Author Topic: Transmission slipping at high revs and have no idea why  (Read 2009 times)

Offline owain

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Righto, I've had this problem for a while now and I can't seem to find a solution. The issue is that I'm losing transmission at high revs i.e. it feels like the clutch is slipping. I've fitted new friction plates into the clutch and clutch was nice and dry when I inspected it. The clutch springs are set really tight. A few more turns on the spring nuts and the springs would be completely compressed. The shock absorber spring nut is on tight and the spring is fully compressed. I'm scratching my head as to what the problem is. Any ideas would be appreciated! Cheers
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Online Klaus

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Hi owain,
check the sideplay of your cluthrod. There must be a non working space about 1,5 mm at the rod befor the plates lift.
cheers Klaus


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Online bsa-bill

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Have you done anything to your clutch lately
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline owain

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Cheers Klaus, will have a look if there is a gap on the clutch push rod.

Yeh, the bike has had a full mechanical restoration (bought it as a running basket case) i.e. crank grinded. oversized bore. replaced damaged gear sprockets. no new parts for the clutch though except for new friction plates. Difficult to say whether that is to blame as I didn't ride it with the old friction plates on.
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Offline duTch

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 I'd like to give a solution, but can't but let's specify here that I believe yours is a 6 Spring Plunger clutch, and mine also does it sometimes but only under load if I give it some...

  I also can't get any more spring preload than you for the same reason (just short of coil binding). I had five friction plates in as per list, but I wasn't happy with the minimal engagement of the adjuster nuts, left one out last time and swap one out/one in each time I have it apart...
 The only thing I can think of is the springs may have to many winds (too soft)
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
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Offline RoyC

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Have you tried using ATF ? Dexron allows some slippage but Ford F type gives a much  more positive grip.
My bike is a 1958 A7SS
Staffordshire UK

Offline owain

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Are these different types of friction plate? (ford f type, ATF, etc). I'm not sure the specs of the friction plates fitted, I bought them from Draganfly though..

Yeah it's a 6 spring clutch dutch. It certainly is under load as it's pulling a heavy sidecar as well. Haven't even dared taking it up any hills either (currently in mountainous North Wales)
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Offline muskrat

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G'day owain.
RorC refers to Automatic Transmission Fluid of the Ford F type.
What oil do you have in the primary? If it's a multigrade car oil it will have friction modifiers that will cause slippage.
Cheers
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Online KiwiGF

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Wear on the chain wheel and inner clutch basket can cause clutch plates to stick and clutch to drag and slip, no amount of spring pressure will overcome that problem, a file taken to make the surfaces smooth again can be used to fix that up.

It sounds like you have had to compress the springs too much, this should be making it really hard to pull the clutch lever in! If not I would suspect incorrect springs.

Note even with some free play in the clutch cable when the engine is cold, this can disappear when it's hot and even a small error in adjustment this can cause slip.

Some of the cheaper all metal clutch plates are made too thin and can can cause problems. They should be around 1.6mm thick from memory.



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Online bsa-bill

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some clutches require a plain plate to be put in first to take up play as the first friction pale will not reach the base of the clutch basket ( the tangs stop it going in far enough), If I recall correctly I also think the usual BSA diagram used in many places  has the plates in the wrong order, this mat be one and the same thing.
This might explain why it drives at low revs and slips at high
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline duTch

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Re: Transmission slipping at high revs and have no idea why
« Reply #10 on: 15.09. 2017 09:30 »

 
Quote
.. but let's specify here that I believe yours is a 6 Spring Plunger clutch, ...
*????*

 Before we get carried away,  let's confirm that it's a Plunger six spring clutch, which is a completely different animal to swing-arm six spring clutch (emphasis on 'animal')...?
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Offline Topdad

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Re: Transmission slipping at high revs and have no idea why
« Reply #11 on: 15.09. 2017 10:52 »
Looks like a plunger in Owain's picture . So should be a great clutch ,well up to dealing with a mere double sidecar. By the way Owain how the hell do you miss hills/mountains in north wales ??? where are you at the moment .cheers Bob
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Offline owain

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Re: Transmission slipping at high revs and have no idea why
« Reply #12 on: 15.09. 2017 12:40 »
Yep, can confirm that it is 6 spring plunger clutch. I'm going to remove the clutch plates, measure the spring length and file the inner basket to make sure that all the friction and plane plates can travel freely i.e. don't jam up.

Haha I'm severely limited to the promenade in Llandudno  ;D
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Offline owain

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Re: Transmission slipping at high revs and have no idea why
« Reply #13 on: 15.09. 2017 15:58 »
Righto, I've taken all the clutch plates out there are 4x 1.6mm thick plain plates and 1x 3mm thick plain plate as well as 5 friction plates. Springs measure approx 36mm in length. I'm using 20w/50 mineral oil in the transmission case...but it's a dry clutch so I wouldn't expect oil to be the culprit if the clutch is staying dry.

I lightly filed the clutch plate 'tracks'  in the inner and outer clutch basket. Removed some muck that was on the clutch basket wall. Degreased it all then applied a thin layer of lithium grease into each clutch plate track. I thought this last step might be a bit risky as I don't think grease on the clutch plates would be particularly helpful but I applied it carefully so that it is only a thin layer in the tracks only. My rationale was that it should facilitate the free movement of the clutch plates when pulling the clutch lever in.

Everything is back on now and so I'm gonna go and menace the pensioners on the prom with a lot of throttle. ;)
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Offline owain

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Re: Transmission slipping at high revs and have no idea why
« Reply #14 on: 15.09. 2017 17:16 »
No luck. Still slipping. Quite hairy when I'm pulling out of junctions. Slips a lot.
Sweden & North Wales
'50 BSA A10
'69 BSA A75R