Leaky hydraulics....?

[Ham]

A confession: my Metrea build bike has not been ridden for about 4 months until last week.

Why is this relevant? because, sometime over the non-ridden period the front disc has become contaminated, apparently by brake fluid, on the basis of the noise and lack of stop.

This is a little on the weird side. I got the build done by a shimano specialist LBS (who have now folded) on the basis that while nobody will have experience with Metrea, they would likely be able to find out how to build and do a decent job (also, I bought the bits through them on bike scheme). When I first collected the bike, I had a problem with front pad contamination, which they ended up resolving by replacing the caliper. It was fine after that, and used for several months without issue.

My inclination is that it has to be the pipe to R785 caliper, but given the history, I have to wonder. Also, I'm surprised that any fluid seeps out when not in use, of what must be a pretty well sealed system given that it worked well, just doesn't sound logical. I'm going to take it into an LBS anyhow (not ever made a hydraulic connection, I don't intend to start now) but wondered if anyone else has had similar experience or suggestion.

[Torslanda]

If the bike has been stored upright then the contaminated pads are a symptom. My guess would be that a hose connector was loose but I'm many miles away from hands on...

[Ham]

Well, yes, that's what I thought, but how come a  system that was fine for riding has deteriorated on keeping ? (and it is only about 9 months since it was finished)

[Cudzoziemiec]

If it's been stored in a shed or garage, could some solvent have corroded the connectors? Petrol or WD40 or something? Just a random guess based on complete ignorance and wild imagination.

[Brucey]

the piston seals in (AFAICT all) shimano  hydraulic brakes are subject to leakage, arising because of corrosion. If the bike has been used it might be that.  If the bike has never seen the weather, the leak could be somewhere (anywhere) else.

To find the leak, clean the oil up as best you can, and then leave the bike with an elastic band around the brake lever (pulling the brake on) and with some tissues in/around the caliper.  Any significant leak will show on the tissues in a few hours (or less) and can be located.

cheers

[Chris N]

Leaky calipers are a known problem with Shimano brakes. Sometimes it’s the piston seal but it could also be the o rings between the two caliper halves. Leads to lots of noise and not much braking.

[jiberjaber]

Leaky calipers are a known problem with Shimano brakes. Sometimes it’s the piston seal but it could also be the o rings between the two caliper halves. Leads to lots of noise and not much braking.

+1 on the o-ring between the caliper shells - you can get replacement nitrile ones from ebay which are slightly thicker - though don't forget your Shimano parts may have (2 year) warranty still with Madison - worth exploring before you go to the extents of splitting the caliper to repair.

[Torslanda]

Practically speaking the first thing you need is some brake cleaner. Remove the wheel and brake pads then clean the caliper. The brake cleaner will evaporate and leave a clean dry surface. Any leak should be obvious after a day or so.

Soaking the pads in the solvent may or may not restore the friction quality. It's a lottery but there are loads of alternatives for little money, no great loss.

[Ham]

Thanks, there's definitely a few ideas to try. While it hasn't been mollycoddled, I don't think it has seen much bad weather, certainly much less than my stainless CDF, which has the same caliper, and no obvious signs of corrosion. It's spent the time under a tarpaulin hanging on the wall of the side alley to my house, so may have become damp, not wet. I wouldn't bother trying to save contaminated pads.

[Brucey]

the #1 killer is any winter use and then a period of storage/dry use only. Any salt water that might have penetrated down the piston bores is not pushed/rinsed out and the corrosion goes on apace. I've examined multiple failed calipers and in each case it was clear that (salty) water accumulated in the low spot in the piston seal groove and corroded the groove until the seal was lifted and caused a leak. 

I have heard tell of leaky caliper half O-rings but none of the failed calipers I have examined have had this fault.  Calipers with bad O-rings all leaked straight away (pretty much from the start) and went back for warranty. You never know of course, but not leaking for a reasonable period of use and then leaking is more suggestive of piston seal groove corrosion to me.

Anyway once you find out the leak location you will know what to do for the best.

cheers

[Ben T]

the #1 killer is any winter use and then a period of storage/dry use only. Any salt water that might have penetrated down the piston bores is not pushed/rinsed out and the corrosion goes on apace. I've examined multiple failed calipers and in each case it was clear that (salty) water accumulated in the low spot in the piston seal groove and corroded the groove until the seal was lifted and caused a leak. 

I have heard tell of leaky caliper half O-rings but none of the failed calipers I have examined have had this fault.  Calipers with bad O-rings all leaked straight away (pretty much from the start) and went back for warranty. You never know of course, but not leaking for a reasonable period of use and then leaking is more suggestive of piston seal groove corrosion to me.

Anyway once you find out the leak location you will know what to do for the best.

cheers

Is there a maintenance regime to ward this off, on a " prevention" rather than "cure" basis?

[Brucey]

the best way of preventing this is to

1) on a clean/new caliper, extend the pistons as far as is safe (about 3mm) coat the pistons with silicone grease, and push them back. or
2) use Silicone plumbers spray as per Hope's recommendations
3) don't ride in the winter
4) wash the bike every time it is used in the winter (clean water does not produce the same kind of corrosion, the salt is the killer)
5) use the bike regularly; water is pushed out of the seals every time the brake is applied and heat helps to drive moisture out too.

BTW in most cases when the piston seal is leaking, the caliper body (which is usually painted) is showing signs of distress too, with the paint bubbling and lifting in places, for similar reasons.

Note that if you apply grease to a used brake and there is water in the seal area already, you may just trap it in there, which could be worse than doing nothing.


cheers

[zigzag]

front mudflap almost reaching the floor is good prevention against salty crud, only it has to be bodged one way or another