clutch slave cylinder piston seal

cape

Hero member
Location
Finland
In past ten years, I have replaced clutch slave cylinder piston seal three times. The last one lasted 20000km before starting to leak. So obviously the epdm O-ring I have used (29.74x3.53) isn't a robust solution. Would anybody know a source for better seal for 30mm piston? I belive the original had rectangular cross-section (same as brake piston seals). So, looking for dimensions, product codes or direct online source.

Ciao,
Sami
 

sfcpiet

Administrator
Staff member
Location
NRW, Germany
No Sami, the originals were simple o-rings, no better than the replacements we fit every couple of years. I've never found a rectangular ring in there. I don't think rectangular rings would last long in this application anyway, piston travel is too much for them to cope. Then there would also be the resistance for the returning piston, not good for a clean clutch action.

piet
 

cape

Hero member
Location
Finland
OK, thanks for the info piet. I value your experience, but that's still just your opinion, or have you tried a cross-sectioned seal? Or has anyone else? The point you make about possible disadvantages with new seal type may turn out to be true, but I'm considering to give it a go anyway, if I'm able to find a suitable one. Replacing the O-ring every couple of years is just frustrating, so an alternative solution is worth a try.

Sami
 

CLEMTOG

Hero member
I would suggest that somewhere in the drive train of your clutch actuatuion there is a sticky bit, causing the piston to turn, (rotate) when you lift the clutch, check out the cross push bar for wear and straightness, the two pushrods, check their ends and the ball in the middle of the rods and the ball pressed into the slave piston.
The O ring you quote is a British Standard type and is .25mm under sized, I agree that metric 30mm seals (30 x 3.5) in EPDM are hard to find, (strangley the 31mmx 3.5mm are not) this makes your failure sooner rather than later

BS 217 EPDM 70 is 29.75mm x 3.53mm
CLEM
 

cape

Hero member
Location
Finland
Thanks Clem. Cross bar is OK, recently turned 90 degrees. Pushrods and balls were renewed maybe two years ago, so they should be OK as well. Good tip about the O-ring size though. I just checked and 30x3.5 is actually quite easy to find.
 

Laverdalothar

Hero member
Location
Germany
Modifying a clutch slave cylinder to accept the rectangular type of sealing ring is an interesting idea. It works on brake calipers (that only move very short distances though, as Piet correctly pointed out). I checke for clutch slave seals/oil-seals/O-rings and could not find any application that uses a rectangular shaped sealing ring for a clutch cylinder. Must be a reason and I suppose it is what Piet wrote: it is to sticky and would cause to much wear.

If your piston turns inside the clutch slave housing, there is something seriously wrong. Do you pull the clutch lever when at traffic lights for longer and stand there with the gear engaged? If so - don't do that! This gives a lot of force to the whole mechanism and is causing a lot (!) of wear...

The replacement every couple of years is nothing that would frustrate me. You need to exchange the fluid anyway every 2 years or so latest, replacing the O-Ring is another 10 Minutes during that operation... Just make it a preventive habbit instead of a road-side fix. Also: using round type O-Rings increases the chance you can buy one at a local shop rather than rectangular shaped ones that you need to order...
 
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piranha-bro2

Hero member
Location
Melbourne
I'm pretty sure the rectangular profile of caliper seals is specifically designed to add some 'spring' force to the piston to enable it to move inward for braking and then retract ever so slightly after application, creating clearance between pad and disc rotor.
 

CLEMTOG

Hero member
hello cape, i couldn't find them and I use the BS (British standard) ones with very little trouble, when they do start to leak a buit, it is easy to top up the reservoir and that will (usually0 be ok for another 2000 miles, but I carry spares and they can change at the roadside ESPECIALLY if you have a Jota Joe side stand kit.
I would (however) like the correct seal of 31mmx3.5mm in EPDM if you point me to your supplier I will buy 50
CLEM
 
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