Adapting Rear Wheel from V brake to Disc Brake

[Carmageddon]

Hello!

I have a bike with very bad and weak rear brake (which requires adjustment all the time, and rubs against the rim (very hard to adjust it not to, and still be efficient at braking).
Front wheel is simple Disc brake with wire, but also requires adjustment once in 1-2 months.

Here are pictures of the rear engine area:



I have been recommended to start with this:
http://www.aliexpress.com/item/MTB-Disc-brake-flange-disc-tray-adapter-screw-thread-switch-disk-disc-tray-refires-disc-brake/32312668990.html

Then adding this on top of it:
http://www.classic-cycle.de/en/Brake/Brake-Disc-Rotor-160-mm-with-fixing-screws.html?cur=1&lang=1
Instead of this, can I order this cheaper part? will it fit?
http://www.aliexpress.com/item/Brand-New-AVID-HS1-Brake-Rotors-160mm-or-180mm-6-inches-Disc-2PCS-12-Blots-BB5/32278258472.html?spm=2114.01020208.3.1.qoyFMg&ws_ab_test=searchweb201556_9_71_72_73_74_75,searchweb201644_5,searchweb201560_9

Now the real problem starts:
The guy who helped me with those recommendations - I met him in the train, and suddenly he almost missed his exit so I didnt get his phone number, so I dont know what to do next for the Caliper fitting.

I think I need to find some kind of adapter which I can fit to this frame, and mount the Caliper on it, or find a caliper to which I can bore holes for mounting...

This is where I need your help please... I'd like to at least make a rear wire Disc brake, and if possible without big expenses, preferably Hydraulic Disc brake (the one with oil) so no constant adjustments would be required...


Please assist...

Thanks!

 

[amberwolf]

Can't access dropbox, so can't see your pics. It would be helpful if you just attach them to your post.

Without knowing what you've got there, then, maybe you just need to change the pads on the v-brake, something like koolstop salmon or one of the dual-compound ones.

Might also be an issue with the brake levers (and/or cables) themselves.

If you get a lot of rubbing on the wheel in just some places, then you just need to tension/true the wheel to fix that; it's pretty easy though it can take a little time if you've never done it before. If it's a hub motor wheel, it's unfortunately really common that they aren't true or tensioned properly, and that should be fixed anyway before problems arise from it. (might not happen, but does on at least some--all of the ones I've had from various vendors had serious problems later if I didn't fix them when I got them).


That said, if you just really want disc brakes, and your frame doesn't have built-in mounts, there are threads discussing opinions and results on converters / adapters, might take a bit of searching to find them though.

If you have a hubmotor, you'll need to be sure the calipers you get (and the adapter to mount them) will clear the hub itself, too--that's a common problem that doesnt' always have a good fix.

Your hub also has to be able to mount the rotor, and it has to clear the frame at whatever diameter rotor you use..



Another thought: when you brake, if the rear wheel is skidding on the ground, it's not the brake, its' the traction, and that's common for rear braking on many bikes--just the nature of braking pushing down on front and lifting rear. Won't matter how strong the brake at that point--it's already doing all the work it can.


All that said, your front brake is still the most important one on most bikes, and will limit your stopping power anyway--once that one grabs and locks the wheel, on many bikes you'll just stoppie (rear wheel lifts off ground and isn't doing any braking at all).

On surfaces it can't grab that hard and skids, the rear brake may also help until it, too, locks the wheel and skids.

 

[Carmageddon]

I edited the post, hope pictures are visible/accessible now.

In case they are not, here are they:


Viewing angle showing the V brake:


I did not understand your reply yet, will re-read it and search a bit more before responding, but now that I've uploaded pictures, I would appreciate if you could give more precise answers.

I CAN tell you however, that the pads were already replaced at least once, the braking wire was replaced once, countless times the V brake adjusted, the tension on the spikes adjusted (all of that by the store which sold me the bike) - it sometimes worked better, sometimes less, but I was never satisfied with the way the rear brakes work, that is why I need to find a way to replace it.

 

[docw009]

Maybe the luggage rack is covering them in your picture, but are there lugs on your rear frame for attaching the brake calipers?

My old, but electrified Trek 800 had cantilever brakes. The rears didn't work well at all. Couldn't get any clamping power from the e-brake lever and cable. I tried a different style e-brake lever with a longer pull. Tried two different sets of pads too. No good. Finally bought a set of v-brakes off ebay, for less than what I had paid for the pads. The new v-brakes are great.

Can't see what kind of brakes you have from your picture. Does the cable pull from the center or from the side?

 

[amberwolf]

The type of brake arm you can see in his pic shows it is a side-pull type of brake, AFAICT.

@Carmageddon: Which part(s) of my post are you having trouble with?

I CAN tell you however, that the pads were already replaced at least once, the braking wire was replaced once, countless times the V brake adjusted, the tension on the spikes adjusted (all of that by the store which sold me the bike) - it sometimes worked better, sometimes less, but I was never satisfied with the way the rear brakes work, that is why I need to find a way to replace it.

Well, you can't directly replace it with disc brakes, because you don't have any mounting point on the frame for the caliper. You'd have to find and buy an adapter to allow you to mount the caliper before you can use disc brakes on there.

Your motor appears to have threads on it to allow mounting the rotor adapter, at least--I dont' know how well those adapters work--I do know there are different "BCD"s for them, meaning the diameter of the circle for the bolt holes, so you have to be sure to get the right one for the disc you want to use or the holes won't line up.

So, if you can find the right parts, you can add disc brakes back there, without getting a new bike frame.

You can also have someone weld mounting points to the frame for the brake caliper; if it's a steel frame it would be relatively easy. (I've done that on a steel front fork).


Beware of cheap disc brakes, too, because there's lots of bad ones (I've tried a few off cheap bikes and they are generally much worse than even bad rim brakes). I haven't had any good disc brakes yet, but there are lots of those, too--I just don't know which ones they are; that's where the threads should come in handy to get info from (and regular bike forums probably also have a lot of good info in their threads).



One thing I think I see on your rim is that the braking surface appears to be painted (or anodized?); this may be making the surface slick and not allowing it to cause enough friction to brake well, especially since from the rust/etc you appear to ride in wet conditions.

Removing the paint (if that's what it is) from teh rim's braking surface could dramatically improve braking. If that's not possible, replacing the rim with one that has a good braking surface would probably fix your rear brake issues.


Can your brake lockup the rear wheel?

If your brake can't lockup your wheel, then it's either not squeezing hard enough (in which case you may simply have the wrong kind of brake lever on your handlebars for the type of brake you have on the wheel--see Sheldon Brown's website for good info on that stuff), or the braking pads can't grab the braking surface--don't have enough friction (in which case one or both of them is the wrong kind to match with the other, or is just too slick).

If the brake can lockup the wheel when it's dry but not when it's wet, then it's more likely to be the second problem.

If it can't lock it up even dry, it coudl be either (or both) of the problems.

If it can lockup the wheel both wet and dry, then the brake is not your problem; the traction of the tire is--and that coudl be perfectly normal as weight transfers from the rear to the front as you slow down--the more rapid the deceleration, the less weight in back and the worse traction back there.

 

[Carmageddon]

Maybe the luggage rack is covering them in your picture, but are there lugs on your rear frame for attaching the brake calipers?

My old, but electrified Trek 800 had cantilever brakes. The rears didn't work well at all. Couldn't get any clamping power from the e-brake lever and cable. I tried a different style e-brake lever with a longer pull. Tried two different sets of pads too. No good. Finally bought a set of v-brakes off ebay, for less than what I had paid for the pads. The new v-brakes are great.

Can't see what kind of brakes you have from your picture. Does the cable pull from the center or from the side?

Here are more pictures to help you see everything (downsampling forces me to reduce original quality unfortunately):

 

[Voltron]

Sometimes the problem with v bakes like that on e bikes is they paired them with brake levers with the cutoff switch that are made for caliper or center pull brakes. They don't pull enough cable, leading to mushy feel, and needing to set the brakes crazy close to the rim for any braking at all.

 

[Ykick]

I successfully use that type of rim brake across many eBikes with no major issues.

However, they gotta be clean, pivots lubed, good cables - basically well setup. If you can do that, they’ll work fine.

Probably better than any disc brake you might be able to cobble-up onto that frame.

Looking at that frame, there’s no caliper mounting lugs and who knows what the spacing will end up being once you find screw-on rotor adapter? Ill-advised to go down the path of disc brake onto that frame, IMO…

 

[999zip999]

Kool stop brake pads.

 

[amberwolf]

I note you have some kind of brake pads that say "anti lock brake system" on them. If they won't lock up, maybe they are part of the issue--if they won't grab the rim they won't stop the wheel.

At least the new pics more clearly show the braking surface, which is worn but not painted, so that's good.


But I really suspect it's your levers being the wrong kind, at this point.

Since you're not answering all of the questions, it's hard to give you better answers.

 

[Hillhater]

If you do fit a disc + calliper (very difficult) , be prepared to have to lose that rear carrier which will obstruct the calliper position.

 

[Ykick]

Kool stop brake pads.

Then what? use ‘em with junk cables, pivots and improperly assembled and adjusted components? If so, they’ll perform just as crappy as the cheapest generic eBay pads.

TBH - I’ve gotten great service from some of those cheap eBay pads but I’ve also gotten some horrific squallers too. Trial & error but still cheaper than the Kool Stop which I’ve used too.

 

[ecycler]

I wouldn't try to convert that bike to a rear disc. You are going to have some major alignment issues and based on your questions and answers it is clear you have neither the level of skills or tools to fabricate something with the necessary clearances/tolerances necessary for the job. Sounds like a huge headache based on the setup and the juice won't be worth the squeeze unless you really, really like that frame. Follow the others' advice and try to tune up your existing brakes - levers, cables, housing, clean them up, lube them, adjust them, and get some good pads. True your wheel so it tracks wheel, that is likely the major contributor to your problem.

 

[dogman dan]

You just need to get the rear brakes to work better. It might mean replacing the brakes, if one of them has a bent, or broken spring.

On the side of the brakes, there is a small screw that can be used to adjust the tension, so that both arms retract when you release the brakes. Try adjusting them. Many bikes also have three holes on the frame for the tension spring to engage in. Remove the brakes, and put them back so the springs have maximum tension. this will help them both retract.

Then get good brake pads. Nothing is really wrong with your bike that some competent tuning won't cure. Learn how, or pay a bike shop to do it.

 

[amberwolf]

Well, he's already had them tuned by a bike shop, according to his posts, including parts replaced. But I think there is something else wrong that they are not checking (like the levers), or they are not checking them under the same conditions he rides in---until he replies with that info, though, we can't know or provide really good info for him.

 

[Chalo]

My guess is the wrong kind of lever, a stupid brake limiting mechanism ("anti-lock"), poor setup, or a combination. A crappy disc brake is not a cure for a crappy rim brake.

Use something like Deore V-brakes, with or without upgrading to Kool Stop pads, with a V-brake specific lever. Set it up correctly, or pay a competent professional to do it for you.

Disc brakes are problematic on small wheels. When they work with a damn, they come on abruptly. This results in unintended lockup of small wheels because the disc rotor is a large proportion of the wheel size.

 

[dogman dan]

I know of bike shop mechanics I'd never let touch my bike. They just hate anything you didn't buy in their shop.

Get the wheel straight, increase the spring tension, and likely replace both cable and sheaths should get them to both spring away from the rim eliminating the rub. Then he only needs to tighten the barrel nut as the pads wear.

It's possible though, only replacing the cable, but still removing, cleaning, and lubing the sheaths will do er. Some bikes have very funky routing of the rear cable. So it might require extra lubing.

If the bike is stored outside, say no more.

But short of welding new disc brake mounts on the bike, I'd say work on the rim brakes.

 

[Chalo]

I know of bike shop mechanics I'd never let touch my bike. They just hate anything you didn't buy in their shop.

Heck, I hate some of the things I sell in my own shop. That won't keep me, or any other ethical service professional, from doing my best job to make it work as well as possible, just like anything else that comes across my workstand.

Some bike shops (maybe most) aren't service shops, though. They're retail, with obligatory service as part of the deal. My shop is a service shop, with obligatory retail as part of the deal.

Any one of the mechanics at my shop would make the OP's brake work fine for no more than twenty bucks parts and labor. For a little more, we could replace it and it would work even better.