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Leaky master cylinder mk3 850



New to this (Norton and classics) and am having some problems with my master cylinder/ brake. When I bought the bike it had rust on the piston etc and it was apparent there was a slow leak (see previous post). In line with advice and the manual I have replaced the internals seals etc but also the spring and piston. All was looking okay as it pressured etc. But a couple of days later it still look to be leaking/ weeping v slow. I am thinking next step is to replace the whole part as the must be some pitting inside but wanted to see if there was anything other ideas apparent from have another go as I am sure it went together properly. Also if I was to replace is it best just to get the part from Andover Norton or other?




Instead of a new part why not get it sleeved to a smaller diameter to improve brake feel and fix the leaks.


RGM's resleeve is for the front, so you just need to ask if it also applies to the MK3. As the master cylinder repair kit and the piston as well, sold by Andover Norton, fit all Norton front master cylinders its highly likely it does.

No need to apologise for the this website, that should come from the NOC for still using it when much better forum software is available.  



Just a short note to suggest that John might try using the "Search" facility at the top of each page?

When I entered the words "Sleeve Master Cylinder" It found 3 pages of references within 2 seconds?

The site's Drupal Forum software is'nt the latest but it does allow members not to have to log in twice on the website and it's fairly fast and simple to use?




You know the forum is useless but you still do nothing, all talk no action.


Website jumping, still doing it even know. The best the committee can come up with is




Another one

This jumping is another one of the failures of this web site. It has been like this, getting worse for many months/years. The spell checker does not work on a 'post' in Chrome either. At the AGM the Committee was tasked with a new eCommerce site and and a new web site provider.'

Results in

 'Smith Webmaster on Mon, 19/04/2021

Website jumping


The existing web site (excluding the NOC Shop) will continue for the foreseeable future, but will be subject of improvements and investment at a later stage.'

So doing nothing yet again.



Hi John,

The web site jumping has been vastly improved some months ago - it was caused by to many photos of our bikes in the top ribbon causing delay in the page loading. Since we have removed many of these photos the issue is vastly reduced, but not completely.

The NOC Shop is now on a new platform introduced on 31st August.

Regards - Paul.



So you acknowledge the issue is still there but at a lower level in Sept but did not see fit to post to the original thread with an update despite several posts confirming the issue was still there in June.


Update, I have spoken to RGM and they no longer carry out the sleeving service only the kits so am looking for another company as it is not something I can do. If anyone knows a company please send through as my initial research isn't proving fruitful :). If not might need to replace, which would be a shame but at least I'll be getting her up a running.



Evening Nathan

I have relined a couple of master cylinders for clients using the RGM kit bits. Send me your master cylinder and i can do it for you.

Where abouts are you in the country?

PM me for more info




Your wrong - I explained the issue and the action we took at the time of the issue within a forum thread that described the issue.

Regards - Paul.


But the fix was not a complete fix, the issue is still there at a lower level.

Why don't you start a thread asking members what improvements are required for a new/replacement forum so you know what's needed. 


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