Disc brake issue, help!!!

[SoCalSteve]

Hi all,

On one of my bikes, the front SRAM HRD disc locks up after riding it for awhile. I started out my ride today and the wheels spun freely. By the end of the ride, it was pretty much locked up. Put the bike away and just checked it after about an hour and it’s spinning freely again...weird!

Is this a piston issue or a hydraulic brake line issue? Or something else? Gonna take it into my LBS, but wanted to check with you guys first.

Oh, ended up getting a pretty terrific workout!!!

As always, thank you all in advance!

Steve

[dddd]

This could be related to the position of the lever, if it doesn't return fully the heat-expanded fluid will not return freely to the reservoir.

Or the valve inside of the lever could be obstructed or seized, or I suppose the hose could be pinched shut (seems less likely).

Possibly the caliper piston could have an interference issue, but I see this as also unlikely.

[nmrt]

could it be a sticky piston that does not retract? there were some issues on certain models of sram brakes having stick pistons.

[SoCalSteve]

could it be a sticky piston that does not retract? there were some issues on certain models of sram brakes having stick pistons.

My gut feeling is this. What is the fix? Thanks!

[dddd]

Outside over a sun-lit sidewalk, you should be able to see the light gap between pads and rotor, should allow diagnosis of whether one piston isn't moving as freely as the other.
I've freed a caliper piston (while trying to retract pistons during pad replacement) by flooding the affected piston's seal area with rubbing alcohol, then doing the back-and-forth at the lever.

[jtakeda]

Outside over a sun-lit sidewalk, you should be able to see the light gap between pads and rotor, should allow diagnosis of whether one piston isn't moving as freely as the other.
I've freed a caliper piston (while trying to retract pistons during pad replacement) by flooding the affected piston's seal area with rubbing alcohol, then doing the back-and-forth at the lever.

Yup^
I’d maybe start with some compressed air to see if you can blow out whatever it is then move to wet stuff

[John H.]

Get a set of Hope calipers for SRAM and be done with it-

[pdonk]

I remember hearing about this on the nerd alert podcast. No experience with this issue, but it may answer your question.

https://cyclingtips.com/2020/05/nerd-alert-podcast-ask-a-mechanic-returns-zwift-cheating-and-more/

[Hilltopperny]

I had this issue with Sram hydraulic mountain brakes. When they would heat up they would lock up and stick until they cooled down. Especially when it was humid!

The quick fix was to shoot cold water on them.

The actual fix was to use Shimano XT hydro brakes instead. Now there are more options and I am running Magura brakes on my fat bike with Sram drivetrain.


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[Jaybee]

Its probably the plunger inside the master cylinder. There are fixes on YouTube or SRAM is replacing a bunch of these under warranty (for certain dates of manufacture).