Cessna 120-140 Association

Another tailwheel shimmy post! I had my Scott 2400 changed to a 3200 earlier this year. Since then I’ve experienced high speed shimmy (above 40 mph or so). The wheel behaves below that, so I can wheel land and taxi fine.

I’ve experimented with tire pressure and found lower works better than higher (I’m running about 30 psi right now). I also had the tailwheel spring changed to one that wasn’t as fatigued out as mind. I have an early serial number and the only spring my IA had from his stock was one with the bend at the end. However, by visual inspection the assembly appears to have the proper forward tilt kingpin angle. I also believe I have the correct springs per the articles on here. The new spring helped some as far as magnitude of the shimmy but didn’t eliminate it. I should note that perhaps the wheel is coming down canted as the tire is wearing on one side as if it got dragged sideways. I found I can nearly eliminate the shimmy if I run lower than 30 psi but that seems to be asking for a pinched tube.

I’ll grab some pictures later today but any ideas on where to look next? I’d really like to be able to put three point landings back in my toolbox.

Maybe you have read this?

http://www.airframesalaska.com/v/vspfil ... ention.pdf

If you have an old tired 3200 unit check here, otherwise the previous post from Alaska is gold-

I would go after adding a fiber thrust washer Part# 06-00726
MFR Model# ABI-3207-00 and figuring out why its wearing on one side of the tire ( could be caused by the shimmy itself) for starters, it will last a long time with little maint. once corrected if not parts will wear in short order.

Thanks for the advice, I’ll be looking at the internals some.

I had previously seen the Airframe Alaska article, and the one thing that stood out to me is the recommendation for the king pin angle - it’s the opposite of what’s recommended in the Tech article on the association website (viewtopic.php?f=10&t=134)

As for the tire wear, it’s along one edge like it was dragged sideways, not traditional tread depth wear.

The tail wheel wearing on one side might be causing the shimmy. Look at your plane from the rear. Does one wing look low? Does the tailwheel look normal or is it cocked to one side? Maybe a gear leg is bent? Maybe the tail wheel attach bracket is somehow twisted? Do you have the right tail spring set for your Serial Number? Cessna went from a straight set to a double bend set.

I had to tighten up the abrasion strips and rubber pieces that secure things a little tighter. There was simply too much slop and play. This is the 'before' pic when I first got my bird (and yes I got rid of the Maule springs before anyone does a 'gotcha'). Only a possible contribution to your wear issue.

The nuts and bolts and rubber pieces (you can fabricate) are pretty much nickel and dime stuff. The main bolt forward that holds the whole shebang together should be replaced if you don't know the history. Some folks advocate replacing the tailwheel spring set after 'x' years. Do check which spring set you need- double or single bend per serial number.

Any comments on this....

https://www.aircraftspruce.com/catalog/ ... ey=1234807

Don't buy maule.

8474 wrote: ↑Mon Sep 07, 2020 3:35 pm Any comments on this....

https://www.aircraftspruce.com/catalog/ ... ey=1234807

Not approved for the Scott, and, when the spring bottoms out it'll bend your rudder bellcrank.