Which units? Which railroads? Which shops? What year? Many early boosters were semi-permanently coupled to cab units. So, where you found one, you found the other, at least when they were new. In later days, the units often didn't get their maintenance at the same time, so when the cab was in the shop, the booster was as likely as not out on the road, working...
A few B units, like FT's, were dedicated to their A units. But most others could be separated and coupled with other locos. They could run with other F units, E units (if the gearing matched) GP units, ect. Many of them had a very basic set of controls so that a hostler could move them around the yard or engine facility by themselves.
I've never heard of dedicated B unit shops, but my modern era doesn't have many B units left, so it probably wouldn't be safe to call me a B unit expert. The B unit usually had the same prime mover and traction motors as an A, so crews probably could easily work on both. I have heard the very early EMC 1800HP locomotives built in 1939 had a 1200HP Booster for the Nebraska Zephyr. That is the only time I can think of that the power would be different between the A and B units.
A B unit is exactly the same as an A unit except for the cab and a different body. Internally, they're identical. Maintenance is identical. Most Bs were cab-type locos but some roads like UP had road-switcher B units made (GP9B, GP20B, etc.) Santa Fe had GP60Bs. BC Rail had M420Bs. All were serviced in the same facilities as their cabbed counterparts. It would not have been a very wise sales move to make B units so different that they needed different maintenance facilities (costing big $$$$ for the railroads, which don't like to spend money on unnecessary extras).
LOL And the worst thing is it's absolutely true. Sometime I wonder why we don't put half the terms and buzzwords we use in the backshop and overhaul them! I believe the Santa Fe was also the very first road to buy road switcher boosters, with the four 2789A-Class GP-7B units. That would, last I heard, give the Santa Fe the Alpha and Omega of the type. Good post.
