Hi Guys,

Sorry if posted in wrong section. Have had Wilwood Dual Master Cylinders (One for front / One for rear) on my MK for last few years with no issue. I noticed the pedal suddenly went a little spongey so have gone to do a fluid flush and the rear MC was empty. Thinking it was a leak I topped it up and tried to trace the leak but have struggled to see where it is coming from or if there even is a leak at all! The fluid level seems to be staying full now which is odd.

The pedal is impossible to get bled up now so i am assuming a leak is coming from somewhere. Just wondering if anyone has experienced similar or if i should be looking more towards the rear callipers being the issue.

Thanks,
Will

[Edited on 29/3/17 by WillisRR]

A leak from the MC would be obvious so its gotta be somewhere else. Cant imagine it being hard to spot TBH.

what rear callipers do you have.
it was/is quite common for these to be fitted upside down, which makes bleeding bleedin difficult.

How big is your fluid reservoir? And how worn are your brake pads?

Along the way, the thinner the brake pads become because of wearing out, the lower the brake fluid level is in the reservoir, because the pistons in the calipers are more "out" to compensate the loss of pad's thickness. There is a bigger volume of brake fluid in the caliper, so less in the reservoir. It is even truer with multiple piston calipers. And if the reservoir is too small, this can even empty it.

So if you have no leak, and your brake pads are worn out, it might be the problem?

Try removing the rubber boot around the actuating rod, mine was full of fluid when the master cylinder seal had give up!

Thanks for the help guys. Yeah totally with you on the rear pads but they are ok so can't be that. The reservoirs are tiny though but we flushed so much through.

Interesting about the calliper being mounted upside down. I think they are actually so this could be it! They are oem sierra rear callipers and the bleed nipples are at the bottom of the calliper so can see how air could easily be trapped in the system!

Agreed that the leak should be a very easy spot!

Thanks Se7enspot, i will try that before I commit to a new MC! At £40 each it's worth doing for such little outlay.

Thanks again for the help guys.

But you said in your original post that it had worked "for last few years with no issue."

This confuses me.

What has introduced air where none was before?

No clue mate, as Voucht mentioned, maybe the pad level got low enough to reduce fluid res and it sucked up a portion of air which is now trapped at the top of the rear callipers.

Had a good chat with Sean at MK at lunch and he has given me the lowdown on how to properly bleed these (remove and place at the top of the disk).

Will give this a go, check master cylinder actuating rods for leak and then be in a better position I hope!