It might be hard to come up with now... but way back in the day... When Micro-Trains was still Kadee in N scale... They actually made a repair bolster for the Minitrix passenger cars that worked like a charm.
I had a bunch of them 35 years ago.
The part is out there that solves everything, but you could just build up th floor with Milliput brown putty and drill and tap it.
EDIT With added information:
It looks like Micro Trains kept the Rapido/Minitrix bolster inserts as part of their packaging to today.
The instructions from the Micro-Trains website still show the different underframe inserts in their instructions.
Hopefully some of this helps.
It would be helpful if you could share pictures of the passenger car in this topic.
Have Fun!
-Kevin
Living the dream.
wblock I finally got the truck off, but the only way I can get the new one on will be with a screw and nut. Any suggestions what I should use?
This illustrates that the 'correct' screw is, as I had thought, 'shouldered' -- it has a smooth cylindrical portion next to the head for the truck to pivot on, and it can't be screwed in too far to jam or crush the truck bolster or make the truck bind in rotation.
Compare the screw you removed to the one in this illustration -- they should be similar. I assume the metal threads are not damaged.
I do not know what damage has occurred to the part of the car this screw goes into, or why you are certain a nut is now required. I do not have one of these cars to 'consult' and you have no pictures, but 6B appears to indicate that the screw goes into a hole in a molded plastic post, and it will be this that is cracked, enlarged, or torn out to make the screw loose or the truck not ride straight.
If that is so, I'd think about fixing the plastic before going to a captive nut. There are various ways to fill or weld this to restore both the material that will engage the screw and provide a proper surface for the truck bolster to ride against. There are kits to provide a proper drill and tap with a small tube guide to assist in precise right-angle orientation (to preclude breaking these very small tools, otherwise almost an occupational hazard!) and I would get one of these that fits the screw you have. Fill and repair the post, carefully center, clearance-drill and retap the hole, and adjust the surface for the truck (or pictured washer, etc.) to ride against, and then use the factory screw.
If you elect to go inside the car, cut off the post or whatever inside, and install a nut there, you may need a different screw and nut. If you cannot find a shouldered replacement you will need to provide the effect of the shoulder. This could be done by filling the threads next to the head with an appropriate material and then chucking the screw in a Dremel or pin vise and carefully filing or cutting to smooth cylindrical shape.
You will also have to cut a flat inside the car for the nut to bear 'flush' on.
As noted you will probably want to try to make the nut 'captive' inside the car so you can remove and replace the truck later (e.g. for adjusting the ride height or level of the truck fit) without having to take the car apart. That could be done with adhesive, or perhaps by heating the nut briefly with something like a soldering-iron tip so it melts the plastic slightly at the point of contact. You could glue a small structure of strip plastic or metal to hold the nut in and engage at least one flat on the nut to prevent turning.
If you choose to leave the nut 'loose' inside the car you could use the analogue of glyptol to hold the nut on the screw at the right position -- I would not use Loctite for this purpose as it might be too difficult to remove later.
If you can link pictures of what you have, it would be helpful in providing less firehose-word-salad advice...
I finally got the truck off, but the only way I can get the newe one on will be with a screw and nut.
Any suggestions what I should use?
wjstixIf the trucks work OK, I'd consider just changing the couplers.
I believe the OP is talking N Scale. It would help to have a photo, of course.
http://www.spookshow.net/passenger/trixcorr.html
Micro-Trains offers a replacement truck which may be the best solution for reliability:
https://www.micro-trains.com/index.php?route=product/product&path=63_113&product_id=598
Good Luck, Ed
If the trucks work OK, I'd consider just changing the couplers. Kadee makes couplers made to fit the NEM European style coupler mounts. On my Trix caboose, it was just a matter of pulling out the European coupler and snapping in the Kadee.
https://www.walthers.com/catalogsearch/result/?q=Kadee+NEM
Start by assuming the screw is a little loose in its bore. Take a small thin screwdriver or shim and lever it between the truck and the frame to 'preload' the screw against the threads, then start backing the screw out, keeping firm pressure on the truck to push out on the underside of the screw head.
I was given a couple of Mini Trix passenger cars that have Rapido couplers.
I would like to switch them to knuckle couplers, which I have, but I can't seem to remove the old trucks to switch them out without doing damage.
There appears to be a tiny screw with a Phillips head holding the trucks in place. I have a Phillips #000 screwdriver, which seems to sit properly in the screw head, I can wiggle it without it coming loose.
But no matter how many times I twist the handle the screw does not come out. It is a tiny bit looser than before, but not much.
Any suggestions?