DenisH

I recently had a shop add Bafang mid-drive to two Bacchetta Giro 20 recumbents. They also installed Clark's CMD-17 mechanical disk brakes. I am having some difficulty adjusting them and some problems with squealing and pulsing.


First, the adjusting. Since the Bafang installation called for using their brake levers with a cut-out switch I wonder if the levers are satisfactory. The distance from the handle pivot to the cable pivot is about 32 mm. Anybody here have a idea if these levers are satisfactory?

I found Park's videos and text instructions on adjusting disk brakes excellent; I try to follow them carefully. The opposite is my opinion of Clark's videos. He mumbles, is imprecise ("move the pad in a little bit"), and vague. One question concerns his reference to a "little 2 mil screw..." followed by an unintelligible word or two. I think this is a reference to a small set screw intended to lock the inner pad adjustment knob. Is this used on other brands? Have I damaged something by adjusting the pad without checking that screw?


Second, squealing and pulsing. The shop guy said mechanical disks do not require bedding in, so I had to go through that after the bike had been ridden a bit. How to go back to the beginning to properly bed the rotor and pads in? It probably does not make sense to discuss disk noise until that is done.


Thanks for any advice.

andrewclaus

Are the rotors new? I see some rotors are recommended for certain brake pad materials.

Is the pulsing once per wheel revolution or more frequent? Both wheels?

Disregarding noise and pulsing, how is the stopping power?

I see Clark's makes a CMD-17R model specifically for road drop levers. The CMD-17 model listing is confusing--it lists MTB, hybrid, and road bike compatibility. The measurement you give sounds like MTB levers, which should be compatible with CMD-17, but not -17R.

Pop N Wood

On my bafang I bought a hidden wire brake cut out switch that allows use of stock Shimano levers. Since you have mechanical discs it will work. Just run the cable through it, easy as can be.

https://california-ebike.com/shop/ba...-brake-sensor/

In all honesty I don't notice that the brake sensor does much. The shift sensor is pure gold however, works like a champ

https://california-ebike.com/shop/ge...r-derailleurs/

For squealing and pulsing lots of threads on how to get discs to behave. Keep them clean, even oil from your fingers can cause that. Maybe you need a better brand of pads, kool stops are highly recommended. Taking sandpaper to the rotors has helped in the past as well.

DenisH

I just responded to your helpful comments, but I guess I took too long to type, as I was logged off and all I wrote is gone. So this will be brief. One front brake pulses once per rev. Am trying degreasing.

DenisH

Rear stopping was terrible. Lever to grip. I fixed that; they are adequate now, but not as good as the front.

DenisH

The rotors are new.

andrewclaus

This was happening on my first set of disk brakes on a used bike. It was caused by a deformed disk, possibly from being held in one spot under pressure while very hot. At least I read somewhere that's possible. The deformation was measurable with a caliper.

A sloppy mechanic could easily get a greasy fingerprint on a disk. Good luck. And grease or oil on the pads may mean they're ruined. They're not so easy to degrease.

andrewclaus

The front will always stop better. The cable's shorter and more direct. But mainly the front is always the more effective and preferred brake. (I like to think of how I stop when I'm running--I use my front foot, not the rear.)

Double check your cable housing for kinks, or excess length leading to an extra bend in the routing. If you take it apart, dress the ends of the housing by filing or grinding flat (unless it's compressionless housing).

Pop N Wood

That happens all the time on car discs, it is a layer of pad material that has melted to the rotor. Has different level of friction hence the pulsing/grabbing with each revolution

Car mechanics call it "rotor warp", fix is to turn or replace the car rotor. For bike rotors I've had excellent luck using a small power sander to take off any rotor glaze. Take the rotor off the wheel, clean everything before and after, and use a garnet type sandpaper, no metal oxides.

I've tried using the sander on pads that got oil in them, but that doesn't work very well. Usually need to replace contaminated pads.

andrewclaus

Thanks--that makes more sense than deformed steel.

DenisH

I agree that the front brake can contribute more to stopping than the rear due to weight transfer, but before either wheel looses traction they both should be able to contribute equally to slowing the bike. However, this bike has a 20" front wheel and a 26" rear wheel, so with disk brakes the front wheel as an advantage. This would not be so if I had rim brakes. And because of the difficulty I am having with these brakes I wonder if I made the correct choice.

DenisH

Update: I got out riding down some local hills to allow me to put in some front-wheel braking. The pulsing lessened as time went on, and the brake seemed to fade somewhat. Eventually the brake lever made it to the grip, so I came back home to inspect the situation. The gap between the inner pad and the rotor looked larger. As I believe I mentioned earlier Clarks has a set screw going into the adjustment. This time, being aware of that set screw, I backed that screw out before adjusting the pad. I was able to get the pad much closer to the rotor, and the lever travel was much improved. Testing on a ride will have to wait for another day, but I am encouraged.

The fading may be due to heat; the lever travel issue was likely due to pad wear. Maybe the pad was not parallel to the rotor, so wear happened quickly.

This brings up another question regarding the cable housing. It is new, it is labeled Jagwire, but it appears that it is a coil, not straight wires as I had thought I read was recommended for disk brakes. Is this an issue?

Pop N Wood

Jagwire makes some quality gear. Sounds like your cables and pads set a bit. Perfectly normal to have to readjust after the first couple of rides.

If you have to readjust something every other ride than something is wrong.

hokiefyd 

It sounds like you're on the right track. In general, disc brakes like these work best if you adjust the pads closest to the rotor with no cable tension at all (with the cable unhooked, even). Get the pads as close as you can get without rubbing so that engagement is very early in the travel of that torque arm (where the cable connects). Once that's good, then take up any slack in the cable and fasten it to that torque arm. You should have a pretty early engagement now, with no risk of the brake lever bottoming out on the handle bar. You can, of course, fine tune everything from there to your liking, but that should be a good start.

You can use compressionless housing, such as Jagwire's KEB-SL or similar. With good cuts on the ends of your housing and good ferrules, I'm not sure you'd see a huge difference in performance. But...every little bit counts, right? I suspect the Clarks brakes are not top-end, and you may get better return on your investment by first changing the brake calipers themselves to something like an Avid BB7.

I am curious -- why did the ebike shop change your disc brakes? I presume you had disc brakes that were already working...why did they swap them for the Clarks?

andrewclaus

As I mentioned in post #8 above, if you have coiled housing, you can get marginally better performance by filing the cut end flat.

I have the same housing on my "new" disc brake bike. I've never tried compressionless housing. I'm not sure I want to--mine feel fine.

DenisH

I had v-brakes prior to electrification. Given what I know now, I would not pick Clarks. They provide virtually no information. The videos they offer, as I mentioned earlier, are uninformative and vague, even if I could understand what he says. I asked them what the difference is between the 17 and 21; no response. As a learning experience I will continue with these for a while.