Are there any Shimano MTB callipers that don’t microleak?

I’ve used Shimano calliper’s for years and with the exception of some LX ones years ago they’ve always been great.

Since changing to SLX M7100 brakes I’ve had no end of micro-leaking. I probably should have warrantied them but just bought another to get back riding ASAP, but I’ve just had another one go and I’m getting fed up.

Is there a Shimano post mount calliper that’s more resistant to micro-leaking or is it just luck?

I’ve got a pile of 4 or 5 leaky calliper now, should I be looking at repairing them and is it easy & affordable to do?

I dont have enough data but anecdotally (and my experience also) Deore are the least likely to leak and XT the most.

I would also counter that outside of ‘the internet’, Shimano brakes are still regarded as fit and forget based on people I talk to, riding mates etc.

I have 3 bikes with M8000 XT calipers. None of them leak. I also have 3 bikes with other Shimano calipers. None of them leak either.

Go figure.

I think you’re just gonna get people saying “my XYZ are fine/terrible” here, but maybe that’s what you were after.

I’ve only conclusively experienced leaking calipers on a secondhand set of Tiagra. Currently on Zees and Deores and touch wood no leaks.

Anecdotally backing up snotrag, my Deore m6120s are solid 3 years on.

I did a top up bleed after I bought them (fitted to a bike). I bled the front 1.5-2 years ago after a trashed hose. The rear’s feeling a touch spongy now so I’ll bleed it at the weekend.

I keep looking for excuses to swap them for something blingier (silver Cura 4s maybe), but they work, I like them, and I’m a bit of a skinflint.

I’ve had lots of shimano disc brakes over the years.

One XT caliper, a very old M785 one, spilled fluid everywhere. it was showing signs of leaking, but one hefty pull later and there was oil on the floor. However, it was fit and forget for many years and had very very little attention other than the odd bleed every now and then. I think the pistons just got dirty and worn and it gave up.

One SLX M7100, micro leaks, again, not touched since fitting, probably me.

all others I had, from LX and flappy shifters to XTR level have been great, coped with neglect admirably.

and for balance:

SRAM level (T, TL and TLM), OK, but not great, doesn’t leak but lets you know when the pistons need a clean as it rubs and rubs, and squeals.

Magura MT4 – neglected, seals swelled while in storage and the brake binded. again, probably my fault!

Hope (Mini’s, moni mini’s M4’s etc etc) great for many many years, until fliud corrodes the caliper, pistons dont retract and it’s never going to be reparied without polishing and reanodising. timescales have varied for that to happen, from a couple of years to well over 5 years of use.

so, keep your kit clean, clean your pistons fairly regularly, don’t be clumsy with brake fliud and most brakes will probably be OK.

Fit and forget, that just depends on whether you are lucky.

I should probably clarify here that I’m not denying it’s a thing. I’m genuinely interested in why it happens to some folk (repeatedly) and not to others. I do wonder if there is some contributory environmental and/or behavioural factor involved.

When I was working with a large bike hire fleet, I dealt with hundreds of Shimano-equipped MTBs and hybrids, all using lower end hydraulic calipers. We never had any micro-leakage. On the other hand, we had a year of multiple spoke breakages which wasn’t being recorded elsewhere, leading us to believe we were somehow a contributor to them.

Deore here, not used very often but stored in a warm dry garage. Faultless performance, no leaks, and since I fitted Swisstop Yellow pads and toasted them in the Cairngorms they are also the only disc brake I’ve used that doesn’t howl in the wet, not sure what other factors contribute but I’m guarding them jealously.

how do you detect a microleak? brake dust stuck to the caliper?

I’ve had 2x Deore, at least 1 SLX, and 785 XTs all leak on one particular bike.

Those 785s were fine for years first on another bike, as have the 8000XTs that replaced them.

I think the significant difference is that the first bike lives in my parents garage in Scotland, regularly going 6 months+ between uses. Not sure if the temperature is a factor, but fairly sure the lack of use is.

I do wonder if strapping the lever to the bars would help, but don’t plan on buying any more to experiment with.

I’ve seen it plenty in recent years (never on older brakes) and anecdotally it’s been on bikes that haven’t been ridden much – two s/h MTBs that the first owners barely used had microleaks on deore 4-pot, and a couple of cross bikes that I hadn’t ridden in a bit on grx. Finished with them now – use dominions on the MTB and have just got hope rtx4 calipers for the cross bikes (not fitted yet).

It’s probably worth a fix if you enjoy putting things right, piston kits are usually £10-20 depending, so it’s not a huge cost saving over a new caliper. You need to thoroughly clean the seal seat area which is tucked away.

Sometimes the O-ring between the two halves of the caliper is the culprit (fluid transport port) and this is pennies to replace.

only disc brake I’ve used that doesn’t howl in the wet

I’ve been demoing bikes recently and noise is quite noticeable from brakes that otherwise feel great. eg Magura MT7s and Hope V4.

Other than when they’ve pissed themselves following a micro-leak I haven’t had any noise issues with Shimano

4yr old XTR M9100 on one bike, absolutely fine. Older XT M8000 on two others, fine. Bogo sub deore ones on one of the kids bike, fine. 4 yr olf Ultegra, fine.

I have slx, xt, deore, ultegra/grx brakes.
all fine, no micro leaks.
the slx are 10yrs old, the xt 9yo, the deore 2yo, the grx calipers 2yo.

I don’t do anything special to them, just use them.
the internet can easily give a false impression of how reliable (or not!) ‘something’ is.

Had a few- only road ones leaked.

My deore 2 and 4 pot seem fine.

If it’s a seal issue, might be worth asking what people clean them with? I don’t clean mine unless there’s a problem. And don’t clean bikes often in general as chain wax keeps the important bits clean. And mostly it’s with nothing more aggressive than car shampoo.

I did have an XTR caliper (circa 2010) completely fail, one of the seals just blew out under heavy braking .

Have RS785 calipers on my all road bike since Feb 23, 2400 miles done, no leaks. Also had GRX400 on a gravel bike from Jun 20 until Feb 23, 3400 miles covered, no leaks. The rear M6000 Deore on my old commuter leaked from a worn piston at 3200 miles and then the replacement M6000 caliber leaked in the same way 1000 miles later. Replaced it with a M6100 which was fine when I sold the bike.

I think contributing factors to leaks are letting the calipers stay dirty with brake dust and road/trail dust/dirt and also not replacing the fluid when needed – in my experience changing the fluid every 12-18  months (dependant on use) seems to be a good interval.

No proper evidence, but I have had lots that leak, sometimes the levers too. The common factor is lack of use. Ie bike used a lot and all is fine, then put away for a reason, then 6months later there are leaks.

Anyway, I used to repeatedly buy another caliper, or lever. But this is stupid as eventually each brakeset ends up being a triggers broom of many replacement bits of brake with the associated cost of doing so. So new rule is bin it at the first leak, and replace with a magura, or sram, as that’s what I have bleed kits and fluids for.  Originally, when shimano were universally reliable, I did the opposite and got rid of the leaking Hayes, avids, etc and standardised to shimano.

I’ve had about 12 through my hands, including but not limited to:
2x 105
2x m675
2x deore whatever the age of the m675 slx is
2x m6120
1x m785
1x m6000
2x Zee
The one thing they all had in common was that they all had been sat unused for at least a few months. I’m convinced this is what kills them.

I have had several sets of assorted calipers on my commuter bike with lots of leaky Shimano calipers. This was a few years ago. I rode this bike every single week day going to and from the centre of Manchester. So about 60-70 miles a week and in 10 years of comuting it did lots of miles. I got fed up with replacing calipers and bought some Hope brake which have never had any kind of fault.

I had 105 brakes on my Genesis CDF. The first set leaked and were replaced under warranty, these also leaked and were replaced with Hope RX4. This bike did not do massive miles.

One of my partners MTBs has Deore brakes and has never had a problem. It only gets used infrequently as she prefers her other bikes.

I have wondered if it was to do with salt or other road contamination.

It’s like all these problems some people have them and other don’t, and it’s not easy to work out why.

I thought the accepted solution now was simply to fit a different brand of calliper i.e. Magura (to make it a ‘Shigura’ brake)…

Are there any Shimano MTB callipers that don’t microleak?

Just based on my experience, Deore, Saints (old single pot and twin pot), XT, SLX  and XTR – all faultless.

I’m genuinely interested in why it happens to some folk (repeatedly) and not to others. I do wonder if there is some contributory environmental and/or behavioural factor involved.

I think I mentioned it on another thread, but I’m deeply suspicious of mineral oil brakes.

I think the hydrophobic nature of mineral oil means that if any water does end up in the system somehow then it is going to migrate to the lowest point, ie, the caliper.

From there I can see it either causing issues with corrosion or with the seals (or both).  It maybe also tallies with folk saying the problem seems to be worse with bikes that get little use given that any moisture will be allowed to pool and do whatever damage it’s going to do undisturbed.

Just my theory though, could be wrong.

My shimanos nearly all fail at the lever after a few (4-5) years which is a wear and tear failure. In fact, I’ve replaced the levers of my Zee brakes with some latest model SLX levers just a week ago.

I’ve had a few transfer port micro leaks over the years too, but the fix is so easy I just crack the caliper open and replace the o-ring and they keep trucking.

Never had a piston seal failure before they died of something else first.

Pair of m501/520 that came on the ebike. Front started leaking immediately, the shop replaced it. After that worked fine and no leaks. Then about 3 months in the rear started to squeal, leak detected(little piston marks on the back of the pads)

I keep meaning to do something about it but cant be arsed.

Currently using t4v4 on the front, which is pretty much all it takes to stop the bike. I’ll eventually put the other t4v4 on.

My M988 XTRs (almost) all died (7 of 8 callipers)

My 9120 XTRs all died (4 of 4 callipers)

My M8120s partially died (1 of 2 callipers)

My R785/R685 road callipers partially died. (3 out of 5)

The XTRs we’re lightly used, the XTs moderately used and the road callipers heavily used.  Most of the road callipers made it into the 10k km range, the XTRs barely made it into 500km range, the XTs somewhere in between.

So, in my experience, they all fail at some point and no set was immune, but lifespan did vary a lot.

My now all Hope fleet hasn’t missed a beat in 5 years.

So, in my experience, they all fail at some point and no set was immune, but lifespan did vary a lot.

My now all Hope fleet hasn’t missed a beat in 5 years.

Agreed. It used to be less of a problem because shimano brakes were cheap to buy and cheap to run. Replacement levers or calipers where also cheap and you got new pads with the calipers.

Those days are gone now and I’m phasing them out of my own fleet.

The last set will probably be replaced next month by some Hopes, which will be the first since 2004!

SLX m7100 on my commuter for 18 months.   No issues. Ridden 4 days a week. Gets covered in road shite.

SLX M7000 on the DJ (6yrs old), fine once I swapped out the utterly shit g02 resin OEM pads.    Bike rarely gets used.

9 yr old Deore m615 on my HT.  No issues.  Sat unused for well over a year, only needed a bleed.  (Originally on previous commuter). Rarely gets used now tbh.

I’ve never experienced this microleaks problem.

IME.

There are plenty (probably 80%+) of Shimano Mtb callipers that don’t microleak – but it is pot luck which model.

I see above that an impression has been created, roughly, that the more expensive ones do it more. But perhaps that’s because those who’ve paid more for their brakes are more likely to complain and/or be more attuned to possible faults?

TBH – with something that used to be so safety-sensitive (being able to stop) it surprises me that more isn’t made of faulty brakes. The arse with micro leaking is that, by the time you’ve worked out what is going on, you’ve most likely got pads and rotor to replace too. 🤦

We’ve sold thousands and warrantied many. From my experience the best of the current crop is SLX for reasons I do not know they’ve fared quite a bit better than Deore or XT. Not perfect mind, just better.

Overall in the last 10 years Saints are by far the best brake Shimano has made. They’d still make it into my top 5 brakes 10+ years on from launch.

One thing I did notivce with my shimano’s that leaked, that, like above. it was noticable after a period of storage for more than a month. Where the bike had been in regular usage, the brakes were fine.

Now I’m not saying that it is a factor, but both my leaky ones weeped after storage.

but it is pot luck which model

I see what you did there, nice, subtle.

I have some 2014 Deores that are still going and never had any issue.

Had some XT M785 for about 18 months with no issues.

Then had 3 sets of XT M8000, first 2 leaked (about 6 months and 18months in from memory) and replaced under warranty and so the 3rd set I just immediately sold on.

The M8000s were used probably 4 times a week.

I’ve been fighting a set of R785s for a bit. I’ve changed all the seals and pistons, and somehow the front one still leaks. I’m going to have another go at rebuilding it this weekend, but I think I’m going to end up just replacing the calipers with something not-Shimano.

Who’s compiling the data?
I’ve had a pair of XTs from new, 2016 – never leaked.
A pair of RS785s from 2015 (or thereabouts) – never leaked (done 1000s of miles)
A pair of Deore twin pots a few years ago – 1 leaked, the other didn’t. Sent back.
Oh and the old Deore’s on my son’s ride-to-school, now commuter, never leaked. Powerful as you like.
All except the twin pots still going strong.

Never had an issue till I started using muc off. Or at least I had 2 sets get micro leaks while using muc off. Swapped cleaners and never had an issue since. Probably utter coincidence and I know that’s how superstitions are made but there you go.

My commuter has had both ends fail.

I’ve had a few others go as well.

There was a thread on replacement seals. Might be worth it, I’ve got a couple I should do as I’m sure the front on my commuter has gone in the lt week.