I recently rebuilt my bike which has been off the road for 3 years.

I refitted my Shimano SLX M675 brakes, which I bought three years ago used them for a few months and just as the bike have been unused since.

I cleaned any dirt off the pistons with a cotton bud soaked in shimano mineral oil and also lubricated the pistons before pushing them back into the calliper, I then cleaned it all off with a cloth lightly soaked in isopropyl alcohol.

I bled up my brakes and fitted the pads on new discs (new wheels not centrelock, so new 6 bolt discs required) they squealed like mad, I removed the pads, sanded them down, cleaned the discs with isopropyl alcohol, cleaned all inside the callipers again with a cotton bud soaked in isopropyl alcohol again, I even soaked the pads in isopropyl alcohol, refit the squeal stopped.

After a shakedown ride it is back, I have removed the pads to find mineral oil on the back of them and on my pistons too, however this is true for both my front and rear brakes, with both pistons wet on the rear brake. So I assume my piston seals have failed, surprising… with both front and rear failing, what could have caused this to happen, could it be something else? Also considering I haven’t done many miles on these brakes still on original organic pads….

Thank you mt

You sure its not just excess mineral oil from when you cleaned them up prior to reactivating them?
Clean them again and then see if they get wet again.

As much as I love Shimano brakes and still use them I have to admit they are not the most reliable with leaking piston seals being one of the most common faults with them. This is purely based on my experiences and from reading online comments. So a seal failure could be highly likely.

Possibly the lack of use has meant the seals are not lubricated by the oil and have dried and perished?

I’ve always used shimano, but last week came back to my fs that hadn’t been used since last summer and the rear caliper had leaked from the piston seals. Slx m665

I’m in a similar boat. The lever on my RS-785s road brakes pulled to the bar yesterday. Mineral oil everywhere.

I bled the brake last night, but after any pressure, the same thing happened again.

I was hoping to take the bike away this weekend, and there are no RS-785 calipers available anywhere in the UK that I can find any more. 🙁

I guess the closest other option is M785 XT caliper and new banjo hose. Do I have other options? XTR race is super expensive.

Highly unlikely to be a seal failure, even less likely that seals in two different calipers have failed simultaneously. Clean and re-check would be my advice. It’s probably residue from your previous work.

Brake noise; because you have fitted a new rotor then it’s perfectly possible this has caused the noise. Changing one component can be enough to initiate a noise that you never had before.

It’s about accidental alignment of resonant frequencies and forcing energy. This new disc probably has a different set of resonant frequencies to the previous disc and one of them aligns with the force/energy you use to brake.

matts – try Swinnerton Cycles in Stoke On Trent or Cambridge Cycle Co in Pampisford, Cambridge.

Thanks. Full RRP. Nightmare.

In my experience shimano seals deteriorate over time, me and mates have numerous instances of said problem. Great brakes but probably best to think of them as disposable

Hmm,
Same issue with rs785.
Just been sent a new caliper under warranty.
Still squealing!
Just put a new olive on and tried some different pads.
Gonna bed in later.
Did notice a drop of oil behind pads though!
Mite be going back again under warranty!
Max

Did you clean the disc? It could be contaminated causing the squealing

I too have just had issues for months with old Shimano brake sets. Compounded by me trying to clean them and buying useless Disc Brake Cleaner from Halfords – that made matters worse.
I could resurrect all three brakes by either IPA cleaning and/or oven baking – but within a ride or two they had reverted to less power and no bite…

I have shiny new Magura’s now.

I could resurrect all three brakes by either IPA cleaning

Although it can cure most ills, I don’t think beer is the answer here.

Sorry to contradict you JAG, but this is a very common problem with Shimano hydraulics with lots of folk posting similar experiences. The only brake they do that doesn’t get this problem regularly reported is XTR. Possibly because it is so expensive that very few folk actually buy it…
Joking aside, it is a royal pain when this happens. I’ve had it 4 times on my rigid road 29er with just one brake; front BB7 has been fine for years of use, while I’ve replaced the rear caliper 4 times now. originally it was an XT, then 2 x Deore and then one new 2015 LX (not SLX- they do a touring LX groupset now too). All went on brand new, all have leaked visibly from their piston seals after 8-16 months on the bike. Unfortunately, BB7 doesn’t fit inside the rear triangle of this bike or I’d have changed it years ago. Hope is the only major brake manufacturer that doesn’t have a serious flaw in their design or reliability. Avid/Sram tend to have the opposite problem; their seals dry out and stick in the caliper, equally writing it off after they’ve had enough hard use.
If the contamination of a Shimano brake is slight, you can burn it off, clean up and get going again but it will soon return.

Having similar issues here on a set of SLX with less than 200 miles on them .

Squealing brakes so new pads , Cleaned the rotors after lightly sanding them and still squealing with loss of feel in the front brake , took pads out and they were wet and i could see fluid weeping from around the piston seals .

Guess i need to suck it up and buy new calipers and Rotors to eliminate these issues ?

If they’re less than 2 years old you can send them back under warranty.

Mine were from CRC (can’t fault CRC’s service on this), and they offered me either new Shimano brakes, a credit note or cash.

I *Hope* you can get a credit note and get something else.

I’m with @highlandman – Shimano did go through a period of seal problems, and their retailers were happily replacing calipers. as per @oldandpstit said – 2 years is EU standard for warranty – if they’re older, a new caliper should fix it – i believe the newer calipers should be backwards comaptible with most recentish levers in terms of master/slave cyclinder volumes. I’ve looked several times and not been able to find a seal service kit. No need for new rotors though – just clean them up with Isopropyl or brake cleaner.

Warranty ran out 6 days ago lol .

Bought them from Wiggle so will send an email nothing to lose i guess.

Had this with a set of Deore brakes. Rear went first which was eventually replaced by On-One (don’t ask) under warranty. In the meantime I’d bought another set new to keep me riding. Then a couple of months ago the front caliper exhibited the same behaviour as the OP. So took the spare caliper from the warranty replacement and popped it on. I’ve found that they seem to go after a period of no use. Don’t know if the seals dry out or what.

Anyway when the next set goes I’m probably going to bite the bullet and get a set of Hope brakes. Expensive but I got a rebuild kit for my old mini brake a few years back before flogging them on eBay.

Warranty ran out 6 days ago lol .

Bought them from Wiggle so will send an email nothing to lose i guess.

Well Wiggle dont wanna know and quoted Shimano are strict and would not take them back as 6 days over the warranty period .

So will bite the bullet and buy new calipers .

https://www.bikeradar.com/road/news/article/shimano-r785-road-hydraulic-disc-caliper-failure-45088/

My front Caliper was replaced under warranty after diagnosed with a split piston – it would be all good if the warranty replacement hasnt also failed.

I have had the bike 18 months and have not had a banshee free ride!