Friction and hydraulic steering dampers for the BMW motorcycle
The R69S Hydraulic Steering Damper
Thanks to Steve Sawtelle for the photos and notes.
These parts may not be correct. The broken part is not identified. The small nut (middle row) on the left is 12 mm, and getting a socket wrench on it is tough. 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 replace 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 on which to tighten down. 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 of 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 are partially assembled.
Some history of the BMW motorcycle steering damper
BMW has tried both types over the years. During the first Earles fork models, they 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 best way to go. In practice, BMW used both types (R69S and /6) and failed miserably. 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 well. When the 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 /5 damper photo.
The only practical 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.
Hydraulic dampers will work well 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 might wobble if they had the hp to reach 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 setup 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 diagnose and repair them safely.
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 them.
We have seen the SWB wobble just about “out of the crate.” That one was caused by fork misalignment. As the bike got older, it had normal 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. You want to 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 know the reasons (factors) for a wobble and know how to test it at a low speed. One can get on a bike and be surprised. I know I shall never forget “my” one bad experience. Link for more wobble info.
Here are 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 we wouldn’t test ride one over 40-50 mph in my shop. 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. The trunk on the luggage rack. This is also about aerodynamics. It is worse when there is no passenger to fill in the empty space between the rider and the trunk. All SWB BMWs will have a low-speed wobble, even with an empty trunk. Don’t mount a trunk on an SWB /5 model.
3. Fork alignment on the BMW telescopic forks. My site has the fork alignment fix by Randy. Thank you for your 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 about aerodynamics and balance. They must have about equal weight in each bag. Hard bags are worse, soft bags are better. A heavy weight is worse, light is better. Weight forward is better, rearward is worse. 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. The window of stability is small. Get the LWB for touring two up.
Updated 13 July 2022