Vitpilen 701 Clutch master cylinder seal

[monkeynuts]

I’ve had to dreaded clutch master cylinder failure again, the first time it happened, I stripped, cleaned the cylinder and seals. Reassembled it and it all worked.
It finally failed again. On dismantling the piston and seals, I noticed that the seal seems to have swelled, and this is what has caused it to jam and not return.

So looking at the extortionate price they charge for the seal kit, £65 in the uk, I thought that I would see if I could obtain the main seal, or a similar seal !
I found a company that sells small hydraulic seals, so thought is would give it a shot, nothing to loose. Two different type of seals ordered. On delivery one seems to be a little too hard and would be very difficult to fit over the plunger body, and possibly too hard for the cylinder walls. The other seal is firmer than the original , but as that seal has swelled, it would of gone soft.
Long story short, it fits, it bled up straight away, and when the clutch was held in, it didn’t pass and lat the clutch start grabbing.
So I have the £65 kit on order as a backup just in case , but fingers crossed this will work.
I will give some feed back if it fails in the future.

Cost of the seal. £4.44, postage £5.78.

Hydraulic seal US-6X12X5-6-NBR90 - 6x12x5 mm | 123Bearing

<p>The Hydraulic Seal with the reference US-6X12X5-6-NBR90 has an inner diameter of<span> 6 mm, an outer diameter of 12 mm and a thickness of 5 mm. It is made of NBR.</span></p>

www.123bearing.co.uk

 

[Vatte]

Thanks for sharing your experience and for the investigation.

Regarding the specs shouldn't a EPDM type suits better for the brake fluid which is used for the clutch, also?
The NBR is listed for oil only.

 

[monkeynuts]

Im seeing how it goes, the standard seals are crap. Nothing to loose as it is the clutch and not the brakes

The EPDM seal is a bit stiff and hard to get onto the plunger. Hot water would help !

As I mentioned, I’m going to see how it goes, any problems with the seal and I will let everyone know. For a fraction of the price compared to the seal kit, nothing ventured, nothing gained !

 

[monkeynuts]

Update.
I managed to get the EPDM seal onto the plunger, the NBR seal is currently in a contain with some DOT 5.1 brake fluid to see if it swells.

I had my first ride with the EPDM seal fitted and all is well, no signs of any kind of leak, the leaver is returning fully. So all good

 

[monkeynuts]

Update
So far the new seal is working with no problems at all.
I have just picked up the Madura seal kit and thought I would measure the new seal against the old one. The old seal has swelled to increase the diameter of the seal by approximately 2mm. For a small seal it is quite a lot.
Going to leave the seal in that I have already got and keep the kit as a backup for future if the is a problem. If there are any changes, I will come back with some feedback.

 

[Ben Oldschool]

Last Summer in the extreme heat & humidity of South Louisiana my clutch lever seemed to be failing at a traffic light. The clutch was not disengaging completely. I actually had to kill the engine to stop from pulling out into the intersection. I was able to restart and stay in clean air for the next 5 miles home. I have not had that problem since. That was the hottest day ever riding that bike in traffic and working the clutch so much… wondering if and when it might happen again.

 

[monkeynuts]

Has your slave cylinder been changed or upgraded ?
There is also a possibility that with the high heat, any moisture in the clutch fluid could have been boiling. Same as if you had air in the system ! That maybe BS

The usual symptoms of the master cylinder seal failing is the leaver not retuning correctly and the clutch slipping under full load.