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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?

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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

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.


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I used a different approach to the the diaphraghm issue.    I notice mine would hook inside sometimes on curves.  

I cut clear plastic pieces the same shape and size as the striker plate on the diaphragm and glued them on the  ends.    that way both diaphragms have smooth flat surface to slide on.   It worked great for me.

I used a glue that did not mar the surfaces too, so if I want to remove the covers, it can be cleaned off.

I just dug out my 30-2158-0 MTH D-bug. It has the 4-rib diaphragm. I purchased this unit new in 1999, so the diaphragm on it is the one it came with. On the LIRR, these were used during the depression in lieu of steam to save $$$. I plan to remove the diaphragm on mine when in service, I'm sure there was no diaphragm prototypically when in use here.

Here's mine on a O72 curve and a straightaway, I like the looks much better than a big open space between the cars.  Also, since the cars don't have even a dummy door, they look stupid with no diaphragm.  I trimmed one section off the right hand side (powered unit), it had four folds (5 ribs) when I started, the unpowered unit only had two folds (3 ribs).  Since these were used when I got them, I'm not entirely sure if the diaphragms are stock.  However, on O72 curves, the extra rib on the powered unit was a problem, now they run great.


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Last edited by gunrunnerjohn

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