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R100RS bouncing

plehman

plehman

New member
Can't believe it, everything is going wrong with this new to me 1981 R100RS with about 55,000 miles. Noticed the rear suspension feeling very soft. Now it actually rebounds more than once when I jump up and down on it. I think I know the answer - the shocks are toast. I tired the tightest setting and the middle setting, both the same thing. Bouncing. What felt like a stable bike now feels like riding a swing set.

I guess the question is how to know they're no good and what's a reasonable solution? Reasonable being not terribly expensive.

thanks
 
I think you've established the "test" for shocks! Sure sounds like there's no damping left. Any idea what brand is on there? Maybe they're rebuildable.

We've had some discussions in the recent path but I can't seem to find them now. Generally, from memory, what's been talked about are:

YSS - Tom Cutter on the east coast offers them
Wilbers - Ted Porter on the west coast has them
Hagons - probably a variety of places
Ikons - these are replacement for the Koni shocks of the day - https://www.ikonsuspensionusa.com/
Bob's BMW sells a shock which targets the older style shocks for the /5/6 series
 
Reasonable being not terribly expensive.
Click to expand...

BMW = Bring Mommas Wallet.

Hagons are probably the cheapest way out.

Ikons not so cheap, but what I opted for, and glad I did; the difference in performance is like night and day. I got mine from Ted Porter BeemerShop.

If your rear shocks are toast, your front fork probably isn't far behind. Might was to check out rebuild parts for them as well.

Let not your heart be troubled ... once you get through these rough spots (aka: $$$) your scooter is going to be a great ride.
 
Great advice as always.

The issue with the front forks that I can't seem to find is a pretty bad clunk when I hit a pothole (and I avoid them like crazy). Can't tell if it's the big RS faring or the forks. The steering head bearings seem to me to be well adjusted. What do you mean, rebuild parts? The two bumpers? Any suggestions who carries that?
 
khittner1 said:
Call Tom Cutter at Rubber Chicken Racing; he has complete kits for fork rebuilds. He did my ‘84 RT’s last Fall.
Click to expand...

There are also Race Tech cartridge conversions for the forks. They are a bit pricy, but worth looking into.
 
I believe that Race Tech sells cartridge emulators, not cartridge conversions... very different thing
 
Right—-and Tom Cutter’s fork rebuild kits are made up of OEM pieces. I don’t think that the ‘81-‘84 bikes had bumpers in them like the earlier /6 and /7 bikes did. Tom didn’t recommend any aftermarket fork springs, and didn’t think my 33yr-old, 70K mile OEM springs were tired, either, so they were re-used. He may recommend somewhat zootier shocks than Hagons or Ikons, FWIW.
 
Last edited:
Tom didn’t recommend any aftermarket fork springs, and didn’t think my 33yr-old, 70K mile OEM springs were tired
Click to expand...

A lot of these old bikes had Windjammers, Luftmeisters, and other heavy fairings installed. They took a toll on the springs, but whether new springs are really needed is up for consideration. A PVC spacer can always be added to pre-load the forks after the springs are re-installed. If needed.
 
Tom Cutter said:
That clunk is caused by the damper valve body moving in the bottom of the fork. BMW sold shim kits for curing that, I don't know if they are still available. It requires removing the fork springs, then the circlip that retains the damper valve assembly, and installing shims above the circlip, then a new, flat clip. I've done some, and it does work.
Click to expand...

And he suggested GAZI SportX shocks and a fork kit to balance it out. Not cheap, but very high quality, made to my specs, and I am hopeful this will be very good.

I ordered them...
 
Last edited:
plehman said:
...Noticed the rear suspension feeling very soft. Now it actually rebounds more than once when I jump up and down on it....
Click to expand...

It's not for nothing these bikes were called "gummikuhe's" (rubber cows) by the Germans - even with fresh OEM shocks. :)
 
I started this thread a while ago, so to continue the saga...

I installed fancy rear shocks (Gazi SportX twin shocks) and a Hyperpro front fork kit sourced from Tom Cutter. He had a pretty good info sheet on how to adjust, but I don't think I have it right. Here's the symptom.

There's a subtle front to back bounce or pulse that becomes quite pronounced at high speed. I looked down (around the big RS faring) and actually seemed to see the front fork vibrating - looks to be front to back. I can't take a good long look and stay on the road. Not bad at lower speeds but I can notice it sometimes.

Tires are new and balanced
The ride overall is good - as in absorbs the bumps well
The wheels are straight and seem OK
Just did the steering head bearings

I keep messing with the easy adjustment (softer, harder) on the bottom of the rear shocks. 10 clicks, 12 clicks, more... I think the rears are fighting the fronts in some way.

Not sure what to do.
thanks
 
plehman said:
I started this thread a while ago, so to continue the saga...

There's a subtle front to back bounce or pulse that becomes quite pronounced at high speed. I looked down (around the big RS faring) and actually seemed to see the front fork vibrating - looks to be front to back. I can't take a good long look and stay on the road. Not bad at lower speeds but I can notice it sometimes.

I keep messing with the easy adjustment (softer, harder) on the bottom of the rear shocks. 10 clicks, 12 clicks, more... I think the rears are fighting the fronts in some way.

Not sure what to do.
thanks
Click to expand...

You may have lingering handling issues, but Cutter is among the best there is to help sort things out.

You "seemed to see the front fork vibrating--looks to be front to back." There's a good reason for this---they do "vibrate" in pretty normal operation. Airhead fork legs, particularly those on the pre-'85 twin-shock bikes, are, by any contemporary comparison, quite skinny and "flex-y". Many owners go to significant lengths to stiffen up the front fork structurally with a variety of fork braces, revised/improved triple clamps, etc. They reason something along the lines of: "The heroes on the Superbike teams did these things, so that must be the way to go." While some continue to swear by the efficacy of the spending they've done on their airhead's modifications/customization/personalization, they often create different sets of problems, rather than solving all problems. Your airhead's fork was the state of the art for a long-travel, smooth ride. Trying to quell the fork tube vibration you're seeing around the side of your fairing may only increase fork stiction and impede handling. Present your concerns to Cutter, and take his advice and counsel.
 
I never had the vibrating forks but I did all I could (afford) to my R100 to improve the handling -- Progressive fork springs, 7.5 wt fork oil, Telefix fork brace, billet upper triple clamp, Koni shocks. To be sure, I was going for sportier handling but it still made for a good touring bike (full disclosure, my only touring bike until the 1290). If I were to do it again, I'd skip the triple clamp. I'd ask Tom and see what he says. Alternatively, try maxing out the adjustment on the shocks in one direction, take a ride, and then the other. Work up to speed carefully as the handling will be compromised. That should help you figure out whether the rebound is what's causing the problem.

Also, check the sag at both ends. If the front is not adjustable, set the rear to match the front, i.e., if the fork is a bit too soft, set the shocks a bit too soft.
 
plehman said:
Not sure what to do. thanks
Click to expand...

There are a couple of things you can still do:

- install an aftermarket upper triple tree (I think they're .030 aluminum)
- brace the swing arm

With the thicker triple tree, you shouldn't need a fork brace.

Good luck.
 
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