Is my caliper causing squealing?

[murbot]

New Rad Mini 4 with mech brakes. The rear was squealing bad over about a 3-4" section of the rear rotor. Have rode a total of 3 miles.

Removed front and rear rotors
Soaked rotors 20 minutes in 90% alcohol, then wiped thoroughly with lint free cloth
Wiped pads down with 90%
Sanded rotors and pads with 320 grit and a block (have done and seen this done at shops before),
This allowed me to ride all the way up to 1.5 miles before the squealing started again. Not as bad, but seems to be building.
I've adjusted the pads as far from the rotor as possible, then turned the nut a couple clicks to be closer, but it doesn't effect the squeal either way.

With the bike upside down and slowly spinning, the top of the inside pad seems to be touching or almost touching the rotor. The mounts look good, but I'm thinking the caliper might be offset slighting causing the inside pad's top edge to rub. The squeal stops if I apply the brakes. If I'm cresting a hill with no squeal, using the pedal assist or throttle, then stop pedaling or throttling, it's almost like a queue for the squeal to begin when the motor stops...though it's not 100% of the time. Maybe 80%.

Any thoughts on either the throttle (or pedal assist) somehow triggering the squeal?
Any thoughts on on the top edge of the pad rubbing? Should that pad naturally sit closer to the rotor?

Thanks for any thoughts or suggestions.

 

[indianajo]

When I sand a rotor, I make radial stripes, not circular. That is what works to stop squealing on cars. I haven't had a bike rotor squeal yet. If the pad touches the rotor on my bike, I have to pedal harder & sweat more, but it doesn't squeal.

 

[murbot]

Thanks!!

Radial strips: You mean swiping around the rotor like going around and around a pizza crust?
Circular: You mean swiping in circles like waxing a car, but smaller circles?

If my descriptions are correct, then I also do Radial. I didn't mention in my OP that I swapped the front with the rear rotor\pads and still have the same sounding squeal. Though it's not as bad and was completely quiet for that first 1.5 miles after cleaning. With the limited knowledge I have, this seems to point to the caliper.

 

[indianajo]

Study a geometry source and discover what a radius is. The stripes from grit should look like that. I never worked in a pizza restaurant. I used a belt sander and rotated the disk around in a vise as I sanded around radially. Outward from center.

 

[PedalUma]

There could be residue on the pads. Also they may not be aligned. Try sanding them and wiping them and the rotors with a little acetone. For alignment use rubber bands lightly on the levers. Loosen the calipers, turn the wheels and slowly retighten as you turn the wheels. This can be done with the bike upside down. Put down a white piece of paper so you can see the gaps. When you are done there should ideally be a gap the thickness of a business card visible on each side of the rotors at the pads.

 

[murbot]

Study a geometry source and discover what a radius is. The stripes from grit should look like that. I never worked in a pizza restaurant. I used a belt sander and rotated the disk around in a vise as I sanded around radially. Outward from center.

LOL - I know what it means (I'm still collecting vinyl), but I can't be sure others learned the same till I verify... Seemed like a curious thing to bring up and folks get basic language incorrect online frequently, only reason I wanted to double check.

 

[murbot]

There could be residue on the pads. Also they may not be aligned. Try sanding them and wiping them and the rotors with a little acetone. For alignment use rubber bands lightly on the levers. Loosen the calipers, turn the wheels and slowly retighten as you turn the wheels. This can be done with the bike upside down. Put down a white piece of paper so you can see the gaps. When you are done there should ideally be a gap the thickness of a business card visible on each side of the rotors at the pads.

Super instructions !! Thank you
I'm hesitant with the acetone. But I'll work on alignment. I knew the bike was coming with lower quality parts (due to availability) and plan to replace most components, but hopefully not all at once.

 

[elliot friedman]

Radial means like the wheel spokes on your bike

 

[PedalUma]

Dollar store nail polish remover is the same as acetone. It is amazing how much black crud it will clean off brakes. Just use a little outside with a soft cloth. When ever I go to a Dollar store I ask for a price check.

 

[murbot]

Dollar store nail polish remover is the same as acetone. It is amazing how much black crud it will clean off brakes. Just use a little outside with a soft cloth. When ever I go to a Dollar store I ask for a price check.

Thank you. I'll give the acetone a shot tomorrow on my day off.
I'm going to ask the question below in the Rad forums, but thought I'd note it again here. Rode it last night and again today. Squeal starts up when the power to the motor cuts off and I'm not applying the brake. If I stop pedaling, the sound lightly starts for 1-2 revs, then by the 3 time around, it's hitting that squeal, squeal, squeal pretty loud until I apply the brake either hard or light.
Any idea why it does this?

 

[PedalUma]

Thank you. I'll give the acetone a shot tomorrow on my day off.
I'm going to ask the question below in the Rad forums, but thought I'd note it again here. Rode it last night and again today. Squeal starts up when the power to the motor cuts off and I'm not applying the brake. If I stop pedaling, the sound lightly starts for 1-2 revs, then by the 3 time around, it's hitting that squeal, squeal, squeal pretty loud until I apply the brake either hard or light.
Any idea why it does this?

Double check the tightness of the axle bolts. On this model they are made out of cheese. You can bring one into a place like Fastenall as a sample and the will sell you much better ones.

 

[Dave Rocks]

 

[murbot]

Yep. That's exactly what mine looks like. I guess I should replace them then. :-D

I tightened the inner pad, loosened the calipers, strapped down the hand lever, slipped an index card in between the inner pad and rotor, tightened the caliper (took a couple tries and had to apply light pressure with my free hand to center it on the rotor as I tightened) and it now sits with a perfect gap on either side. Just took my first completely brake squeal free ride looking at Christmas lights. Sooooooo great.
Gonna wear out these funky Mongoose tires I got to break things in and replace with a better 4" or a fat looking 3-3.3".

Thanks for the help. I'd never have fixed it this quickly or expletive free without your assistance.

 

[AHicks]

First time around these can be a pain in the butt to set up, but as you've found, it is a setup issue. A big congrats on working your way through it. Well done!

Why are you considering replacing the tires so soon? Are they noisey?

 

[murbot]

Thank you. I wanted it to ride and also to tinker with. It's perfect all around.

Rad is unable to get the Kenda 4" tires they were selling with the bikes. One of the reasons the price dropped by $300. They're using the 3" CST Big Boat road tire from the Rad Runner for now. I wanted a better off road option and figured I may as well get a 4" so I got the Mongoose tires from Amz. They're flimsy and I should have sent them back. But I installed them instead... along with the Tannus protectors, and now getting them off is very, very difficult. I bent 3 out of 4 Park tire levers trying. Some new Pedro levers just arrived from Amz a minute ago, but I'm not up for dealing with them again now. I'll wear out the cheap Mongoose tires and put some Kendas or Schwalbes or anything else on.

I can see where I might even prefer something like a 3.3" for some things, but overall the 4" will probably provide more cushion, which I need for an injury.

 

[elliot friedman]

helps with squealing as well

 

[Solarcabin]

It is a Rad Power bike. what did you expect?

Slowly backs out of the room...

 

[murbot]

It is a Rad Power bike. what did you expect?

Slowly backs out of the room...

Got exactly what I expected. My first eBike that fits well within my budget, allowing easy upgrades. Which are inexpensive and readily available with compatible connections. The price dropped so I put the extra money into upgrades that leave me with an eBike with better components than I could've afforded to buy as original equipment. Half the point of getting this vs another bike was because I wanted something new to tinker with as well as enjoy riding.

Supplies are low everywhere. There's other tires that aren't available besides what Rad offers. Just like any regular bike, I upgraded a few things from the start.

It's not a QuietKat, but it does more than I need it to and didn't cost $3k+. I couldn't be happier with my choice. I'll upgrade to something else in 2-3 years maybe, but this is for having fun around my neighborhood and camping.

This bike is serving its purpose perfectly.
Happy holidays !!!