Can Bad Caliper Piston Cause Mush?

Okay, before I start, I'm not a noob, I've done plenty of work on bikes and brakes for that matter.

I've had pretty mushy/spongey brakes for about a year now but decent enough to ride the trails behind my house. Recently, I found myself with some money so I thought I'd do something about them so I bought an OEM Master Cylinder Piston and Seals, Brake Pads, and a Steel Braided Brake Line.

I installed all of this, bled the crap out of it, only to find out that brakes felt the exact same as before. (I know how to bleed brakes) I got curious and took the caliper off and realized that one piston was doing the majority of the work. The other would move but not much. I then pushed them all the way in and the "bad" one wouldn't move at all after pulling the brake lever.

I know this needs replacing but can this cause mushy brakes or is it something else that I can't think of? I thought usually a bad piston in the caliper made the brakes stick. I just can't logically think of why it would act spongey. (Btw they aren't leaking fluid and the rotor isn't bent).

If the piston is getting cocked sideways in the bore and not impacting the brake pad, ya, it can definitely act mushy.

You need to get a seal kit for the caliper and scrub that thing spotless and get some good brake specific grease for the pins and the pistons. If moisture has gotten into the caliper it can corrode the casting and cause these kinds of problems. Ive got an old XR that has the front caliper corroded out so bad the little grooves for the seals are gone entirely. The pistons literally fell out.

Wow, okay. Yeah, it's definitely not that bad but I do think it's getting cocked a little sideways. So how does that cause it to act squishy then because I thought the pressure would equalize once the piston and pad hit the rotor. Either way, I'm about to place an order now..

Should I get seals AND pistons or just seals?

.. just fyi, they frown on posting the same topic in multiple forums.

.. and now im confused, in your other thread you said you replaced the pistons, seals and line..

Can Bad Caliper Piston Cause Mush? (Not a noob, brake experts needed)

Okay, before I start, I'm not a noob, I've done plenty of work on bikes and brakes for that matter.

I've had pretty mushy/spongey brakes for about a year now but decent enough to ride the trails behind my house. Recently, I found myself with some money so I thought I'd do something about them so I bought an OEM Master Cylinder Piston and Seals, Brake Pads, and a Steel Braided Brake Line.

I installed all of this, bled the crap out of it, only to find out that brakes felt the exact same as before. (I know how to bleed brakes) I got curious and took the caliper off and realized that one piston was doing the majority of the work. The other would move but not much. I then pushed them all the way in and the "bad" one wouldn't move at all after pulling the brake lever.

I know this needs replacing but can this cause mushy brakes or is it something else that I can't think of? I thought usually a bad piston in the caliper made the brakes stick. I just can't logically think of why it would act spongey. (Btw they aren't leaking fluid and the rotor isn't bent).

If youve got a post in multiple forums, do me a favor and go delete it so I dont have to delete this one.

Sorry guys, I wanna delete this one but I can't find out how... Guess I am a noob in that respect :thumbsup:

I had this problem also.. make sure the caliper mounts aren't bent. Mine was just a hair. Loosen up the two bolts on the caliper but keep it in place and see if you have good pressure then, and if you do you might have the same problem I did.

Edited by crfbrap

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