Clutch Lever Fulcrum radius? (2017)

On a Commando with standard factory handlebar levers, what is the distance from the pivot hole centre to the centre of the cable nipple? (pivot centres?)

I have found aftermarket levers (mostly alloy) that differ from 25mm (1"?) to 33mm. The shorter pivot centres seem to be a problem with a diaphragm clutch, which appears to need more lift at the pushrod than coil sprung clutches. Really I would like to know what the correct, or minimum acceptable is. The lever I have currently fitted is 28mm and I want to know if I should invest (significantly!) in a 33mm one.

In other words, how short can the lever be at the pivot centres to prevent clutch drag?

SteveA said:

On a Commando with standard factory handlebar levers, what is the distance from the pivot hole centre to the centre of the cable nipple? (pivot centres?)

Click to expand...

1-1/16" (about 27mm)

L.A.B. said:

SteveA said:

On a Commando with standard factory handlebar levers, what is the distance from the pivot hole centre to the centre of the cable nipple? (pivot centres?)

Click to expand...

1-1/16" (about 27mm)

Click to expand...

Thanks. I was sort of guessing it would be, that is a standard figure for British levers, 7/8" or 1 1/16". The lever that was fitted came out at 25mm, sort of not really suitable for anything even though it is a well made, nice looking (Domino) Tommaselli part.

Doesn't really resolve my problem though, I feel that more lift is needed, of course as it is on a race bike I am not as concerned as some about lever pull weight, once the lights go out it never gets all the way back to the bar before the change is done!

A tidbit of interesting info on the radius is that the Production Racers came with a lever with a shorter radius, 7/8" if I recall correctly. At least mine did. You could never be sure what parts would show up on a PR. If they didn't have the right part on the shelf when they assembled them, they would sometimes substitute something else. It was a simple steel Doherty style lever. I have measured later Commando levers, the aluminum ones with switch gear attached, and they all were as LAB said, something like 1 1/16". I discovered the difference when I replaced the clutch lever assembly (after a crash) with a later one, and noticed the difference in the force required to pull in the clutch. I always wondered if the steel lever was from an early Commando model, or just something from the race shop, but never managed to find out. The shorter fulcrum made clutch pull much lighter, but it did require careful adjustment to get full travel. It looked to me like a standard aftermarket steel Doherty ball-ended lever, but I never managed to track down the model. The catalogs at the time didn't include info like lever ratios and distances, so I would have had to find someone with the levers in stock to measure, and I didn't ever get around to doing so. I also wondered if the shape of the cam on the opening lever might also have been different. I seem to recall that the Atlas piece had a different profile. Maybe the early Commandos did too?

Anyway, that's all old history now, but I thought I'd pass it on.


Ken

Interesting Ken, further confirmation that mismatch is a problem.

With a TTi box you have Triumph actuator and another variable. I think I should be OK with a lever between 27 and 28mm pivot. 33mm may help clearance (most are expensive anyway), but will probably end up with a heavier pull than it need be, even if in itself that isn't a problem.

There will have been some 7/8" pivot centres kicking around AMC in the late '60s, that weren't being fitted to AJS singles!

I surmise cam on the operating lever was reshaped on the Commando because NV increased the fulcrum radius to 1-1/16".

-Knut

Another change happened between 72 and 74, the lever fulcrum point was moved inwards along the bar so the hand fell further out on the lever. Silver is off a 72, black off a 74, RGM look to have recast some as both types are on their site.

SteveA said:

In other words, how short can the lever be at the pivot centres to prevent clutch drag?

Click to expand...

In your case can a different stack height help? Also, are the clutch hub and/or basket splines showing any signs of divots? I would think that with a divot free hub/basket that it wouldn't take much lever travel for full disengagement. I apologize if my questions or my thinking is too rudimentary.

Best.

It looks like on the Norvil PR racers had discovered that the 7/8 inch Atlas levers have a higher lift than the standard Commando ones as discussed earlier on this website?

RoadScholar said:

In your case can a different stack height help? Also, are the clutch hub and/or basket splines showing any signs of divots? I would think that with a divot free hub/basket that it wouldn't take much lever travel for full disengagement. I apologize if my questions or my thinking is too rudimentary.

Best.

Click to expand...

Not much opportunity to change stack height, but....I am planning to change the clutch centre, pricing isn't too bad and I have a centre bearing to change anyway. Norman wants my old centre back to confirm exact variant, since he changed the design a couple of times.

Not a lot of marking, but maybe enough to contribute to the issue.

mdt-son said:

I surmise cam on the operating lever was reshaped on the Commando because NV increased the fulcrum radius to 1-1/16".

-Knut

Click to expand...

I'd say the operating lever was reshaped and the lever fulcrum (pivot) radius increased to 1-1/16" (increasing cable movement) due to the design of the Commando's diaphragm spring clutch which, unlike a 'conventional' clutch where the pushrod lifts a pressure plate so basically all pushrod movement is converted into 'clutch lift' whereas only approximately half the diaphragm clutch pushrod movement is converted into clutch 'lift' because the diaphragm only lifts half the 'centre' distance at its mid-point where it bears against the thust ring of the pressure plate therefore requires more pushrod lift than a conventional pressure plate clutch.

Edit: This information is contained in the BDM notes (link, below) sections 3, 10 & 11 for anyone who wants to read it if they don't mind wading though the rambling.
http://a20b767e.magix.net/#xl_xr_page_1

Could the factory have stuck with a 7/8" pivot radius lever for the Commando and profiled the operating lever to suit the required lift? Probably, but I think that would've put an additional strain on the cable and pivot mechanism.