SRAM Code rear brake keeps exhibiting contamination symptoms

[ah1]

Hi, I have SRAM Code RSC on two of my amish bikes and on my Levo SL ebike. Only on the Levo SL I'm running into this issue: after 1-2 rides the disc makes loud squealing noises and I sometimes even feel the vibrations through the frame. I've tried everything - new rotors new pads, different pad material, sanding/cleaning existing rotors and pads. I take care to properly bed in the pads every time I do this. It works well for a few descents and then the squealing comes back.
Before I replace my brakes completely to something else - anyone ran into this and had a solution? Could my rear rotor be slowly contaminated by something in the system?
Thanks!

 

[irie]

Please post pics of your worn pads and squealing rotor.

 

[vertrkr]

I went thru this, might need your brake post mounts refaced:

Had to face my brake post mounts myself

Bike: 2021 Trek Rail 5 alloy Short story: My rear brakes never worked well, rubbing, noisy, lack of power or uneven wear. Tried everything I know, new hardware, LBSs, nothing worked completely. Broke down and bought the ParkTool facing tool, now it's perfection. Longer story: I've fiddled...

www.emtbforums.com

 

[irie]

I went thru this, might need your brake post mounts refaced:

Had to face my brake post mounts myself

Bike: 2021 Trek Rail 5 alloy Short story: My rear brakes never worked well, rubbing, noisy, lack of power or uneven wear. Tried everything I know, new hardware, LBSs, nothing worked completely. Broke down and bought the ParkTool facing tool, now it's perfection. Longer story: I've fiddled...

www.emtbforums.com

Just what I was thinking, pads and rotor would tell a story.

 

[Ou812]

I had the same issues with the Code RSCs that came on my Levo, tried everything but nothing fixed it. I ended up having the post mounts on my fork and frame refaced and that solved it. Still hated the Codes so they got tossed in the parts bin though.

 

[ah1]

@irie @vertrkr I've attached photos of new and old rotor (both exhibited same issues) and my current pads which have got 180 miles on them. The rotor and pads look very aligned in the garage test. Please LMK if you think it's a postmount issue, and if so: that tool is very expensive, could I just get away with trying another postmount?

 

[John_likes_bikes]

Do a piston massage then with the pads removed see if they extend evenly. Could be a pad virbrating if one of the pistons is sticking.

For reference:

 

[vertrkr]

@irie @vertrkr I've attached photos of new and old rotor (both exhibited same issues) and my current pads which have got 180 miles on them. The rotor and pads look very aligned in the garage test. Please LMK if you think it's a postmount issue, and if so: that tool is very expensive, could I just get away with trying another postmount?

Mine looked fine too. I'd suggest calling around to see if a lbs has a facing tool. Some shop in Santa Cruz must offer that service.

 

[Rod B.]

Hi, I have SRAM Code RSC on two of my amish bikes and on my Levo SL ebike. Only on the Levo SL I'm running into this issue: after 1-2 rides the disc makes loud squealing noises and I sometimes even feel the vibrations through the frame. I've tried everything - new rotors new pads, different pad material, sanding/cleaning existing rotors and pads. I take care to properly bed in the pads every time I do this. It works well for a few descents and then the squealing comes back.
Before I replace my brakes completely to something else - anyone ran into this and had a solution? Could my rear rotor be slowly contaminated by something in the system?
Thanks!

ah1,

In response to your questions, there are two issues at play when it comes to SRAM brakes. I will explain below. My hope is this will help you and others who have a similar issue with their SRAM brakes or possibly any other manufactuer's brake system.

At the end of this message you will find a Shimano Part # 3 brake maintenance article that deals will issues causing squealing brakes and loss of brake performance due to brake rotor wear.

Below is contained general information pertaining to SRAM and squealing brakes caused by pistons sticking in a SRAM brake caliper.

1. SRAM Code brakes, Guide, Level, or G2 all use D.O.T. 5.1 or D.O.T. 4.0 brake fluid.

The Dept. of Transportation (DOT) sets brake fluid standards. DOT classifies brake fluids (DOT 3, DOT 4, DOT 5, and DOT 5.1, etc) based on their performance characteristics, primarily the boiling point of the brake fluid. DOT fluids are mainly used in automotive applications and in most instances should not be mixed, i.e. use DOT 5.1 with DOT 3. To do so will alter the chracteristics of the brake fluid, i.e. boiling point.

All DOT brake fluids are "Hygroscopic", meaning the fluid readily absorbs moisture from the air. This applies to fluid sitting on a shelf in it's storage container, or flowing through brake lines and calipers. Because of the mositure absorption properties, DOT fluid must be flushed from a braking system on a regular basis and replaced. I personally like to do so about every six months or so. If the brake fluid is not replaced regularly, the fluid will become contaminated. This is indicated by the DOT brake fluid becoming discolored. In severe contamination instances the fluid will turn black due to moisture contamination. In mild contamination instances the fluid will turn a dark amber color.

Contaminated fluid will reduce braking performance due to the moisture altering the boiling point of the fluid. If you've ever accidentally touched your brake caliper or rotor after a hard downhill run, then you know how hot your brake system gets. You want your brake calipers to be able to apply maxium pressure to the brake pads and rotors and not fade due to loss of braking pressure. It is also important to point out that moisture contaminated brake fluid will lead to corrosion within the braking system, i.e. pistons sticking, brake lever action become sluggish, etc.

Note: Because DOT brake fluids are hygroscopic, some brake manufactuers such as Shimano, TRP, Magura, etc. use a mineral oil based braking fluid which is not hygroscopic.

There are numerous online videos online which detail how to bleed and flush your SRAM brake system. Fortunately, SRAM uses a tool called the "Bleeding Edge", which makes brake bleeding very easy to do on SRAM braking systems. You will need to purchase a bleed tool kit in order to flush your SRAM brake system. In many instaces the bleed kit will not come with a "Bleeding Edge" tool and you will need to purchase it seperately and incorporate it into your brake bleed kit.

2. All brake calipers, whether Shimano, SRAM, etc. use a flexible rubber seal to retract pistons back into the caliper once brake lever pressure has been released. I obtained the diagram below from a Singletracks online article which depicts how a brake caliper operates.

Note in the diagram that when brake pressure is applied, the piston glides outwards from the piston bore and also rolls and stretches the piston seal outwards. It is the stretching action of the piston seal that retracts the piston back into it's caliper bore when brake pressure is released ast the lever.

The resistance of the seal to being rolled outwards is not strong. If a piston is contaminated with dirt build up on the exposed surface and or deformation from scuffing has occured, the seal will not be sufficiently strong enough to retract the piston back into the caliper. This is the bane of all mountain biking systems, a "Sticking' brake caliper piston.

SRAM Guide, Code, etc. calipers use Phenolic resin based plastic pistons. These soft pistons are easily scuffed and scored from the repeated inward and outward motion of the piston. After about two to three months of hard use the phenolic pistons in your SRAM caliper will begin to stick. This will lead to uneven brake pad wear between the two sides, or front to back on one brake pad side.

A sticking piston(s) will cause your brake lever to feel spongy and have a lot of free play, i.e. the lever will travel almost to the handlebar before the brake engages. No amount of bleeding will fix a SRAM spongy brake lever action if the pistons are sticking. Repeat, if a piston is sticking in a SRAM caliper it is almost impossible to achieve a hard and firm brake lever action. I believe the cause for the spongy brake lever to be the small cavity created behind the sticking piston(s) which are usually stuck in the extended outward position. The small cavity behind the piston traps air and therefore no amount of bleeding will fix the issue. You must free up the piston(s) and fully retract them back into the caliper before you start the bleed process.

It's easy to determine if the pistons in your SRAM Code/Guide caliper are sticking. You visually look at your brake caliper while you squeeze the brake lever. If all four pistons move outward, then your caliper is functioning normal. If you see one or more pistons not moving, or you see some pistons moving more freely than others, then you have sticking piston(s).

SRAM caliper pistons seem to stick quicker than other manufacturer brake calipers. SHimano uses a hard ceramic piston, whereas TRP uses a piston incased in a stainless steel sleeve. SRAM caliper piston use a resin base piston which seems to scratch and score quicker.

All brake caliper pistons regardless of manufacturer, will become scored after a period of hard use. Seen below are pistons removed from my TRP DHR-Evo brake caliper. The caliper has approximately 6,000 miles of use and the pistons were beginning to stick in the caliper. Note that the upper piston has light scoring on the outer stainless steel piston sleeve. The scoring was causing the piston to stick. The piston depicted below the scored piston has been buffed and the scoring has been removed. This allowed the piston seal to to retract the pistons in a normal fashion again.

I do not recommend buffing and restoring pistons. Many manufactuers such as SRAM sell caliper rebuild kits. The kits are inexpensive and rebuilding a caliper is a fairly easy process. You must possess the tools and sufficient mechanical skill to perform a caliper rebuild. If you do not, do yourself a favor and take your bike to a local mechanic. TRP unfortunately does not currently sell a caliper rebuild kit for the DHR-EVO caliper. I was left with the option of trying to restore the piston's surface or buy a brand new caliper. Hold my beer, lets do this.

There is a slight short cut that can briefly remedy a SRAM sticking pistons. This is a temporary fix and will not last long term. The only long term solution is to rebuild or replace the caliper. The process involves cleaning the caliper and pistons and applying brake fluid lubricant to the pistons. This will allow for a successful bleed and a firm lever once the pistons have been freed up.

The process involves taking your wheel off and removing the brake pads from the caliper. When removing your brake pads, be sure to mark the pads left and right side so that they will be returned back to the same side they were removed from. Take alcohol and a rag, scrub the brake caliper clean. Very carefully, extend one piston and using a thin strip of cloth or a Q-Tip, buff around the base of the piston to remove any debris/crud build up. Take a second Q-tip dipped in DOT fluid and lubricate all around the base of the piston. Cycle the piston back and forth in the piston bore until the piston slides smoothly inwards and outwards with no stiction.

Note: Use caution when extending the pistons. You want to extend the piston only a short amount. If you extend the piston too far outwards, the piston will exit the piston bore and your brake fluid will drain from the caliper. This will require an "Ah Shit" expletive and a total re-bleed of the brake system if this occurs. Note that several sellers on ETSY sell a 3D printed cleaning block. The cleaning block tool is placed incide the caliper and allows only one piston at a time to be extended. The tool also prevents the piston to be cleaned from extending out too far. To use the tool, you just flip it side to side for each piston.

I've written a three part series of articles on brake performance for the eMTB forum. The articles are for Shimano brake systems, however the information contained in Part # 1 and Part # 3 can generally be applied towards SRAM or any other brake system.

Part # 1: Shimano Brake System Service

This will be a three part technical article discussing Shimano braking system components, how to service your Shimano brakes and brake system modification on your Rise. Part # 1 will discuss basic maintenance on your Shimano brakes. Part # 2 will discuss brake modifications to your Orbea...

www.emtbforums.com

PART # 2: SHIMANO BRAKE SYSTEM – Orbea Rise Brake System Modification

This technical article is the second installment in a two part series on Shimano brake systems. Refer to “Part # 1: Shimano Brake System Service”, for information on bleeding and servicing Shimano brakes and brake pad compounds...

www.emtbforums.com

Part # 3: Shimano Brake System Service

After submitting Part # 1 and Part # 2 of the tech series on Shimano brakes, I realized I had not included anything on checking your Shimano brake rotor for minimum thickness or signs of uneven rotor wear. You can review Part # 1 and Part # 2 in the series here...

www.emtbforums.com

Be safe,
Rod

 

[irie]

The rotor looks horrible, my guess is that the caliper is leaking fluid.

 

[Mikerb]

The rotor looks horrible, my guess is that the caliper is leaking fluid.

my thoughts as well............that contamination is coming from somewhere and the most likely culprit is the calliper. It is clearly nothing to do with pads and rotors...they are just victims!!

 

[John_likes_bikes]

The rotor looks horrible, my guess is that the caliper is leaking fluid.

I don't see contamination, I see a cooked rotor that has seen a lot of heat. Seeing as this is only happening on the heavier ebike I suspect that's the case. Along with the compound that MTX uses.

I would clean those rotors up, use metallic pads and see how that goes.

 

[Ou812]

Those things have had some serious heat put through them, you can see the discolouration. Do you ride the brakes? If not it’s more than likely a piston not fully retracting.

 

[Rod B.]

my thoughts as well............that contamination is coming from somewhere and the most likely culprit is the calliper. It is clearly nothing to do with pads and rotors...they are just victims!!

Mike & Irie,

It's possible the rotor has been contaminated however, I'm not 100% sure on that. We would need to see a picture of the caliper to see if it is leaking fluid. It could also be something as simple as washing the bike with a high soap concentrate and contaminating the rotor.

I'm leaning more towards a worn rotor. When I look at the rotor, I see the rotor has been subjected to high heat, i.e. the toasty brown color. I also see that the rotor has high and low spot wear grooves on the rotor face. I've dealt with this on several occasions. High and low wear grooves will cause brake squeal. It's similar to running your fingernail on a chalkboard as the brake pads chatter in the grooves on the rotor.

Typically, when i encounter high and low grooves on a brake rotor I like to look at the brake pads. They will usually display some type of streaking like what is depicted below. Unfortunately, ah1 said the brake pads have been sanded and cleaned. This would erase the streaking.

A rider's first reaction when encountering brake squeal is to clean and re-surface the brake pads. This will make the noise go away for a few rides however, the squealing will return as soon as the pads bed back down into the high and low wear grooves. My guess is the high heat friction is due to the pads not making optimal contact with the rotor and causing high heat thus the brown toasty color.

As you guys suggest it may very well be contamination. However, I think I would take a spare rotor from the used spare parts bin and put it on the bike to see if the noise and discolorization go away. If it does, then buy a new rotor.

 

[ah1]

Do a piston massage then with the pads removed see if they extend evenly. Could be a pad virbrating if one of the pistons is sticking.

For reference:

Thanks! I actually followed that exact same video instructions So I've already tried that, works great for aligning the rotor and calipers but the problem keeps coming back (even when they do seem aligned). BTW that 4mm wrench hack is genius!

 

[ah1]

Thanks all for the replies! And thanks @Rod B. for the great detail! To respond to some of the things:

• I don't know exactly what "high and low" means, but the photos of my pads above are *before* any sanding. They currently squeal but I haven't gone through sanding with these yet. And in the past when I sanded I didn't see those horizontal streaks on the pads, they seemed uniform.
• I tried two rotors. In the photos above, the current rotor which is on the wheel only has about 110 miles - so yes it seems like it cooks quickly. The rotor that's photographed uninstalled was on for about 800 miles.
• I did initially use the SRAM metallic pads but they produced similar noise so that's when I switched to MTX to try and alleviate the noise. Also, I use the MTX Gold on the front and it's not giving me the same issues.
• Lastly I forgot to mention but this wasn't an issue for the first few months of the bike (although my rotors do get discolored quickly - maybe I'm using rear too much...) . It only started after about 800 miles, that's when I replaced to the previous rotor that's seen uninstalled in the photo.

Thanks

 

[mrtrinh]

even though the brakes are squealing are they still providing bite and stopping power? I just put MTX gold on my trp's and they do squeal a bit. I bedded them in properly and they do provide good stopping power.

 

[ah1]

even though the brakes are squealing are they still providing bite and stopping power? I just put MTX gold on my trp's and they do squeal a bit. I bedded them in properly and they do provide good stopping power.

Yes, they're still stopping albeit after a while with vibrations - but they do still stop and the lever feels firm. Which leads me to believe maybe it isn't an oil leak per se (could be another contamination that's somehow reoccurring )