Tandem Cycling - tapping rack mounts?
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05-06-11, 06:48 AM
Are Cannondale rack mounts unthreaded? I had to tap both the m5's (didn't go well) in the rear and the front has the braze-ons for the lowrider racks but I see no threads. Is this how Cannondale made these? Should I run a pilot drill thru the braze-ons and use an m6 tap? For anyone else who is interested if you try to tap with a quick release chuck in an impact drill it will wobble too much and you will ruin your m5 tapped hole in your frame. You will then have to drill and tap it the correct way to the next size tapped hole. I did this before I realized that there was too much slop in the quick release type chuck. :( I now have a rack with an m6 on one side and an m5 on the other.
Did they really make them like this?
05-06-11, 07:03 AM
Maybe the braze-on holes just had paint in them so it looked like they weren't tapped? That's what my Specialized Tricross was like when I bought it last year. I had to run a 5mm tap through the braze-ons to clean out the paint.
05-06-11, 09:16 AM
We had to have the rear rack mounts tapped on our Cannondale too.
05-06-11, 10:29 AM
I'm not sure what kind of front lowrider mounts C'dale uses. One type only has braze-on on the outside of the fork blade; they should be threaded (you need to use a lowrider rack with a hoop on these types). The other common setup uses braze-ons on both sides of the fork blades, allowing a bolt to be passed through the fork and secured with a nut on the other side (I prefer this type, myself). So, if your fork has a pass-through hole, then it should not be threaded. If only one hole on the outside of the fork blade, then it should be threaded.
As an aside, I would recommend against tapping using a power tool. You should use a tap with a handle and do it manually, using cutting oil if necessary. The only time I use a power tool when tapping is if I need to drill a pilot hole first for the tap.
05-06-11, 11:29 AM
We have '90 and '91 C'dale tandems...both have 5mm with 0.8 thread pitch on all the tabs for fender and rack mounts. We also have a 2010 C'dale Road Tandem 2 and all tabs on that one are 5mm x 0.8 as well, although there is a lot off paint on the threads on the 2010 Tandem. A simple chasing of those threads, by hand, with an appropriate tap should have cleaned up the threads nicely.
FWIW..I'm not a fan of mixed sizes on any set up as you now have for your rack even though you had no choice. But, since you have already gone over-size on one of the tabs...I would be sure to always carry a spare bolt for it and mark that tab somehow to remind you down stream that it is an oddball size... or...if it were mine, I would try to have a helicoil put in and bring it back to 5mm.... or worst case, just resize all of the tabs so everything on the rack attachment points are the same......
My '05 rear rack mounts were threaded. My fork is not standard.
05-10-11, 06:20 AM
I had a bolt head break off when installing it because of paint in a threaded rack braze-on a few years ago on a new frame. Since then, I've bought taps in M4, M5, and M6 sizes and tapped every braze-on on my new frames and on frames I've built up for friends and family - I've found many with paint in the threads. If the hole is already threaded, there is no need for power tools, I just have a simple manual tool, which is much less likely to cause problems.
05-10-11, 10:29 AM
One word of caution on tapping 5mm threads.....if you buy a large set on metric taps and dies or if you borrow someone's 5mm tap, be sure you get the correct thread pitch. Some sets have taps with both a 5mm x 0.8 thread pitch and a tap with 5mm x 0.9 thead pitch.....be sure to use the correct one. All the bike stuff I've taped has been 5 x 0.8....but I'm always careful.
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