# Hydraulic disk brake problem



## John90 (1 Jul 2011)

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.


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## Angelfishsolo (1 Jul 2011)

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.


John90 said:


> 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.


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## John90 (1 Jul 2011)

OK, thanks for the quick response.


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## Angelfishsolo (1 Jul 2011)

You are welcome. 


John90 said:


> OK, thanks for the quick response.


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## 02GF74 (3 Jul 2011)

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.


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## Dave W (4 Jul 2011)

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.


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## 02GF74 (4 Jul 2011)

^^^^ 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.


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## Dave W (4 Jul 2011)

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.


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## Angelfishsolo (5 Jul 2011)

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.


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## MacB (5 Jul 2011)

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?


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## Angelfishsolo (5 Jul 2011)

MacB said:


> 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.


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## jethro10 (5 Jul 2011)

MacB said:


> 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


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## Angelfishsolo (5 Jul 2011)

jethro10 said:


> 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.
> ...


A far better explanation than mine. Thank you


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## Dave W (5 Jul 2011)

Angelfishsolo said:


> 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.


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## Angelfishsolo (5 Jul 2011)

Dave W said:


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



No problems


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## 02GF74 (6 Jul 2011)

MacB said:


> 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?



The pistons will retract in hydraulic systems else each time you applied the brakes, they would never unclock.

The system is designed so that when the lever is released, the pistons are pulled in by the hydraulic fluid. If the pistons go too far out, i.e. there is no disc to limit how far out they go, they cannot be pulled back enough so that gap between them closes.

This is a good system as it takes up any wear in the pads and disc - mechanical systems need adjsuting.


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## John90 (17 Jul 2011)

Anyway, the solution was to put a knife between the pads and push them apart. Worked fine - so much for the supposed complexity of hydraulic brake maintenance!

Thanks again for the help.


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## Angelfishsolo (17 Jul 2011)

John90 said:


> Anyway, the solution was to put a knife between the pads and push them apart. Worked fine - so much for the supposed complexity of hydraulic brake maintenance!
> 
> Thanks again for the help.


Glad it worked


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## Cubist (18 Jul 2011)

John90 said:


> Anyway, the solution was to put a knife between the pads and push them apart. Worked fine - so much for the supposed complexity of hydraulic brake maintenance!
> 
> Thanks again for the help.



The whole "hydraulics brakes are hard to maintain" thing is simply perpetrated by those who have rim brakes and are actually afraid of new things........

Hydraulic brakes need to be kept clean with a squirt of brake and clutch cleaner every so often, and a good clean out with a rag when you change the pads, but as long as you don't let them get gunged up they will work trouble free for years


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## Dave W (19 Jul 2011)

Cubist said:


> The whole "hydraulics brakes are hard to maintain" thing is simply perpetrated by those who have rim brakes and are actually afraid of new things........
> 
> Hydraulic brakes need to be kept clean with a squirt of brake and clutch cleaner every so often, and a good clean out with a rag when you change the pads, but as long as you don't let them get gunged up they will work trouble free for years



I'd have to agree. My discs have been less trouble maintenance wise than any other type of brake I've ever used not to mention more effective.


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## 2Loose (19 Jul 2011)

Apart from re-aligning the calipers a few times after removing the wheel, hydro's are pretty adjustment free. Even with the realignment, it is painless compared to realigning calipers...but it looks complicated to the uninitiated.


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## Angelfishsolo (20 Jul 2011)

2Loose said:


> Apart from re-aligning the calipers a few times after removing the wheel, hydro's are pretty adjustment free. Even with the realignment, it is painless compared to realigning calipers...but it looks complicated to the uninitiated.



Agreed. HDB's are so simple to maintain. Pads can be expensive but worth the power you get


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