I'm the new caretaker of an MTH RailKing Doodlebug 30-2158-1.

This twin motored car might have been test run once in16 years, but this "bug" is like new.

With a freshly charged  8.4 volt battery, it fired right up.  After re-reading the startup insturctions, it took off running like it was built to do, it runs nice and smooth just like a new old "bug" should.

Right now the diaphram on the Bug sits over the rear knuckle.  When going around 072 curves it causes the trailer car to derail. In reverse it's even worse. When operational, it will be navigating 031 curves on a special public display layout.

I've tried a K Line 18" heavyweight, an MTH 18" streamliner coach with the same results. The diaphragms fight each other.

My question is, what has been done over the years to make the diaphrams work as they should?

Original Post

Mine came with a different diaphragm for tight radius, but I don't see how your would derail on O-72 unless it is not original.  G

Mine only had one diaphragm and it has never touched another one when I put a passenger car behind it.  Perhaps someone before you put a larger one on, or yours is not on correctly.  I ran mine on O36 with things behind it all the time.


EDIT: Another thought, I think this had the long coupler on the back, so maybe someone replaced it with the short one, which would also cause this issue.  Perhaps you can post a photo or two.  I'll try to remember to take some of mine tonight to post.

Last edited by sinclair

IMG_8887xxDoes seeing this MTH doodlebug and its trailing-coach help? It has traversed 0-54 and -72 curves with ease and has ever been a problem. I love that chug-chug start-up sound it doodlin byIMG_8887xmakes when powered -up.


Images (3)
Last edited by Moonson

I greatly appreciate your replys.  I will take some photos and post them some time today.

Please come back and take a look.

Here are the photos that were requested.

Note. Yesterday's reply, "G" mentioned a different diaphram.  In the MTH parts breakdown, they did show a 4 rib for the B & O and ATSF.  The 2 rib was for the PRR & C&NW.  MTH part # FL-0000026

This is a PRR and must have the wrong rib diaphragm.

Look at my photos.  One of them shows a curve at 072. Note the interaction.


Images (3)

If I'm not mistaken there was a thread sometime in march called "Passenger Car Diaphragms" which had some great information.  Worth a look, may help.  Thanks,



Were it mine, I'd be slipping an Exacto knife in between the folds of the diaphragm to trim that thing back. It's a very nice Doddlebug, but I would not be at all concerned about impacting it's long term resale value.

You are correct.  An appointment was made with the surgeon for a complete makeover.

Stay tuned to see the results once the bandages are removed.

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