T H E O L D G R E E N B E E M E R
RIDING A 1974 BMW R90/6 FLAT TWIN
BRAKE PERFORMANCE PART FIVE, CALIPER ADJUSTMENT
ATE brake calipers are not what you call extremely powerful, and to give yourself
a fair chance to survive modern day traffic you better adjust 'm very carefully!
The method recommended by the workshop manuals: Mark the disks with
radial lines, using a felt pen, and adjust the excenter pin located at the
underside of the fork in such a way, that all marks are wiped clean
from the disk when rotating the wheel, and applying the brake.
This way of working involves a lot of fumbling at the low end of the forks,
where the slots in the excenters are pretty much out of sight, quite a
tiresome job, not really something that helps to make your day !
I found another manner of doing with a lot less hassle involved.
As you can read in Part two I now can turn the excenters by means of a normal
ring or open end spanner, and that makes a motorcycle man's life a lot nicer.
The thing is, now I can squeeze the handle and rotate the excenter pin the
same time! The procedure: First rotate the excenter pin and move the
caliper towards the outermost edge of the disk. Than I squeeze the
brake handle gently and don't let go. Now while rotating the pin
slowly in either direction I can feel if the piston has reached
its maximum out position. On that point the handle clearly
starts to harden up significantly, meaning that the pads
are pressing the disk flat, and are lined up properly.
Now I pull the lever stronger, and check for movement between the caliper
and the disk. When the caliper is not aligned properly, the pads grab the
disk under an angle ( left drawing ) and a chewing motion can be seen
between the two.Just have a concentrated look, it can be seen clearly.
A spongy feeling handle and bad braking performance is the result !
CHECK THIS OUT
The drawing on the right shows the excenter pin rotated over 180 degrees
placing the caliper at the innermost position of the disk. Theoretically
speaking, brake performance will now suffer a bit ( slightly smaller
diameter disk ) but in practice, you will not notice. But what does
happens over the long run is, the disk will now not wear out
on the outermost edge and an ugly thick rim is left ....
So better place the caliper in the outward position!
AND THEN ...
Finally, I rotate the wheel and without touching the brake lever,
check for pad rubbing. I usually have to turn the excenter a
tiny small amount inwards ( spanner handle pointing to
the rear of the bike ) to solve this. All OK? Done !
Off course, I first made sure if the caliper can swing freely
otherwise this last check is difficult to judge. If all is done
right, you have a functioning brake that doesn't drag.
LESS HASSLE ? YES, I KNOW ...
You can also do as the manuals tell you, but for me this works like a charm.
Hopefully now, you can stop safely without having to use an anchor !
WHO THOUGHT OF THIS DESIGN IN THE FIRST PLACE ?
Looking at it now, it's a crazy design indeed. BMW was not the only brand
utilizing this idea, have a look at the Honda CB 750 for example. The
floating caliper that followed later on, is a much better brainchild.
Continue to Fork / Seals wear
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