So after bleeding my really mushy brakes , I was quite pleased (my first attempt) that the levers had a nice solid feel. Now I’ve noticed the rear master cylinder/reservoir weeps slightly when left over night and a small amount of fluid collects just under the lever….. Almost like condensation.

After I bled the brakes, I topped up the reservoir and rolled the rubber seal in so as not to trap air. The brakes are still holding strong and no fluid leaks when the lever is squeezed. I’m at a loss as to what it could be. Any ideas?

take the rubber seal out and hold it up to a light to check for any holes in it.
The seals are not very strong so could have a hole/cut in it.
Seals only cost a couple of quid from CRC.
Also the bolts aren’t supposed to be done up super tight, just nip them up and the seal should do the rest of the work.
I’m reckoning thats whats causing the leakage

Ah thanks mate. I’ll have a look at the seals tomorrow. I do remember tightening them really really tight :-/ Cheers for the advice.

I did this a few weeks ago and got the same thing happening. I took out the seals and dried them off so the top was fairly dry. Rolled it on and tightened up. seemed to sort the weeping.

It also only takes a tiny amount of brake fluid residue to create a condensation effect as it’s hygroscopic and so attracts moisture from the air. And there’s quite a bit of that around at the moment.

“hygroscopic”. No shame in admitting I had to google that 😀 When I checked yesterday it is only a small amount of fluid and it’s not as strong smelling as ‘neat’ brake fluid, so your hygroscopic theory makes sense. Thanks for that…. I’ve learned something new today.

Ok. So last night I cleaned and dried the rubber seal, inspected it for holes etc and rolled it back into the reservoir, replaced the cap and was careful not to over tighten the bolts. Checked it this morning and i still have a slight amount of fluid gathered under the lever reservoir.

Any ideas? or is it just a case of replacing the seal with a new one and seeing how that goes?

Many thanks. Steve

Is it coming from the breathing hole?

Not sure that’s what it’s actually called but there’s a small hole near the top of the cylinder somewhere IIRC.

Mine leaked from there a while back, I reseated the cap and diaphragm and everything was cool again.

Maybe you need to experiment with how tight your fastening the cap down, or try new diaphragms (they’re probably cheap enough).

It could well be the breathing hole, I did wonder what it was for. I cant see anything weeping out of it when I squeeze the lever. I guess it’s gonna be trial and error… at least it’s not pissing out. I’m due to ride it this weekend so I hope i can sort it by then.

Thanks for the reply.

I rode mine like it a few times, nothing bad happened.

Disclaimer: Poster assumes no responsibility if something bad happens.

I’ve just been through the ‘fluid at the lower vent hole’ scenario. It was weeping for about three weeks before I took off the top cap to look carefully. I figured it must be leaking diaphragm, and Nick at Hope kindly sent me replacements. After cleaning / checking the original diaphragm for leaks, (filled it with IPA and sat it on a tissue)- no leaks; I realised it must just have been excess fluid that had got into the upper folds of the rubber when I’d bled the brakes after hose shortening.

So, a further three weeks after meticulously re-fitting & ensuring no excess fluid, and no more fluid at the vent hole. Sorted.

Hopes’ service is great I have to say, I emailed Nick to ask what I owed them for the diaphragms they’d sent (only fair, as it wasn’t a warranty issue after all), and he told me to keep them with their compliments.