aka Mr Floyd
03-31-2005, 01:18 PM
Ok, this comes up all the time. I've seen alot of really dodgy ways to convert 4 bolt magura specific brake mounts to V's at home and a lot of profesionally designed adaptors that don't work worth a crap. Here's one way to make your own adaptors that work well, don't cost much, and don't take specialized machine tools.
Tools you do need: a drill (preferably a drill press), a hacksaw, a handfile (or grinder to do it faster), and something to measure with (a good ruler if your careful, a set of calipers is best).
Start with two plates of aluminum (I think it was 1/4" plate) that you will cut out to the shape of your booster (mine is very square as this was a test to see how well this would work, it would be better to round the top off more). To speed up the shaping process I drilled the holes for the V-brake mounts first and bolted the two plates together to shape them simultaneously with your choice of hacksaw, grinder, and handfiles.
http://www.observedtrials.net/album/data/500/279conversion1-med.jpg
Here's the lower plate completely shaped. Four holes are drilled to match up exactly with your 4 bolt mounts and can be easily recessed by carefully partially drilling with a larger drill size to keep the screws flush when installed. The V-brake studs are mounted by grinding off the prethreaded portion that they come with and then screwing them on with an allen bolt from the bottom of the plate (eliminates the need for making a threaded hole). To make an indexing hole for the V-brake rebound spring I bought two premade shear pins that just fit over the little stub on the brakes and drilled two holes to tap them into (they are made to press fit into standard drill diameter holes and you can see them just inboard of the V-brake mounts).
http://www.observedtrials.net/album/data/500/279conversion2-med.jpg
Here's the lower plate/booster installed. I would have rather used counter sunk allen bolts than the flat screws, but the hardware store didn't have the size I needed. Should work fine with liberal use of Loctite. Note that I provided too much tire clearance and should have spent more time rounding off the upper contours...
http://www.observedtrials.net/album/data/500/279conversion3-med.jpg
Here's the finished package with the outer booster and brakes installed. The outer booster is basically the same as the lower with just a few less holes (yes, it's a bit ugly all squared off... the next one will look better).
http://www.observedtrials.net/album/data/500/279conversion4-med.jpg
Here's finished from the side. You can see the allen bolts on the lower plate that hold the V-brake studs on. Also you can see that with the studs I used I had to add one washer underneath them to allow for enough clearance between the brakes and the lower plate.
I have not provided any measurements for the holes, etc. because you will need to measure your own setup to determine that (and note that the finished product will most likely not work on other bike frames). This is just to give you an idea of what can be done with a little spare time and some basic tools. Note that with some slight movement of the brake mounts in and out this design can also be used to acomodate very wide (or thinner than normal) rims.
Now, I've had these pics for awhile but I didn't post them because I hadn't tried out this setup. Finally finished the bike buildup and have done two rides on the setup so far and it is working awesome. I changed from Maguras with plaz pads and a booster to this setup with Avid SD-7s and plaz pads and I have to say they work just as good if not better (some of that is probably due to the decreased flex of the chainstays by running essentially two boosters and wouldn't be as big of a difference in frames with very stiff chainstays to start with).
Hope this helps some folks out there.
Todd
Tools you do need: a drill (preferably a drill press), a hacksaw, a handfile (or grinder to do it faster), and something to measure with (a good ruler if your careful, a set of calipers is best).
Start with two plates of aluminum (I think it was 1/4" plate) that you will cut out to the shape of your booster (mine is very square as this was a test to see how well this would work, it would be better to round the top off more). To speed up the shaping process I drilled the holes for the V-brake mounts first and bolted the two plates together to shape them simultaneously with your choice of hacksaw, grinder, and handfiles.
http://www.observedtrials.net/album/data/500/279conversion1-med.jpg
Here's the lower plate completely shaped. Four holes are drilled to match up exactly with your 4 bolt mounts and can be easily recessed by carefully partially drilling with a larger drill size to keep the screws flush when installed. The V-brake studs are mounted by grinding off the prethreaded portion that they come with and then screwing them on with an allen bolt from the bottom of the plate (eliminates the need for making a threaded hole). To make an indexing hole for the V-brake rebound spring I bought two premade shear pins that just fit over the little stub on the brakes and drilled two holes to tap them into (they are made to press fit into standard drill diameter holes and you can see them just inboard of the V-brake mounts).
http://www.observedtrials.net/album/data/500/279conversion2-med.jpg
Here's the lower plate/booster installed. I would have rather used counter sunk allen bolts than the flat screws, but the hardware store didn't have the size I needed. Should work fine with liberal use of Loctite. Note that I provided too much tire clearance and should have spent more time rounding off the upper contours...
http://www.observedtrials.net/album/data/500/279conversion3-med.jpg
Here's the finished package with the outer booster and brakes installed. The outer booster is basically the same as the lower with just a few less holes (yes, it's a bit ugly all squared off... the next one will look better).
http://www.observedtrials.net/album/data/500/279conversion4-med.jpg
Here's finished from the side. You can see the allen bolts on the lower plate that hold the V-brake studs on. Also you can see that with the studs I used I had to add one washer underneath them to allow for enough clearance between the brakes and the lower plate.
I have not provided any measurements for the holes, etc. because you will need to measure your own setup to determine that (and note that the finished product will most likely not work on other bike frames). This is just to give you an idea of what can be done with a little spare time and some basic tools. Note that with some slight movement of the brake mounts in and out this design can also be used to acomodate very wide (or thinner than normal) rims.
Now, I've had these pics for awhile but I didn't post them because I hadn't tried out this setup. Finally finished the bike buildup and have done two rides on the setup so far and it is working awesome. I changed from Maguras with plaz pads and a booster to this setup with Avid SD-7s and plaz pads and I have to say they work just as good if not better (some of that is probably due to the decreased flex of the chainstays by running essentially two boosters and wouldn't be as big of a difference in frames with very stiff chainstays to start with).
Hope this helps some folks out there.
Todd