MKIII Clutch Problem

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Jul 24, 2007
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I am now officially baffled with this problem and would greatly appreciate any insight anyone here can offer. My MKIII had developed hard shifting this summer which I originally thought was the cable, so I changed that. It made for an easier pull, but didn't help the shifting. It was very hard to get into 1st unless there was way too much tension on the cable (no free-play) and then it would tend to jump out of 1st under acceleration. Because I couldn't get a proper adjustment, I thought it was probably some worn part and replaced the push rod. No difference. I had fairly new Barnett plates and tried switching back to Norton plates and discovered the clutch center was badly notched so replaced it. No difference. I then changed the actuator lever, roller, bushing and ball in the gearbox, but no difference. Tonight I disassembled the clutch on my '69 "S" and tried the diaphragm spring from it - no difference. I then assembled the entire 4-plate clutch from the '69 into the MKIII and still no difference. I really don't know what to try next and would like any ideas anyone can throw at me. I've been at this for several weeks and now have both Nortons out of commission! Thanks for any assistance you can offer.
Sounds like you have proven it's a transmission problem. Before you spend another dollar on parts check the wear on the left hand gear selector They can become a sloppy mess. The slipping out of gear is your clue. It's not engaging because it's not shifting all the way. Put the bike on the center stand and while rolling the rear wheel shift through the gears. Use your ears and come back and tell us what you find. The mark three is not prone to the moving trans syndrome where the main chain gets tight and the primary goes loose. Nice to have the spares about but now it's time to find it and than spend it. Hey you could have a BSA and have to grind spacers to get all the shifts clean. It could be worse , you may just need to tune your hair pin spring. Do mark three's have those things?
The only time it has slipped out of gear is when the cable is adjusted too tight. It is easier to get into 1st, but it doesn't fully engage, so is prone to slip out. If the cable is adjusted even right at the point of no free-play you have to force it into 1st, but once there it will stay there and shift through the rest of the gears easily. Neutral becomes very difficult to find though and impossible if the bike's not moving. The MKIII does have that hair-spring, but it seems to be fine.
Normal for the clutch to cause the shifting to get bad. I was assuming you had done the major adjustment (actuating rod)with the cable loose and then just set the cable for normal free play. Please do that and then go do the shifting though the gears while listening and feeling the ratios change in the hand your turning the rear wheel with. With the motor not running and nothing hot the clutch should be an on-off affair. It should free off using the kick starter and bind right up as you release it turning the motor over. As you say new center, good flat plates, new cable, everything traded out with no change in behavior. It's a mark three how sloppy is the shifter? Does a mark three still have that thin little clip behind the basket did it collapse when you torqued it up?
Norbsa48503 might be onto something here.
How much lateral movement (ie in and out) do you have on the mainshaft? I don't think the clutch basket moving would effect the gears. But any lateral movement in those two will take up all the clutch lever throw.
Once Norton gear is selected and under power it shouldn't jump out as the dogs are positively ground and bite in.
Thanks for the suggestions. When I adjust the pushrod and cable to spec, it is just about impossible to get it into first. I have to take all the play out by adjusting the cable in order to get it into first. When I tried riding it like this, it would occasionally jump out of first under acceleration. With the proper adjustment it shifts through the other gears fine, but won't easily go into first unless I'm moving at just the right speed and then it will stall the engine when I come to a stop because it isn't totally disengaging. Some suggestions on the INOA forum suggested the circlip holding the clutch center. I pulled it all down tonight and the circlip and bearing look good. I did try running the bike in neutral with the primary cover off and did notice that the top plunger of the chain tensioner seemed to be "pumping" up and down quite a bit more than I would have expected, but the chain tension seemed good when it wasn't running and it didn't appear overly tight or loose when it was running. I'd never tried this before so I don't know if this is fairly normal or not. I didn't find any discernable movement in the mainshaft and the clutch basket runs very straight with much less wobble than my other bike. I'm all ears for any suggestions on what to check while I'm at this point before going back together this weekend. Thanks for any ideas.
The chain tensioner will pump cos it needs oil to work correctly.

Now the primary cover is off.

Can you try;

With the gearbox in neutral and the clutch adjustment backed off, get hold of the clutch basket and push and pull it, or use a lever with care. Is there any movement at all, if so how much?

And, when the clutch is rebuilt and the adjustment to book when you pull the lever is there any movement at all, if so how much?

Remove the diaphragm and measure the exact stroke of the pushrod?

Let's know what you find.

It's probably unlikely since you had the problem before changing all the actuator parts in the inner cover but are you sure you haven't been sold a Dominator lever by mistake. They look similar but have only slight different profile on the roller side (more leverage but less travel). I lived with this for years wondering why I had a one finger clutch but difficult neutral finding. The other issue is bent diaphragm fingers. If they are bent (mine was) and the fingers are not all at a similar height the effect is the same as an unevenly adjusted coil spring clutch. You'd think that under pressure any differences would be spread over the other fingers. Seems not at least not in my case. But you swopped in the other Commando clutch and it made no difference so probably not the source.
I had a similar prob wi my MK111
I took all gearbox the parts to Norman White and he could see nothing wrong, untill he looked at the dimple on the camplate which accuates the neutral switch. This had a groove worn in it which showed that the neutral switch was scewed in too far and was causing the problem. I got back home und unscrewed the neutral switch and prob solved.
Back together again and no change. I measured the stroke of the push rod and it was within a couple of thou. of the other bike. I didn't write the amount down, but believe it was about .13". I switched the diaphragm with the other bike. It seems that the second group of fingers aren't moving as far as they did on the other bike. There's no discernable movement in the clutch basket and I backed the neutral switch way out. Still baffled!
A real long shot; both chains, they aren't tight are they?
Man this has to be something stupid.
The chains are fine. You're right it has to be something stupid - I've checked everything else!
Did you say you'd changed the clutch plates for a complete set of known straight plates?
Yes, it currently has a relatively new set of Barnett plates which have been cleaned and checked. I've also installed an older set of bronze Norton plates after cleaning as well as the entire 4-plate set from the other bike.
The clutch basket bearing is good and smooth with no play. The circlip is good and when I reinstalled it yesterday just torqued it to about 40 ft-lbs with loctite. I wouldn't think that something in the gearbox could keep the clutch from fully releasing, could it?
The only thing I can think of is the main shaft ball race could be lose or had failed. The clutch wouldn't release until all the end float was taken up. But you reckon there's no end float.

You haven't fitted a plastic pushrod have you? :wink:
Still searching for the cause of this, but took some measurements over the weekend that hopefully will offer some clues. I tried screwing the clutch rod adjuster in until the clutch released with the bike in 1st. I measured from the outside face of the clutch basket to the diaphragm spring center carrier. I then compared this to the normal adjustment with the adjuster backed off about one turn. This dimension was more than the throw in the pushrod. When I backed off on the adjuster until the clutch engaged fully, it was less than .08" difference, well within the range of the pushrod. So it seems that the diaphragm spring in actually under center. Could this be that the pressure plate is worn down in the center where the diaphragm spring makes contact? Does anyone have a measurement of how thick it should be there? I found the thickness for the outer rim on the Old Britts website, but not for the center. Thanks again for all the help.
It seems that you've eliminated just about let's circle back. You initially thought your shifting issues were caused by the clutch cable, but after replacing it everything got worse. And now when you "adjust the pushrod and cable to spec, it is just about impossible to get it into first."

It was bad, you changed the clutch cable, and it got worse. Could the new clutch cable be defective? Could an outer sheath that buckles or moves in the ferules be causing the issue?

I've never seen a bad cable, but you've just about eliminated everything in the clutch itself, and this doesn't really sound like a transmission issue (but *I* can't rule it out.) Regardless, another clutch cable is a much cheaper and easier next step than tearing into the transmission...
You must follow the clutch adjustment procedure to the letter in order to give the mechanism the best possible throw.

Now Lurker828 might have point here. If the cable inner is too short the operating lever inside the gearbox wouldn't move far enough back to achieve the longest throw.

Take the nipple out of the handle bar lever and reset the clutch centre adjuster to see how much of the outer might need removing. Cut bits off the old cable I don't want blamed for ruining your new cable.
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