Disc Brake Conversion

There are a lot of ready made conversion kits out there, so if you're building an eBike using a generic mountain bike frame, you may be wasting your time fabricating your own conversion kit for a disc brake setup.

However, in this case, the frame is not generic at all, it started out as an eBike (early Pedego Intercepter) that out-lived its service life, it was ridden until the battery and hub motor were both worn out. I have two of these bikes actually, I bought the second one for parts, my original bike has a battery issue, but the hub motor and controller are good, so I will continue to use the original brake setup on that bike, even after I fix the battery.

As you can see in the picture below, these bikes originally came with some sort of coaster, or drum brake setup in the rear. At a glance it looks like there is a brake disc, but it's not, and to be honest, I'm not sure what purpose that disc serves, there isn't a PAS sensor either, so who knows! The actual brake mechanism is inside the housing in front of the disc.


I scored a good deal on a hub motor wheel, controller, and throttle, so I decided to rebuild the parts bike. As you can see below, the new wheel is made for a disc brake setup, but the frame is not, and due to the abnormal width of the frame, which has extra distance between dropouts to make room for the original drum brake, a ready made conversion bracket is not ideal here without additional fabrication of some kind, but if I'm going to start fabricating, I might as well make my own bracket, right!

Below is a side view with the new wheel installed with the caliper temporarily clamped onto the rotor. The bike is upside down, sorry if that makes it hard to see what's going on, but from this angle it appears like a ready made bracket would work, but the next picture shows why that is not necessarily true.


In order to take up the extra distance between the dropouts and to keep the wheel centered in the frame, I have the torque washers and one extra 1/8" washer on the inside of the frame on each side of the wheel, but note that on the caliper side I could move the torque washer to the outside and use 1/8" stock to build the bracket out of, which happens to create the perfect amount of inset for the bracket to match up with the mounting holes of the caliper bracket.


This is as far as I've gotten so far, stay tuned.

I'd strongly suggest not using any sort of aftermarket disc brake conversion kit, as they're very often mechanically unsound, and in the event of a structural failure, could result in your rear wheel locking up unexpectedly.

Since you have a rear direct drive motor.. if your riding is mostly in the street, i would recommend that instead, you use regenerative braking for rear braking, and tune the rear regenerative braking to be strong enough that it can be used for >75% of your braking, and use an oversized brake on the front to account for the very small possibility of regenerative braking not engaging.

I have done this on a few bikes and with the correct amperage for regenerative braking, have not found it unsafe in any way, and i also optimize the amount of momentum that flows back into the battery by engaging the rear brake first. And as a bonus, you can do all of your bike's braking from one lever... although you do lose fine control over rear braking.. hence i would not consider this unsafe on an offroad bike.

neptronix said:

I'd strongly suggest not using any sort of aftermarket disc brake conversion kit, as they're very often mechanically unsound, and in the event of a structural failure, could result in your rear wheel locking up unexpectedly.

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I noticed that most of the aftermarket disc brake conversion kits look like they are designed for light duty usage, so I'm glad you mentioned that because it confirms my suspicion of eminent danger there. I did see one that looked heavy duty, but I'd still have to deal with some sort of spacer between the mounting bracket and the caliper, and that would probably make it less safe.

neptronix said:

Since you have a rear direct drive motor.. if your riding is mostly in the street, i would recommend that instead, you use regenerative braking for rear braking, and tune the rear regenerative braking to be strong enough that it can be used for >75% of your braking, and use an oversized brake on the front to account for the very small possibility of regenerative braking not engaging.

Click to expand...

Yes, this will be a street bike ridden on streets that are mostly flat with a few small hills. I have seen a few threads about regenerative braking, but I didn't really pay much attention. I'll do more research on it but I'm guessing the controller that came with this kit does not support regenerative braking, and it didn't come with any documentation either. I will admit that the idea of regenerative braking sounds awesome, but I might opt to do that in a phase II of the build, I'd be happy to just get this thing on the road and I don't think the fabrication involved to mount the caliper is going to be extensive.

You'd love regenerative braking. I live in rollercoaster like terrain, so i get a huge benefit from it, as well as at stop and go; just like a hybrid car. I would love to have regenerative brakes on both wheels exclusively if possible. It's nice to have a brake which never truly fades in power, nor needs any future replacement.

I'd like to see this heavy duty disc brake adapter you're talking about. It may be useful on one of my front forks which is a light duty one. I've also seen the cheesy/flimsy looking adapters aplenty.

neptronix said:

You'd love regenerative braking. It's nice to have a brake which never truly fades in power, nor needs any future replacement.

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I'll search for documentation on my controller, it has a model number on it, maybe something will turn up. If not, we'll buy a new controller for phase II :wink:

neptronix said:

I'd like to see this heavy duty disc brake adapter you're talking about. It may be useful on one of my front forks which is a light duty one. I've also seen the cheesy/flimsy looking adapters aplenty.

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The one I saw was for the rear dropout on a typical MTB frame, it won't work on a front fork, but here is a picture anyway.

And in case you or anyone wants more info on that:
https://amzn.to/2R5qX9L

FWIW, the thing that looks like a disc rotor is a heat sink to help cool the brake.

If your adapter plate is stiff enough to maintain alignment between caliper and rotor, you only need a torque arm connected to the frame. Motorcycles use the design quite a bit with the caliper mounted both above and below the axle, with the torque transmitted into the swingarm by a tubular rod.

Voltron said:

FWIW, the thing that looks like a disc rotor is a heat sink to help cool the brake.

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That makes perfect sense, and I would imagine it being necessary where it's hilly too.

ATinkerer said:

If your adapter plate is stiff enough to maintain alignment between caliper and rotor, you only need a torque arm connected to the frame.

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Good point. If you look closely, there are two threaded holes in the dropout, which are probably intended to be used for mounting a fender, but I plan to run bolts through the bracket into both of them to deal with the torque. If it seems necessary, I'll also add a bracket to the frame at the caliper bolt that is furthest from the axle. I'll make an attempt to draw up a mock up of the bracket I plan to fabricate.

Here's what a floating caliper on mountain bike looks like... Part of the having it floating thing is it helps keep the suspension from stinkbugging (flexing upward and locking out the suspension) under rear braking.


P.S. don't know if you noticed, but on the old brake the rear cap flips up and there a lock over there for the brake, for quick stops.
It's such a heavy hunk o metal for what it did. Good job getting rid of it.

Voltron said:

Here's what a floating caliper on mountain bike looks like... Part of the having it floating thing is it helps keep the suspension from stinkbugging (flexing upward and locking out the suspension) under rear braking.

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That is an awesome setup, and I can see how that would be the only way to go on a full-suspension bike.

Voltron said:

P.S. don't know if you noticed, but on the old brake the rear cap flips up and there a lock over there for the brake, for quick stops. It's such a heavy hunk o metal for what it did. Good job getting rid of it.

Click to expand...

The picture of the old brake is on my other identical bike, and I used the lock all the time before the BMS in the battery fried. I still plan to use that bike with the existing old brake when I fix the battery because there's no way to convert that wheel to disc brakes. The brake has OK stopping power, but not great, fortunately there's a disc up front for when you really need to stop!

Here is a mockup of what I plan to fabricate. I think I'll go with 1/8" steel instead of aluminum just to be safe. The bracket will be a one piece construction it goes on the inside of the dropout, so part that is translucent is what you normally wouldn't see from this angle.

I'm actually having trouble finding the raw materials (1/8" steel or aluminum bar/plate) close to home, but I am still pursuing this and will post an update as soon as I do.