johnlink

Unable to leave well enough alone, I recently loosened the arm bolt unit of my front brake (in the pictures I’m pointing at the ends of the arm bolt unit, which is part #1 in the attached diagram). My problem is that if I tighten it so that it isn’t loosened by vibration, the springs are not strong enough to fully move the brake pads away from the rims. How was the brake originally assembled so that there wasn’t such a problem? More importantly, what do I do to solve the problem?

Crankycrank

Here's a good video on overhauling your brakes. Proper tightening of the #1 bolt starts at 5:00 mins.

dedhed

How are the cables?

Andrew R Stewart 

This caliper pivot uses simple bushings and thus has a narrow window of best adjustment. A complete take apart, cleaning of surfaces and greasing can do wonders. BTW take care if the other arm's pivot is taken apart, at some point along the Shimano high end dual pivot caliper timeline a "spacer/washer" with REAL tiny balls was used as a bushing. Loosing these tiny bearings is very easy to do and near impossible to replace. Andy

Dave Mayer

These are the best road rim brakes ever made. Powerful with great modulation. First class hardware and finish. So cherish them and restore them to 100% working condition.

I have completely disassembled and reassembled the 7403's several times; with most road calipers this is not worthwhile, but these outstanding calipers deserve to be completely disassembled (down to the 2 rows of tiny tiny ball bearings in each of the 2 main pivots), lubed properly, and put back together.

Brace yourself: this is rocket science-level bike maintenance stuff, and your first time with these will take at least an hour of trial and error and terror - per caliper. Take you time, do not lose any of the tiny ball bearings, and carefully tune the tension on each of the pivots. 10 degrees of rotation in each of the 2 pivots will be the difference between the pivot being locked up, and being loose and floppy.

johnlink

At 5:30, how does one tighten the nut without tightening the bolt? I don't see that the threads screw into anything other than the nut.

Andrew R Stewart 

The caliper back "plate" is threaded for each pivot. So the nuts are lock nuts, meant to trap the pivot bolt in place. I forget (having serviced many dozens of various dual pivot calipers I just look and see what each has) if these calipers have tiny set screws that press onto the pivot bolts. If they do, loosen then before doing and pivot bolt work. Andy

johnlink

That solves the mystery, and my problem. There are no set screws pressing on the bolts.

johnlink

Does the spacer/washer with REAL tiny balls correspond to the Pivot Bushing Unit (items 2 and 6 in the diagram attached to my original post)?

Andrew R Stewart 

Yes. Andy