Disc brakes

[berty bassett]

New to disc brakes and having problems , I cannot stop them rubbing - it’s only slightly , but it’s driving me mad . SRAM rival 160 if that makes any difference . So far I have - took wheel out , cleaned protruded pistons and pushed back as far as they would go ( a lot better than they were but still binding ) - I’ve loosened calipers , pressed brakes and tightened up while pressing levers ( no different ) - under hood there is a hex bolt to release levers a bit - done that both ways , one way made me have to press brake lever harder to stop but still ribbed when released . I have never bled disc brakes and don’t know if this is the answer so any advise as to what to do next would be very much appreciated, don’t want to do something that isn’t necessary, all these other things I just looked up on YouTube but can’t find answer to this !

 

[88robb]

Bleeding probably isn't the issue. It's usually alignment. Loosen the two caliper bolts just enough so the caliper can wiggle. Spin the wheel and squeeze the brake lever hard. While still squeezing, tighten the bolts back up. This often centers the caliper over the rotor. If that doesn't work, your rotor might be slightly bent.

 

[raleighnut]

your rotor might be slightly bent.

I'd say that was the problem.

 

[berty bassett]

Bleeding probably isn't the issue. It's usually alignment. Loosen the two caliper bolts just enough so the caliper can wiggle. Spin the wheel and squeeze the brake lever hard. While still squeezing, tighten the bolts back up. This often centers the caliper over the rotor. If that doesn't work, your rotor might be slightly bent.

I’ve tried that ! No luck and also swapped wheels over ( 2 pairs ) and still have same issue ! I am at a loss

 

[raleighnut]

I’ve tried that ! No luck and also swapped wheels over ( 2 pairs ) and still have same issue ! I am at a loss

Disc brakes on a bicycle are just another thing to go wrong

 

[berty bassett]

Disc brakes on a bicycle are just another thing to go wrong

Probably- but I got caught out on a downpour on top of a mountain and rimbrakes didn’t do anything - I was so cold and wet and had no choice but to walk as I couldn’t stop - don’t want to do that again

 

[chriswoody]

Going back to basics, you mention you have SRAM Rival calipers. So are the pads SRAM pads and the discs themselves SRAM? Different manufacturers have different thicknesses of discs. If it's all the same brand stuff then we can assume that's not the issue. If the rubbing noise is consistent across the entire rotation of the disc then there's a good chance the disc won't be warped.

The last thing I would be looking at is the pistons themselves, tolerances are quite tight on discs, the pads run really close to the disc itself, so it may be that the pistons are not fully retracted because there's too much pressure in the system. In that case I would look at potentially bleeding the system and remembering to not pressurise it too much at the end. This is an old article, but I've still found it to be the best guide when I've bled my SRAM Rival brakes:

https://road.cc/content/feature/how-bleed-sram-hydraulic-road-disc-brakes-171725

 

[figbat]

I have a MTB that I bought second hand and was built up by the previous owner. The front disc rubbed and I couldn’t stop it using conventional wisdom until I realised that the disc was rubbing the caliper itself as it was a huge disc and the caliper wasn’t spaced out from the fork enough (very marginally).

 

[Punkawallah]

Possible cause could be excess fluid in the system.

 

[berty bassett]

Going back to basics, you mention you have SRAM Rival calipers. So are the pads SRAM pads and the discs themselves SRAM? Different manufacturers have different thicknesses of discs. If it's all the same brand stuff then we can assume that's not the issue. If the rubbing noise is consistent across the entire rotation of the disc then there's a good chance the disc won't be warped.

The last thing I would be looking at is the pistons themselves, tolerances are quite tight on discs, the pads run really close to the disc itself, so it may be that the pistons are not fully retracted because there's too much pressure in the system. In that case I would look at potentially bleeding the system and remembering to not pressurise it too much at the end. This is an old article, but I've still found it to be the best guide when I've bled my SRAM Rival brakes:

https://road.cc/content/feature/how-bleed-sram-hydraulic-road-disc-brakes-171725

thanks I will look into that - yes everything is sram and continual very very slight rubbing - it does seem like the pistons do not ever go back enough

 

[sevenfourate]

To be 100% clear….. Is this a continual rubbing. That despite everything you cannot rid.

Or an on and off rubbing ?

I take it this is on a Brand new - or new to you bike ?

 

[dicko]

I would have thought having Disc brakes on a bicycle would put a lot of radial bending stress on the wheel spokes. Are the wheel spokes of higher quality steel? Having calliper brakes this problem is less as the brakes grab the rim the tyres slow and the braking force is transmitted through the callipers that are attached to the frame through the callipers bolts.

 

[Punkawallah]

thanks I will look into that - yes everything is sram and continual very very slight rubbing - it does seem like the pistons do not ever go back enough

Have you considered there might be too much fluid in the system?

 

[chriswoody]

So what I would do if this was my bike is pop the bike up on the stand and put my head torch on. I'd very slowly rotate the wheel whilst looking at it from every angle. If as you say it's the pads not retracting enough, then I would have a pop at relieving the pressure, which is essentially caused by too much fluid as mentioned a few times above.

I would get an old rag and then wrap it around the bleed screw on the caliper to protect everything, then I'd remove the bleed screw and let a tiny bit of fluid escape. Be very careful not to let too much out, also wear nitrile gloves because DOT 5 is nasty stuff. With the bleed screw replaced, gently try to move the pads back and see if it's made any difference.

 

[Regular.Cyclist]

Try and work out if the rotor is running true first. I find measuring it from the fork leg easiest.

If the rotor is true then repeat the re-centering. I find using a spacer under each pad works best when doing this.

This is the sort of thing I use https://amzn.eu/d/iOYaKtc but you can use a feeler gauge or similar.