SPiN 360

This story has a happy ending...
Link to resolution of problem

***

Hello everyone,
I am trying to adjust my front disc brakes to stop the ever-so-slight rubbing.

The problem is that I just cannot loosen the CPS bolts. (See image, from manual.) Edit: Image shows rear brake, but I am dealing with front.

The idea is to loosen these CPS bolts, squeeze the brake lever, and then re-tighten the bolts.

I was trying really hard to loosen them by using a ratcheting screwdriver with a H5 (5mm) bit, but honestly, it felt like I was going to break the screwdriver.

Am I doing something wrong here? Or do I need a better tool? I just don't want to break the brakes themselves! (no pun intended)

And yes, I have a torque wrench to re-tighten things properly in the end.

Other things I have tried:
- I have tried closing the QR while squeezing the brake lever, and the result is "good" but it's still rubbing slightly.
- I observed the disc spinning between the pads, and the rotor doesn't appear to be obviously warped.

jimc101

That's a bigger problem that the rubbing, these are what you need to loosen to adjust the caliper to stop the rubbing, also, you need to be able to remove these to be able to replace the caliper if needed.

Have you tried using a Hex Y wrench (like this AWS-1 3-Way Hex Wrench | Park Tool) or regular hex key?

SPiN 360

I do not have one of those, but I was planning on using a screwdriver-bit adapter with a regular automotive spanner to get some better leverage with the H5 bit I had already tried.

But I think there is a bigger problem...
I may not have been looking at the right version of the manual. My brakes are SRAM Elixir 1, and the PDF manual I screencap'd is for "Elixir", but not any specific version within the Elixir line of products. So after going through some more manuals, I found that the CPS (caliper positioning feature) is on Elixir 3, but not the base model Elixir 1. There is nothing in the Elixir 1 setup about even tightening or adjusting those bolts. I don't know if they are even supposed to come off in this model. So maybe I should be counting my blessings that I didn't break the whole braking system.

My plan for tomorrow is:
1. Remove the brake pads and try to clean all around the caliper to make sure there's no dirt or any crap built up in there.
2. Try adjustment only with the main mounting bolts. (I have already successfully loosened those other 2 mounting bolts in the diagram.)
3. Live with the slight rubbing.

JoMang

Use a standard L Allen as it will give you the best leverage and you don't have to worry about clearance like you do with the Y.

dabac

You really should be able to.


If you truly can't, it's possible to move the caliper further inwards by adding shims between the adapter the caliper is mounted to and the frame. Or move the rotor further in by adding a shim under the locknut on the wheel axle.


I wouldn't do either unless I was certain that breaking the CPS bolts free would break what's the caliper is mounted to. If the caliper is mounted to an adapter(as in the pic), I'd go for it. That's an easily replaceable part.
If the caliper is stuck on a Post-Mount, I'd be more careful.



Never had much luck with that. IME, the caliper will squirm around too much during tightening. I prefer to loosen the bolts some, then use something like a screwdriver held by the blade as a light-weight mallet to tap the caliper in position before tightening down.



Didn't the manual call for 8-10 Nm?


That's considerable torque if you're using a screwdriver. Odds are more leverage is the fix for your problem.




We can't tell from here. When dealing with threaded fasteners, turning in the wrong direction is ALWAYS an option.

dperreno

A screwdriver handle with hex insert is an inappropriate tool for this. You need to use a proper hex wrench or a ratchet with a hex insert to get enough leverage to both loosen and tighten this. Even

corrado33

Use a normal L allen to loosen the bolts.

And slightly off topic: Hey look, another "my disk brake doesn't work right thread." For all the naysayers who say that they don't exist.

ammarolli

If you haven't reset the pistons you should do that with like plastic tire lever and push the pads as far as they go.

That might help with getting rid of the rub.

elcruxio

So first of all you're using the wrong tool for the job. You need an L-shape hex key.
Secondly don't use the "squeeze brake lever and tighten bolts method" as it's the wrong method for hydraulic brakes even if it is stated in the manual. Or rather, it's the idiot's method which is essentially a bandaid for a bigger problem.

Instead use this guide instead This way you never have to touch the CPS bolts again if the disc starts rubbing. Just check which piston is dominating and use a small screwdriver to push it back as is shown in the video.

SPiN 360

Thank you everyone for your comments so far. This has been extremely educational.
I did buy real L-shaped hex keys from Harbor Freight (metric & SAE sets) and I will be digging through my toolboxes to find them. They are not the ball-end type.

I took the pads out again to inspect the hardware and clean the pistons.
And I noticed what might be a bigger and more important problem.

I'm aware that mechanical disc brakes normally have only 1 side of the piston moving, but I thought hydraulic pinches the disc from both pistons. For me, pumping the brake lever only extends the wheel-side piston. The other side doesn't move.

It's starting to make sense now - I was originally fiddling with the brakes due to weak front braking power.

These brakes are SRAM Elixir 1. Is it correct to believe that both pistons should move, and therefore something is wrong?

corrado33

Sounds like one piston is seized. Personally I'd try to push it back into the body just to get it to move a bit, then try braking again. Yes, on decent hydraulic brakes both pistons should move.

Obviously the correct way to fix it is to disassemble the entire caliper and clean everything, but that's a lot more work.

SPiN 360

Yes I tried that. The outer (non-wheel) side piston appears to be pushed back all the way in. It's just not pushing back out when I pump the brakes.

These are entry level brakes anyway, so is it just a smarter idea to get a new front brake installed at the LBS?

dabac

Even entry level stuff should still be functional. It's not an excuse for failure unless hard used.

Try "exercising" the piston, getting it to move again.
Can you block the healthy piston off, pump the lever to force the stuck piston to move?

SPiN 360

Haha you read my mind...

I had the same idea, and held the working piston in place using a nylon tire lever.
With a bit of pumping, the other piston is working again!

So in summary, it appears the real problem was improper brake piston action leading in improper alignment of the disc brake pads. Piston was fixed, everything is back to original, correct alignment.

So by now I've re-assembled everything.
Pistons are working with brand new brake pads.
NO rotor rubbing.
Happy ending!