It was pretty hot the other day, at least 37 C (100F). We were riding up a fairly steep trail when I got the feeling like there was some excess drag on the bike. I thought perhaps the motor/battery had reduced output as a result of the heat. I had also noticed that the both brakes had gradually been lost their “return”; they were not springing back when squeezed. I eventually stopped and spun the front wheel while off the ground. The symptom then presented itself; the brakes were on about 20% of their capacity. Heading up a steep trail, on a hot day, it was very noticeable. I tried adjusting the small adjusting screw located near the brake lever to its extremes, but it had no result. I ended up pushing/deflecting the disc brake both ways to push the pistons back into their seats. This procedure let the wheel spin free and I (slowly) rode down the next 900m (≈3000 feet) into the valley only using my rear brake.
Upon arriving home I looked up on the internet to see what I could find out about regarding my situation. I ran across a very random video:
In “broken” English text, it said that when the environment gets hot the piston inside the lever expands and sticks in its bore. The remedy was to remove some material from the outside faces of the piston to reduce the outer diameter leaving the piston some room to move (as pointed out).
I don’t have much experience with bicycle brakes, although I have rebuilt several car brakes, and looking at the warranty it said that the brakes are covered so off to the local bike shop I went with my story.
The local bike shop was very helpful, and basically said that the SRAM bike components were not the best, and that Shimano components were superior in general and that switching the brakes over would be the best long term course of action. They also gave me the option to start a warranty on the SRAM brakes to get them fixed. I asked the local bike shop to start the warranty process…..
I did a bit more digging on the internet(s) and found that this is a common problem and that SRAM is aware and will /may send out kits to replace this. I will need to see what happens, and if the new kit will really fix the problem. Either way, I am out the labor (theirs or mine) to bleed the brakes and take them apart.
I have also read on some German websites that the Shimano bike chains are also superior for this application. It’s upsetting to think that on the “flagship” mtn ebike Specialized chose to go with less than stellar components.
I will have to see how this plays out and will update with the results, until then if this happens to you – at least you have a known way to keep moving along with one rear brake; push the pads out by slightly deflecting the disc brake right next to the caliper, ciao.adios.goodbye.