It sounds like your damper has leaked out a little of it's oil and it's been replaced with a little air. It's a hydraulic unit, so just like having air in your brakes, you gott'a compress the air before the hydraulics can do their job. You need to replace it.
While we are on the subject of the Super Beetle Shimmies I'll share what I've learned (mostly the hard way) . . .
First thing you want to do is check every part of the steering and suspension system for wear and tear (and bend and breaks). If you are not positive that a part is perfect condition, you probably need to replace it. Even it you are sure it's good, you might want to replace it anyway. Don't worry, there isn't much to the front suspension of a Super Beetle. That may be why everything has to be perfect. :wink:
When everything is perfect, take it a good alignment shop and have them do a 4 wheel alignment (yes, there is an alignment setting on the rear wheels and if it's off, your car will not go down the road straight . . . get behind my son's Super Beetle sometime and you'll see what I mean :wink: ). Make sure your wheels are perfectly straight and perfectly round. A wheel that might roll OK on a standard Beetle could beat you to death on Super. The wheels have to be perfect. Then put good tires on them and make sure they are ballanced. If you can find a shop that will spin ballance them on the car, that's the best way to do it . . . but the last time I saw the machine to do that I was taking Auto Mechanics at Walker Tech . . . that was during the Carter Adminstration.
Anything you fix will probably help, but the only cure for the "Super Beetle Shimmies" is to fix EVERYTHING (or drive faster . . . sometimes the Shimmies will go away when you get over 55 or 60 . . . depends on what's wrong though . . . sometimes they just keep getting worse as you speed up.)
Here's a list of things you might need to replace:
The strut inserts, strut mounts, and strut bearings. Once a wheel tries to bounce once for any reason (bump, pothole, etc.), without good struts to stop the motion, your car will do down the road dribbling the front tires instead of rolling on them!
SAFETY WARNING -- DO NOT take the nut off the top of the strut insert until AFTER you have compressed the coil spring with a good set of coil spring compressors. Failing to do this can be deadly.Steering Damper and bushing. If a tire hit something and trys to pull to the side, without the damper it will pull all of the play in the suspension to one side, then bounce back to the other then bounce back to the other and so on . . . the bounce will get harder, faster and more violent until you slow down and get control of it. It COULD be that this is your only problem. Probably not, but it would be a good place to start.
Ball Joints
The short shaft with universal joints on each end that goes between the steering collumn and steering gear. I can't think of the "correct" name off the top of my head. You have to have the gas tank out to get to it.
Bushings - Idler arm bushing, Control arm bushings, and sway bar bushings. Don't even check these. Go ahead and replace them. Use the aftermarket urethane bushings instead of the stock rubber ones. I recommend using the ones from Top Line Parts - I think they are at
http://www.toplineparts.com . . . That's what we put on Justin's 74 Super about 10 years ago and they are still like new.
If they are worn, those last three things (ball joints, the shaft and bushings) give your suspension free play . . . and once some bouncing gets started it's got room to keep bouncing no matter how good your struts and damper are.
Sorry to be so long winded again. It took us about 2 years to get the front suspension right on Justin's Super. Trying to save you a little time.