I've done a bit of googling on this one (apparently "they" dont like you using that word as a verb because "they" want to keep the word as a trademark
)
Anyway, the QMs were originally Southern (hooray). Built pre-WW2 from spare bogies. Apparently Bluebell has one that is almost completely restored. They were used on fast fitted freight.
Having never heard of them a week ago, I am now quite curious. I thought one of the trechnical problems with multi-axle brake vans was that you could never balance the brakes evenly. So, under braking, one wheel would be over-braked and skid. Sliding friction being less than static friction the extra load would be transfered to the next axle and it would start to skid too. So the maximum braking force of a multi-wheeled brake van was actually LESS than the good old 4-wheeler.
Or maybe an unfitted van behaves differently to a fitted van.
BUT if the whole train is fitted, then why do you need a big brake van at all.
OW, my head hurts through thinking too much.
