I have a Milwaukee Road Superdome and it was one of my more troublesome cars to get to run reliably. The clearance between the top of the truck and the car floor is very tight.
Besides a very short bolster screw, which doesn't give you mush leeway in making them just a little "looser" the design of the Walthers cars rely on four screw heads that contact slightly sprung metal strips in the car floor.
I've had success at making some cars run better by using a good, fine mill file and knocking off a bit of the "crown" on these screws. Sometimes the slots are a little buggered up so evening them with a file can help.
Here's a four-wheel truck but the screw heads are similar:
Rapido-Truck1 by Edmund, on Flickr
When you put the bolster screw back in I like to put a small drop of PVA or any good white glue (Elmers) to act as a thread locker. Not quite as aggressive as Locktite but enough so that you can loosen the screw without it eventually working out.
I also seem to recall having to file "something" on the truck tops to gain more clearance for the truck to rock. It may have been brake cylinders or equalizer arms. Don't recall at the moment but I can look at the car later to see if it jogs my memory.
These ARE some big cars:
Super-Dome by Edmund, on Flickr
I have also run into some cars running better in one direction over the other. Not just six wheel stuff, either. Many of my main line curves are superelevated and I'm sure the transition is smoother in some places rather than others. As previously mentioned, a lot of trial and error, close inspection and shimming, filing and tweaking of the trackwork has to be done.
Good Luck, Ed
What is the track radius ? ... If too tight, it may be an issue.
I would check to see if the trucks are pivoting without any obstructions. Possibly one corner of the truck is striking agains a step or a coupler box.
GARRY
HEARTLAND DIVISION, CB&Q RR
EVERYWHERE LOST; WE HUSTLE OUR CABOOSE FOR YOU
Trainman440(3) Also make sure the screw that holds the truck on isnt too loose, but also not too tight (there should be SOME body wobble).
That was my first thought, whenever a car derails I generally check out the truck screws. I've found that loosening them a bit often fixes the problem. I'd rather have a car that wobbles a tiny bit but doesn't derail if push comes to shove.
sounds like some trucks on the passenger cars are able to swing more one way than the others. From my personal experience the best way to fix this is to record the cars going past various trouble spots in slow motion with your phone and diagnose it that way.
The shorts are likely caused when the wheels touch over various parts of turnouts.
In any case, it just sounds like either poor track work, or overly tight curves. The best idea is to fix your trackwork. That being said, if you want to make your cars perform better, here's some advice from someone with tight curves:
(1) I had to mod all my heavyweight equipment by cutting down on the centerbeam frames of the passenger cars to allow the trucks to swing more left and right in order for them to run reliably on my 22" radius curves. I know they look terrible on them but you gotta work with what you got.
(2) Other cars, I noticed the diaphrams were too stiff and would push against each other and derail the car. This can be resolved by using longer shank couplers, or bending the diaphragm springs to be less compressive from the inside of the car.
(3) Also make sure the screw that holds the truck on isnt too loose, but also not too tight (there should be SOME body wobble).
Good luck,
Charles
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While the 6-wheel trucks are manifesting the problem, the problem is likely your track work. 6-wheel trucks are much less tolerant of track flaws than are 4-wheel trucks.
I have had similar problems on my new layout until I methodically tested every inch of track. Most of the problems were on curves and on turnouts.
Any humps or valleys, no matter how minor, can raise a truck off the rails.
If one rail is higher or lower than the other rail, that is another problem.
Kinks on rail joints on curves will derail 6-wheel trucks.
Slight vertical rises where track sections connect, caused by poorly fitting rail, joiners will do it.
You need to do some detective work at slow speeds to find the glitches.
Rich
Alton Junction
1. Tested with the NMRA standards gauge all the passenger car wheels. Some were out of gauge.
2. Also used the NMRA standards gauge to check all the flanges and points near the spots where I am getting derailments or shorts.
3. All the passenger cars now have Kadee couplers. I tested them with the Kadee gauge to verify they are aligned correctly.
4. I cleaned the wheels of the passenger cars.
5. I resoldered some drops where I felt with my fingers that the solder was interfering with the top of the tracks.
6. Verified that all the cars are properly weighted.