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A Clutch of Questions

Posted: Tue Aug 10, 2010 3:01 am
by Airbear
Patient: Brunhilde, 1974 R90/6, with 200,000 kms.
Symptoms: A gearbox on its last elbows, or at least in its autumn months - clunkier, louder whining and some false neutrals recently. Also a clutch that has always been a bit heavy and grabby. Two broken clutch cables in 45,000 kms.

It has been 5 years and about 45,000 kms since I last had the gearbox out. I am impressed by how much cleaner it looks in there compared to last time, when I replaced the input shaft and RMS seals and cleaned out decades of gunk.

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Ok, not clean, but mostly dry, and that’s good. Splines still well greased but badly chewed, as they were last time. Anyway, I now have a reconditioned gearbox to install and I’m checking out the clutch.

Thickness of the friction plate is still within spec. The splines look ok and it slips onto the new gearbox input shaft nicely, with not too much slop.

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The pressure plate side has uneven wear. Not much of the inside 50% of the friction surface has had contact with the pressure plate.

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There are no scores on either pressure plate or pressure ring surfaces, but there is some detectable unevenness. It is sounding worse, isn’t it?

Now for the really troubling bit. The diaphragm (such an odd word) spring does not measure up. Mr Clymer would like the spring height to be in the range 18.5 to 19.5mm, and mine measures 17.5mm. The finger tips have quite sharp edges –

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- and have left significant teeth marks where they contact the back of the pressure plate. Depth appears about 0.5mm

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As I type this and ponder just what questions I want to ask, I discovered that the answers were being shouted at me by the anal, obsessive side of me. GET NEW PARTS, etc. (bastard thinks I’m made of money).

The other side, the one that gave me permission last time to just shove everything back together after cleaning the oil off the friction plate, the ‘she’llbe right, mate’ side, would rather spend the money on fuel, tyres and beer. (we have mate, thanks for that)

Ok, please help me. Would you put it back like this? Any of it?

All comments welcome. Please feel free to shout.

I’m off to make a call or two about used parts …

Re: A Clutch of Questions

Posted: Tue Aug 10, 2010 3:19 am
by Deleted User 61
You can spend a few handfuls of cash now, and most likely never have to worry about that part, again.
Or you can put it off a while and replace the spring and pressure plate.

Has the clutch been slipping at all?

With the history of cables breaking (are you keeping your barrels lubed?), you might want to consider a complete new package. That is what I have always heard to do. I figured I would just buy a couple of parts at a time, to lessen the blow.

Re: A Clutch of Questions

Posted: Tue Aug 10, 2010 4:42 am
by Airbear
G'day Rob.
No, the clutch has not slipped since I replaced the seals 5 years ago, and I'm a great believer in the lubing of the barrels - it's one of my favourite things. One of the clutch cables was a sadly deficient example purchased from BMW at great expense. It only lasted a month. I now have a spare permanently taped to the bike.

I've just been checking prices of new parts from Motobins. Not bad at all, and the Oz Buck is pretty good against the Brit Quid just now. I'm thinking that I'll get the pressure ring skimmed a bit locally, and maybe buy a new spring, pressure plate and friction plate (I have just discovered that it is significantly thicker towards the centre (O, all right Mr Fekkin' American Fascist Bastard Spellchecker, center).

Your line, "... and most likely never have to worry about that part, again" appeals.

Anyway, a bit more price checking. I'll get back.

Re: A Clutch of Questions

Posted: Tue Aug 10, 2010 7:21 am
by Kurt in S.A.
Where did you cables break? If they broke up by the hand lever, then the fitting inside the lever is not rotating with hand lever movement. I had one cable break that way...I didn't understand what was happening. I haven't heard of a cable breaking any other way.

If it were me, I'd replace all parts just for the peace of mind. The spring is at a minimum height. It left marks on the pressure plate. Unevenness on other parts. Seems to me that things won't match up if you keep some parts and install other new ones. Methinks you won't be happy when you get it all together and you'll grumble at every gear change.

Kurt in S.A.

Re: A Clutch of Questions

Posted: Tue Aug 10, 2010 7:43 am
by dougie
New parts.
And you were correct - c e n t r e (we gotta stick together).

Re: A Clutch of Questions

Posted: Tue Aug 10, 2010 5:39 pm
by Deleted User 61
I got no problem with centre. 'uck em.

Re: A Clutch of Questions

Posted: Tue Aug 10, 2010 6:13 pm
by dougie
Rob -
Some folks down your way might view that as treason.
Remember "Freedom Fries"?

Re: A Clutch of Questions

Posted: Tue Aug 10, 2010 6:24 pm
by Airbear
Okay, with my first coffee of the day slipping down nicely there is some resolve happening. I am going to buy a new friction plate, pressure plate and diaphragm spring from Motobins. About OZ$ 185 plus postage from the UK. The postage will hurt a bit, and it’ll take some time to get here, but there is a lot to do in the meantime. I’ll get a little bit of material skimmed off the pressure ring by my favourite local machinist.

Thanks Kurt. Both cables broke at the handlebar lever end. The first was an old one, and yes, the barrel in the lever was dry. The second one is still a sore point. OEM from BMW, $82, and it was well greased at the lever barrel. The cable inner simply pulled out of the barrel after a month. I may never enter a BMW boutique again.

Doug, thanks for not shouting. Despite my invitation to do so, I am relieved - got a bit of a hangover this morning. And yes, CENTRE it is. I think god made Canadians to give North America some respectability. I still want one.

Rob, I don't care what anyone says, you are a true gentleman.

Another question. Mr Clymer stresses that the clutch parts should be marked so they go back the same way. Does anyone know of a (simple) way to balance these parts?

Re: A Clutch of Questions

Posted: Tue Aug 10, 2010 6:57 pm
by Deleted User 61
$82 dollars? Wow, was this before the internet?

I can't decide if my connection to the world has saved me more money or cost me more!

I have yet to remember to mark parts when I take them apart. :oops:

If the parts could be rigged on a lathe some-how, perhaps. Or, start up your engine with the transmission out? That might prove interesting.

Re: A Clutch of Questions

Posted: Tue Aug 10, 2010 8:18 pm
by Airbear
The $82 OEM clutch cable saga happened two years ago in The Wrong Side of a Strange City (the leafy middle-class suburbs of Melbourne). I had to find a working phonebox and phone a friend who had the courage to drive into the city, brave all the shiny things at BMW Southbank, and deliver the cable to me. I am forever indebted, but really pissed off at the quality of the cable.