As the saying goes, “Brakes are over rated, all they do is slow you down!”
And let’s face it, most of the time that’s exactly what you want. But there’s a difference between the ones that suggest you might slow down, to the ones that say STOP right now. And a lot of that can be in the adjustment.
Recumbent trike brakes fall into 2 camps, drum brakes, and disc brakes. And of the disc brakes, they are predominately cable operated mechanical discs. It’s this last group I’d like to address today.
What are Disc Brakes?
The disc brake concept is very simple: a disc of metal is attached to and rotates with the wheel. The caliper is attached to the frame and contains some friction material that is forced into contact with the rotor. With luck, this generates heat and a highly satisfactory retardation of the rotor. The brake pads are the friction material, the force to squeeze the pads onto the rotor comes from the brake lever, cables, and a cam arrangement within the caliper. And your hand of course.
Properly adjusted, the disc brake system can provide reliable and consistent braking. And there’s the catch, “properly adjusted”.
Disc Brake Installation – the basics!
Let’s go through the process of installing my favourite mechanical brake, the I.S. mount Avid BB7.
We’ll start the caliper installation assuming the disc is already attached to the wheel. Hit the internet, find the brake manufacturer and download the instructions for the brakes (BB7 User Manual).
First thing to notice is that the calipers have a whole bunch of funny shaped washers on the attaching bolts. These let the caliper sit at all sorts of weird angles yet still be done up tight. I guess these came from a time where frame manufacture wasn’t as accurate as it could be and let the caliper be installed on frames that might not quite meet the drawing specification. Sadly some of these frames are still being made… If the brakes are new then most likely the washers etc will be held captive by a tiny O-ring. Leave it there and skip on to the installation. If the brakes are old, I’d suggest separating the washers, cleaning them and putting it all back in sequence with a smear of grease on the mating surfaces.
I generally attach the cables before fitting the brake to the trike. It’s simply easier rather than with the caliper upside down alongside the wheel, while lying on the ground trying to see through the wrong part of my glasses. Pull the slack out of the cable but make sure the brake lever and caliper arm are against their stops.
Wrestle the caliper and cable into position on the trike. Do the bolts up and then back them out a little so that the caliper can wobble around on those funny washers. Some trikes need the wheel and disc rotor in position for this, others not, but now is the time to fit the wheel assembly.
Referring again to the instructions, the BB7 caliper should be positioned with the disc rotor in the ratio of 1/3:2/3 towards the actuating arm side of the caliper (the moving pad side). Do this by turning the other (fixed) pad adjuster so that it pushes the rotor into the 1/3 – 2/3 position. Apply the brake using the brake lever and tighten the caliper attaching bolts.
At this point – with Avid BB5 and BB7 brakes – 99% of the time the caliper installation is complete and only pad adjustment is to be done.
Initial Adjustments
First adjust the fixed pad (the one closest to the wheel) so that it just does not rub on the brake disc. As close as possible but not touching. Then adjust the moving pad (ie. it moves when the brake lever is pulled) to give the amount of lever travel desired. At this point the caliper is aligned, and the pads adjusted. When the brake is applied the disc should deflect a little towards the wheel – only a little – and that’s just the way it should be. And that’s job done!
As the brake pads wear, the disc is deflected more and more towards the fixed pad and braking effectiveness drops away. Simply re-adjusting the pads restores the correct clearance and design geometry and all is good in the world. No need to touch the cables – this is why I like the BB7 brakes! The BB5 and other generic calipers are somewhat different in that only the fixed pad is easily adjusted, and the moving pad position is set by the cable adjustment. In all cases though, correct adjustment of the fixed pad is critical for proper brake operation.
Oh, and a tip for easy maintenance – as long as the caliper position is correct, you need never touch it again! Caliper removal from the bike can be done by unbolting the brake caliper adapter plate that fits between the caliper and the frame, removing and re-fitting the caliper assembly can be done without re-doing the alignment.
Brake caliper installation and adjustment across all styles and brands is essentially the same, but do refer to the manufacturer’s instructions for their recommended procedures.
Fixing the problems
Of course, it’s a fair bet that it doesn’t go swimmingly well all the time. Sometimes it just needs to be done again with a bit more care, but I’ve come to the conclusion that if it doesn’t work after a few goes then there is something else wrong that needs to be addressed.
These brake mounts are not accurate.
The main symptom is that the pads need a lot of clearance to stop them rubbing, and the brake lever has a lot of travel and the brakes don’t work well. This is usually because the brake caliper is not in plane with the rotor. First step is to watch the disc as the brake is applied. It’s highly likely the disc is being twisted as the brake is applied. Sometimes the caliper needs the mount faces cleaned and a burr or paint removed then reassembled with a smear of grease, but often the frame has not been finished accurately enough and that’s where it gets difficult.
This is distressingly common with brakes that bolt straight onto the mount as the build tolerances must be maintained within a very small margin. Unfortunately, the options are limited when they are not. Best and easiest fix is to install the BB7 brakes (if available), followed by the BB5. Failing that, the only real option is to find someone to identify where the error is and come up with a fix. Park Tools make a very nice Brake mount facing tool that works wonderfully on bikes, but doesn’t fit on trike front wheel installations… At least not without making special adapter tooling for each trike variation.
Summing it up..
In summary then:
- Caliper and cable installation should be done as accurately as possible,
- Fixed pad should be adjusted as close as possible to but not touching the rotor,
- Moving pad is adjusted to get the desired lever movement, and is done by independent pad adjustment or by cable adjustment,
- Adjust the pads as often as needed to keep the brake operating at best efficiency.