Hydraulic brake issue

Whorl
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Hydraulic brake issue

Postby Whorl » Sun Aug 27, 2023 2:41 pm

Hi brains trust

My commuter bike runs a SRAM Apex 1 groupset, with corresponding hydraulic brakes. Due to various life issues it has been several years since I've been able to get out and about on it. As a result, it seems that the brakes are currently contacting the rotors and there is little to not play in the brake levers.

My question relates to what I should do to check and resolve. I am presuming that I will need to remove pads and check pistons are moving, and perform a bleed of the hydraulic system to freshen up the brake fluid. Am I on the right track here, or is there anything else to check?

Thanks!

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trailgumby
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Re: Hydraulic brake issue

Postby trailgumby » Sun Aug 27, 2023 3:30 pm

That's a good start. You can try dropping the wheels out of the frame, removing the pads, and pushing the pistons back in with a plastic tyre lever, then reassemble everything and pump the levers until you get the bite point you want.

that will allow the brake fluid to lubricate the caliper piston walls, which should reduce friction enough to let the pistons act normally.

However, I would recommend a system flush and bleed as the DOT fluid used by SRAM is hygroscopic (absorbs water), which can cause brake failure when you get some heat into the calipers on a long steep descent.

Whorl
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Re: Hydraulic brake issue

Postby Whorl » Sun Aug 27, 2023 4:18 pm

Thanks mate, appreciate the response. Exactly what I was after. :)

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Duck!
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Re: Hydraulic brake issue

Postby Duck! » Sun Aug 27, 2023 6:00 pm

trailgumby wrote:
Sun Aug 27, 2023 3:30 pm

However, I would recommend a system flush and bleed as the DOT fluid used by SRAM is hygroscopic (absorbs water), which can cause brake failure when you get some heat into the calipers on a long steep descent.
This is why the brakes have locked on - the DOT fluid has absorbed moisture and expanded. That expansion can only go one way, and that is to push the pistons out and onto the rotor.

A full bleed with fresh juice will sort it out; push the pistons back when you have the top syringe connected & open, you want that old fluid in the caliper to push up into the hose where it will then be displaced by the new fluid being injected into the caliper.
I had a thought, but it got run over as it crossed my mind.

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trailgumby
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Re: Hydraulic brake issue

Postby trailgumby » Sun Aug 27, 2023 11:26 pm

Duck! wrote:
Sun Aug 27, 2023 6:00 pm
trailgumby wrote:
Sun Aug 27, 2023 3:30 pm

However, I would recommend a system flush and bleed as the DOT fluid used by SRAM is hygroscopic (absorbs water), which can cause brake failure when you get some heat into the calipers on a long steep descent.
This is why the brakes have locked on - the DOT fluid has absorbed moisture and expanded. That expansion can only go one way, and that is to push the pistons out and onto the rotor.

Ha! I'd never have thought of that as root cause. Makes perfect sense.

Whorl
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Re: Hydraulic brake issue

Postby Whorl » Mon Aug 28, 2023 6:46 pm

Duck! wrote:
Sun Aug 27, 2023 6:00 pm
trailgumby wrote:
Sun Aug 27, 2023 3:30 pm

However, I would recommend a system flush and bleed as the DOT fluid used by SRAM is hygroscopic (absorbs water), which can cause brake failure when you get some heat into the calipers on a long steep descent.
This is why the brakes have locked on - the DOT fluid has absorbed moisture and expanded. That expansion can only go one way, and that is to push the pistons out and onto the rotor.

A full bleed with fresh juice will sort it out; push the pistons back when you have the top syringe connected & open, you want that old fluid in the caliper to push up into the hose where it will then be displaced by the new fluid being injected into the caliper.
Noted! I'll source a kit to service the lot. Had been tempted to just put it into a shop to have it done, but would rather learn the task myself as it's one that is likely to repeat.

Cheers!

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DrShifty
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Re: Hydraulic brake issue

Postby DrShifty » Sun Sep 10, 2023 8:34 pm

Another tip. When you have the pads out of the brakes, file the front and rear edges of the backing plates to remove any paint. The pads should be snug in the calipers but any paint on the edges can bind against the caliper and prevent free movement when you release the brake lever.

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