rain miles count double

With the official start of British Summer Time, rain that isn’t absolutely freezing and other definite signs of spring being in the air, the winter of 2008 would seem to be passing into history. But today it claimed one last victim before leaving us enitrely, the Avid BB5 disc brake caliper on the rear of my Commencal Normal Disc commuting bike.

Eight months of commuting duties had worn out the front and rear Avid brake pads that came supplied with the Commencal from new, so it was time for a change. It should have been a simple job, but the rear caliper had other ideas.

Avid BB5 disc brakes have two braking surfaces; a static one and one that moves inward with the brake lever action. To compensate for brake pad wear, the static surface can be adjusted by means of a screw plate connected to a big, friendly looking, red adjuster knob. This is known officially as the “inboard pad adjustment knob”.

Avid BB5 Disc Brake (front) showing inboard pad adjustment knob

Unfortunately for me, the salt and grime kicked up from the wet winter roads into the rear brake caliper had caused the metal screw plate (that lies underneath the adjustment knob) to seize to the caliper body, and no amount of force on the adjustment knob would make it turn.

I tried the usual methods of freeing seized components: application of brute turning force with the Big Spanner, shocking them apart using hammer impacts, bathing overnight in penetrating oil (good old WD-40) but to no avail, the plate and caliper were still as one. Furthermore, the adjustment pad seems to be made of a very soft alloy and didn’t take at all well to this rough treatment, as you can see from the picture below.

Avid BB5 Disc Brake (rear) after failing to un-seize the inboard adjustment plate

Note the sheared inner and outer surface of the central Torx bolt, gouges on the plate surface and outer screw threads and the dents and paint chips on the caliper body. None of this damage took much force to inflict, so be careful if you find yourself in the same unfortunate situation.

After all this effort, I’m left with a destroyed, useless rear caliper, the expense of a replacement unit and a commuting bike lacking a rear brake and therefore too dangerous to take on to the roads.

This inconvenience and expense could have been easily avoided with a couple of simple precautions:

1. Apply anti-seize compound between the caliper and adjustment pad when fitting the brake. Mine came factory fitted so I didn’t think to check, but it would have been a ten minute job to apply the compound retrospectively.
2. Once a week give the adjustment knob a turn in both directions to ensure it is still moving freely. If I’d noticed the pad was in any way sticky, I could have cleaned and greased it before it got to the point of a full seize.

Preventative maintenance. You know it’s a good idea.