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Brakes seizing up (binding)


Longbarn Killer
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I'm no expert, but I do have a reasonable knowledge of bike repairs, but this is something I have never experienced.

 

A few months ago, I replaced the cable discs on my daughter's bike with Avid Elixir hydraulic. Twice, she has been out on a ride and the brakes seize up. The brakes clamp on to the discs and hold the wheels solid. It happens to front and back at more or less the same time.

 

Once we get home, we put the bike in the garage and a few minutes later they are free again. Both times that this has happened, it has been an exceptionally hot day. Could it be that the heat causes the hydraulic fluid to expand and once in the cooler garage it contracts again?

 

I have no idea what fluid is in the brakes. Surely brake fluid shouldn't expand in the heat? Is it possible there is some other crazy fluid in the brakes? 

 

Any other ideas on what it can be and what I can do to fix it?

 

 

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Brake fluid won't but other contaminants might, but it might also be the Piston as on the guide brakes

 

 

Give the brakes a proproper flush and bleed and see if the issue goes away

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I'm no expert, but I do have a reasonable knowledge of bike repairs, but this is something I have never experienced.

 

A few months ago, I replaced the cable discs on my daughter's bike with Avid Elixir hydraulic. Twice, she has been out on a ride and the brakes seize up. The brakes clamp on to the discs and hold the wheels solid. It happens to front and back at more or less the same time.

 

Once we get home, we put the bike in the garage and a few minutes later they are free again. Both times that this has happened, it has been an exceptionally hot day. Could it be that the heat causes the hydraulic fluid to expand and once in the cooler garage it contracts again?

 

I have no idea what fluid is in the brakes. Surely brake fluid shouldn't expand in the heat? Is it possible there is some other crazy fluid in the brakes? 

 

Any other ideas on what it can be and what I can do to fix it?

 

It is not likely to be the fluid heating up but rather the brake lever. This is a known issue with some models.

 

There's a little (usually plastic) cylinder head inside the brake lever that drives the brake. What happens is that it overheats and expands inside the barrel, causing the brake to seize (the return spring is no longer strong enough to return it back to the neutral position once depressed).

 

Asssuming you're out of warrantee, you can strip the lever, lightly sand the cylinder head piece, and then reassemble. Not as difficult as it sounds - look for instructions either on the hub or on youtube. Otherwise look for a new lever.

 

Edit - Also possible you've pinched the brake hose, although seems unlikely you would have done both.

Edited by 100Tours
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This is a description of the fix for the Shimano lever

 

Fix/Workaround: Shimano XT M785 Brake Lever - Tech Q&A - Bike Hub

 

This for the Avid

 

elixir_5_service_manual_rev_b.pdf (sram.com)

 

 

Also found this advice (no idea if it works though)

I find that letting a bit of fluid out of the caliper whilst pushing the piston solves this easy peasy. You might want to bleed after, but I have not found this neccesary.

 

Anyone ever actually had success unseizing an avid piston | Singletrack Magazine Forum (singletrackworld.com)

Edited by 100Tours
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How old is the brake set you installed? If it's an elixir set, I'm assuming it was used. Recommend taking servicing the calipers, remove the pots clean, lube the sealing rings with some dot and rebleed the system. Just taken apart and old set of CR's myself and the pots where very sticky and dirty.

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How old is the brake set you installed? If it's an elixir set, I'm assuming it was used. Recommend taking servicing the calipers, remove the pots clean, lube the sealing rings with some dot and rebleed the system. Just taken apart and old set of CR's myself and the pots where very sticky and dirty.

It was used. Not sure of the age, but it has worked perfectly until now.

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This is a description of the fix for the Shimano lever

 

Fix/Workaround: Shimano XT M785 Brake Lever - Tech Q&A - Bike Hub

 

This for the Avid

 

elixir_5_service_manual_rev_b.pdf (sram.com)

 

 

Also found this advice (no idea if it works though)

I find that letting a bit of fluid out of the caliper whilst pushing the piston solves this easy peasy. You might want to bleed after, but I have not found this neccesary.

 

Anyone ever actually had success unseizing an avid piston | Singletrack Magazine Forum (singletrackworld.com)

I was wondering about letting out some fluid, but I would imagine the trick would be not to allow in any air.

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Brake fluid won't but other contaminants might, but it might also be the Piston as on the guide brakes

 

 

Give the brakes a proproper flush and bleed and see if the issue goes away

I've never bled brakes before, probably my best bet is to leave it to the pros.

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Even the newer SRAM versions of Avid have know issues. I've had my SRAM Level TL's replaced twice under warranty after they started binding and the rear lever pulled all the way to the bar. Having said that, Avid are probably better than the early generation Srams... One day I'm going to upgrade to Shimano...

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This has happened to me with a pair of Avid XO Trail 4-piston brakes. One day, while out on a ride I had full stopping power on the rear brake and my finger was nowhere near the lever - was wondering why I suffered so much. Ended up taking the caliper off it's mount and taped it to the chainstay, finished the ride on front brake only.

I got a piston and seal kit, and rebuilt the rear caliper completely. Full bleed of the brake system as part of that process, new brake pads too. Worked great for two weeks, then same issue happened all over again even with brand new pistons and seals. Confusion. 

Long story short, we released a tiny amount of fluid out of the brake lever end and the problem went away for good. No idea how or why, but it worked.

Apparently if the system gets contaminated at all, usually with water, the brakes can bind. Could be from washing bikes, riding in the rain or just moisture in the air. The brake fluid/mineral oil is fine, but the moisture expands and boom, brakes on permanently.

Goodluck OP! New brakes are expensive so I hope that you get yours working again.

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There is Water in your "fluid".

Flush and Bleed before ordering Parts.

(Replace all the Brake Fluid)

Edited by dasilvarsa
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The avid brakes use brake-fluid. Brake fluid is hygroscopic and will attract moisture over time. So it is probably better to replace the brake fluid.

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