The R69S Hydraulic Steering Damper
Thanks to Steve Sawtelle for the photos and notes. Email
me for corrections, or additions.
These parts may not be correct. The broken up part
is not identified. The small nut (middle row) on the left is 12 mm
and is very hard to get a wrench on it. I use a hand ground socket
to fit the nut that is nestled into the cupped washers.
Parts in order of assembly. "The black spacer in the
middle of this picture is the substitute I made from Delrin to substitute for
the original that fell apart on mine. I'm guessing from the color and
brittleness of the pieces I have that the original was a hard fiber part."
"I am looking at the parts book now and I realize I may be
missing a spacer (31422054219). It goes in between the two cupped washers
and gives the bolt something to tighten down hard on. The two cupped
washers don't butt up against each other, so the spacer takes up the extra space
- I figure it needs to be a bit over 3mm. I'm using a couple washers since
it seems to be NLA. Hmm that may make my photo a bit deceiving.
I guess it could be noted."
The same parts partially assembled
Some history of the BMW motorcycle steering damper
BMW has tried both types over the years. During the first Earles fork
models, all had the friction type. In 1961, with the advent of the /2
series, they came out with the hydraulic type on the R50S and R69S, the "sport"
models. The "low" tuned models, the R50/2 and R60/2 still had the friction
type. The /5 series came out in 1970 and all three models had the friction
type. In 1974 the /6 came out with a hydraulic type again.
The R25/3, R26 & R27 singles had only the friction type.
In theory, a hydraulic damper is the way to go. In practice, both types
that BMW used, (R69S and /6) have failed miserable. The reason for the
failure of the hydraulic damper is that BMW tried to make them so that they
could be disabled. They could be turned "on" or "off" depending upon
conditions. This "changeable linkage" is what killed it. The
mechanical linkage parts get sloppy and loose. The slop makes it so that
the damper is no longer effective enough to dampen a wobble. They
are soon worthless.
In practice the friction damper has worked better. At least there is no
linkage to fail or get sloppy. As far as dampening a wobble, they don't
work really well. When damper gets tight enough to stop a wobble, it
causes a weave. I have never heard of anyone (that I remember) going down
on a BMW from a weave, only from wobbles. A weave can be dangerous,
but it builds up slowly and one has time to release the friction damper.
Thanks to Marc Hammel for the photo.
The main use for the friction damper, especially on the /5, is to hold the
front wheel "straight" for service work. It keeps the front wheel from
flopping around. The way that hydraulic dampers will work well is if they
are mounted fixed and can't be released. That way there is no linkage to
wear out. The mounts are welded onto the frame and some item is bolted to
the forks. I have seen this often on sidecar rigs. B&S used this
scheme for Reg Pridmore's race bike and it worked.
By now you are wondering why BMW would even mount dampers that didn't work.
The bar-room scuttlebutt that I have heard is to provide a fallback position in
the event of a lawsuit.
Bikes wobble because it is their nature. Even the "stable" ones would
wobble if they had the hp to reach really high speeds. The idea is to
build a motorcycle that is stable in the reachable speed range. In the
real world, a wobble is evidence that something is wrong with the set up or
design. That is where we came in. That became one of my passions.
I wanted to learn enough about wobbles, on a BMW, to be able to safely diagnose
and repair them. Eventually we were very successful at both.
I must say that we were able to fix the ones that we encountered and that the
customer would pay for.
We have seen the SWB wobble just about "out of the crate." That one was
caused by the fork misalignment. As a bike got older, it had wear and
tear, plus the junk that owners insisted on installing. That would
increase the chance of a wobble. Ride the SWB with European low bars
and naked to minimize your chance of a wobble.
All wobbles terminate. Most by coming under control and some by
crashing. Avoid the latter. Don't mess around with a bike that has
shown you any instability. Get it fixed. Don't ever think that you
can control it. The best way is to have the knowledge to see the reasons
(factors) for a wobble and know how to test it at low speed. One can get
on a bike and be surprised, I know, I shall never forget "my" one bad
experience. For more wobble info.
Some of the reasons for a wobble in the order of danger (as well as I
remember them) It is assumed that the bike is in good mechanical order.
That means: properly adjusted steering bearings, wheel bearings, swing arm
bearings, shocks, balanced wheels and the list goes on. Every one of
the previous items can cause a wobble.
1. Handlebar mounted fairing on the BMW telescopic forks with the SWB.
This is about aerodynamics. All of them have a low speed wobble.
They are so dangerous that in my shop we wouldn't test ride one over 40-50 mph.
For one thing, not a single one could be mounted without disturbing the fork
alignment. The idiot manufacturers used the structural fork mounts for
fairing mounts. Duh
2. Trunk. This is also about aerodynamics. It is worse when
there is no passenger to fill in the empty space between rider and trunk.
All SWB BMW's with an empty trunk will have a low speed wobble.
Don't mount a trunk on a SWB /5 model.
3. Fork alignment on the BMW telescopic forks. My site has the
fork alignment fix by Randy a thank you note
for his wonderful job. It saved me from doing it 1/2 as well as he
did it.
4. Tires, balance and air pressure.
This is a very important aspect of low speed wobbles.
5. The way an individual rider dresses and grips the bars.
I am not sure where to put this one; Saddlebags. This is aerodynamics
and a balance thing. They must have about equal weight in each side.
Hard bags are worse, soft bags are better. Heavy weight is worse, light is
better. Hard bags that are mounted far from the bike are worse, close is
much better. The Enduro was the best in those days.
Something about the air space, but we never knew if it was related to the air,
the lever arm effect or something else.
The SWB is not an ideal bike for two up touring. Too many things make
it too close to the edge of safety. Get the LWB for touring two up.
Email photos and please put "damper photos" in the subject.
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