Rear Brake bridge hole

gcgizbourn

Hi all, am new to this forum.

I have pieced together my bike from flee bay bits. It good and am proud of it. The frame is carbon and the brake bridge hole has somehow widened, I don't know how and not truly concerned as I accept this is a second hand, prototype frame from a small producer.

Problem is, when tightening the nut in recess onto brake bolt it keep on tightening straight through the hole and out the other side. I can't afford to replace the frame with a like for like so I am trying to come up with ideas on how to fix it.

I essentially need to narrow the bolt side of the hole, so that the nut isn't allowed to go all the way through when tightened onto the bolt. 1 idea I got from reading this recent thread Gluing carbon? If I can plug the nut end of the hole (inner frame hole entrance) with something right up to a couple of mm to the bolt end of the hole (outer top end of the hole) and then stick a straw through the hole and pour arildite 24hrs into the hole around the straw, the inner frame end will be blocked from the arildite running out with the plug.

After arildite is hard, cut off ends of straw, use fine drill bit to open the hole to 4mm and that should A allow for a straight hole from the straw B create a stopper, so the bolt, when tightened, does not get tightened all the way through the Brake Bridge.

How does that sound, if it makes any sense at all, will arildite be hard enough and be drillable. Alternative is to just arildiate my 7900 Dura ace rear caliper into the hole and hope I never need to remove it.

Many thanks

GC

topdude

How about aralditing a short length of metal tubing into the hole, outside diameter just small enough to fit in the brake bridge. Inside diameter just big enough to take the fixing bolt

Or fit a front caliper which has a longer bolt and fit an nut and washer outside the brake bridge

Or completely fill the hole with Araldite and drill it out to fit the correct nut

Enough for now, how about some photos

gcgizbourn

Am off to friendly hardware store for arildite tonight, so will follow up with some photo's of project.

Thanks for the thoughts and ideas TopDude. found old ultegra brake so will use that to test me thinks.

nicklouse

i would be off to a machine shop to make a little alloy top hat insert to fit and take the load.

gcgizbourn

Job done!
Araldite rocks.
Bearing in mind this frame is going to be a long lasting Tri/TT frame which probably isn't going to be bettered I have done 2 jobs on my bike.

1. Headset, the frame was a prototype for the frame builder and so had some chipping and the headset bottom cup for the bottorm bearing always wobbled slightly so it would be tight at the beginning of a 40-50k ride but at the end there would be play in the forks and handlebars. Araldited the bottom bearings into place in the bottom cup. Sorted.

2. Original issue. hunted for perfect object to fit in brake bridge hole to allow some araldite into the hole but big enough to allow brake nut through and something to plug the whole the other side. Small birthday cake candle with candle cup holder, the bit with a pin you stick in the cake. Cover candle in clingfilm, tight as possible, ram candle up the bolt end of the brake bridge and follow up with plug, such as folded card to keep in place. mix up araldite (non fast setting one) dribble into hole around the candle. steady the candle as straight as possible, go back periodically and check the candle is in place. candle.jpg

16hrs later give the candle a good press through the from brake side out the back. candle pops out like a dream, leaving clingfilm. skin.jpg skin above.jpg. cut away the clingfilm, test the size of the whole with brake nust, check bolt connects with brake nut.

End result, reinforced the brake bridge area with arildite as it was hole was caving in under pressure to try and tighten the brake. Problem sadly still remains.

The brake if used in anger will turn slightly in it's housing so that 1 pad slightly engages with the rim, causing me to go even slower. Now unsure whether it is a problem with the actual brake, it's been greased, cleaned, re-greased with teflon TF2 grease, cleaned again and lubbed. So as this is the only frame I am going to use for a while, have araldited the brake in place on the frame.

I don't it's going to win any medals, but as I said araldite rocks.

Yossie

I'd have just used a washer that is bigger than the hole but with a smaller hole in the middle to fit the brake thingy through.

Or a rivnut.

But that's just me.

gcgizbourn

yup, that is what I thought but the added issue was that when I tighten the nut it would end up going all the way through the hole, so had to add something solid to the frame that the brake could tighten on.

it's kind of rambling really as you wouldn't need to do this on an off the peg frames as I would take it straight back to the LBS if it happened, but this was a second hand flea bay small uk carbon frame builders prototype so not much recourse for refunds :-)