Spectrum cast metal truck frames are very fragile and will crack/break easily if you would try to spread them a bit, so you could put a new axle in the frame.
How do you install new axles in this type of rigid frame without cracking the side frames. I have six that I need to do because those existing side frames have cracked and need replacing. New truck frames and bolsters will be here any day and I will need to reinstall the axles in the new frames.
Help, please

Jim, do not try to spread the cast trucks. The trucks are held together with small screws, two at each side frame on the top of the truck. To change axels, you only need to remove one side frame, insert the new axle into the stationary frame (the one you didn't remove) and then replace the removed frame. When you look at the axle, please note that one of the wheels is insulated from the axle so that it doesn't create a short. I find I get best performance if I place both of the insulated wheels on one side of the truck. Hope this helps.

Thank you Fred Klein for that answer. I didn't realize those were very small screws. I thought they were just part of the casting. I have now used my small Phillips screw drive on one of the broken trucks and see they are easy to remove. All set now. Thank you for solving the mystery.
Fellow Florida Garden Railroader,
Jim Jerele
Fort Myers, Florida

Jim, you're welcome.

Fred