Mexican overdrive.

[G-CPTN]

This describes when a driver climbs a steep hill in a low ratio gear then 'coasts' down the other side (not in neutral, but by 'simply' depressing the clutch whilst remaining engaged in the low gear).
As the vehicle speed increases, the propeller (drive) shaft drives the gearbox and, in turn the clutch driven disc (which, being unclamped, 'bursts' as it reaches rotational speeds way in excess of its 'structural' strength and throws off the friction linings). Of course, especially in the case of a 'pot' type flywheel, the pieces jam between the pressure plate and the flywheel so the driver discovers that he is subsequently unable to declutch.
It might be a phenomenon that is specific to test hills rather than normal transport operations (we had several severely steep gradients, though each had a suitable run-off area in event of brake or transmission failure).
At least one driver engaged a low gear in anticipation of descending a steep gradient but let the vehicle roll with the clutch depressed, gathering speed until the clutch burst - then claimed that he had done nothing wrong . . .

Subsequent stripping of the transmission proved him wrong.

That's all, folks. Have any of you had engine or transmission failures leaving you disabled en-route?

[Energumen]

Least said soonest mended. Says he sheepishly.

[G-CPTN]

One of the most difficult recoveries that we had to do were half-shaft breakages. It was bad enough that these usually occurred on steep gradients, but unless the driver realised and stopped immediately, any attempt to restart or back down frequently mushroomed the broken ends of the shaft, making removal difficult or just impossible. Subsequent analysis of the failure to determine cause was difficult when you had only splinters, and the entire rear-axle had to be stripped to remove the debris. A clean break could be dealt with on-site by fitting a new half-shaft (we had a special probe for pushing the broken stub out - provided the differential spider had clearance for this).
Doing a suspended (rear) tow - specially if the vehicle had a tandem bogie (not to mention that it probably had a laden trailer) taxed the ingenuity of the recovery crew.

Anybody been part of a breakdown crew?

There is a story (which I cannot recall the precise sequence) where a laden drawbar trailer dragged the recovery vehicle backwards down the hill (at gathering speed). It was quite a ride, apparently.
The trailer had been chocked and the original tractor vehicle towed off satisfactorily, but there was a mismatch of brake air connections and the recovery crew decided to dump the trailer air and try a 'dead' recovery tow but had insufficient traction, so they decided to reverse down the slope . . .
Chocks away!

[Western SMT]

We had an AEC Matador for a breakdown wagon and as it was kept inside it looked good.
Into work one morning and no Matador and just thought it was out on a job, it wasn't long before the story unfolded.
Exact details lost in the fog of time -
The Matador was called out the night before and all ready to lift the stricken bus up so one of the mechanics starts turning the wheel and up comes the bus but the ratchet mechanism broke allowing the winding wheel to spin back and it clouted him on the face breaking his jaw in three places.
After his hospital stay I visited him at home and still had his jaw wired up, liquid feeding only.
Improved safety gear was fitted after that.

[G-CPTN]

Ouch!
We never had any injuries as serious as that (among our crew) though we did lose a driver on the M1. He stopped to help another (not our company) driver change a wheel on an artic trailer (at night) and was run over (and killed) by another trucker . . .
Seems he had seen the trailer being driven with a burst and flagged down the driver (typical Ray) then stayed and helped him fit the spare.