stiff wheels on MPC cars

A drop of oil at the end of each axle should do the trick.

Art

Is this on passenger cars?

Sometimes foreign debris gets wedged between the truck sideframe and the axle. If so, push out the axle and clean the ends with a drop of oil as Art suggested.

-John

Don't know why this would happen, but I've actually bought a car or two at a swap meet only to find someone took out an original wheel and axle and replaced them with a slightly longer axle version that looks the same, but must just be one or two mm longer on the axle. 

Lots of reasons for Railgon's length issue. Someone didn't notice, didn't care much, used what was available, only for display and rolled off shelves, a mistake, just to sell it, etc. etc. I have noticed this size difference also. Variances in production tolerances, or by design with a part number? I really haven't a clue about it, but would like to know. Nobody has an axle spec list? I cant seem to find one. Could plastic wheel axle vs metal wheel axle be the root of the length issue?

Cleaning and inspecting for axle seat melting, wear, or other damage would be my first action. Free of rust too? No? Polish the tips. Oil or lube may help. Doesn't help? Check the length and swap with another car. Or swap with a free spinning axle from the same car. Does the problem follow? In repair, I have used a homemade/custom ground, short, fingertip drill bit for scraping new seats. Long axels (or broken drill bit shank or dowel/rod) in a drill sharpening jig to create custom repair tips and lengths. One I even drilled one out till it was a hole on each truck, adding old non tapered long axels with a thin nylon thrust washer between wheel and truck. I have also heated and bent main and side frames due to warping after long term abusive storage. Switching to a set of new trucks was cheaper than expected for me last time I shopped. Better operating, easier rolling (best! but heavier. Grades?). The bolster height, and attaching method may need some attention for new trucks too, but the overall performance was well worth the $5-$6 more than new wheel sets I found.(offline,local)

Thank you every one for the help. it is a NP 9120 flat car. I have a pic of it on a thread of wrong color Lionel (I guess now misplaced in set as well now). the axes on it do not turn as freely as the rest of the Grand National set it came with, and one of the couplers no longer stays coupled (I tied a string around it to hold it up, being 40 years old I rather not risk fixing till I find a replacement). I have tried cleaning the ends to no avail. The axes seem correct for length,  and make a rather nice off center thumping hum when spun, like the wheels are mounted off center. Moving the wheels back and fourth it seems the trucks have had uneven amounts of wear, since one axle sits off center. Any recommendations? Good replacements? Die cast is fine since it would lower the center of gravity.

Ah, just spotted it was built in 1970 making it a year one or close to it MPC flat car, ha haha, no wonder. Sorry just saw that and could not help myself. I should explain the silliness here. The set has cars from 1970, 72, and 73. Making it a great example of build quality over the early MPC years, and the NP flat car having the most issues and the later cars having few to none makes a great timeline of what happened. Anyway back to the question I asked, what are good replacement tricks, since they are worn and the axles are ascue I assume that is the best direction is replacement. Since the tips are fine and still have spin issues, or what oil would you recommend I try using?