V brakes to discs

dilemna

Hi, my first post in the MTB forum so go easy.

I have a Trek 7500FX one of the first, so about 10 years old now. None of the poncey city boy plastic frames and carbon forks that make up the new range of Trek 7.5fx.

My question is how feasible would it be to convert the frame which is aluminium 7005 set up for V rim brakes to accept calipers for disc brakes? The frame is pretty solid, robust and strong. I guess in the factories when bikes are made they have jigs to make sure everything is properly aligned when they are welding everything up eg bossess/lugs for mounting calipers for disc brakes. I guess I would have to find a frame builder who would be prepared to weld on some mounting points for calipers. In doing so the localised paint may well become discoloured meaning the frame might need a whole new paint job? The paint of the frame is still in pretty good condition. What would the likely cost be and who might be able to do it?

Ideally I'd like to fit something like Hayes hyrdaulic disc brakes front and rear.

Any constructive advice gratefully received.

Thanks,

Dilemna

supersonic

It will be expensive to weld on disc mounts. Also got to think about heat treatment. The frames stays may not be strong enough for the stresses either.

However depending on the type of dropouts you may be able to use a clamp on style mount. Flat plate type dropouts are best for this.

Of course you will need disc hubs too, and if have STi shifters, new shifters too.

cobba

Do you have problems with the power of your rear v-brake ?
Can you lock up your rear wheel with your current v-brake ?
How much better do you think a rear disc brake will be over your current v-brake ?

It be easier, cheaper to leave the rear as a v-brake and just put a disc on the front.
More brake power is needed in the front than the rear.
Bikes used to be sold that way about 10 years ago.

konadawg

cobba wrote:

It be easier, cheaper to leave the rear as a v-brake and just put a disc on the front.

+1

Went for that setup on one of my first MTBs. Power where you need it most.

mariecross

I've just swopped my deore disc brakes t my friend Scott which he has had for 6 years. It took 4 hours and I ended up having to give him my brakes, wheels and front fork. In the end it wasn't really worth the effort but he got a very good deal! £100!!!

POOO

*AJ*

Have you looked into the HS33 magura's?...they have the advantage of being hydraulic but are still rim breaks! They are very powerful and feel much nicer than a cable brake!

Sets on eBay go cheap too!

Anonymous

Serious question. Are you that attached to the frame?
You could pick up a bargaineous modern frame from OnOne for very little money, which will of course, have disc mounts.
Also, have you considered that you will need new wheels?

dilemna

Thanks for all the replies so far.

Yup, I have considered the bike will need new wheels with disc hubs plus the actual disc brakes themselves - levers, calipers, rotors, pipework. Just want to know at this stage whether mounting bosses for calipers could be welded/brazed onto the frame? I guess nothing is impossible if money is not an issue .......... The frame is really robust. Surely a frame builder would braze on lugs to mount the calipers. It is the positioning of these caliper mounts which I believe is crtitical?

My reason for doing this is to create a rugged touring bike that can go anywhere carrying a fair load, out into the middle of nowhere, racking up a fair few miles without the rims wearing down and splitting due to V brakes grinding them down due to all the mud and grit on the roads where they exist. Disc pads and rotors are far cheaper and easier to carry than spare rims, spokes or brake blocks. Plus disc brakes would perform far better on a loaded bike than rim V-brakes especially in the wet.

Anonymous

Hmm. I'd be weary of having a re-welded aluminium frame (or, for that matter, any aluminium frame) for trekking into the middle of nowhere.
Steel is easily repaired, with even basic welding tools. If something happens to an alloy frame, you're pretty much stuffed unless you're near an expert fabricator with access to a heat treating facility.

cobba

dilemna wrote:

Just want to know at this stage whether mounting bosses for calipers could be welded/brazed onto the frame? I guess nothing is impossible if money is not an issue .......... The frame is really robust. Surely a frame builder would braze on lugs to mount the calipers. It is the positioning of these caliper mounts which I believe is crtitical?
My reason for doing this is to create a rugged touring bike that can go anywhere carrying a fair load, out into the middle of nowhere.

Mounts could be tig welded to the frame by a frame builder who knows what they're doing, yes they would have to be in the right position but it wouldn't be cheap.

If money isn't a problem, a new steel frame with disc mounts would be better option, it probably wouldn't cost much more then modifying the old frame, with steel you'd have much stronger frame that'll last a lot longer and it'd be easier to repair if any problems arise.

As for your old frame being robust, I'm not sure I'd call a 10 year old aluminium flat bar commuter/road bike frame robust and it's not the sort of frame I'd take anywhere that's too rugged. Aluminium frames don't last forever, they can become brittle with age and crack.

As for your choice in brakes maybe the Avid BB7 might be a better then hydros. What are you going to do when you're out in the middle of nowhere and you bust a hydraulic hose or develop a leak ?

Foobies

i managed to convert mine for about £65 quid, £40 for a new shimano hub and £25 for an "A2Z Mountain Bike Disc Brake Frame Adaptor"

off fleabay... dont look like theyre doin em anymore tho, but should be able to find one with a bit of a hunt... works fine, no slips or anthing here, and best of all no welding so no damage to the frame.

A2Z Rear Disc Brake Frame Adaptor - Makes your frame Disc ready in minutes!!!

The revoultionary rear adaptor that converts Aluminium none disc frames into a disc frame.
MBUK review 4/5
For this to work with your frame you need to have a Alluminum frame with a flat style dropout on both sides which is normally about 8mm thick, the A2Z adaptor then opens up and sandwiches over your frame and creates an International mount - No drilling or bolting into your frame is needed.
It does not affect your hub or Q/R in anyway.
Not Compatible with Hope BigUn Hubs.
It will only work with Vertical dropouts.
Not compatible with Specialized Frames where the dropout is slightly angled backwards

Anonymous

And how much for the spokes and wheel rebuild?

Foobies

spokes i stole off an old front wheel i had kicking around, and rebuild, did it myself

Anonymous

Pretty lucky they were the right size then, huh?

unixnerd

Something like this is compatible with your existing levers:
http://www.chainreactioncycles.com/Mode ... elID=17722

Was planning to fit a disc on the front of my old Marin. Back is fine as a V. I recently put on new forks with disc mounts so all I need is to have a new hub fitted to the front wheel (I want the front and back rims to match, vain know).

02gf74

supersonic wrote:

It will be expensive to weld on disc mounts. Also got to think about heat treatment. The frames stays may not be strong enough for the stresses either.

.

not necessarily true. I am looking at having this done to convert proflex xp-8 to discs. if the alloy is 7000 series (sorry, don't have exactt number) then heat treatment is not required, unlike the 6000 series (again don't have the eact number nor the meaning of all the numbers).

mine is 7000 series so I'll be ok :P - had contacted k2 bikes (useda be proflex) about this and is what they said, confimed by other sources.

nicklouse

strange as most 7000 are heat treated to T6.

yes over time at room temp the 7000 series will age harden.

sorry but I would be talking to the certified welder who is doing the work.

but for what you want on the XP8 you have a few mounting points and also some interesting cast/forged and extruded parts.