Leaking Shimano Caliper Update

An attempt at consolodating some info and sharing my experiences.

Background:

Like many people, I have had a fair few leaks on Shimano brakes. Mostly Deore My current problem ones are BR-M447
But the issue seemed to span a wide range of Shimano callipers.

The fluid ends up on the pad surface. Starts with a squeak. Ends with 80% power loss and replacing pads every other ride.

The obvious assumption would seem to be that a leak coming from behind or around the piston. Eventually it makes it’s way onto the pad surface and …… :-0

After trawling this and other forums, I read about the possibility that it’s more likely to be a leak from this tiny ‘sharing/splitting’ port between the two halves of the calliper.

I read about the magic O rings….. These ones

Thanks to Wiskey for the tip.

They arrived pretty quick (within a week). Cost less than a set of non brand pads, so had to be worth a go.

Replacing the O ring was very simple.

1) Remove pads
2) Unscrew two Torx bolts that go through the calliper latterally.
3) The fluid is now free to flow around, so make sure you are not in the lounge. though in the garage setting I was in, there was only a few drops of leakage
4) The tiny O ring is fairly easy to spot. There are no springy out bits to remember the order of. Just gently pry it out and swap it for a new one. The old one was fairly flattened. Like it had been sat on. So I thought, a new, squidgier one could well make a better seal.
5) While the calliper is open, I read it was wise to rub down any points of corrosion. On the two main faces of the exposed halves, I found a fair bit of oxidisation/discolouration. It ddidn’t appear to be rough, so I wasn’t concerned it had compromised the join of the two halves. But the colour made me think it had never been a perfect seal. So I rubbed it down with some fine grit we & dry… gently.
6) Screw the calliper back together.
7) Bleed the brakes

So far so good. First ride felt good…. But on return I thought it wise to extract the pads and inspect the rear…

Oh! PLenty of visible fluid. So it didn’t work.

Could it be the piston seal after all?

With Pads being a minimum of £5 a set and potentially ruined if the leaking fluid goes a few mm further.
A calliper being around £20

It’s a really annoying 1st world connundrum. I hate having this bag of old callipers. They seem so potentially useful and I’m forced to buy new ones? Or bite the bullet wnd go Hope etc?

Anhow, there’s my attemp at consolidation.

Any thoughts feedback gratefully received. I will one more time with the 447s and try fixing some older calliper models too. I have another 9 ‘O rings’ and it’s Lockdown 😉

Shimano seem to have a real problem with this from the number of threads about it. I had some older model deores which seemed to have the issue when they weren’t even very old at all / only been used a few times (I hated the 2 finger levers on them so I was quite glad of an excuse to get something better though).

I’ve got shimano road discs which are just over 2 years old now so I feel like I’m in the zone where I could start to see issues. My solution will be swapping them for Hope RX4 road calipers which have been designed to work with shimano mineral oil systems.

I have this issue on my old XT calipers, it’s on a bike I only use infrequently and I used to need to do a brake pad bedding in procedure at the start of every ride to get them working but they have recently got worse and I think only any good for the bin.

I’m toying with buying some SLX calipers and replacing them but not sure if it’s worth retaining levers that are getting on for 10 years old, or if I should just bin the lot.

I like as much crossover as possible. Having two hard tails and a full sus and a commuter and my Wife’s stuff…. also got two growing kids about to enter the world of proper bikes… By speccing it all with Shimano and the odd bit of Clarkes, means ! big bottle of mineral oil and one bleed kit. And loads of interchangeable parts. Just makes life a little less ‘update/ungrade’ oriented.

But I’d love to be able to keep more of it working for longer. For general trail use, Deore work great for me. It’s only ever been on a wet welsh mountain, descending on my ful sus, that I’ve ever really thought about having a little more bite.

Is it just the Hope road stuff tha uses mineral oil?

dc1988, this is the problem. It’s not expensive enough to weigh up a complete upgrade. So we generally just do it. But there may be nothing much wrong with your old stuff. I mean a good bleed and some new pads and a working ‘old’ calliper is way better than a baddly set up, pad worn bit of bling. IMO

I was amazed at the ease of the procedure. I’m fishing now for one of the super experienced STW crew to come to my aid and tell me “left a bit, right a bit… that little grub screw there…”

🙂

Is it just the Hope road stuff that uses mineral oil?

I think it is – they specifically make the RX4 as a replacement for Shimano Road calipers from my understanding. They look a bit overkill with 4 pots but they also look like mtb bling for my road bike!

Whether they would work on an mtb system I don’t know. Maybe – given the post mount caliper on my shimano road system is the same as on xt mtb brakes I guess it might do?

I persevered with Shimano for a couple of years, all the same problems – squealing, contaminated pads etc, worrying that theyll fail on big rides away and constant servicing. Sacked them off for sram that I havent had to touch for over 2 years.

I think it is round the piston seal… usually.
I’ve had some XTs (around 2015) one had the squeaking problem, was just squeaking, not a noticeable loss of power – this one was sorted by replacing the hoses with Uber, which involved changing all the joins. Sorted it and the brake is still in use.
Have road calipers (R785s) on my Tripster – pretty much used every day and they’re now 6 years old and no leaking problems at all. The rear caliper has been replaced but that’s because the piston seized due to corrosion, (daily use in all weathers, see). No leakage though.
Bought a pair of the new Deore twin piston jobs for my son’s bike and one was good, the other practically pissed fluid out, didn’t get one ride out of it before returning it. Was from Rose and annoyingly they refunded without asking, so I replaced it with an XT, which is fine.

Whether they would work on an mtb system I don’t know. Maybe – given the post mount caliper on my shimano road system is the same as on xt mtb brakes I guess it might do?

No, they won’t. They are designed for the Shimano road lever master cylinder, except GRX di2 which apparently they don’t work with.

Reply I posted on another thread.

I’ve stripped and rebuilt a few of the Shimano 2 piece calipers without replacing any parts. All of the calipers that I’ve had apart have had corrosion issues in the sealing ring groove allowing fluid to seep out. Once properly cleaned and reassembled they’ve held pressure and didn’t leak. For how long???

There are plenty vids on youtube showing how to strip the calipers. Where it get awkward is getting the pistons out. I used compressed air with the caliper halves wrapped in a rag. Once out the seals are exposed and can be removed. All of the seals I looked at were like new. The O ring between the halves also in good condition. Once the seals are out it was obvious that there was dirt and corrosion in the ring groove. I polished this out using some metal polish and a synthetic brush on a Dremmel. The pistons got a quick clean up with some 1200 wet and dry and soapy water.

Reassembling I put a wee bit corrosion inhibitor in the ring groove & used an anaerobic sealer between the caliper halves. Pistons and seals given a light coating of silicon.

The alloy Shimano have used doesn’t seem very resistant to corrosion and the calipers aren’t anodised. The other thing that became obvious was how much the caliper flexes when under pressure. The two halves visibly distort & this makes the bores go out of line with each other. There were witness marks in the caliper bores where I assume the pistons had been binding.

As pointed out you can get a new caliper for 22 Euro. I don’t think I would bother refurbishing any more of these. It’s simply not worth the effort.

From the calipers I’ve had in bits they all had corrosion under the square section o ring that was creating a leak path underneath. Easy but time consuming to sort & at 22 Euro it’s a toss up whether or not to fix or replace.

I have suffered my fair share of leaks and redundant calipers. It did occur to me that when the pistons are pushed back in, for new pads for example, if they are not perfectly clean and smooth the seals could be damaged.

This leak/squeal/power loss also happens on Shimano 1 piece XTR M9000/M9020 and M9100 callipers, so I’d not be 100% certain that you’ve fixed it b replacing that o-ring when these callipers don’t have that feature and still have the same problem.

I’ve had 4 sets of XTR brakes and 4 additional callipers that have broken over a 5 year period.

With the exception of 1 set of Dura Ace callipers (because I have no choice) I have now replaced all of my brakes (8 sets) with Hope callipers or systems.

Gave up on Shimano brakes years ago, ive had leaky XT M8000, ZEE & BR785 road calipers

Wont ever run their Hydraulic brakes again

Only run Hope brakes now, never had any issues with them in the last 20 years

New Gravel bike has Sram Rival calipers, as soon as any issues arise with them they are being replaced with Hope

Stop wasting money trying to fix Shimano calipers and wasting money on new pads every time they leak

Bin em or move em on, just get rid and stop buying Shimano brakes

Mine were definitely piston seals rather than connecting port O-ring.

There does seem to be a definite pattern with the problem occurring after bikes have been left for a while, rather than ridden daily.

I would add that I’ve had no issues with reviving contaminated pads with a bit of heat. After I got my calipers replaced under warranty, I stuck the old pads back in and used them without issue until they wore out.

There does seem to be a definite pattern with the problem occurring after bikes have been left for a while, rather than ridden daily.

One of the misunderstood points about mineral oil based brake fluid is that people see it as beneficial that it doesn’t absorb water like DOT fluid. This is a mistake – when water gets into a mineral oil system, it will collect in the caliper), where it will boil when it gets hot. In a DOT system, it will be dispersed throughout the system and not affect the boiling point of the fluid as badly. Water collecting in the caliper may be the cause of the corrosion and leaks around the piston seals.

Well there’s thick piece of Marmite coated toast for ya.

Bin ’em and never look back all the way to several years of extended use.

The big benefit (apart from any ethical/ecological soundness) for me, in regards to fixing stuff, is the iprovement in general bike tuning. I find if I let elements of a bikes ‘System’ become consigned to my ‘unconscious’… I allow myself far more time spent in the ‘shonky zone’. You know that place? Where you’re not quite sure about the difference between low and high speed compression damping and whether your tyres really are 22 psi, because your pump guage actually probably doesn’t read psi very acurately? Whether your mech hanger is slightly bent or your shifter is clogged? So you just kind of deny it and ride with a slight limpness and uncertainty? “Ah bollox, I missed that double again, because I couldn’t stand up on the pedals for fear of slipping, because I can’t tune my rear mech”.

To be fair, there can be benefits. Like getting to the bottom of a black run and realising the ‘Hare & Tortoise’ symbols on my rear shock, were actually relation to the little red dial, not the little red lever. Said lever actually had a lock symbol pointing vaguely at it. So I had just ridden down that trail, not on a slightly faster rebound, but on a locked out ful sus hardtail! Result! In relation to my self esteem anyway.

But mostly, I find solving these issues (like the shimano brake one), really help with my relationship (oneness) with the bike.

If it wasn’t for the incredible improvement in performance, that these new fangled bits n bobs allow, I’d almost be pining for the days of cottered cranks and seperated loose ball bearings 😉 At least I knew once I’d learned how to strip a bike… that was it. I could strip any bike.

I think I’ll try one more session after I use up these O rings (whether they actually do anything or not). I’ll attempt the Square section ones behind the pistons next. If that doesn’t work…. well at least I tried. Then I can look forward to some new Hope stickers for my old Passat’s bumper.

Anyone know where to get those Square O rings?

I find if I let elements of a bikes ‘System’ become consigned to my ‘unconscious’… I allow myself far more time spent in the ‘shonky zone’.

This is the point where I realized that I have no idea what you’re talking about.

I find solving these issues (like the shimano brake one), really help with my relationship (oneness) with the bike.

N+oneness, surely.

Anyone know where to get those Square O rings?

https://www.aliexpress.com/item/32817169236.html

THanks hols2. Both for the clarification of the oil types and the water dispesion and the link to the rings.

With your level of technical understanding, I’m not surprised you know nothing of the ‘Shonky Zone’. I on the other hand, have a holiday home there.
🙂

hols2, Which brakes do you run and how do rate their value to their performance?

@Stablebarns I was reading that hoping you’d sorted it, downer. I had originally thought it was the piston seal and bought what I thought was a pair, but it turned out to be just one (eBay search for shimano hydraulic brake piston). While I was waiting for it to arrive from China I had found out about the orings and tried that instead.

Mine are the very old Shimano LX M585 brakes (dating back to approx 2006) and it’s the rear brakes affected after long periods of not being used (over 6 months). After fixing them early last year I had another long spell of not riding and the symptoms are back, but to be fair I didn’t do much cleaning of the caliper while it was stripped down. Symptoms are they make a lot of noise but don’t grip the discs until they’ve been well warmed up, so contaminated pads. I’ve never been able to see any fluid which is why for ages it was always a mystery as to what was contaminating the pads.

Anyway, thanks for the update and good luck fixing your leaks.

I haven’t had the leaky caliper problem. I run some M810 Saints on one bike, some M7000 SLX, on another, Hayes El Caminos on my old XC bike, Avid Juicys on my spare bike, plus basic Deores and lower on other old bikes. I used Hayes HFXs for years. The Saints are the most powerful, the Saints and SLXs don’t modulate that well, the Deores are excellent if you’re not racing DH, the Juicys work fine but haven’t been serviced in years so the pistons are stuck, the HFXs were very powerful with an 8″ rotor, but had terrible modulation. I have a box full of old HFXs that still work but need the calipers stripped down and rebuilt, but parts aren’t available so not worth wasting time on. The El Caminos are my favorite, they still work perfectly and are more powerful than Deores but better modulated than Saints and SLX. I’ve also played around with some Tektro hydros and some other more recent low-end Hayes model on a friend’s bikes. They were comparable to basic Deores – perfectly good for a bit of moderate trail riding.

Edit: Apart from the HFXs and El Caminos, I bought all the rest second-hand, so no idea about VFM if you’re paying new prices.

I’ve run Hope for years, and they have always just worked. I’ve only had one issue in 8 odd years on my last set.

I decided to get a new set recently, although they are basically the same as the old one, just a bit more refined in the lever.
My only pain I ever have is fitting new pads, where I just have to sand down the pads before I can get any clearance, else everything is jammed in so tight the wheel hardly turns. I have tried everything with sanding being the only option. This is with Hope brand organic pads and Shimano XT disks.

Bin ’em and never look back all the way to several years of extended use

That would be dopey eh? Except bikey people seem to love to buy new stuff just for the sake of it. Wish I could afford to.