M.T.H. HO 4-8-8-4 Big Boy Engineer's Manual page 11

Now, very slowly and carefully lift the wheel set upward. Keep a close eye out for
the driver springs as they sometimes stick to the bushings and lift out. If you drop
one, you'll need some really good eyes or a magnet to find them. If they should lift
out with the wheel set, carefully set them back into cavities from which they came.
Driver springs
Drop the replacement wheel set into the chassis. Make sure the bushings are in the
correct orientation. The small rectangular tabs on the front and rear must be
upward (with the engine upside down) toward the chassis bottom cover.
Reinstall the gearbox cover with 2 screws...and then reinstall the chassis bottom
cover with 5 screws, gently press the plastic molded brake shoe detail back into
place, and install the rear drive rod screws. See, you've done it.
M.T.H. HO 4-8-8-4 Big Boy Steam Engine
11