Diagnosis - caliper...
 

[Closed] Diagnosis - caliper or master cylinder fault

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Offline  hooja
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Wondering if anyone else has had this problem?
SRAM force rear brake has gone stiff, at the lever, no modulation, it’s either on or off. Caliper is binding too.
I have cleaned and massaged the pistons but it hasn’t improved.

I’m tempted to just get a new caliper but also thinking it may be the master cyl?

Anyway of finding out?
Cheers

 
Posted : 16/10/2020 11:10 pm
Offline  tjagain
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master cylinder - its a well known issue with the piston sticking in the bore

 
Posted : 16/10/2020 11:28 pm
Offline  pdw
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TJ's right that the master pistons stick, but I think your problem is the caliper seals. I had something similar:

https://singletrackworld.com/forum/topic/sram-force-hydro-binding-on/

Replacing the caliper seals fixed it. My theory is that the seals go hard and stop flexing, so the pistons advance through the seals then don't retract, leaving you with no lever travel and a binding caliper.

The seals on my master cylinder were also knackered, but that has slightly different symptoms: after applying the brakes, the lever returns slowly and is "floppy" i.e. it has a a load of completely dead travel as the master piston hasn't returned.

 
Posted : 16/10/2020 11:57 pm