Elixir CR pad rub and bleeding

[SwissVan]

Perhaps someone has a fix and reason for the following, apologies for the long story but I try to get all the info into one post.

 

I have an Elixir CR disk brake set up on my Zula and have done +/- 50 hrs / 850 km of riding with them. Over the last few weeks I’ve noticed that the outer pad on the rear brake is making contact with the disk without any input from the brake lever, gradually it has got worse to the extent that it noticeably slows the wheel if you lift it off the ground and give it a gentle spin.

 

I’ve always used V brakes before this and as a result have kept a close eye on the performance of my first disk brake system, and I know that originally there was a slight gap between all the pads and disks and that the pad / piston retracted slightly after applying brakes leaving this small gap. The front brake and the rear brake inner pad gap still exists and performs the same as when it was new, it’s just the rear brake outer pad that is now contacting the disk and seems like it is not retracting enough after each brake application. It also seems to be getting progressively worse.

 

 

What I have done so far without any improvement:

1. Checked that the caliper is square and centered relative to the disk, the disk is true and runs as close as dammit thru the centre of the “disc slot” in the caliper.

2. Exercised the pistons in and out (carefully) a few times by pushing them flush and gently applying the brake (did not remove or try and lubricate the guilty piston).

3. Pushed both pistons flush and released a small amount of brake fluid from the lever bleed screw.

4. Swopped the front brake “spring clip” (between the 2 pads) with the rear brake. Yes a waste of time I knew but easy to do and in desperate times….

 

What I have done so far with some improvement:

1. Last night out of desperation I bled the rear brake. (Out of desperation because its not fun doing it as per Avids method for the first time).

There is a noticeable improvement in that the wheel now spins normally without to much obvious drag. Of concern is that the outer pad is still noticeably closer to the disk if compared to the front brake and inner pad on the rear. I have that gut feeling that after a few rides the problem will return again i.e. continue to get progressively worse.

 

What I have not done but probably should:

1. Try lubricate piston o-ring with brake fluid – Worried about creating a dust magnet causing more problems later.

1. Remove said piston and clean cylinder / piston look for reason why it (seems to) stick slightly.

 

My questions for the hubber disk brake experts are:

1. Anyone had this problem before and how do you fix it, permanently.

2. What pulls the piston back in after it has been extended by lever pressure? (Vacuum in the system or return pressure from the disk or...?).

3. The Avid 2 syringe 3 stage method of bleeding requires a supple body with 3 long arms, which I don’t have. Is there a better way that works i.e. just to pump fluid from the caliper bleed screw upwards thru the lever bleed screw until air is expelled?

 

Muto Obrigado for your advice…

[SwissVan]

Hmmm

BUMP

[SwissVan]

Raait!!!

 

Problem solved...So far anyway.

 

Seems like all it required was a few minutes to realign the brake caliper relative to the disk. The gap between the pad and disk is quite small and the tolerance for aligning the caliper to the disk even smaller...so even if it looks aligned it might not be.

 

Thanks to Manbearpig for providing the link below to a similar discussion which seems to cover most of the bases wrt my issue.

 

https://community.bikehub.co.za/topic/68685-xtr-pads-touching-rotor/page__st__20

 

And yes I'm still not convinced that discs are....