DIY brake adapters, need advice...

[Rik]

I have a little project, to put discs on my bike with as little cost as possible.
Now, part of this plan is to use cheapass cable discs (either shimano or tektro), and run 8" rotor. Obviously these are designed for 6", so I need to make an adapter.
Here is where I need help, I have the idea, just need opinions... so, the plan is this (excuse my crappy art skills)

Get some alu plate, the same width as the disc tab. Cut it into 3 pieces, parts a, b and c.
Parts a and b are the same shape, they will be mounted either side of the tabs, and have bolts running through to clamp them together (I do realise rotor clearance will be an issue). Part c runs in the middle of a and b, and will be bolted in 4 places, it'll have holes for the brake caliper to mount.
In theory, this should give the same spacing as the original disc tabs, and providing I support part c enough it should have minimal flex.

Is this idea viable? Has anyone else done it?
I guess I could run the shimano brakes with hayes adapters, but that'll increase my costs by 50%, something which I am very reluctant to do.
The costs have been added up, and if this adapter idea is possible, then I'll go ahead with it, but if it won't work, I'll give up the idea of discs for a while (I'm trying to keep a very tight budget).

 

[Gutty]

where in Sydney are you Rik ? (out homebush way from memory but that was a year or 2 ago)
If you wanna make the trip to Kirrawee some day i'm sure i could knock something up for ya. Kinda need the bike infront of me though.

 

[Rik]

I'm in Concord, which is near Hombush. I have some mates in Kirrawee too...
Thanks for the offer, I may just take it up, but I still wouldn't mind having a go myself.
You know I'm from Hombush way, do you know me from another forum, if so, what is it? /paranoid

 

[Grip]

Think you'll find that rotor clearance might be more of an issue than you imagine, Rik, as clearance is usually pretty tight even without a nut (or bolt head) on the turning side of everything.

Also, be careful of "sandwiching" the disc mount between the plates (I think that's what you're intending) as usually only ONE side of a mount (the side an adapter or caliper would normally mount to) is actually machined off to be both true and 90 degrees to the axle (and therefore parallel to rotor). This is especially true with "cast" fork legs and disc mounts but also occurs with fabricated mounts too. If the surfaces of your mount are not parallel you'll probably find it impossible to set up the caliper spot-on OR keep it there even if you can.
I think you'l find a single sided adapter... exactly the same as any other but longer to suit the 8" rotor... will work fine and be stiff enough. Don't forget you're not trying to overcome "twisting" forces here so much as "sheer" forces (in the direction of rotor travel.

Oh... and nice offer too Gutty. Can I come up this weekend? HAHA

 

[Rik]

Thanks for the advice grip, these issues were in the back of my mind, I should give them alot more thought. And yes, i intend on sandwiching the adapter (part c, bolted between a and b).
As for making a single sided adapter, I don't know how much luck I'd have, considering it'd need to be aligned parallel as you said, and retain the same spacing as the original tabs.

Next time I cruise out to the shop I'll stop by the metal recyclers, and see if I can find some pieces to suit, and give it a go just for an experiment. Alignment can be acheived by using a pair of vice grips and a bit of force :s But I'd have no way of measuring how accurate it is...

 

[Gutty]

You know I'm from Hombush way, do you know me from another forum, if so, what is it? /paranoid

You gotta be kidding me. Who was the first Sydney rider on Ridemonkey. Hint: You were the second.
I tried to tee up a ride with you when you first joined up. I was banned from there a while ago now so i'll forgive you for forgetting me. :cry:

 

[Rik]

Ahhh yeh! Good ol' ridemonkey, sorry, I forgot about that forum, it's been years since I've been on it.
Now I'm wondering how many forums I've left behind in my trail of destruction, since I use the same name for each one, I wonder how long it'll be until someone hunts me down :lol:

 

[Ev]

for the adaptor, try gettin one piece of aluminium double the thickness of the disc tabs on the frame, then find the correct shape, cut that shape out of the aluminium, and then machine as necessary.
or you could go to www.grcomponents.com and get some of thiet adaptors and rotors, cheaper than hayes adaptors and they work with shimano

 

[dhd]

Try www.dhdirect.com.au
then "components"
then "brakes"
then "adapters"

All will be good!