How much brake drag should I tolerate?

Wily-Quixote

My rear disc brake seems to suffer from excess drag.

My front wheel spins forever but my rear wheel stops in a short space of time although i don't notice excess drag when riding.

I have tries the usual stuff, changed pads, rotor, recentred brakes by loosening adjustors etc.

when i remove the pads and spin the wheel there is a marked difference (the wheel spins freely for much longer, but not as long as the front - so i attribute some drag to the freewheel).

When I spin the wheel with the pads in but brake adjustors loose I can see the caliper housing moving, as if the rotor was buckled. The rotor is new which makes me think that the frame is not true... the frame is carbon, high end and new but the dropouts are not thruaxles...

i know the answer is taking it to the bike shop but is there something i am missing here?

addit: they are avid elixir brakes around 4 years old.

Rightarmbad

Wily-Quixote wrote:

My rear disc brake seems to suffer from excess drag.

My front wheel spins forever but my rear wheel stops in a short space of time although i don't notice excess drag when riding.

I have tries the usual stuff, changed pads, rotor, recentred brakes by loosening adjustors etc.

when i remove the pads and spin the wheel there is a marked difference (the wheel spins freely for much longer, but not as long as the front - so i attribute some drag to the freewheel).

When I spin the wheel with the pads in but brake adjustors loose I can see the caliper housing moving, as if the rotor was buckled. The rotor is new which makes me think that the frame is not true... the frame is carbon, high end and new but the dropouts are not thruaxles...

i know the answer is taking it to the bike shop but is there something i am missing here?

If the caliper is moving as the wheel rotates, then the disc must be bent.
There should be no contact between the pad and disc when freewheeling.
Disc is probably a little out of straight.
System may have too much fluid in it.
Pistons may have been pushed out by squeezing the lever without a wheel in.
Caliper may be out of alignment.
Piston or pistons may be sticking, often happens on new bikes from sitting.
Wheel may be fitted crooked in frame if it doesn't have through axles.

Remove wheel.
Push pistons back into caliper, squeeze lever and check if they both move freely, if not clean piston sides with alcohol.
If you cannot push pistons all the way back into the body then let a little fluid out. You should be able to fit a bleed block in there.
Fit wheel, check it is seated in dropouts properly.
Loosen caliper and and pump brakes until pads come out and contact rotor, checking all the time that they come out evenly, sometimes they need a little help if you have pushed them hard in.
nip down bolts and check alignment by eye looking for even gaps both sides, both pistons moving equally and the pads hitting square on the rotor. Repeat as necessary.
Tighten up bolt to spec, don't overtighten, checking that the caliper didn't loose alignment as you do so.
Spin wheel, it should run clear.
If it hits in any one spot then true the rotor or replace it.

Wily-Quixote

I've already done everything on your list except:

Rightarmbad wrote:

Nip down bolts and check alignment by eye looking for even gaps both sides, both pistons moving equally and the pads hitting square on the rotor. Repeat as necessary.
Tighten up bolt to spec, don't overtighten, checking that the caliper didn't loose alignment as you do so.
Spin wheel, it should run clear.
If it hits in any one spot then true the rotor or replace it.

I'll try that.

Cheers,

Wily

The Rookie

The frame not being 'true' cannot make the calliper move as the wheel spins, obvious if you think about it!

lpretro1

Avid elixirs seem to often suffer from one piston (usually the inside one) sticking open causing drag especially if they don't get regular use. Sometimes this is because the system is too full of fluid as well. You can check - remove pads and see if u can push the pistons in - if it is impossible try letting a little fluid out by the bleed screw - just a v small bit - then try again. Also if you push one piston in and the other pushes out then it's the same problem. If the pistons won;t go in at all then it's new piston seal time

Wily-Quixote

The Rookie wrote:

The frame not being 'true' cannot make the calliper move as the wheel spins, obvious if you think about it!

yeah, should drag evenly or if the loosened caliper is being pushed and then returns it wouldn't happen at regular intervals like I am experiencing.

Wily-Quixote

lpretro1 wrote:

Avid elixirs seem to often suffer from one piston (usually the inside one) sticking open causing drag especially if they don't get regular use. Sometimes this is because the system is too full of fluid as well. You can check - remove pads and see if u can push the pistons in - if it is impossible try letting a little fluid out by the bleed screw - just a v small bit - then try again. Also if you push one piston in and the other pushes out then it's the same problem. If the pistons won;t go in at all then it's new piston seal time

cheers, will try this.