Poor disc brake performance

[Jody]

But his basic problem seems to be lack of performance, and it seems to me a bigger rotor would likely result in an improvement.

Changing the disc size (sorry, hate the US term of rotor) won't make the problem go away. There should be sufficient stopping power using 160's to put you over the bars

 

[Jody]

When breaking them in, did you do about 20 stops from light to heavy, one brake at a time until you could feel an improvement?

I was initially really disapointed when I swapped to SLX brakes. First pull of the brakes from high speed..... nothing and felt like there was oil on the discs. Second pull.... slightly more than nothing. 3rd pull..... the back wheel is over a foot off the floor and i'm having thoughts of losing my teeth when I hit the tarmac. Really didn't expect them to grab like that

 

[DWM]

@Jody - you describe what I expected to happen, but unfortunately for me did not. I must have performed more than 20 stops from a reasonable speed, and whilst there was some improvement, it was still a case of a gradual rather than sudden stop.

Thanks again to everyone for your comments and suggestions. As you may have gathered I am determined to sort this out!

Dave

 

[Kajjal]

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 not true even with a combined hydraulic and cable brake system. Take a pure hydraulic system like mountain bike brakes, if air gets into the system the lever pull needed to brake increases until the point you can't brake as the lever hit the bar first. Bleed the brakes and this resolves the issue. On the OP's brakes this could still have an effect by making the brakes feel sharper if there is too much air.

Even brand new discs can get mildly contaminated. Normally the bedding in process burns this off bit not always if it continues after.

 

[Crackle]

What were the pads you bought? I went through this myself after accidentally getting mineral oil everywhere. Cleaned everything, changed pads twice and only on the third change to Superstar resins did the brakes come back to life. A few stops and they were as sharp as a tack. Not all pads are equal.

 

[Kajjal]

I was initially really disapointed when I swapped to SLX brakes. First pull of the brakes from high speed..... nothing and felt like there was oil on the discs. Second pull.... slightly more than nothing. 3rd pull..... the back wheel is over a foot off the floor and i'm having thoughts of losing my teeth when I hit the tarmac. Really didn't expect them to grab like that

Every spring when i switched from my rim braked road bike to my XT braked mountain bike it used to be deadly the first few times i braked

 

[Yellow Saddle]

This is not true even with a combined hydraulic and cable brake system. Take a pure hydraulic system like mountain bike brakes, if air gets into the system the lever pull needed to brake increases until the point you can't brake as the lever hit the bar first. Bleed the brakes and this resolves the issue. On the OP's brakes this could still have an effect by making the brakes feel sharper if there is too much air.

Even brand new discs can get mildly contaminated. Normally the bedding in process burns this off bit not always if it continues after.

I am not even sure where to start.....

 

[Kajjal]

I am not even sure where to start.....

Trying to appear superior makes you seem very arrogant which i don't think is your intention. You seem to be trying to help but have never had a bicycle with hydraulic brakes to have practical experience. Others on here have and have experience of installing and resolving faults with them.

 

[Yellow Saddle]

Trying to appear superior makes you seem very arrogant which i don't think is your intention. You seem to be trying to help but have never had a bicycle with hydraulic brakes to have practical experience. Others on here have and have experience of installing and resolving faults with them.

I am not even sure where to start.....

 

[Kajjal]

No more needs to be said.

 

[Profpointy]

Perhaps because that has nothing to do with brake performance?

Not quite sure what you are trying to say there. If there's air in 'em they will work very poorly if at all. Bleeding gets rid of the air, then they work properly.

Of course, there may be an underlying problem causing air to go in, but that's another story.

 

[Levo-Lon]

Air in the reservoir is not a problem ..air in the caliper or brake line Is a problem.
low fluid wont affect the brakes as long as its not airiated full of moisture etc and not gone below the point of entry from the Res ,small pin hole in the bottom that feeds the lines and caliper.
a few mm of lever traval seals the system and the pressue cycle begins..the Res is no longer in use..lever released..Res is open again.

you can actually bleed air out of the lines by moving the lever a small amount ,slow process ..but air in a caliper must be forced out..

the older avids need a perfect bleed and this often confuses the issue as standard brakes work with a small air gap in the reservoir, avids have a bladder type thing ..when there good there good.and awfull when there bad

 

[Psycolist]

This whole post just supports my theory that the use of 'disc brakes' on pedal cycles, has been an manufacturer lead policy, making us believe that unless we have a bike with disc brakes, we are in some way, second class cyclists. I don't ever remember, in over 50 years of cycling, not being able to stop in time, with my traditional rim brakes. There has been significant improvement in the braking capability of rim brakes over that time span, and in my world, disc brakes are a backward step. They are heavier, more expensive, more prone to unreliable operation, harder to set up and require more maintenance than the rim brake. I have posted this opinion on other threads, so my apologies if I am repeating myself, but I will stick to my good old fashioned rim brakes thank you very much. Anyway, they allow the purchase of new wheels when the rims become worn, and Mrs Psycolist cant complain because "its not safe to keep using the old ones dearest".

 

[Levo-Lon]

Lol

 

[T.M.H.N.E.T]

This whole post just supports my theory that the use of 'disc brakes' on pedal cycles, has been an manufacturer lead policy, making us believe that unless we have a bike with disc brakes, we are in some way, second class cyclists. I don't ever remember, in over 50 years of cycling, not being able to stop in time, with my traditional rim brakes. There has been significant improvement in the braking capability of rim brakes over that time span, and in my world, disc brakes are a backward step. They are heavier, more expensive, more prone to unreliable operation, harder to set up and require more maintenance than the rim brake. I have posted this opinion on other threads, so my apologies if I am repeating myself, but I will stick to my good old fashioned rim brakes thank you very much. Anyway, they allow the purchase of new wheels when the rims become worn, and Mrs Psycolist cant complain because "its not safe to keep using the old ones dearest".

You're repeating yourself and others who have spouted the same nonsense before you. Take a ticket and join the queue