HELP! Have i knackered my master cylinder?

[jetblack]

Just been bleeding my brakes.

Rear went fine, then came to do the front. Followed the usual process. Started ok, got a bit of fluid starting to move through the bleed hose on the first 2 or 2 squeezes of the brake lever then nothing- i squeeze the lever and nothing is happening. Its just gone sloppy and no fluid is moving.

Tried re-tightening the bleed nipple on the caliper and the lever is still sloppy and it is not applying the brakes.

tried on both bleed nipples, couple of times and same symptoms.

Have i just knackered the master cylinder seals or am i missing something?

[CMSMJ1]

Any fluid in the reservoir??

[jetblack]

yep.
Its 3/4 full.

And i should add, there doesn't appear to be anythng leaking from the cylinder- which i would expect if the seals had gone..?

[amorti]

If only the front seal has givn out, it wont make pressure but it also won't leak.

This often happens as when bleeding the seal is running dry, and along more of the bore than it usually uses. This can mean that bit has corrosion or dirt, which can finish of seals.

[jetblack]

So a refurb kit requured then?

[amorti]

So a refurb kit requured then?

Most likely yes.

You can open it up and have a look, remember that any damage AT ALL to the seals will cause them to leak at the pressures involved.

When building back up, lube ONLY with silicon grease, normal grease will eat rubber seals. I usually pack out behind the top hat seal with silicon grease, they last forever this way.

[jetblack]

Ive got some red rubber grease that I use on slider pins on my car. Will that be ok?

[jetblack]

Oh and do I need to buy a genuine kit or are the pattern ones fine? And is the kit all I need or do I need new washers on the hose banjo bolt?

[amorti]

red rubber grease is silicon grease with dye in it, perfect to use.

you will need the rebuild kit and it is sensible to replace the two copper washers that you disturb, otherwise you will get a mystifying air leak from where they are no longer exactly flat. I have had mixed success with pattern brake (caliper) seals, so if you want to be sure it works first go I would prefer to recommend OE. I only ever tried OE repair kits and funnily enough they fit first time and work.

Top tip - also splash a bit of silicon grease on the end of the cylinder piston where the lever activates it, makes for a nice smooth lever action. A lot of people assemble this dry which simple logic says is wrong, and a lot use mineral grease, which dissolves the tophat seal.

[jetblack]

Well, the refurb kit arrived today. i've fitted it and er...still nothing. Cannot get the fluid to pump through. just get a soft lever. i can see bubbles move down the bleeder kit hose as i apply the brake and then when i come off the lever the bubbles move back to where they were.

Have tried bleeding the master cylinder by squeezing the lever whilst loosening the banjo bolt and then nipping it tight before i release the lever and repeating. no difference.

Any ideas?