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mounting a disc brake on a BMX fork??

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mounting a disc brake on a BMX fork??

Old 10-28-15, 02:47 PM
  #1  
jawnn
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mounting a disc brake on a BMX fork??

I need to fit a disc brake on my BMX fork on my cycle truck. I think it maybe just a matter of using a larger rotor.

How large of a rotor can I get and how can I make a jig to hold the mount while brazing it on? Any photos?

maybe I can just clamp the brake to the rotor to set the mount right....?


The old fork looks like this one.... not enough room to use a small diameter rotor.

Last edited by jawnn; 10-28-15 at 02:53 PM.
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Old 10-28-15, 03:33 PM
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Build a Drum Brake hub wheel and you dont have to do things like Grind off the chrome plating..

It's Toxic if burned . and you have to heat to those temperatures , it to weld.
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Old 10-28-15, 04:00 PM
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I would install the brake mount on the drive side and on the back of the fork. Also, hopefully the fork you are trying to braze is to is not chrome.
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Old 10-29-15, 03:47 PM
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most of the chrome is worn off any how.... I may have it powder coated. and I already have the front wheel. the fork was very rusty inside so I poured Ospho in it and there was no rattle after that.

The rim cost me $95 before I started building the frame. I should have waited to think about it later.

I will draw out a diagram to see if I can use a 220 mm rotor or a 200 mm rotor. They don't make 240mm rotors for bicycles, maybe only mopeds (different mounting to wheel)


Originally Posted by Cynikal View Post
I would install the brake mount on the drive side and on the back of the fork. Also, hopefully the fork you are trying to braze is to is not chrome.
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Old 10-29-15, 10:29 PM
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A bmx fork so old/used that the chrome is gone and its full of rust?
New fork time.
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Old 10-30-15, 10:37 AM
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Companies that Make Recumbent bikes Use A 20" wheel fork they are fitted with Disc Brake Mounts ..

but it seems you prefer Re Use of refuse bin sourced parts ..



at the hospital ..
Tell Your Lungs 'I thought most of the chrome was Gone'.

want to weld stuff on yourself? its easier to strip off paint, so Dive again, get a painted Bin fork

Last edited by fietsbob; 10-30-15 at 10:44 AM.
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Old 11-03-15, 02:14 PM
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some times I get the distinct feeling that some people are just not paying attention.....
a new recumbent fork costs $100, and if I wanted it to be stronger, I would have to use a Trials bike fork, much more expensive.

which way is easiest to apply?
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Last edited by jawnn; 11-04-15 at 02:24 PM.
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Old 11-03-15, 04:42 PM
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I don't see what the problem is and why you think you need a large rotor. I don't see why a 160 or 180mm rotor won't work on that fork. Put the mount on the rear of the left fork leg. The cheapest way is to clamp the caliper to the rotor to align the mount for tacking. You can make your own mount from some 1/4" plate or buy one from Paragon Machine Works.
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Old 11-04-15, 02:19 PM
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well I don't understand why you think I could mount a brake on the fork with only 160mm rotor. is there another way of doing it? did you look at the diagram I drew?

Maybe the posts could be a little farther down, but not much.

I am not going to use the chromed fork. I have another one with just paint.


Originally Posted by dsaul View Post
I don't see what the problem is and why you think you need a large rotor. I don't see why a 160 or 180mm rotor won't work on that fork. Put the mount on the rear of the left fork leg. The cheapest way is to clamp the caliper to the rotor to align the mount for tacking. You can make your own mount from some 1/4" plate or buy one from Paragon Machine Works.
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Old 11-04-15, 03:03 PM
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Your drawing looks nothing like the picture of the fork in the original post. That fork has legs that extend past the dropouts and your drawing shows a fork with dropouts extending past the fork legs. You could try something like this photo, where the IS mount extends past the fork leg and attaches to the dropout.

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Old 11-05-15, 08:25 PM
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I fear you may not be able to mount a caliper on those forks without going to a bigger rotor, mostly because of the offset of the axle slot. You will most like have spoke interference with the caliper. Maybe build a custom fork to solve the issue?
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Old 11-07-15, 01:56 PM
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How would the spokes get in the way?

The drawing is more like what the fork I ma using now looks like, but I am going to use a different fork.

I am also afraid that if the mount is too far down the axle will be rotated out of the slot too easily.

How about this kind of mount?? I think I should just buy several different kinds to try them in real life.

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Old 11-07-15, 02:11 PM
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Those Lawyer Lips are there for a reason on fork dropouts ..



Consider the front of the right fork blade ..


The Physics in a Nutshell is the disc pad becomes the new Torque axis , thats why It swings out of the dropout.

If you mount the disc brake on the front of the right blade that force arc is pushing the axle IN More firmly.



you can add Hook washers on the axle that grab in a hole on the fork , like that Blue one above..

or like the old Schwinn safety tab,

snaps over a screw Head on the inside face of the fork leg.
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Old 11-07-15, 06:10 PM
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I have to disagree that lawyer lips are there for a purpose. I know I'm drawing a fine line but discs hadn't seen mainstream use when lawyer lips were conceived. It's just a coincidence that they help keep the axle in the dropout on a disk bike. Lawyer lips are a horrible idea on any bike that doesn't have discs and they are actually less safe than dropouts that don't have them. I'll get off my soapbox now.
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Old 11-08-15, 12:05 PM
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Originally Posted by busdriver1959 View Post
I have to disagree that lawyer lips are there for a purpose. I know I'm drawing a fine line but discs hadn't seen mainstream use when lawyer lips were conceived. It's just a coincidence that they help keep the axle in the dropout on a disk bike. Lawyer lips are a horrible idea on any bike that doesn't have discs and they are actually less safe than dropouts that don't have them. I'll get off my soapbox now.
While "lawyer lips" were conceived well before front disk brakes became common, the purpose they are intended to serve was actually to prevent the axle from coming out of the dropouts, either because the axle nuts were not securely tightened or the quick release was improperly secured. That this problem also occurs with front disk brakes is just a coincidence (perhaps exacerbated by the proliferation of external cam quick releases). While the traditional "lawyer lip" may not be an especially effective means of preventing wheel ejection with disk brakes, I disagree that "lawyer lip" dropouts are less safe than those without the lips. At worst, they obviate the convenience of a quick release wheel.
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Old 11-09-15, 03:07 PM
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maybe I can braze some lips on the drop outs.....do I have any volenteers?

Last edited by jawnn; 11-09-15 at 03:14 PM.
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Old 11-09-15, 03:12 PM
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you shouild take closer look at the drawing above.....



Originally Posted by fietsbob View Post
Those Lawyer Lips are there for a reason on fork dropouts ..



Consider the front of the right fork blade ..


The Physics in a Nutshell is the disc pad becomes the new Torque axis , thats why It swings out of the dropout.

If you mount the disc brake on the front of the right blade that force arc is pushing the axle IN More firmly.



you can add Hook washers on the axle that grab in a hole on the fork , like that Blue one above..

or like the old Schwinn safety tab,

snaps over a screw Head on the inside face of the fork leg.
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Old 11-09-15, 03:32 PM
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Meh. Not My Project. good Luck ..

Bene sugg: fabricate washers with a Hook in them to go in one of those 4 holes on each side .

use a Solid axle and Nuts to hold the whole thing On.

Last edited by fietsbob; 06-16-16 at 09:20 AM.
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Old 06-15-16, 06:08 PM
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Greetings.

Joined this site specifically to look for advice on this exact topic. Glad it's been discussed, and within the last year no less.

My question is about strength of mounting a disc brake in front of the right fork leg, which seems to be my only option. I want a fork I can market to dirt jump / skate park riders. Though it's not the same kind of stress a mountain bike front brake would have to endure, it does need to be durable. I have access to professionals to do the welding, and the fork will even be heat-treated afterward. Are there any concerns with the disc brake pulling off the fork leg? If there aren't, any way to put in to words why it's just as safe as mounting behind the fork leg?

Thanks for your time. No need to read on, but here's the whole story: I have S&M Bikes making forks for my own brand of unique 24" bikes (commongroundbikes.com). I have a customer looking for a front disc brake, and S&M is willing to have a prototype made, but only if they will end up with something they can also sell to their 20" and 22" customers. The long dropout offset (which gives the feel I want) prevents me from using an I.S. mount behind the fork using any rotor smaller than 170, which I believe Sram still makes. Problem is, that's too big even for my 24" wheel, and especially too big for a 20" or 22". Mounting in front of the dropout would allow for even a 140mm rotor, and on the right side the cable could still point upward on a standard caliper.

Any input on the strength of a front-mounted front disc caliper would help.

Thanks again!
Travis
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Old 06-15-16, 06:35 PM
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putting it on the front should work fine
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Old 06-16-16, 08:32 AM
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If the forks are being fabricated new then I would keep the brake on the non-drive side and switch the direction of the dropout like a traditional disk brake fork. I wouldn't worry about the strength of a BMX fork, they are fairly thick and strong.
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Old 06-16-16, 09:23 AM
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Originally Posted by commonground View Post
Greetings.

Joined this site specifically to look for advice on this exact topic. Glad it's been discussed, and within the last year no less.

My question is about strength of mounting a disc brake in front of the right fork leg, which seems to be my only option. I want a fork I can market to dirt jump / skate park riders. Though it's not the same kind of stress a mountain bike front brake would have to endure, it does need to be durable. I have access to professionals to do the welding, and the fork will even be heat-treated afterward. Are there any concerns with the disc brake pulling off the fork leg? If there aren't, any way to put in to words why it's just as safe as mounting behind the fork leg?

Thanks for your time. No need to read on, but here's the whole story: I have S&M Bikes making forks for my own brand of unique 24" bikes (commongroundbikes.com). I have a customer looking for a front disc brake, and S&M is willing to have a prototype made, but only if they will end up with something they can also sell to their 20" and 22" customers. The long dropout offset (which gives the feel I want) prevents me from using an I.S. mount behind the fork using any rotor smaller than 170, which I believe Sram still makes. Problem is, that's too big even for my 24" wheel, and especially too big for a 20" or 22". Mounting in front of the dropout would allow for even a 140mm rotor, and on the right side the cable could still point upward on a standard caliper.

Any input on the strength of a front-mounted front disc caliper would help.

Thanks again!
Travis
travis@commongroundbikes.com

A fork made for rim brakes may be too flexible and light, for compliant confortable ride, to put a disc mount on.

a Cheap heavier thick tube-wall High tensile fork May be a better choice for your experiment.

Last edited by fietsbob; 06-16-16 at 09:27 AM.
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