1992 and later K75s came with
Showa forks that are better than the two earlier types of
forks that BMW used prior to 1992. I decided to swap
some Showas in on one of my K75s to replace the earlier S
forks. Although the Showa forks came from the factory
with progressive springs, I decided to upgrade the forks
with stiffer springs from Progressive suspension. Part
number 11-1509 for the Showa forks. (11-1126 for earlier K75
(Since the Showa forks are 0.3 mm
smaller in diameter I also swapped in some later fork trees
Note: It's a good idea to work on
forks one at a time so you don't get the parts confused.
Before disassembling them, I
drained them and measured how much fork oil came out.
It was a little over 400 ccs. (Which is close to the 410 cc
BMW spec for refilling them after draining them - or 420 cc
if you disassemble them.)
With the fork mounted in the
upper fork tree, I depressed the fork cap with a wheel
puller in order to pick out the C clip that holds the cap in
Since the Progressive springs
take up more volume in the fork, the forks need less oil. I
refilled the fork with 410 ccs of fork oil and used a piece
of wooden dowel to measure the distance from the top of the
stanchion to the top of the fork oil with the factory spring
still installed. The oil level was just under 11" below
the top of the stanchion with the fork fully extended. This
is how much oil I put in once I installed the Progressive
The length of the spacer that
came with the new springs was 4 5/16". When I laid the
factory factory spring and spacer next to the new spring and
spacer they were just about identical in length so I decided
just to install the new spacer as is and not trim it.
This will probably give more a bit more preload than
original but I can always go back and trim it later if the
front end feels too stiff.
I emptied the fork by inverting
it and letting it sit for a while. Then I installed the new
spring and, with the fork fully extended, added enough fork
oil to get it to the correct level. Then I installed the
washer that came with the new springs, the spacer and
finally the fork cap.
Then I did the other fork and,
along with the new fork trees, installed them on the bike.
© 2013 Drake Smith - Please do
not use or reproduce this elsewhere. Feel free to link
to it though.