Shimano SLX Brake - Piston Fell Out.

raven

Squid
Hi Guys

Bleeding my rear brake which is the Shimano SLX.

The pistons needed resetting and I forgot to place the spacer block in the caliper after opening the reservoir. After a couple of squeezes of the lever the left piston dropped out and all the mineral poured out.

I replaced the piston and placed the spacer block in the caliper to complete the bleed. :mmph:

When I was finished I had replaced the back wheel and was just feeling the brakes when the wheel locked up, the same piston has come out as far as the pad and rotor would allow. It is almost half way out.
I feel if I try and reset the piston again its just going to flop out again as soon as I squeeze the brake lever.

Is the caliper stuffed? :brick:
 

SummitFever

Eats Squid
Caliper is not stuffed. The piston that came out is now moving easier than the one that remained in. This means it will always come out before the other piston. You need to free the other piston up to get them both working together. Popping both pistons out, giving them a good clean, make sure the seals are clean and then reassemble.
 

PerthMTB

Likes Dirt
Caliper is not stuffed. The piston that came out is now moving easier than the one that remained in. This means it will always come out before the other piston. You need to free the other piston up to get them both working together. Popping both pistons out, giving them a good clean, make sure the seals are clean and then reassemble.
Or alternatively, both pistons are extending as they should, but the one you popped isn't retracting again when you release the lever. Its the deforming of the square profile rubber seal which retracts the piston, so if the seal is twisted or not seated properly in its recess, the piston is not exactly straight in the bore, or a bit of grit got in between piston and bore wall, it won't retract properly.

If its any help, I had to overhaul one of mine last week, and this is what the innards of an SLX calliper look like...

img6250683x1024.jpg

Pretty simple eh? Not much to go wrong really, so if all else fails, just take the whole thing apart, clean with IPA, re-assemble and give it a good bleed, and you should be right...
 
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raven

Squid
Repaired SLX

Thanks for the advice.

My slx has the older pad configuration and an internal seal
Opened up the caliper and the piston which fell out just needed to be pushed in firmly,
It clicked into place under the seal and works fine now.
No way I could get the other piston to come out.
 

northvanguy

Likes Dirt
Any hints to getting the caliper bolts out?

I'm doing a bleed at the moment, wasnt paying attention and the one piston is 90% out on an angle and doesnt want to be pushed back in, so looking like i might need to open it up but the two bolts holding the caliper together don't want to budge, and of course if i strip them i'm done.
 

creaky

XMAS Plumper
Any hints to getting the caliper bolts out?

I'm doing a bleed at the moment, wasnt paying attention and the one piston is 90% out on an angle and doesnt want to be pushed back in, so looking like i might need to open it up but the two bolts holding the caliper together don't want to budge, and of course if i strip them i'm done.
Impact wrench?
 

stirk

Burner
@northvanguy a quick .1 of a second rattle might help but you'd want to try other options first. I've broken bolts after they have cracked loose.

Heat, penetration oil and leverage, start there first.

How did the piston become on an angle? Seems like some fwittery happened for sure.

I'd try to pop the piston out and if no damage reinsert straight.
 

northvanguy

Likes Dirt
@northvanguy a quick .1 of a second rattle might help but you'd want to try other options first. I've broken bolts after they have cracked loose.

Heat, penetration oil and leverage, start there first.

How did the piston become on an angle? Seems like some fwittery happened for sure.

I'd try to pop the piston out and if no damage reinsert straight.
Cheers Stirk.

Severe case of fwittery for sure!

I managed to get it straight with a tire lever and force it back in... Hopefully no damage to the piston seal. I'll find out probably on the trail when mineral oil everywhere! Nah it seems good to go.

Crisis averted... Just this thread as a reminder I'm a peanut.
 

stirk

Burner
Cheers Stirk.

Severe case of fwittery for sure!

I managed to get it straight with a tire lever and force it back in... Hopefully no damage to the piston seal. I'll find out probably on the trail when mineral oil everywhere! Nah it seems good to go.

Crisis averted... Just this thread as a reminder I'm a peanut.
Cool, if the piston was not severely angled and you managed to push it back in major scoring of the bore may have been averted.

If you had to release some hydraulic fluid from the master cylinder in order to push the piston back in then a confession is mandatory!!
 
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