if its a success I will do it on my other builds.
How did you overcome the 'gap' between thrust release bearing and diaphragm assuming you got that far

[swifty]

If you’re using a paddle clutch plate and grey diaphragm etc then the easiest way to make it lighter for drivability is to fit a remote in line servo to the clutch slave cylinder. This can be hidden underneath the wing or under the dash etc . So much easier than getting involved with lots of mechanical complexity. Done this many times over the years …. Shirley

[imack]

I never ended up machining the back plate horns, I left them at standard height.
I run with 3 drive straps. With just one drive strap fitted I found the diaphragm was virtually flat so I was going to machine the thickness of two drive straps off the horns, but I found that I had less clamping force than with 3 straps fitted and the diaphragm at about 10°. I left the horns at standard height and just machined up thicker spacers to sit between the drive straps and the flywheel so that the straps were 'flat' weren't under any tension when the clutch is engaged.
Running MED clutch arm and a NOS 'competition type' clutch release bearing. Release arm lies pretty much parallel to the face of the wok.
Just assembled the clutch and flywheel and re did the torque test now that it's done a few thousand miles - no slip at 150 lbs/ft but that's the limit of that particular torque wrench.

[Oneball]

I’m not sure I understand, surely if you change the position of the spring to reduce the force needed to press the pedal to disengage the clutch you are also reducing the clamping force?

[imack]

I think Paul at HRE (and I believe AC Dodd as well) are suggesting that maximum clamping effort is when the diaphragm is flat and that pedal effort is reduced as the diaphragm goes over centre when the pedal is pressed. But in my experience that doesn't appear to be the case. I wasn't able to measure pedal effort though.

[Oneball]

That’s clearer. Thanks.

[1071 S]

Many years ago, a Canadian called Marcel Chicak (not sure of spelling) provided a bunch of technical data on Minimania ‘s website that examined this issue.

I can’t find the graphs any more, but they showed quite conclusively that clamping pressure increased as the spring moved towards flat and then decreased as the spring curved the other way. Pedal pressure reached a minimum as the spring became flat.

Of course, if you set it flat with a new clutch plate, clamping pressure will fall off as the plate wears.

Cheers, Ian

[Spider]

The Diaphragm Clutches work on a Bevel Spring. Like most Springs, the more they are compressed from their natural state, the more pounds per inch of compression they exert, though these will eventually get to a point where they do reduce in pressure.

It's not necessary to get Bevel Spring in the flat for the most force in fact, going past that, they'll have more, but don't go too far, about 0.050" is about it. maybe a bit more.

Indeed Marcel Chichak did do quite a few tests. Here's one of his charts;-



According to his tests, it's clear that with new diaphragms, the clamping pressure increases the more it's compressed, even beyond 'flat', but as they age, they do loose some ommph.

While it might be nice to have a high poundage diaphragm grabbing at your crutch,,,, errr,,, clutch, keep in mind the down sides of a heavier pedal and reduced crank thrust life.

[rolesyboy]

Some interesting comments on here.
I'd be keen to hear how folk overcome the noticeably increased gap between the clutch arm/thrust release bearing and clutch plate as my gap is huge.
I've bought a new backplate now but I'd still like to hear what others have done here.
Cheers. Mark

[imack]

In the past I've had a shim (I think 60 thou) between the release bearing and the plunger. I've also previously lengthened the push rod between the arm and the slave cylinder.
I presume you've eliminated wear/free play elsewhere in the system? Eg: release arm pivot in the wok, all clevis pins, clutch pedal and master cylinder clevis pin bores, worn release arm.

[rolesyboy]

Thanks Imack. Yeh everything is new or in tip top condition. What you say makes sense.
Will message you tomorrow for a bit more insight
Cheers

[1071 S]

Spider, ".... According to his tests, it's clear that with new diaphragms etc etc...."

Do you have other graphs that show this? I don't see how the graph you posted relates to clamping pressure. The graph shows pedal pressure on the system as the clutch is released.. ??? ie the only point you have full clamping pressure is depicted at the extreme left bottom corner of the graph.

Clamping pressure is at a maximum when the clutch is fully engaged.... ie there will be no load on the release bearing or the thrust washer. Am I missing something?

imack, you only need to lengthen the slave push rod to take up the gap (cut the push rod and add a bit of rod in the middle so that the slave piston sits about 3/4 the length of the slave bore away from the open end.) With the release bearing sitting on the diaphragm wind in the adjuster bolt to give the required clearance (attach spring ... or not).

Cheers, Ian

[Spider]

Spider, ".... According to his tests, it's clear that with new diaphragms etc etc...."

Do you have other graphs that show this? I don't see how the graph you posted relates to clamping pressure. The graph shows pedal pressure on the system as the clutch is released.. ??? ie the only point you have full clamping pressure is depicted at the extreme left bottom corner of the graph.

Clamping pressure is at a maximum when the clutch is fully engaged.... ie there will be no load on the release bearing or the thrust washer. Am I missing something?

Cheers, Ian

Ian, I don't have that a graph that shows that, but like Marcel did, I just applied one of Newton's Laws 'For every action, there's an equal and opposite reaction'. The pressure of the spring that Marcel measured was at the thrust plate of the diagram.

[Exminiman]

Many years ago, a Canadian called Marcel Chicak (not sure of spelling) provided a bunch of technical data on Minimania ‘s website that examined this issue.

This one ?
https://www.minimania.com/Clutch_FAQ__non_Verto_

[1071 S]

Exactly, much appreciated...

Cheers, Ian

[Exminiman]

In case your interested this is Marcel’s (from Canada) website where the original article and lots of other well researched Mini stuff is

https://starchak.ca/tech/tech.htm

[1071 S]

There is a lot of data ...wondering if MC is still about.

Some thoughts: What are the differences between Graph 8 and 9?? They look the same to me ...and 9 doesn't seem to present the described data???

Also interesting that he recommends against synthetic oil in the conclusion. Especially when he concludes that the thrust bearings on his test engine failed due to insufficient oil film strength ...partially caused by high oil temps. Synthetic oils have higher film strengths than comparable mineral oils and better resists loss of strength due to temperature rises (according to discussion with the Oz militaries Head of our Materials Testing Unit.

Cheers, Ian

[mascher]

Keep in mind, that article was written about 23 years ago. Thoughts on synthetic oil and even the synthetic oil itself have changed since then.

Kelley