The effectiveness of a drum brake has a lot to do with setting them up
correctly. Most people don't mess with them so I assume that variations of fit
and assembly can make the difference between a good and bad one. The best and
worst drum brakes I ever used were the Arai tandem drum. One provided almost
imperceptible retardation. Another, on Bill McReady's original Santana triple
prototype, hauled 500+ pounds to a stop quite nicely. Bill claimed he rarely
used the front brake.
Back when I was riding motorcycle Observed Trials in the '70s, brakes were
snuff tin sized drums and were often submerged in one section and then sorely
tested on a tricky downhill in the next. Those of us who knew how to get the
most out of them got fewer bruises.
drums on my 1st 3 tandems because rim brakes weren't very strong back
then. Now with Roller Cams, V-Brakes and Maguras, I wouldn't bother.
"Mushy" brakes are caused by flex in the system, mostly the shoes. The best way to eliminate this flex is to ensure that both shoes come into full contact with drum simultaneously. With mushy brakes, if you back off the cable adjustment
until there is no drag, you can't pull enough cable to apply maximum force.
1. If brake is new.
Squeeze the brake arm so the shoes contact the drum, and rotate the backing
plate in relation to the drum so that the high points on the shoes become shiny
due to rubbing on the drum.
As soon as you remove the backing plate, permanently mark the brake shoes so
that you will NEVER switch them. Left & right or top and bottom or whatever.
If the arm can be removed from the cam, mark the cam so that you will NEVER
install it 180 degrees from its original position. As the movements are so
small inside the drum, the fact that the cams aren't *perfectly* symmetrical
means that a perfectly functioning brake can turn to mush by simply flipping
the cam over.
3. Shoe Fitting
Now disassemble the brake, wiping off 99% of the original lube. from the
cam(s) and pivot(s). If the brakes are used, and are evenly shiny all over,
then they were probably already working pretty well and all you need to do is
break the glaze with some fine (120 grit or so) sandpaper. If it's new, or
used but not evenly shiny, sand down the shiny spots with fine sandpaper backed
up with a flat metal bar. I use a file. Remove very little material.
Reassemble, without the springs. Repeat Step 1 to put new shiny spots on the
shoes. Sand them down again. Repeat the process as often as necessary, until
the whole shoe gets shiny. When the entire shoe is making even contact, then
the shoes don't flex as much and don't feel as "mushy".
Disassemble everything including cones and bearings. Clean out everything and
put fresh grease in the bearings, and sparingly, on the cam and pivot. Be
careful not to get any on the brake lining surface or the drum. If you do get
some on the friction material remove it with electrical contact cleaner spray.
I used a soap or PolyUrea based wheel bearing grease, which is more resistant
to high temps than the petroleum based stuff. I did some testing which
convinced me that it was no more vulnerable to water.
This is the part that is hard to describe verbally, so please bear with me.
The results are worth it. The goal is to ensure that when the shoes are
expanded, they are perfectly concentric with the drum. Most drum brakes have
an unthreaded hole thru the backing plate, which the axel passes thru and a nut
on the axel to hold the backing plate in place. This hole is a bit larger than
What you need to do is make sure everything is concentric when the
nut is tightened. Install the wheel and brake on the bike with the nut
slightly loose. If you have a non-QR axel, tighten only the axel nut on the
side opposite the backing plate. Install the cable and lever. Rotate the
wheel, by hand, in the direction of travel while gradually applying the brake.
Did I mention that this part of the job is easier with 2 people? With the
brake lever squeezed tight, tighten the backing plate nut with a cone wrench.
If everything goes right, everything should be in full contact and the shoes
should be flexing very little.
Levers that pull lots of cable are very desirable. Also, cable routing is
critical. The good news is that most of what I described is just accelerating
the "bedding in" process. Once set up the brakes should get better with use.