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What happens to shimano brake pads when my bike sits in the basement for 6-8 weeks without riding? Help me, I'm baffled.

Backstory:
In the last 2 years, my wife have had over 7 bikes in our house each with either Shimano M98x or M78x brakes on them. They either came stock on a bike, or I bled them and installed them myself.

We'll ride a bike for couple months in the fall, brakes work great-- quiet, powerful, zero drama. put the bike in the basement for a couple months, pull it out in March to ride, and boom-- brakes squeal like crazy, less grabby, less power. Bikes are stored right side up, in various parts of my basement, leaning against a wall, etc.

This has been happening on various bikes. Various pad compounds, organic and metallic, finned and not finned. Genuine Shimano and truckerco pads.

Removing and sanding sometimes helps, but often only for a minute or two-- full power just doesn't return.

My solution is to buy cheap (truckerco) pads in bulk and replace when this happens.

My LBS has said the same thing about their XT equipped demo/rental bikes that sit for a month plus without use. What gives?

What the heck am I missing? Please share your well thought out hypothesis.
 

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Did you notice any oil residue or any other sign of leaks or pad contamination?

One thing I can think of, at least on the M78x brakes is a slow leak on the o-ring between the two caliper halves on the banjo bolt. If the bike is ridden frequently it keeps the oil burned off so the pads don't get contaminated, but let the bike sit for long enough and the oil will get into the pads. This however doesn't explain the M98x since with one piece calipers it doesn't have that o-ring. The only other possibility is bad piston seals, but this isn't Avid here so it's very unlikely.

One possible solution would be to remove the brake pads when you put the bikes into storage, then check the calipers at the beginning of the season and clean them if needed. As an experiment, you could try leaving the pads in on one bike and then compare it against the bikes where the pads were removed. If both sets are bad, it's a pad problem, if only the set that was left on went bad, it's a leaking caliper.
 

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I just rode my bike with xt brakes for the first time in 2.5 months and the front brake has significantly less bite and requires more force than the rear. It also squeals sometimes. I suspect it's the phenomenon discussed above.

What is the solution? New pads?

Have others experienced this?
 

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I'm having issues with my rear XT. Front works great but the back has much less power and squeals. It lever feels firm but just no stopping power so guessing the pad are dodgy.

Also noticed last time I bled them when I removed the rear pads it looked a bit gunky and slimy around the calipers. I suspect that I have oil leaking out from the calipers or the seal between the two halves of the caliper.

Going to take another look after upcoming race and might try getting them warrentied. Bought online though so not holing out much hope...
 

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Bizarre but likely from minor leak in caliper.pull the pads next time but leave them in the same room to see what happens?
 

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Yeah, sounds like a caliper leak and some bleeding necessary. Of course just bleeding is a very short term fix if you've in need of a caliper seal.

Racing on compromised brakes huh? I would at the least do a bleed job before the race. This is one of the few situations where I would do a top down bleed given the origin of air would be at the caliper.
 

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Try scuffing the rotor up with some sand paper and clean them ... Then try them out... I kinda feel when they get contaminated there really is no great save... I just lost a pair of barely used icetech rotors due to sitting
 

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Does it get pretty hot in your basement - boiler down there or something? I have the same when my bikes have been sitting in the shed in my garden for a few weeks during the summer heat. I'd assumed it was a bit of oil weeping past the piston seals due to the heat causing expansion. Seem to return to normal after the first few minutes of a ride, with the help of a bit of deliberately heavy braking to help burn off any contaminants.

I read somewhere that Shimano brakes can only release pressure from the system by actuating the lever, otherwise they are a 'closed' system. So if they heat up in a car interior during the summer for example, expansion may cause oil to escape from the weakest part of the system - the piston seals.
 

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Why do you say bleeding is needed? It doesn't feel soft or spongy at all. It just has no bite. It feels like a coefficient of friction at the pads kind of thing.

Ok, I should have replied with a quote from skinnybeans (below). Obviously, I wasn't replying to Matto6 because Matto6 didn't say anything about the caliper looking "gunky and slimy" or "having oil leaking around caliper". If your caliper is leaking then you likely have introduced air and thus a bleed would be required.


I'm having issues with my rear XT. Front works great but the back has much less power and squeals. It lever feels firm but just no stopping power so guessing the pad are dodgy.

Also noticed last time I bled them when I removed the rear pads it looked a bit gunky and slimy around the calipers. I suspect that I have oil leaking out from the calipers or the seal between the two halves of the caliper.

Going to take another look after upcoming race and might try getting them warrentied. Bought online though so not holing out much hope...
 

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I can't believe this thread is on here I came on to post about the same situation with my Shimano SLX brakes(latest generation). Rode my mtb for the 1st time since November. Bike was stored in a dry basement, upright. Brakes were fine when bike was last ridden. I took the bike for a road ride tonight and the brakes squealed like a pig. Back brake felt like it had no bite at all, front had some. levers felt normal. I took some automotive disc brake cleaner and wiped off the rotors and the rag really took off a lot of blackish grime? gunk?. This helped some but still not ideal at all. I will look at pads tomorrow.

Could what ever brake dust and grime that was left on the pads and rotors, from the end of last season, have hardened into some sort of film or glaze that just needs to be burned off? Like they need to be bedded in again, like when the brakes are brand new?
 

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Thought I'd pass this info onto you guys. Above I reported the same problem with my SLX brakes. I cleaned the rotors with automotive brake disc cleaning spray. A lot of grime(brake dust?) came off the rotors. I then pulled the brake pads and also cleaned them with the same cleaning spray. again a lot of black grime(brake dust/dirt?) came off the pads. I unbolted the calipers and inspected inside where the pistons are. I could see no traces of any fluid but there was lots of brake dust. I thoroughly cleaned the calipers too but with rubbing alcohol.

I then went on my first trail ride of the season, about an hour ride. At first the brakes still felt the same- plenty of power and correct lever feel but no bite. About 1/2 into the ride all of a sudden the "bite" started returning, even to the point that I went into a skid a few times. By the end of the ride the brakes felt pretty much back to normal, more so in the front than in the rear. After my next trail ride I am hoping they'll feel 100% normal. I might bleed the back brake if it doesn't feel perfect.

Not sure why we are experiencing this issue but thought I'd share my findings.
 

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What happens to shimano brake pads when my bike sits in the basement for 6-8 weeks without riding? Help me, I'm baffled.

Backstory:
In the last 2 years, my wife have had over 7 bikes in our house each with either Shimano M98x or M78x brakes on them. They either came stock on a bike, or I bled them and installed them myself.

We'll ride a bike for couple months in the fall, brakes work great-- quiet, powerful, zero drama. put the bike in the basement for a couple months, pull it out in March to ride, and boom-- brakes squeal like crazy, less grabby, less power. Bikes are stored right side up, in various parts of my basement, leaning against a wall, etc.

This has been happening on various bikes. Various pad compounds, organic and metallic, finned and not finned. Genuine Shimano and truckerco pads.

Removing and sanding sometimes helps, but often only for a minute or two-- full power just doesn't return.

My solution is to buy cheap (truckerco) pads in bulk and replace when this happens.

My LBS has said the same thing about their XT equipped demo/rental bikes that sit for a month plus without use. What gives?

What the heck am I missing? Please share your well thought out hypothesis.
Dust. Just wipe the rotors with a clean damp cloth.
 

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Corrosion would be my guess, there's lots of metal in sintered pads. Leaks don't just happen overnight, it's likely the pads need a scuff and a re-bedding...
 

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I have this same issue. I got my bike with 2013 XT brakes (don't know the type, just that they're not with the ventilated, finned pads) in September last year and rarely rode it during the winter. When the bike was brand new, the brakes were grippy as hell, genuinely one-finger brakes as two would've been too much. No I have to squeeze with two fingers really hard (esp. the front brake) to get them to lock. Especially the front one is really noisy, too. The bike has 300km on it!
 

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Magically Delicious
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I have this same issue. I got my bike with 2013 XT brakes (don't know the type, just that they're not with the ventilated, finned pads) in September last year and rarely rode it during the winter. When the bike was brand new, the brakes were grippy as hell, genuinely one-finger brakes as two would've been too much. No I have to squeeze with two fingers really hard (esp. the front brake) to get them to lock. Especially the front one is really noisy, too. The bike has 300km on it!
All of these experiences are news to me, but I suspect it could have something to do with dust accumulation. I live where I am able to ride with some regularity through most of the winter. So, I can add that I have never seen this issue. Assuming there are no leaks and the pads haven't become contaminated, what else could it be other than some dust accumulation? I really don't know. I have experienced a similar braking situation when riding through very powdery, talcum-like sand and noted reduced braking efficiency something like described on one occasion.

Perhaps a good cleaning several times throughout the winter or during storage periods. I wouldn't squeeze the brakes until cleaned to possibly test the theory. I simply can't think of any other possibility that would contribute to this problem.
 
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