By "looking at" engine revs and wheel revs. But hydraulically, and mechanically, not electronically. There was a throttle pedal position input, and some gearboxes had an engine manifold vacuum input, I think, but they were mechanical, not electronic. They moved hydraulic valves in the gearbox.

Gear selection by the driver was also hydro-mechanical – just a valve block to lock-out a lower gear or whatever.

Those types of gearbox, e.g. Borg Warner 35, only had 3 forward gears and were not as good as modern 7 or 8 speed electronically controlled DSG 'boxes, and were quite inefficient. If you had a big torquey engine they were OK from a driving point of view, but MPG figures were awful – below 20 MPG, owing to the constant slipping of the torque convertor, which replaced the clutch and gave some ratio variation, as well as the actual sun and planet gear sets.

The old boxes were very fluid level and pressure dependant, if you had a small leak, they could misbehave quite badly.

My memory is of auto boxes slamming into gear when you selected 'Drive', shocking the drivetrain, which was not comfortable at all.

John

Torque converters aren't actually as inherently inefficient as commonly thought. Under steady state conditions they approach that of fluid couplings which rarely have worse than 4% losses and can get close to 2% loss if properly specified and fully filled. The extra losses of a torque converter are primarily due to less efficient flow around the stator that generates the torque multiplication when needed. Under steady state conditions at whatever speed the stator is optimised for you can get down to significantly less than10 % losses. But it's generally impractical to operate a car at optimised steady state speed and load. In acceleration mode losses can be much higher due to flow inefficiencies.

If torque converters were as inherently inefficient as raw fuel consumption comparison suggests the losses would rapidly boil the transmission fluid. Assuming you need 40 hp to run at 70 mph and that raw fuel consumption comparison suggests 25% losses you'd be pushing something like 10 hp worth of heat into the transmission fluid. Basically a 7.5 kW mechanical heater. The itty bitty transmission oil cooler radiator fitted to most cars isn't going to cope with that.

For a conventional carburettor or older, more basic, fuel injection systems the tree steady state, cruise, problem is that the torque multiplication in the converter lets the engine run at a much less efficient throttle setting. Basically there is a throttle opening corresponding to peak torque at any engine speed. This engine speed is the most efficient, lowest fuel consumption, one for that throttle opening. Sympathetic drivers can generally run their cars quite close to peak torque at most speeds getting best economy.

(Side comment. Really sympathetic drivers of a manual gearbox car with a properly set-up SU carb will know that once up to speed on motorway the throttle can be backed off to not much above idle and the car will maintain speed on much less fuel. The best speed for this effect depends on the car. For the old 2 litre Montego estate with manual box it was just over 70 mph with a couple or three mph range each side needing only tiny throttle tweaks to hold. 50 mpg being insane for those days from a car that size, well loaded too.)

Put a torque converter in the driveline and the torque multiplication lets the engine run well away from peak torque whilst still generating the power needed to drive the car. Engine efficiency plummets and fuel consumption rises the further away from peak torque you are able to run. It doesn't help that the inherent losses of a torque converter are roughly correlated with the amount of torque multiplication going on. So whilst driving the car with the engine running significantly away from its most efficient throttle position the torque converter is also running at a less efficient power transmission mode.

Loose – loose.

Modern electronically controlled, mapped, engine and transmission ECU systems seek to keep both the engine and torque converter away from the inefficient modes during normal operation. Adding more ratios to the gearbox significantly helps because the speed range demands on both is greatly reduced so much better optimisation is possible. Such controls also allow much greater use of the lock up clutch which is a great aid to economy.

Clive

Edited By Clive Foster on 05/06/2023 17:40:16

Define "early" and "automatic".

Starting with now, automatic boxes are a thing of wonder. Mine has 9 gears which can change in 100 ms. Manual selection is an option, but can you do better?

Then you have the 1960s/70s/80s boxes with 3 gears, which were not particularly efficient so slower and used more fuel than manual ones.

So I think that automatic gear boxes have a poor reputation which is not deserved.

Back to "early": I have had the pleasure of being driven on, and occasionally having driven, a 1930s Daimler. It is difficult to compare one with a manual box. In 1st gear they can crawl along at a snail's pace without stalling. They can go pretty slowly in top gear and possibly start in top gear, but accelerate very slowly. "Automatic" is probably not the right term, but neither is "manual".

ABBA earned more money for Sweden than Volvo. Discuss.

Manual gearboxes were extremely difficult to use until the introduction of synchromesh – mass produced cars were still being made with synchro on only some of the ratios right up until the 1960s. Until then silent gear changing without crunching was a skill and even then a moments inattention could make things noisy – and too much attention could lead to an accident.

Additions to the standard 'crash' box were at first designed just to simplify the gearchanging process and this is where things ended for many manufacturers eg:- Hondamatic (Trimatic) two speed transmissions being a torque convertor and a manual change between ratios allowing clutchless driving.

The Wilson preselector used planetary gears and brake bands to drive but the gear was selected by the driver and the change only occurred when the change pedal was depressed. These needed a fluid coupling (fluid flywheel) to enable starting off. Other preselectors used clutches, electromagnetic in the French Cotal box and racing cars with preselectors sometimes had no primary clutch at all relying on the change from N to 1 to progressively engage the brake bad on the first gear gearset.

Small Citroens had a centrifugal clutch (Trafficlutch) to enable clutchless starting off but the gearbox was normal with a standard clutch. Two stroke Saabs had a similar device but here it was to allow the car to coast with the engine idling as lubrication when idling is marginal with a two stroke.

The whole process of changing gear was then mechanised (close throttle, depress clutch, select gear, release clutch, open throttle) with the driver having to only move a small lever – This was hydraulically driven on Citroens and by vacuum on Standard and Rover cars. Not quite so sophisticated was the VW Beetle system where depressing the gear knob closed the throttle and disengaged the clutch enabling the next gear to be selected by the driver in the normal way by moving the gearstick. Taking the hand off the gearlever engaged drive again.

With all of these development the move to fully automatic transmissions was a small step, and in fact the technology to detect driver input, speed and load had been available for many years in infinitely variable, sliding cone and belt gearboxes so just needed to be combined with the noiseless gearchange system to make the automatic gearbox as we know it – although the dual clutch gearbox where one clutch changes a gear not under load while a second drives the vehicle is such a clever idea that one wonders why it was not thought of before!

Personally I enjoy driving a range of cars with my order of preference being full automatic, a decent manual box second equal with a crash (non synchro) gearbox, semi automatic and finally, way at the bottom of the pile a synchromesh gearbox with worn out non-functioning synchro as it is unpredictable at best.

Dear Nick, Thank you for the long description, brings back many memories, pre selector boxes in buses of the 50s and a mini 1963 with only syncro on top 3 gears, this taught me to let the revs drop on up change and blip the throttle on down change, a habit I never got out of ! John Doe,then there was the night my cluch release bearing failed and I had 65 miles to do with a very heavy trailer on – amazing what you can do when you try – though an understanding of the box helped ! The starter just got us moving as the engine fired, and it was late so no need to stop all the way home.  Noel.

Edited By noel shelley on 06/06/2023 12:57:42

But Volvo distributed it more widely.

Edited By Mick B1 on 06/06/2023 13:56:31

None of my motorcycles had synchros or needed then in their gearboxes. A few times I had to drive them without a clutch when the cable broke. No problem on the open road but a bit tricky in London with the traffic lights.

CS

A few years ago I had a Renault with an auto gearbox, during the warranty period it developed a very obscure and very infrequent fault, you would be driving along quite smoothly and all of a sudden there would be a jolt from the transmission accompanied by a loud metallic clang. Took it to the agents that I bought it from and they gave me a blank stare when I explained what had happened, they drove the car and of course the fault wouldn’t perform, their answer was well keep driving and if it still happens bring it back but they had no idea what was causing the fault. I carried on driving the car and periodically it reoccurred so I decided to fault find it myself, so I studied the ins and outs of the type of auto gearbox and eventually after much study and head scratching I worked out that the fault was in the valve chamber, it was one of the many valves that was sticking and suddenly freeing as pressure built up. I returned to the garage and explained my findings to the service manager and he openly admitted that he knew nothing about auto gearboxes but was prepared to accept my diagnosis as it would be charged to Renault as a warranty repair. This meant replacement of the valve block assembly, which I can only assume was a very expensive piece of engineering, it formed a plate bolted to the underside of the gearbox, the assembly was a maze of oil passages and valves. After the repair procedure the fault disappeared so it looked like my diagnosis had been correct. I still drive an auto but now buy Honda cars and in the words of the service manager at the Honda dealer “they are bulletproof “. Dave W

Hardly a "rubber band". More like a heavy duty V belt.

I owned a modern Audi with a CVT (constantly variable transmission) auto gearbox, which used two hydraulically variable cone pulleys and a belt, and it was really good, although it required a different driving technique: Instead of setting an engine power with the throttle, you used the throttle to set a speed and the gearbox adjusted its ratio according to the road gradient to produce that speed. This was counter-intuitive to many drivers, but as an Airbus pilot, I was open to this type of automation, and got on with it very well.

The post WW2 automatics were basically epicyclics where which brake band was operative was controlled by the manifold vacuum. hence the vacuum capsule. Road speed was sensed from the pressure produced by an oil pump within the transmission, and driven by the output shaft.

The Borg Warner 35 was relatively unsohisticated and in some applications could produce quite a rough ride!

Renauklt sophisticated this in the 70s, using electrical sensing of road speed and load by using a small generator, where the output was moderated by shading between stator and rotor, to snse throttle poisition (implying load )

A torque convertor was a development of the fluid dlywheel, wher a set of intermediate vanes produced torque multiplication.

Matching a torque convertor to a particular engine and installation could be quite a task. At Rolls – Royce, both the car and oil engine divisions employed specialists to calculate the best match. O E D used Twin Disc transmissions, made under licence at Crewe.

A torque convertor required fewer gear ratios. than a fluid flywheel, because it already provided torque multiplication

Unsynchronised gear boxes were used in commercial vehicles until the late 60s, although semi automatic transmissions were available. The Leyland "Moncontrol" was direct air control of the brake bands rather than the electromechanical system where the the tiny gear lever controlled solenoid valves which fed air to the approriate air cylinder to apply or release the required brake band.

The London Transport Routemaster used a more sophisticated electcal contol of the gear box, supercediung the fluid flywheel and epicyclic box prviously used on the RT and RTLs.

An unsynchromised box provided a lighter gear change than a synchromesh box, even if you double declutched any way!

Used cortrectly, a cluch brake (Clutch stop ) upward chnages could be made as fast as or faster than a syncromesh box!

Relaints used unsynchronished boxes into the 50s and 60s.

As Peugeot said of the unsynchronised gear box "C'est brusque; mais sa marche"!

Howard