Hydraulic disk brake problem

[John90]

I had to cart my mtb round in a car yesterday and today so I took the wheels off. Overnight I left the bike upside down in the hallway (I know, not recommended due to risk of oil leaks). Anyway - no oil leaks but the brake pads were pushed so tight together this morning that I couldn't get the disk in between them. Anyone know what caused this and whether the bike being upside down had anything to do with it? Is there an easy cure? I did manage to ease the pads apart eventually with a screwdriver but they are still quite tight against the disk.

 

[Angelfishsolo]

The brake levers have been pressed. Use a thin knife to part the pads and then refit the wheels. The rotors will open the pads futher. All should then be ok. Best of luck.

I had to cart my mtb round in a car yesterday and today so I took the wheels off. Overnight I left the bike upside down in the hallway (I know, not recommended due to risk of oil leaks). Anyway - no oil leaks but the brake pads were pushed so tight together this morning that I couldn't get the disk in between them. Anyone know what caused this and whether the bike being upside down had anything to do with it? Is there an easy cure? I did manage to ease the pads apart eventually with a screwdriver but they are still quite tight against the disk.

 

[John90]

OK, thanks for the quick response.

 

[Angelfishsolo]

You are welcome.

OK, thanks for the quick response.

 

[02GF74]

there sholdn't be any oil leaks as the braking system is sealed, uinless faulty but you can get air moving rom the master cyliner (Ibrake lever) in the hose so that the brakes will feel spongy.

 

[Dave W]

It may also be that the oil has warmed and expanded in your house.

I had to bleed my MTB during the recent hot weather cos the shed got warm and the rear brake locked on.

 

[02GF74]

^^^^ funnily I had that happen for the first time on a rear brake. I don't think it is the oil expanding, more likely some air in the master that applies pressure to the system.

I washed the dust off and left my bike out to dry in the sun - and find the rear disc was dragging and the lever was more or less solid.

It has sorted itself out but does not bode well, methinks.

 

[Dave W]

Dunno, I suspect that if air is able to seep in under very little pressure you'd see oil coming out under braking pressure and I'm not.

It also only ever happened when the bike got warm so looks like the obvious answer to me.

 

[Angelfishsolo]

I still assert that the most obvious answer is that the brake lever was pulled whilst the bike was being turned or after it was upside down. I has been it happen on many occasions.

 

[MacB]

I'm curious, with mechanical discs you can pull the lever wheel in or not and the pad retracts, yet with hydraulics the pad retracts when there's a rotor in there but not when it's absent. Why is that?

 

[Angelfishsolo]

I'm curious, with mechanical discs you can pull the lever wheel in or not and the pad retracts, yet with hydraulics the pad retracts when there's a rotor in there but not when it's absent. Why is that?

I believe the rotor is at the max travel point for the pads. When they go beyond this point they stick together.

 

[jethro10]

I'm curious, with mechanical discs you can pull the lever wheel in or not and the pad retracts, yet with hydraulics the pad retracts when there's a rotor in there but not when it's absent. Why is that?

Well with mine, Avid's, the return spring comes with the pads and is part of the pad system, so when you remove it, at full stroke of the lever, without pads, the pistons stays compressed, and on releasing the lever, it will take more fluid from the master cyclinder reservoir to re-fill the master cyclinder.

so basically in this situation of pistons being too far "out", the master cylinder has less fluid in it than normal.
As an earlier poster said, pushing the pistons back, moves the fluid from the caliper piston, back up through the pipe to the master cyclinder.

I have noticed other systems without external springs also work similarly, probably to keep the piston closer to the pad as it wears, so the lever action doesn't change and get 'long' like it does with cable brakes as the pads wear.
It's common on changing pads, to need to push the pistons back out fully.

Jeff

 

[Angelfishsolo]

Well with mine, Avid's, the return spring comes with the pads and is part of the pad system, so when you remove it, at full stroke of the lever, without pads, the pistons stays compressed, and on releasing the lever, it will take more fluid from the master cyclinder reservoir to re-fill the master cyclinder.

so basically in this situation of pistons being too far "out", the master cylinder has less fluid in it than normal.
As an earlier poster said, pushing the pistons back, moves the fluid from the caliper piston, back up through the pipe to the master cyclinder.

I have noticed other systems without external springs also work similarly, probably to keep the piston closer to the pad as it wears, so the lever action doesn't change and get 'long' like it does with cable brakes as the pads wear.
It's common on changing pads, to need to push the pistons back out fully.

Jeff

A far better explanation than mine. Thank you

 

[Dave W]

I still assert that the most obvious answer is that the brake lever was pulled whilst the bike was being turned or after it was upside down. I has been it happen on many occasions.

I'd agree in this instance, just offering a possible alternative.

 

[Angelfishsolo]

I'd agree in this instance, just offering a possible alternative.

No problems