Revisit the Clutch Stack

swooshdave · Wednesday at 3:07 PM

Thread 'Clutch Pull and Clutch Stack Height'

Jul 10, 2020

Have we ever had a clutch thread? No? Didn't think so.

So I was getting a little weeping from the primary on my Interstate. No belt drive. Not yet.

When I was in there I noticed a bit of play with the clutch basket. Going the cheapest route I replaced the bearing. That snugged it up a little bit. I really suspect a warn clutch hub center.

Then of course there was the issue with the plates. I remember when I first got the bike I think it had the bronze plates. At some point they were replaced with Barnetts.

Well, they didn't look good.

Now I have new plates in...

Apparently it's been a while, six years?, since I looked at the clutch. The result of all of that work was... nothing.

Time to go at it again. Recently (in the last six years) the club had some thinner clutch plates made by one of the members, since you can't get them from Old Britts anymore. So I'm going to see if I can finally get the stack height right.

batrider · Wednesday at 4:57 PM

The clutch basket is always a little wobbly, even with a new bearing.

swooshdave · Wednesday at 11:30 PM

Well, I reread my old thread and aside from annoying @dynodave I'm not sure much got accomplished.

But there were some tips I'm going to try again.

And as a last resort I can take the clutch stack from my 750 (which I think has the 850 pressure plate, but I honestly can't remember and for some reason I can't find a picture of it disassembled.) and see how it performs on the 850.

swooshdave · 2026-07-02T12:53:10-0600

Well, we have a smoking gun now. And no wonder that messing with the clutch stack height made no perceivable change.

I finally swapped the clutch from the 750 (which was indeed a 750 pressure plate) to the 850 and the easy pull came with it. But then I had an epiphany to just swap the diaphragm springs. And that was it. The 850 spring is the culprit. It's significantly heavier than the one that had been on the 750.

So spring differences can make a... difference. So now the 750 diaphragm is on the 850 clutch stack. And it's a light pull. Once I have the bike back together I'll see if the clutch slips or if it's fine.

And I may try to source another spring and see what that's like.

swooshdave · 2026-07-02T12:55:53-0600

I wonder if people have ever tested a sample size of the springs for their rates? What would a test rig look like?

marinatlas · 2026-07-02T13:10:14-0600

swooshdave said:
I wonder if people have ever tested a sample size of the springs for their rates? What would a test rig look like?

I think BDM (Mr Leadbeater) had done it ...but I had lost somewhere in my computer all his list !

Thread 'Diaphragm spring'

Dec 10, 2019

Does anyone know when the diaphragm spring centre design changed. Both my Commandos have the original factory fitted type. For the Atlas I am in the process of building I have just received a spring from RGM & the centre is different to my others. Whilst this doesn't matter to me, there is a problem with this sping, in that when fitted the centre boss will not sit square. I have removed the circlip & pulled it apart but cannot see anything wrong. RGM have said they will send me another but I wonder if anyone else has had this problem.

Martyn.

swooshdave · 2026-07-02T13:51:24-0600

I regret reading those JML emails.

Revisit the Clutch Stack

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