When I was with Wimpey in the 60s in Central Plant in Southall a Driver called Bob Trump and a Mate got into an AEC Mercury hitched to a Low Loader,he started it up and was filling in his Log Sheet revving it lightly when the Gearbox blew up, blew holes in Ergomatic Cabs Mudwings and Floor of Cab bits came up into the Seats, when they pulled it back of it the Gearbox was in hundreds of bits, neither the Driver or the Mate went to work that Day,AEC said the Breather or outlet or something had got blocked and had caused Pressure to build up.
An owner driver in Herefordshire had parked his eight wheeler Foden in a yard. In the middle of the night,someone phoned him to go to the yard,the lorry had started up,it was in gear,when he got there it was spinning away in the same place,smoke coming from the tyres.they seemed to think it was electrical,it cost him a set of tyres.
i clearly remember a friend of mine bernard cody who came to work one morning,walked toward his 1633 merc which was locked with the engine running and nobody in the cab.bernard had the only set of keys the company had to that truck in his hand,we both were amazed to say the least!i am told certain aec’s were, under certain conditions prone to gathering water on top of the starter motor which could short the electrics and start the engine!
ben walker:
When I was with Wimpey in the 60s in Central Plant in Southall a Driver called Bob Trump and a Mate got into an AEC Mercury hitched to a Low Loader,he started it up and was filling in his Log Sheet revving it lightly when the Gearbox blew up, blew holes in Ergomatic Cabs Mudwings and Floor of Cab bits came up into the Seats, when they pulled it back of it the Gearbox was in hundreds of bits, neither the Driver or the Mate went to work that Day,AEC said the Breather or outlet or something had got blocked and had caused Pressure to build up.
Our fitters put a tailers dummy into the sleeping bag in the bunk of one of our motors one saturday then on Monday A.M. the driver was sat filling his tacho in at 5a.m. and happened to look round and crapped himself !! He rolled out the cab and wouldn’t get back in until one of the managers got out of bed and came to the depot to sort it out !!! But there was a sad twist to this tale as many years later this same driver was found dead in his bunk at Gordano services ! Its a funny old world !
I remember years ago in the 60s having just removed both front hubs on a Dodge D308 tipper with perkins 6.354 engine when all of a sudden the engine started on its own and we coud’nt stop it until we removed the main fuel line,it was rocking away on axle stands and then the starter motor burst into flames, dont know to this day how it happened 
How about the Gardner engines,I have heard a few tales of engines suddenly going backwards and without any throttle control,the only way of stopping the engine was to cut the fuel line,on a bus its easy,press the stop button,but on a truck you need to have bottle to stick your head into the engine compartment whilst its revving its head off!those wre the days before key ignition start and stop!!!
glad you mentioned that about gardner’s.i remember being in john raymonds yard in the early 80’s taking photos and a fitter backed a gardner powered borderer under a loaded trailer,just as the unit slid underneath the rubbing plate and took up the weight there was a weird noise and i saw with my own eyes smoke coming out of the air filter and the truck shot forward as the engine was running backwards.
5thwheel:
How about the Gardner engines,I have heard a few tales of engines suddenly going backwards and without any throttle control,the only way of stopping the engine was to cut the fuel line,on a bus its easy,press the stop button,but on a truck you need to have bottle to stick your head into the engine compartment whilst its revving its head off!those wre the days before key ignition start and stop!!!
You could still stop them with the engine stop as they were still running on the diesel coming through the pump and could still be revved up, but as mentioned the exhaust came out the air filter, they did smoke a lot more as the timing was (obviously) miles out when running backwards.
Ross.