Sudden loss of braking performance on rear brake - Vado SL 4.0

[Cycologist]

The other day, I washed the bike since it gets very dusty. I primarily ride on crushed limestone trails which get dry and dusty this time of year. I also cleaned and lubed the chain.

On my next ride, I had almost no friction in the rear brake and it was almost useless, even while squeezing the brake lever pretty hard.
Normally, if I'd squeeze that hard, the wheel would lock up. Not anymore. Even while squeezing the brake lever, I can turn the wheel by hand, if I push hard enough. That shouldn't be possible, and I can't do it to the front wheel, which brakes still work correctly.

I only clean the bike with water (no soap), but I did clean the chain with Parktool chain cleaner, which is a bit oily. I figured I might have gotten some on the brake disc somehow, even though it's on the other side of the wheel. I cleaned the brake disc with some polymer safe solvent and then lightly sanded them. I also cleaned the brake pads.

I still have no braking power back there. My only thought is that the brake pads got contaminated somehow, so I ordered replacements, which should be here in a couple days. The bike has over 2K miles on it and the rear pads are almost gone anyway.

I hope it's just bad pads, but any thoughts on what else the issue could be?

 

[Ben J]

Contamination of the pads/discs will cause this. You can get brake specific cleaner to try to decontaminate. You may need to remove the pads to do a thorough job.

 

[mschwett]

Once the pads (and rotors) are contaminated with chain lube or cleaner, it’s VERY hard to get them back to 100%. I put a ziploc bag around my rotors whenever i use drivetrain cleaner because it really doesn’t take much and we’re talking about rotating parts.

If you really want to try, take the pads out, take the rotors off. Soak the pads in 90% + isopropyl alcohol, and scrub them. Then sand them down a bit with regular sandpaper, and repeat the alcohol and scrubbing. Clean the rotors thoroughly, both sides, and lightly sand. Clean again. Reassemble everything and bed the brakes again. (need to do this since you’ve removed the film of pad material on the rotors.)

I’ve had success with this, but also failure. And it’s a PITA.

 

[fooferdoggie]

yep or just buy new pads and sand the rotor. chain cleaner or such will strip the rotor clean but don't use it on the caliper.

 

[Stefan Mikes]

The bike has over 2K miles on it and the rear pads are almost gone anyway.

If you brake a lot (hills?) then the brake pads may actually be worn. How do they actually look like? A lot of material left on the metal supports?
I'm slightly surprised it is the rear that is worn; usually the front brake pads are gone first.

You would be really unlucky if you contaminated the pads. I usually wash my e-bikes with a low-pressure rim cleaner and then rinse them with low-pressure water from a long distance at a good car wash. I clean and oil the chain with the e-bike upside down. It has never happened to me to contaminate the brake pads...

If you want to be on the safe side, just clean the rotor with an automotive brake cleaner (do not sand it!)