Jo Jo
Back in April, I published a post on how to drive a bus with a crash gearbox, and was pleasantly surprised at the response it generated. I did say that I was hardly an expert on these buses, but wrote to the best of my experiences. It has been suggested that I do another post on a subject that I’m even less of an expert at. Pre-selective buses.
My first drive of one of this type of bus was only May 2014, just over a year ago! But never mind, here goes.
Pre-select gearboxes have been around for some time. Daimler cars were fitted with them in the 1930s and AEC RT type buses had these from 1939. I know there are some surviving Daimler buses with pre-select gearboxes but my (limited!) experience is from driving buses from the RT family thus what follows is based on that. These buses were, by any standard, extremely successful. AEC built 4825 examples for London Transport, designated RT, Leyland built 1631 virtually identical buses, designated RTL and another 500 8′ wide models designated RTW thus the RT family was almost 7000 strong in London alone with further examples being found across the Country.
Right! Climb into the cab and what do you find? To the left of the steering column is the gearstick, mounted horizontally. 1st and 2nd are on the lower slots, 3rd and 4th on the upper. 1st and 3rd are away from you. Reverse is beyond 1st, pull out the silver safety stop to access it. The lever is sprung upwards so its tendency is to find 3rd or 4th. What you have to bear in mind is that this is a gear selector, not a gear changer. Now look down. You have three pedals, accelerator to the right as you would expect, brake in the centre and what looks like a clutch pedal to the left. Except that these buses don’t have clutches! This is the gear change pedal. The drive from the engine to the gearbox is via a fluid flywheel. If you’re not familiar with this concept, the US Defense Dept. produced a very informative film on this subject back in 1954 and it’s available on Youtube. https://www.youtube.com/watch?v=xm8EHTTNPEg
Fire up the engine. The starter is to your left above the emergency window, and looks like a coat hook! If your bus has been standing for any length of time and the air pressure has dropped, then a red flag saying “STOP” will drop down from the top of the windscreen. If this is the case, leave the engine running while the air pressure builds up.
Once you have sufficient air pressure, and assuming the walk round was satisfactory, you’re ready to go. Move the gear selector into 2nd gear. Nothing happens! Press and release the gear change pedal. The bus will rock slightly as the gear engages and the engine revs will dip. Move the gear selector into 3rd. Release the handbrake and the bus will move forward, in 2nd gear, press the accelerator to pick up speed. When you’re ready for 3rd gear, come off the accelerator, press and release the gear change pedal and you’re in 3rd. Move the gear stick into 4th, as that’s probably the next gear you’re going to need and when the time comes, press and release the pedal. It’s that simple! Well, not quite! Unlike a crash box, when you press and release the gear change pedal, whatever gear you have selected, will engage. You will not hear a nasty metallic grinding noise if you get it wrong! However, if you press and immediately release the gear change pedal, the bus will jerk, which is not good for your passengers. Now I haven’t been told this but what seems to happen is that depressing the gear change pedal disengages the gear you’re in, releasing it engages the gear you’ve selected. Thus, if you depress the pedal and hold it down for a couple of seconds whilst the engine revs die down, then releasing it gives you a much smoother ride. Similarly, going from 4th to 3rd, depress the pedal, hit the accelerator and increase the engine revs, then release the pedal gives you a smoother change down.
Once in 4th gear, I then move the gear stick back into 3rd. if I encounter slow traffic, it’s a simple matter to drop the bus into 3rd but if I have to stop, the bus will happily do so, in 4th, without stalling. See the Youtube video. When the bus comes to a standstill, move the gearstick into 2nd, press and release the gear change pedal, move the gearstick into 3rd and you’re ready to resume your journey.
You do have to keep your mind in pre-select mode. There’s a great temptation when the bus rolls up to a stop, to think you have a manual gearbox with a clutch and you must hit the clutch pedal or the engine will stall. Slap your wrist if that happens to you!
There are a couple of things not to do! If you have your foot on the gear change pedal, don’t move the gear selector, or vice versa. That could damage the gearbox. And when you’ve finished with the bus, never leave it in gear. Next morning, someone is going to have real problems starting it up.
To stop the engine, with the AEC examples, pull the accelerator up until the engine dies. The Leyland examples have a wire running up the back of the steering column with a knob at the end. Pull that up. Now in some buses, that works fine, in others it seems to be ineffective. What I was told to do in those cases was move the gear selector into 4th, press and release the gear change pedal and stall the engine. Not sure how good that is for the bus but it did seem to work. Just remember to then put the bus into neutral before you walk away.
If you do get the chance to drive one of these machines, they are fantastic buses to drive and very easy, once you get your head around the idea of pre-select. Have fun!
RTL 1076 at Ongar, Two Brewers. A Leyland example of a bus with a pre-select gearbox.
Dave Moore 
I worked for London transport from 1956 until 1961 in the workshop, first at Dalston and then Hackney. I passed the bus test in 1960.
when getting into a bus to drive and the stop flag is down and the warning light is on, you do
not get out and walk round, you stay in the seat make sure the gear lever is in neutral, put your foot on the Operating pedal and keep it down, make sure the handbrake is on,
start the engine rev hard until the flag goes up and the light goes out, let the engine idle and
lift your left foot and your ready to select a gear and go.
this is the proper way to do it.
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Thanks for that, David. As I said, I’m no expert on pre-select buses!
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Dave Moore thanks for this. My Dad was a master with this and the Ley land crash box. Manchester Corporation had Daimler 4100 pretty selectors. I used to drI’ve them around the shed at Princess Road depot when I was a little boy. The worse thing about the pre select was the peddle could extend right out on a spring if the change was mismatched causing you to bang your knee on the steering wheel. My Dad Terry Maddocks was mustard with both boxes but proffered the Daimler.
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I like semi automatic trucks really,there simple enough to drive.
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I was a LT driver from 1962 to 1965 (21-24 years of age) I drove RT’s out of Merton garage and my main route was the 49’s from Crystal Palace to Shepherds Bush. You made the comment that there was no difference between the AEC and the Leyland and there, I must disagree with you. The Leyland was a sluggish beast with very heavy steering. The AEC was a Rolls Royce in comparison. I drove the bus (drivers option) on a late shift through the worst (and one of the last) London smogs. We had a box of Brocks firelights in the parcel shelf and at every cross roads my conductor lit one to guide me across the intersections as he walked in front of the bus. I also sometimes drove the RF’s – the 200 route. They were nice coaches to drive; the same as the green line coaches. I’m sure you drive these wonderful old antiques with care but, we, on the other hand, used to put the pedal to the metal and try desperately to catch the bus in front whilst not being caught by the bus behind. Sometimes we even got up to about 45mph (and hoped that the brakes would stop us). In rush hour it was dog eat dog.
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