crazzywolfie

i was thinking about modifying a rear hub for a mountain bike so that i could add disk brakes. i was thinking about welding some nuts to the hub and hoping that it would work. i was hoping someone might have try this before or done something similar and may have some advise or in site into some of the problems i might run into.

HillRider

It would be WAY easier to buy a properly made disc hub right off the bat. Welding nuts to an existing hub would require extreme skill to get them aligned properly and not distort the flange. Forget it.

crazzywolfie

i have tons of time and not enough money to buy a proper hub. the only reason i even have disk brake on the front wheel on my bike is because they are so much more popular now they can be found in scrap piles. i never see bikes with rear disk brakes in the scrap pile.

vettefrc2000

The problem is the frame. If you need to make a hub I assume you need to modify a frame. You will have concentricity and flatness issues. For the cost, try to buy a hub, and the re-lace it into a rim.

crazzywolfie

the reason i want to make the hub is because i already have a frame that has the holes in it for the brake calipers to bolt on. i have the brake caliper and disk that i am planning on using.

surreal

if you cannot afford a $35 disc hub, you can't afford the materials and tools necessary to properly complete the project you're pondering. If the $35 price of a rear disc hub is expensive enough for you to consider compromising your own safety, you won't be able to afford a $40 disc caliper/rotor, like a bb7 or similar. If you have lots of time and no money, spend some QT tuning your v-brakes perfectly, and improving your braking technique on the trail.

Just my 3,499 cents.
-rob

vettefrc2000

Hub is about $25 US.

BCRider

First off the hubs are aluminium so you can't weld on the usual steel nuts. Even if by some miracle you can find aluminium to do this with you will not be able to weld them on truly enough. So that means stripping the wheel down and removing the axle so you can hold the hub in a lathe true to the bearing cups to allow turning the seating flange so it is true enough.

This whole idea is a non starter on so many levels that it's just not worth even thinking about it at all.

Meanwhile you can buy disc wheelsets of Fleabay for less than $100.

surreal

True dat. You can still get the ubiquitous deore disc/rhyno lite combo, front and rear, for less than $100 from almost any cheepo online retailer, too.

-rob

crazzywolfie

maybe you can buy bike disc hubs where you live but i would have to order them which would cost more than i could afford. i got the caliper and disk off of a bike that was scrapped. i have most of the tools i would need and i should be able to find any material i need. i plan on using steel hubs not aluminum.

silver_ghost

Good luck!
I've never heard of a custom mod like this for the reasons already explained, but if you really wan't to try it, go ahead. Don't expect amazing results and let us know how it works out.

BCRider

You'd still need to strip the wheel to allow for the welding and turning the edges true. Really, just save your money and buy a disc hub or wheel when you can. Without access to a lathe to true up the mounting face for the rotor after the welding you'll never get the hub true enough.

If you insist on doing this then grind off the chrome on the steel hub. Yes it's chrome plated and yes you MUST grind it off or the weld will be contaminated and will not hold and neither would be my next option. Then make up some sort of jig that will hold the hub really, really square to a face that you clamp down a flat steel ring onto. Then with the flat ring and hub held dead on square to each other BRAZE the ring to the hub. Brazing will produce a lot less stress due to weld shrinkage as it cools and is your best chance of doing this without any need to machine the flange true after the joint is done.

Keep in mind that the flange ring has to be joined to the hub very precisely so that it'll be both square to the axle axis AND spaced at the correct distance from the center line. This isn't a "looks about right" proposition. It has to be done so that the flange is located correctly to within a half millimeter or less and must be square running to an even tighter tolerance. If you don't use a very good holding jig and you're not a very good welder you're doomed before you even start.

And lets not forget that a steel hub means you're limited to a freewheel and that steel hubs are generally the lowest of the low in terms of quality.

Frankly I think you're crazy to try it. But since you're intent on doing so I wish you all the best and hope that my comments on the jig helps you out.

Kimmo 

This is third world stuff.

AEO

orangeville isn't the ass end of nowhere, since canada post still delivers.

take your pick.
https://www.chainreactioncycles.com/M...?ModelID=38215
https://www.chainreactioncycles.com/M...?ModelID=40551
or ebay.ca and amazon.com

you wouldn't be able to modify an existing MTB rear hub with the 6-bolt rotor, because if you do that, you wouldn't be able to lace up the hub again, assuming you disassemble the wheel so that it's easier to work with.

the 6-bolt holes for rotors has a larger diameter than the spoke hole circle and this just makes it impossible to lace up or even replace broken spokes on the wheel. Now, if you could tig weld a center lock on the hub, that wouldn't be a problem, but no such things exist, because all hubs are either machined from a single block of aluminum or forged and heat treated.

Now, if you want to try and weld on bolts with some TIG or MIG welding, then the hub would need to be disassembled, all the grease, bearings and spokes would have to be removed, because you don't want to unevenly distribute the heat flow from the steel spokes and bearings. Once you weld the mount on, you'd have to heat treat the hub, because you've most likely changed the properties of the hub from the heat of the welding. The hub can still be ridden without the heat treatment, but it's very likely to crack. Add to this, the fact that you can't even lace up the non-drive side properly, because the rotor mount is in the way.

And if you're still not convinced that it's a bad idea and unworkable, then knock yourself out in trying to modify it, because I'm always interested in seeing people work around problems that can be solved with money, by throwing time at it.

as the saying goes; time is money. even if you work at the minimum wage for ontario, 8hrs would cover the cost of getting a new hub.

dabac

+1

I have a taste for excessive engineering, access to a lathe and have actually done things like that. If you're good at finding discarded stuff, take a front disc brake wheel, strip the hub out. Set the hub up in a lathe, and cut the brake side flange off. Take a rear hub and cut the drive side flange off. Take a suitable piece of pipe, cut a section off to form the new hub spindle. Countersink a matching recess in both flanges, watch the tolerances closely. Aluminium expands quite a lot when heated, so it's fairly easy to get a good bond by cooling the hub spindle, heating the flanges, and then pressing it all together. Watch the alignment of the spoke holes. If you're a good machinist this will do the trick.
Of course there are possible variations to this theme. You can cut the hubs off dead center, and then use a section of pipe as a sleeve to fit the halves together. Or sometimes you get lucky and one half will be a nice fit inside the other. Or maybe a liner to go inside the hub spindles will make more sense for the materials that you have available. Or you can machine a new NDS flange out of stock.

Anyhow, I can't see any way of doing a disc brake conversion w/o access to a lathe.
If you have to buy ANYTHING, maybe apart from a dount and a coffee to someone helping you out, then the economy (whichever way you calculate it) goes right out the window.

(come to think of it, there USED to be a way. Years ago there was a company that sold a disc brake adapter. You removed the spokes on one side of the wheel, then screwed a puck-shaped thing onto the hub flange using the spoke holes. then relaced that half with new spokes and you were done. Didn't take long before the price of disc brake wheels dropped enough to make the effort of using the adapter pretty pointless.)