Downtube Shifter Bracket Slipping
 

I recently refurbished a bike set up with Campy nuovo record shifters on the downtube. It included removing and polishing the shifter bracket and paint underneath. After a couple of rides I find the shifters are going out of adjustment and the cables are going slack from the bracket slipping down the tube. I can even see an outline of the bracket in the paint that is slightly less sun faded telling me the bracket has slipped yet again! I tried the obvious: tightening the bolt and nut VERY TIGHT but still having the problem. I don't want to shear the bolt off. Anybody got a solution without drilling holes in the down tube?

Over about 30 years, my shifter slid down about 1/4". So, it hasn't ever been a big deal.

I probably would not wax under the paint. :eek:

Newer bikes got braze-on stops for the shifter, which I'd probably put on if I was doing a restoration and paint job expecting to use a clamp downtube shifter or cable stop.

I don't know if you could increase friction under the clamp. You could try a piece of inner tube, and then clamp it down tight. Then trim the excess.

I did try a piece of double sided masking tape trimmed down slightly smaller than the clamp itself. It didn't improve things. What gets me is that this is a standard Campagnolo bracket used on countless bicycles for well over a decade. It surprises me that I am the only person that has ever had this situation come up? I saw a frame recently that had a small bar or pin brazed onto the underside of the downtube to prevent the bracket from slipping. It was painted same as the frame so assume it was original.

Next thing I will try is removing any wax residue and apply a drop of Weldwood contact adhesive. That stuff is pretty sticky but not permanent and won't harm paint.

You are not the only one to have this problem, that is why many builders brazed on a slide stop shoe of some sort, above or below at the shifter location.
If you have a French bike, there is a diameter working against you. French down tubes are 28.0, not 28.6mm
tape will not be stout enough.
3M "grip" tape, they type with the "sandpaper" top, not the vinyl rubber texture carefully applied to the clamp and trimmed should provide enough friction to keep things in place.

Wipe the tube surface and the bracket where they touch with alcohol. Then get some double-sided carpet tape from the hardware store. Cut a piece small enough so it does not get all the way to the edge of the bracket (it will show at the edge). Put it pn the bracket first wiithout taking off the tape cover on the tube side and (dry) fit it. You can trace the bracket with a pencil on the tube first if you need to. It works for me for lots of things. Sigma bike computers have been using it for 30 years that I know of. I have maybe 10 of them. A few of them have over 10,000 miles on them.
Be sure to let the moving clamp part slide without tape under all of it. You don't need much tape. Tighten as much as you normally would.

I have not used it on down tube shjfter clamps. But, on front derailleur clamps and clamp on brake cable stop mounts.

Oops! The last two posts were posted while I left my window open, had dinner, and fed the dog.

I don't know what the problem is, whether you're not tightening the clamp enough for that particular tube diameter, or if the bolt and nut are becoming loose over time. But be sure not to over tighten the bolt. That will often damage the clamp and/or bolt beyond repair. Here, I only use a socket driver with a 5/16" bit. Do not use a wrench.

Maybe alcohol on the paint surface and blue Loctite on the bolt threads to start.

I would never ever drill the tube.

Pics often help.

Yes those can be tricky, the bolts are really tough you won't hurt it, just give it more feedback. Nut drivers with a light touch work good for me. Fingers choked up on a small wrench is good also. The guide at bottom bracket those would pain me also, I do alright now. It should be a less cable pinch bolt feel, those need more than your shifter clamp.

If you have any old VERY thin innertubes, you could trim a piece of one to go inside the bracket, in a way that it's not seen.

It's an Italian frame with Columbus tube but I just now checked anyway to be sure. It's 28.6+ including paint. The most frustrating part is knowing if I'd just left it alone with all the 50 years of accumulated crud I wouldn't have this problem. It didn't start slipping until I did the detail treatment. It seems you and others are suggesting tapes and rubber of various sources. I'll do some experimenting and keep this thread updated.

The 3M "grip tape" or traction tape has a cloth core and is very stable, basically I think the sandpaper finish on the tape is what is going to keep things in place.

I have come to believe that removing the clamp to clean polish, etc.causes it to become slightly misshapen and fatigued so it does not "bite" as it did before.

I also believe you need to remove it without spreading it any more than absolutely necessary to retain its original shape as much as possible. I always remove the clamp bolt completely so it doesn't scratch or hamper the process causing you to spread it more to get it off.

Early on I broke a Suntour clamp thinking it was far more robust than it was, I have proceeded with extreme caution ever since and not had one break or slip ever since.

It can also help if the clamp ears are angled so that the band parts contact the tube first, then the ears apply force to the band instead of touching each other before the band at the tube is tight.

One of the many wonderful PITA little niggles that screws up paint and keeps us up at night. :troll:

Rosin up the inside surface of the clamp like a violin bow.

I want to follow up on this thread in case someone else is having this issue in the future. I looked at adding things like rubber and such but there really isn't room for that. In the end I applied just a round 1mm drop of Weldwood contact cement on each side of the clamp and spread it around slightly. After it dried enough that it didn't smell of solvent I slipped the clamp back on the downtube and torqued it down as much as I dared. I then let it sit undisturbed overnight before taking the bike for a test ride. No slipping! I haven't had any issue with the clamp sliding or slipping for three months since it was glued so I'm calling this one fixed.

It is very important that you apply the Weldwood to the clamp, not the paint! The solvent in this stuff is HOT and will strip your paint down to bare metal if applied directly to it. Even on the chrome clamp wait until the solvent flashes off before allowing it to contact a painted surface of the frame and you're golden.

I think I might have tried a bit of anti-skid paint, or a bit of pumice and glue inside the clamp.

electrical tape will do the job.

shifter slipping
 

One of the funniest sights I recall from bike racing was an obvious noobie in a bike race on Guam. His down tube shifters were sliding down obviously causing his gear selection to be limited. The poor guy was pumping away to stay in the race while holding the shifters as high on the tube as possible. It was a hell of a way to select the proper gearing.

It seems the OP has already solved his problem.

I was going to suggest an option to epoxy-bond a clamp stop to the bottom of the down tube. That is, bond a small piece of metal in place. Brass, aluminum or even steel would work (steel requires painting when finished). A thickened epoxy would fill any small gap between the part and the tube, so you could even use a flat piece.

It would look and function as if it were brazed in place at the factory. It would not require drilling or weakening the tube in any way.

I suggest epoxy as it is strong enough that it would not creep under load the way a pressure sensitive adhesive would (tapes). Also, it does not add thickness to the clamping surface.