Clutch Stack Revisted

http://atlanticgreen.com/ndnsclutch.htm

Easy Pull, No Drag, No Slip, Commando Clutch

David Comeau 27 July 1997 Update Oct 2008
Introduction to the Commando Clutch
Diaphragm Description

The clutch spring in the Commando is a cupped piece of spring steel called a diaphragm. Its center has been cut into 18 radial fingers. A center carrier has 2 rows of slots, 9 per row, alternating HI-LO. These slots in the center carrier receive the ends of the diaphragm fingers. The diaphragm is pressed over the center carrier and 18 fingers get loaded into the 2 rows of slots. The center carrier also carries the clutch adjuster screw and lock nut.
To disengage the clutch the following observations can be made. The clutch carrier is pushed out .035" than the clutch starts to disengage. At this point the high fingers have been well lifted and the lo fingers are now just starting to lift off of the clutch pressure plate. By .050" lift both sets of fingers are free and clear of the clutch pressure plate and the clutch should have almost no engaging properties. The atlas actuator cam certainly has more than an adequate lifting range for a commando clutch, and in fact the commando actuator cam has more than double the lift needed to completely disengage the clutch. This makes the ROD/cam ball free play adjustment of little concern in actual use, with the commando actuator cam.

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I'm re-reading this for the millionth time after trying to help my friend Mike with his heavy clutch. He bought some Barnett plates hoping it would help but it's still way too stiff. I tweaked some stuff and it's a little better but still not right.

I still haven't read a practical description of what is happening. Please correct this attempt.

I'll use outside (where the adjuster screws in) and inside (the side against the pressure plate) to describe the sides. If I understand correctly in its natural state the diaphragm spring is convex to the outside. The clutch spring compressor tool pulls the center out and flattens the plate until it's flat.

When installed the center of the spring center is trying to push in. When you pull on the clutch lever you are acting against the pushrod and pushing the center out.

If your stack is too short you are fighting agaist the full power (or most of it) with your hand.

If you're stack is too high the spring can't clamp down hard enough. The center is too far out, it's like you are partially pulling the lever. This is the problem I had with my slipping clutch, I had one too many plates.

On Mike's clutch it seems that the center is too far in. It's hard to tell how far in but when you compress the spring you just need to pull the spring flat to get it off.

Clutch Stack Height
Since the easiest clutch is when the clutch diaphragm spring is about .68” of deflection (175 lbs) and clutch pull is about .1”, the engaged position should be around .58” of diaphragm deflection to get the sweet spot. Therefore, the diaphragm appears to be about .03” inverted beyond flat (.55”) when engaged. The problem is how do you get the diaphragm to be at a certain position when assembled? You adjust the internal clutch stack height, the diaphragm is usually extended a bit to much. Therefore, you add thickness to a component in the clutch stack height. You could have a custom (thicker) backing plate made to be placed in the rear of the clutch basket, or you can add a clutch steel plate .080” thick. You can see using a straight edge on the diaphragm, if it is flat, extended or inverted. It is interesting to note that as the clutch wears, it always gets harder to pull until it finally gets to .40”extended. Then its up to 325lbs of pressure! I don't necessarily endorse this as a must do modification. But you should understand what is happening if you decide to go through with it. The lowered clamping pressure may cause slipping.

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There are a lot of numbers here and not enough reference. I'm not sure what Dave is saying about .68" and .58" and then .55" clutch pull of .1" and something about .03" inverted. I assume most of these measurements are being made at the clutch center with a dial indicator?

Here's my attempt at the various states:



Am I close?

Hi.
0.03 to 0.5 inch is big movement (best part of 13mm) more akin to clutch lever movement at the handle bars. Are you quoting correctly as the difference between engaged and disengaged at the clutch centre is minute?

Your second picture is wrong because the clutch 'puller' tool cannot work for the lower two 'inverted' drawings. Please redraw using an 'outer is concave' description as in the upper 'natural state' drawing.
Ta.

I interpret the graph (at http://atlanticgreen.com/ndnsclutch.htm) to mean that maximum clutch plate clamping force is achieved at about 5mm concavity from a flat diaphragm. The photo below shows the stack height that I use relative to the clutch basket teeth (light lever action without clutch slipping - achieved using an extra steel plate to offset fibre disc wear over the years.

I see the teeth on your pressure plate are even with the top of the basket grooves. I wonder if that's a good indicator of the correct stack.

swooshdave said:

Am I close?

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Not really
If you don't relate it to the curve/graph then there is no context .
your middle drawing demonstrated my example
your bottom drawing is 10x more than what is happening

0 to .58 deflection gets you to a flat diaphragm as shown on the graph on my page. This whole region is "extended" and is the natural shape if released from the removal tool.

Inverted Region .58”(to be more correct) & More of Deflection

2 conditions
1. The natural pressure/deflection curve which you must understand or you can not move on to the "as installed" discussion, which follows

2 once installed ( from what ever installed position you have built your stack height to achieve)

Therefore, the diaphragm appears to be about .03” inverted beyond flat when engaged.
This is only a suggestion as an example and NOT a final recommendation.
therefore example .58 flat plus .03 = .61" total deflection of diaphragm (from totally extended)

To disengage the clutch the following observations can be made. The clutch carrier is further pushed out an additional .035" (from installed height) then the clutch starts to disengage. At this point the high fingers have been well lifted and the lo fingers are now just starting to lift off of the clutch pressure plate. By .050" lift beyond installed height both sets of fingers are free and clear of the clutch pressure plate and the clutch should have almost no engaging properties

I continue to ask people not cut and paste my work

dynodave said:

I continue to ask people not cut and paste my work

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I have properly quoted and cited the original source.

This is to facilitate discussion, which is not available on your site.

I want to add more clarity to your information. I have a hard time wrapping my head around all the numbers. Hopefully this discussion will help not only myself but other people too.

swooshdave said:

I see the teeth on your pressure plate are even with the top of the basket grooves. I wonder if that's a good indicator of the correct stack.

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Dave, I set my clutch stack height flush with the drum as in needing's photo and it was so easy to pull I couldn't believe it would hold. It does hold (torquey 850 too) I also changed to a Venhill stainless and telfon Featherlight clutch cable which helped a lot. The clutch pull went from extreme to moderate (change to Venhill) to very light (change stack height)

Glen

Seems to me I remember raising my clutch stack height so it was flush with the basket grooves and yes, it was a very light pull, but the clutch slipped horribly. I live with a 3-4 finger pull, but a 1 finger hold. Stock cable. I think if I could find a solid plate that's thinner than the thinnest barnett plate it might get lighter and not slip. I think I used an extra .030 plate as I remember, but could be wrong.

I have a lot of trouble wrapping my mind around dynodave's numbers too. I thought I had it worked out once, but after getting the rod seal and working that into the clutch, all my dimensions are in spec for plates and height and all, but the setup on my clutch cable/actuator/rod/adjuster is very critical and will only work within a 1/4 turn range on the adjuster nut.

Is it the case that all diaphragms have different dimensions for the same pressure? I could imagine that happening.

DogT said:

I have a lot of trouble wrapping my mind around dynodave's numbers too.

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I'm hoping to put some real world reference (not charts or drawings) against the data. I hope to enhance Dave's efforts, not steal or undermine them.

Yes, I think, as stated, the drawings are exaggerated but the concept and numbers for easy pull clutch is right on.

The center diagram shows the diaphragm at rest and assembled with the clutch engaged/clamped. In this position the diaphragm is ever so slightly bowed/proud in the center and almost, but not quite, flat in appearance. This position is just past centerline of the diaphragms function and has the greatest effect against the raised portion of the pressure plate on which it rests.

As the clutch lever is pulled in, the bowed/proudness is more pronounced as the clutch is disengage. In a dry clutch it will be ringing as the plates are free to clatter about. I love that sound.

I purchasing the thick anodize pressure plate from RGM and turn/faced the outer face until this position of the diaphragm could be attained (stack height adjustment). I also wanted to preserve the anodizing toward the clutch so I had to maintain the form of the raised portion of the pressure plate.

As clutch plates wear, this pronounced position of the diaphragm will degrade and so will the ease of the clutch function. It take a long time though especially if you get right to start with.

swooshdave said:

DogT said:

I have a lot of trouble wrapping my mind around dynodave's numbers too.

Click to expand...

I'm hoping to put some real world reference (not charts or drawings) against the data. I hope to enhance Dave's efforts, not steal or undermine them.

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If one can not realize there is a two part relationship in these clutches then all hope is lost.
It is entirely based on the interaction of the spring pressure curve interposed on the selection of a clutch stack height to "create" a final (extended or flat or inverted) shape... therefore controlling the working spring pressure @ engagement.

Yes there are believed 3 variants of diaphragms with no part number change. The characteristic spring curve shapes are very much the same though the actual values vary. For this reason not all clutches can be set up the same. You must obviously have enough clamping pressure to prevent slipping.

http://www.haussermann.com/en/product/index.php

dynodave said:

It is entirely based on the interaction of the spring pressure curve interposed on the selection of a clutch stack height to "create" a final (extended or flat or inverted) shape... therefore controlling the working spring pressure @ engagement.

Click to expand...

And once we translate that into plain English maybe with simple pictures for the slower of us we won't be lost. :mrgreen:

swooshdave,
For simplicity's sake I would not get too wrapped up in all those numbers. I think you only need to be concerned with two things. When fully assembled and adjusted with clutch lever out the diaphragm should be slightly concave (bow towards gearbox). The more concave you are the more pressure you create. With clutch lever pulled in the diaphragm should be almost flat.
I measured everything out on my clutch ( fiber plates, metal plates and PP) and found Dynodave's (also same number Old Britts uses) stack height to be right-on for lever pressure and no slippage. I mixed and matched plates I had to get correct stack height. If you want to worry about numbers these are the one to be concerned about.
Things I learned the hard way
Don't sand blast steel plates
Barnett postage stamp fiber plates did not work at all for me. (Grabby and wore out very fast)
Coat clutch push rod with grease ( I use Napa green disc brake grease)
Get Dynodaves clutch seal
Check your clutch cable for binding. I got the Venhill coated cable. Very nice.
Pete

swooshdave said:

dynodave said:

It is entirely based on the interaction of the spring pressure curve interposed on the selection of a clutch stack height to "create" a final (extended or flat or inverted) shape... therefore controlling the working spring pressure @ engagement.

Click to expand...

And once we translate that into plain English maybe with simple pictures for the slower of us we won't be lost. :mrgreen:

Click to expand...

I never had any luck trying to measure a clutch stack height. The measurement is too dependent on how much pressure you put on the stack.

I just install the spring and look at it with a short straight edge held against the diaphragm spring.
The center of the spring should be slightly concave when the lever is not pulled.
It should be slightly convex when the lever is pulled.

Get it there and it will be happy. Jim

swooshdave said:

dynodave said:

It is entirely based on the interaction of the spring pressure curve interposed on the selection of a clutch stack height to "create" a final (extended or flat or inverted) shape... therefore controlling the working spring pressure @ engagement.

Click to expand...

And once we translate that into plain English maybe with simple pictures for the slower of us we won't be lost. :mrgreen:

Click to expand...

changing spring stack height changes spring pressure
the chart tells you how much.
A flat diaphragm is close to the desired working shape

sorry article off line for rework

I'm slow. Never said smart. :wink:

comnoz said:

I never had any luck trying to measure a clutch stack height. The measurement is too dependent on how much pressure you put on the stack.

I just install the spring and look at it with a short straight edge held against the diaphragm spring.
The center of the spring should be slightly concave when the lever is not pulled.
It should be slightly convex when the lever is pulled.

Get it there and it will be happy. Jim

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I think you're saying what I tried to say before, each spring diaphragm may be slightly different where it's pressure curve (concave, convex) ends up on the plates so it has to be adjusted for each different diapharagm? Which essentially means to me that just making the clutch stack height right to the basket ridge may or may not work for everyone? There's lots of variables in the clutch dimensions.

I think dynodave addmitted that different diaphargms have different pressure curves too, no?

Of course I may be all wet, and wet upon, here.

Dave

Dave that's interesting because I've done all those combinations and found one of my 2 diaphram springs works better than the other to achieve this state. So much mixing and matchings I lost track of which model and year. :|

DogT said:

comnoz said:

I never had any luck trying to measure a clutch stack height. The measurement is too dependent on how much pressure you put on the stack.

I just install the spring and look at it with a short straight edge held against the diaphragm spring.
The center of the spring should be slightly concave when the lever is not pulled.
It should be slightly convex when the lever is pulled.

Get it there and it will be happy. Jim

Click to expand...

I think you're saying what I tried to say before, each spring diaphragm may be slightly different where it's pressure curve (concave, convex) ends up on the plates so it has to be adjusted for each different diapharagm? Which essentially means to me that just making the clutch stack height right to the basket ridge may or may not work for everyone? There's lots of variables in the clutch dimensions.

I think dynodave addmitted that different diaphargms have different pressure curves too, no?

Of course I may be all wet, and wet upon, here.

Dave

Click to expand...

There are definitely different diaphragm springs used over the years. Of course they look the same.

What I have found is slightly concave gives the best holding pressure while insuring a clean release when you pull the clutch.

If the diaphragm is already convex before you pull the clutch it will be hard to find neutral and you will not have that over-center feel to the lever when you pull it.

If it is too far concave when the lever is released then the holding power will be poor and the clutch pull will be hard.

Different baskets , different diaphragms and different clutch stacks may need different modifications to obtain the best result but the needed position of the diaphragm spring once assembled seems to be the same.

I just start out with the thickest pressure plate and machine it a little at a time until the diaphragm is in the right position. All you need is a lathe at your disposal. Jim

I wish I had Jim at my disposal. :mrgreen:

Even w/o Comstock machinist shop/skills ya can buy difference thickness pressure plates that can get the spring in sweet zone with a bit of mix/matching. Peel ran an alu pressure plate I think from RGM that was a bit thicker than factory and I've another steel one that's thinner than stock, so 3 thicknesses on hand. I liked my 2 Nortons clutch action better than my modern and tends to feel like a compound archery bow where there's more initial effort to pull then breaks over leverage point to distinctly reduce effort so can hold still before release to kill innocent deer by sharp point or blunt helmet. Before I knew anything about stack or spring measure from DynoDave I trial error stumbled on just diddling stack and pressure plate so spring able to just slip in groove to touch pressure plate w/o much or any slack. After swtiching to ATF I not had any clutch issues to adjust or clean in 15 yr on 2 Combats - with lots of slipping feathering on loose or slick steep surfaces and silly hot rod lauches or just clutchless shifting I do pretty often once rolling. Here's some more scope on alu pressure plate which some say wear out too fast but Peel's seriously abused clutch, dragster starts, wheelie popping, smoking rubber patterns left on pavement and Mt. area raw off road use didn't bother it a bit.
https://www.google.com/?gws_rd=ssl#q=no ... re%20plate