I liked the trains in Adelaide when I was young. They were all diesel and they were a bit of an experience. They were noisy clattering things and they had their own peculiar smell, a mix of diesel exhaust, cold steel, leather and grease. They often had a baggage carriage too with the big sliding doors on the sides that were always left open, you could sit on the rough wooden floor with the breeze in your face and watch the world slide by.
In the late 80s they switched to diesel electric trains. Quiet, airconditioned, plastic. These days they're installing ugly overhead cables everywhere and going full electric, more ecofriendly and very efficient.
There's no longer anything exciting about them, they're just pieces of plastic furniture. Handy if you live near a station, very cheap and practical, but other than that I just don't even notice them any more.
When you mention them being all diesel. There are three types of gearboxes used. Hydraulic, electric and mechanical.
Mechanical gearboxes can only be used on either lightweight railcars or on very slow speed lightweight shunters which didn't go much past around 20mph (Though railcars could hit high speeds as they did not take much weight), as if one tried using a mechanical gearbox to start a heavy train with gearing designed to run at higher speeds one would end up smashing the gearbox cogs. They tried various experiments such as the "Fell" locomotive in the UK which had two engines each with its own gearbox so one engine would be turned off while the other started at a higher speed, but none of the mechanical gearboxed diesel locos worked for long without issues unless they were slow speed shunters or lightweight railbus type affairs,mand this is due to them needing to have a bit of "Give" between the high torque diesel engine and the weight of the train it needed to shift when the train would be "Cogging" when run at speed.
In other words, take a heavy train of wagons or carriages at speed pushing on the gears in the gearbox when the loco driver let's off the acceleration and all the force of the load behind is on the teeth in the gearbox with catastrophic results (Or if lucky, premature gearbox tooth wear).
For a number of years after diesel engines showed promise (Along with earlier experimental petrol engined shunters and railcars were also used though the diesel engine torque was seen to be more promissing), they had been experimenting to find successful ways to use large high torque diesel engines with heavy express trains, and it was the Germans who built one of the first successful gearbox designs with their DB V200 locomotives that solved the issue using a hydraulic gearbox, which the British then used in their Warship class locomotives. These became known as "Diesel hydraulic" locomotives.
Around the same time, others in Britain (And no doubt elsewhere) were experimenting with using their diesel engines to power generators which in turn powered electric motors to drive the wheels, which became known as "Diesel electric" locomotives.
Realizing that both these two different gearbox designs were both a success, a manufacturer in the UK built two identical experimental shunting locomotives to test which gearbox type was the best to use, and the only main difference between these two shunting locomotives was the gearbox itself. Everything else was built as identical as possible for the experimental tests.
Both these locomotives were then set out for use on the British Railways network to see which design of gearbox was preferred.
At the same time, high speed mainline locomotives were compared over the years though they were not so identical in design, but both were made in numerous volumes, and though all early designs had the odd teething issue, where some designs were let down for totally unrelated reasons such as the Warships wheel bearings which was re-designed to make a successful locomotive at great developmental cost right before British Railways decided on a diesel electric policy and scrapped all the diesel hydraulics, some successful classes being less than 10 years old! British Railways was very well known for making stupid decisions which wasted a lot of taxpayers money usually because of the railway unions which caused unofficial policies of some departments not properly communicating with others, leading to one department ordering masses of locomotives, another department responsible for saving money so cut many un-neccessary lines in which the new locomotives were designed to work on (To replace the steam locos which had worked the lines), and other departments making decisions to promote the long term efficiency of which designs they would use in future years so many rather successful locomotives were scrapped having hardly been used, with a few never had been put into use after being built!
But going back to which gearbox design was better, they found that while diesel hydraulic locomotives way out performed diesel electric locomotives, the diesel electric locomotives could be left out longer between servicing as their engines were lower revving which were more suitable for electric applications so for years British Rail had a diesel electric policy and diesel hydraulic locomotives were scrapped.
Yet in the words of a driver who drove both, a little diesel hydraulic locomotive could not only out-pull a much larger diesel electric locomotive, but it could do it keeping to time, while a diesel electric would struggle to keep to time when pulling a heavy train. (He was comparing a smaller class 35 "Hymek" diesel hydraulic which he took a 16 coach express out if London Paddington with a noticably larger diesel electric class 47 locomotive which could only manage 12 coaches and not be able to run to time on the same journey back into South Wales. One could tell how much the drivers missed the hydraulic gearboxed locomotives, and the Hymeks were not the largest hydraulic locomotives as one had the twin engined Western class of diesel hydraulic locomotives which were much more powerful again! (Though one has to say that there is little point in making locomotives more powerful than the needs of what they are needing to pull, as one will just waste fuel. The UK did experiment with making 4000HP diesel electric locomotives but found the need for such a powerful locomotive in the UK was not there at the time. The experimental locomotive was sold to Russia where it was put to good use on their heavy trains over many years.