PSA: how to break an XT 785 caliper piston :-(

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PSA: how to break an XT 785 caliper piston :-(

20 posts & 8 voices | Started 7 months ago by m1kea | Latest reply from ampthill

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ham fister

m1kea - Member

Unsurprisingly my brakes needed some TLC after D2D. The rear brake had ground along for the whole event and having taken the knacked) pads out, the left hand side (outside piston) was considerably extended.

It wouldn't push back in but after some spray grease lubing and gentle working, I got it to move a bit.

Great I thought, I'll put the yellow block in to realign both pistons.

Unfortunately I can't have pushed the block in as far as it could go because when I closed the lever, the top of the right hand piston must have worked its way over the block. Consequently the piston must have closed at an angle, plissn brake fluid out out around the edge :(.

It looks like Evans have spare calipers and I presume I can just refit the hose and refill the whole system again?

So today's moral is, don't follow my example

Posted 7 months ago #
nigew - Member

Yes you will be able to connect another caliper, it will of course need rebleeding but cant you just push the piston back in?

Posted 7 months ago #
The-milkybar-kid - Member

Which side piston went was it the spoke side?

Posted 7 months ago #
m1kea - Member

Twas the spoke side piston. - I guess the other one was more jammed than I thought?

I pushed it back in but TBH it looks terminal.

Is it unusual for the pistons to become asymmetric with their action? The fact that the brake rubbed without having pads left suggests to me that it got out of alignment during the race and didn't recover.

Posted 7 months ago #
ampthill - Member

Disc brakes. The low maintenanace option.....

Why did we fall for this.

I feel your pain. Hope you get a solution

Posted 7 months ago #
The-milkybar-kid - Member

My piston popped out on the same brake on my last lap at D2D i pushed it back in but it broke around the edges mine was the spoke side aswell.

Posted 7 months ago #
m1kea - Member

The-milkybar-kid

My piston popped out on the same brake on my last lap at D2D i pushed it back in but it broke around the edges mine was the spoke side aswell.

Bummer

I ran out of light last night but will see if I can get some life out of the piston (after I've got a replacement unit).

Posted 7 months ago #
bigyinn - Member

ampthill - Member

Disc brakes. The low maintenanace option.....

Why did we fall for this.

I feel your pain. Hope you get a solution

Still riding fully rigid with canti brakes then i presume?
No?
Thought not!

Posted 7 months ago #
D0NK - Member

Don't think he was saying he didn't use discs bigyinn just bemoaning the fact they aint faff free.

Few years ago I accidentally pushed out a piston on a hope M4 whilst cack handedly bleeding them, popped it back in, still running smooth today.

Posted 7 months ago #
bigyinn - Member

low maintenance is not the same as NO maintenance.

Posted 7 months ago #
daznal - Member

"The rear brake had ground along for the whole event and having taken the knacked) pads out, the left hand side (outside piston) was considerably extended."

mmm running disk brakes without disk pads,let me just check the stupidity meter,as i thought 9.5 out of a possible 10

Posted 7 months ago #
bigyinn - Member

Erm I dont think the OP actually rode without pads.

Posted 7 months ago #
m1kea - Member

daznal
"mmm running disk brakes without disk pads,let me just check the stupidity meter,as i thought 9.5 out of a possible 10"

And incorrectly presuming something of someone you've never met and then calling them stupid?

Hmmm, 9 of 10 for rudeness, all IMHO of course.

15 all, your serve

Posted 7 months ago #
daznal - Member

Having re read the thread its now me thats a 9.5 (goes slightly red and turns away from computer)

Posted 7 months ago #
ampthill - Member

Still riding fully rigid with canti brakes then i presume?
No?
Thought not!

Suspension. Brilliant. I've only ever had one real failure and that was due to a crash. As far as I'm concerned its win win

For me discs have just been a pain. I admit that its part bad luck and part that I haven't yet got the new tools and skilll set.

I was on v brakes until about 18 months ago. I could change the pads and cable easily and cheaply and end up with brakes that worked well.

Discs just seem to have a never ending slightly sticky pistons and they are better than v brakes but not loads

But the marketing bullshiters repeadtedly flogged the disc brake idea as lower maintenance and less hassle. Its just has not been for me

Posted 7 months ago #
Superficial - Member

You must be massively unlucky. I don't remember doing much maintenance to any discs I've owned (mostly Shimano). However I remember v-brakes well, but don't really recall them ever working when it's wet...

Posted 7 months ago #
bigyinn - Member

ampthill - Member

For me discs have just been a pain. I admit that its part bad luck and part that I haven't yet got the new tools and skilll set.

Not really fair to blame the brakes if you aren't used to them then.

Discs just seem to have a never ending slightly sticky pistons and they are better than v brakes but not loads

Avid Juicys??

Posted 7 months ago #
m1kea - Member

Update

Had no joy with reseating the piston so that's probably that calliper fubared.

Fitted a replacement quickly enough and recharged the system with no dramas. I was fully expecting some twatting about here but it seemed painless enough. Didn't have chance to give the wagon a spin so fingers crossed she behaves herself tonight.

Posted 7 months ago #
The-milkybar-kid - Member

Hi do you want to sell your old calliper i just want to see if i can use your good piston?

Posted 7 months ago #
ampthill - Member

Avid Juicys??

Yes but the replacement deore's were little better. My sons Juiscy's are now dragging

I'm not surprised that discs are hard to maintain. I'm annoyed that anyone said it would be less effort than v-brakes

Posted 7 months ago #