Brakes broke. Shimano M785 caliper failed.

[I like Skol]

Just found out I need a new brake caliper for the commuter bike

Front brake started scraping during a canal towpath ride a couple of days ago and a quick inspection revealed pads were getting a bit worn and the piston on one side was out more than the other. Today I finally got around to trying to replace the pads and centre the caliper. Before pushing the pistons back I cleaned out around them with an old toothbrush and some very mildly soapy water then popped the old pads in and gently levered back the pistons. It was immediately obvious that something was wrong. One piston didn't go all the way back. I removed the pads and pumped the pistons out a bit before trying again. Same result, except this time I heard a crunch as the problematic piston bottomed out prematurely.

Now having dismantled the caliper I find the back of the ceramic piston has fractured off. I have changed pads in this type of brake many times and never experienced this. I am convinced the failure has occurred in use rather than me being ham fisted during pad renewal. The pads are not worn to the metal which is common when i normally replace them and given the sudden start to the scraping during the last ride i am led to believe the two are connected.
The only thing i can think of is that the bike has been largely unused for the last 4 months, but has been stored in a warm, dry room.

Anyway, i have to replace the caliper so have ordered an SLX M7000 version which appears to be a direct replacement for the now superseded M785 and while not cheap, won't break the bank at £32 delivered.

 

[Slick]

I have a genesis datum with Shimano rs505 brakes fitted. I reckon it has done around 110 miles before I finally admitted defeat and put it in for repair as the piston were jamming and just getting further out each time they were pulled. It's taken far too long to get the work done under warranty and I wish now that I just paid to replace the entire set up with a stronger upgrade.

I also picked up my other genesis from my own preferred bike shop, who replaced all the cables and serviced the brakes and fitted new wheels. The new wheels felt great until I heard the distinct scrape of a front pad and spun the front wheel to the disappointing sight of it stopping prematurely due to the brake biting slightly which for some reason is more noticeable under load.

Not a lot of help, but don't speak to me about failing disc brakes.

 

[ColinJ]

It is nice to read that you are back on your bike at last! (You may have mentioned it elsewhere but I didn't notice.)

 

[I like Skol]

It is nice to read that you are back on your bike at last! (You may have mentioned it elsewhere but I didn't notice.)

Just testing the water initially. Collar came off just over a week ago and following docs orders to take it easy while I get my strength back. Not too bad so far, some discomfort from the injury and my fitness is also shot to peices.

It's just good to be heading in the right direction recovery wise after a few delays and frustrations along the way. Early days but fingers crossed

Wasnt expecting to be fixing bikes so soon.....

 

[wisdom]

Whilst not opposed in any way to discs.There are pros and cons in everything.
Yes they are better in wet weather.But there's still a lot to be said for the simplicity of rim brakes and the simple adjustments needed.

 

[Drago]

I dont mind discs at all but I've never bought into all the indestructible maintenance free never break guff that people trot out.

 

[I like Skol]

I dont mind discs at all but I've never bought into all the indestructible maintenance free never break guff that people trot out.

My experience has been positive overall. The Shimano kit i run is generally very robust and while not completely fettle free it does require minimal attention.
This incident is an oddity. The pads are worn low but both are worn completely level and equal amounts. This would indicate a perfect setup and a well functioning caliper prior to the onset of the problem. Why the one piston suddenly began sticking in such a catastrophic way is anyones guess. I can't think of a reason for it.

 

[Drago]

My experience has also been quite positive of my Deore and SLX kit. A fluid change every year has seen them to be otherwise attention free.

My Hope brakes were the opposite end of the spectrum. If a sparrow did a wet fart within a 300 mile radius of either bike - and it would seem there are a lot of sparrows with runny bums - then they'd need attention for something.

 

[Levo-Lon]

My experience has been positive overall. The Shimano kit i run is generally very robust and while not completely fettle free it does require minimal attention.
This incident is an oddity. The pads are worn low but both are worn completely level and equal amounts. This would indicate a perfect setup and a well functioning caliper prior to the onset of the problem. Why the one piston suddenly began sticking in such a catastrophic way is anyones guess. I can't think of a reason for it.

Id agree with that.
I had a similar piston failure half way around The Monkey trail with a Hayes caliper.
Shimano stuff is usually pretty bullet proof.
The sram guide R brakes on my Cube are super brakes,they get some bad press from Hope fans but i think its just snob slagging.

 

[Drago]

I don't know why people get high and mighty over Hope kit? It's usually lovely to look at, but otherwise not remarkable.

 

[Levo-Lon]

I don't know why people get high and mighty over Hope kit? It's usually lovely to look at, but otherwise not remarkable.

Me neither,it does look good and work fine but you certainly pay for it!!

 

[Drago]

Erm, their seat post clamps are nice!

 

[I like Skol]

New SLX caliper arrived today. Looks almost identical to the XT one it is replacing, has the same 22mm ceramic pistons and takes the same pads so should be indistinguishable in use. Will try to find time to fit it later.

 

[I like Skol]

Caliper fitted today. Was a straightforward direct swap and bled very easily (did it off the bike using a syringe to force the mineral oil through from the reservoir port initially, then pulled out the plunger from the syringe and used the body as a reservoir during final bleeding). All tested and bike now ready for the commute in the morning.

 

[dan_bo]

My experience has also been quite positive of my Deore and SLX kit. A fluid change every year has seen them to be otherwise attention free.

My Hope brakes were the opposite end of the spectrum. If a sparrow did a wet fart within a 300 mile radius of either bike - and it would seem there are a lot of sparrows with runny bums - then they'd need attention for something.

Not had a peep out of either sets of hopes on my CX (two years) or MTB(5+ years). Honest straight up performance.