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Poor disc brake performance
- Thread starter DWM
- Start date
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- disk brakes
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Kajjal
Guru
- Location
- Wheely World
If you prefer rim brakes then use them and enjoy your cycling which is the main thing. My old mountain bike has v-brakes and is great fun to ride off road.
But given the choice i prefer hydraulic disc brakes for much better all round braking. No problems with reliability or maintenance in my experience and after the first time very easy to setup.
But given the choice i prefer hydraulic disc brakes for much better all round braking. No problems with reliability or maintenance in my experience and after the first time very easy to setup.
Yellow Saddle
Guru
- Location
- Loch side.
Let's liken it to an engine. If it won't start, it isn't performing poorly. It is not working at all. However, if it starts and the fuel mixture is wrong, it will run but splutter and burp and not perform well.
I hope that clears up my position on the issue.
Back to brakes, If there is air in the system, they will fail or, if you quickly pump the lever, they will work and perform well. However, if there is oil on the disc, the lever will work but the brakes won't perform.
My definition of perform in this case is "mechanically (hydraulically) sound but tribologically poor".
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Kajjal
Guru
- Location
- Wheely World
That is very different to what you said originally and good you have completely changed your view.
Pumping the lever can help to a point to settle things down for example if there is air in the system and you turn the bike upside down, once upright again pump the lever and things can improve, unless the lever goes all the way to the bar.
Yellow Saddle
Guru
- Location
- Loch side.
No it is not and I have not changed my view. May I suggest that you put me on ignore? That would solve much of your misunderstanding.
Kajjal
Guru
- Location
- Wheely World
This is your first comment :-
"Topping up wont work. The system is such that even if there is the absolute minimum fluid in there to make it work, it will still work exactly as good or bad as when it is full of fluid."
This is your second :-
"Back to brakes, If there is air in the system, they will fail or, if you quickly pump the lever, they will work and perform well"
They are very different and can be very confusing for people not used to dealing with disc brakes on bikes. If there is too much air in the system you have to bleed the brakes, a little air may not be much of a problem and a quick topup bleed can sort it out if people feel the need.
"Topping up wont work. The system is such that even if there is the absolute minimum fluid in there to make it work, it will still work exactly as good or bad as when it is full of fluid."
This is your second :-
"Back to brakes, If there is air in the system, they will fail or, if you quickly pump the lever, they will work and perform well"
They are very different and can be very confusing for people not used to dealing with disc brakes on bikes. If there is too much air in the system you have to bleed the brakes, a little air may not be much of a problem and a quick topup bleed can sort it out if people feel the need.
Yellow Saddle
Guru
- Location
- Loch side.
Lets look at statement 1:
It says that the fluid level is irrelevant unless it drops to below a level where the system will not work i.e. at a level when air will enter the system. Anything above that is superfluous and only there to supply fluid to the system for when the pads wear down and the pistons have to extend a bit further. Even 1000th of a ml above critical level will do the job.
Statement no 2: This explains the symptoms of air in the system and tells you how to double-check that it is air - by pumping to return the brakes to normal operation. In this case, the brakes have to be bled. No other scenario requires bleeding or topping up.
Where do you find a contradiction or fault in my logic?
I don't understand your use of "too much air in the system." The tiniest bubble is too much. One molecule is too much. The system will only work properly with NO AIR inside the hydraulic line. Air above the reservoir level is irrelevant. There the entire atmosphere sits with no ill effect.
I also don't understand what a top-up bleed is. You can top up the system without bleeding and you can bleed it without topping up? Fluid in a hydraulic system is never topped up unless it has leaked out. The level rises and falls as the pads wear and are replaced, but topping up is not necessary. It is not like engine oil where a tiny bit is consumed by the engine.
Kajjal
Guru
- Location
- Wheely World
That's fair enough you have changed to providing sensible advice.
To give you a practical example my front brake has a little air in it but works fine for my needs giving sharp, controlled braking so i leave it as it is. Previously it had too much air in it which affected the braking until i bled it.
A top up bleed or quick bleed comes from mountain biking. It just means unscrewing the top bleed port, attaching the brake fluid container with a little fluid in and carefully pumping the brake. Air bubbles will come out. Then close the port. Often this means a full bleed is not needed but not always.
To give you a practical example my front brake has a little air in it but works fine for my needs giving sharp, controlled braking so i leave it as it is. Previously it had too much air in it which affected the braking until i bled it.
A top up bleed or quick bleed comes from mountain biking. It just means unscrewing the top bleed port, attaching the brake fluid container with a little fluid in and carefully pumping the brake. Air bubbles will come out. Then close the port. Often this means a full bleed is not needed but not always.
Sorry for the delay in updating the situation - due to work commitments and being unwell, this morning was the first time I have cycled since fitting and bedding in the new pads/rotor.
I can report that the brakes are as bad as ever, and are now very noisy (squealing) as well! I don't brake much on my commute (mostly along the Bristol to Bath railway path), but there was perhaps a hint that the performance was getting a bit better towards the end, but it was still pretty poor. I have read that applying a tiny smear of copper slip on the back of the pads helps with noise so I will try that when I get home.
In terms of the performance, I really am at a loss now. It may be time to admit defeat and take it to a LBS!
Cheers
Dave
I can report that the brakes are as bad as ever, and are now very noisy (squealing) as well! I don't brake much on my commute (mostly along the Bristol to Bath railway path), but there was perhaps a hint that the performance was getting a bit better towards the end, but it was still pretty poor. I have read that applying a tiny smear of copper slip on the back of the pads helps with noise so I will try that when I get home.
In terms of the performance, I really am at a loss now. It may be time to admit defeat and take it to a LBS!
Cheers
Dave
raleighnut
Legendary Member
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Yellow Saddle
Guru
- Location
- Loch side.
