These models should be restored (doing most of it yourself), parked in a shed and brought out for special occasions to show the glorious history of Peugeot. They are most definitely not up to today's road conditions.
Superb comfort with good handling, excellent brakes and low noise levels. A world-beater when released. The body is flimsy and prone to rust. Rust is always worse and more extensive that it looks. Frankly, 404s are no longer good for day-to-day transport. They were never pleasant to work on but now they are old, they can be horrible. Better for DIY owners.
I bracket these models together because they are almost identical with a little evolution with the introduction of an overdrive fifth gear and a more modern overhead cam engine. Last and best of Peugeots rear wheel drive product line. They are big, strong and safe models with good ground clearance and simple engineering allowing them to perform well on bitumen and also do 90% of the work of your average off road vehicle. That is why they are so sought after in Africa and the Middle East and why our old 504s are exported to that part of the world.
They are the easiest models to work on, and apart for some parts shortages, the cheapest to maintain. Resale values have fallen so much that most vehicles are on minimum maintenance and decaying away. They have lost popularity because of recent increases in the price of fuel. Models up to the mid 70s are a little harder and more expensive to maintain. 504s are becoming old cars now. This means that you meet a new generation of problems resulting from corrosion and decay. As a repairer this means that repair times can be hard to predict while at the same time owners are (understandably) reluctant to spend much on maintenance. Better for owners who do their own repairs (DIY).
As for the 504/505 except it has a dreadful engine and auto gearbox. It is stupidly hard to work on. Peugeot had help from Citroen for this design. On the other hand, on the road the 604 is a world-beater, comfortable, quiet, good "French style" handling and very sturdy. They approach Citroen standards with less complexity. The 604 is so good it rivals the 404 for comfort, handling and low noise levels.
Fun to drive, the GTi is very powerful. The bodywork is flimsy by Peugeot standards. Mechanicals are similar to the 405 but the rear suspension is prone to wear and expensive repairs. The engine bay is tightly packed and unpleasant to work in. The 205 evolved from a basic small car to a fully optioned performance car and its design reflects this. Newer models like the 206 are much better thought out and ease of maintenance and reliability are much better.
Good sound car with the usual Peugeot feel. Non-sporty models show a move back towards comfortable suspension compared to the 505. The fascia trim is made from a particularly perishable plastic. Tatty trim and annoying rattles are common. 8 valve engines inevitably develop serious valve guide oil use. All engines are prone to oil use past the rings also and the 8 valve exhaust manifolds commonly crack. The sump to too close to the road for comfort and you cannot drive almost anywhere like earlier Peugeots.
The drive train is sturdy but there is a rare problem where the planetary gears in the diff to fail. Auto gearboxes are a weak link and very expensive to fix. 405 series 1 are now cheap to buy and cheaper to maintain because wrecks are becoming available. They are OK to work on once you get used to tight spaces and having to unpack the engine bay to get at things.
All models maintain the Peugeot feel on the road that distinguishes them from all other makes. From the 405 series 2, Peugeot regain the engine quality of the 504/505 - so much so that demand for engine recon bits is so slow that they are hard to get. Better instrumentation (e.g. temperature gauge, temperature light and low coolant light) has contributed to this. While the bodywork is sturdy and protects occupants during a collision, they have lost all off-road ability. Low ground clearance and exposed engine sumps have seen to that. Mechanical and electrical reliability are improved despite a dramatic increase in complexity.
Owners can do their own maintenance once they wrap their mind around working in tight spaces and the need to unpack the engine bay to get to some things. While there is growing need to plug into the electronics to resolve problems with the engine, gearbox, seatbelts, security system, ventilation, etc; plugging in is not essential for day-to-day maintenance. Parts can be astoundingly expensive and slow to arrive. Ownership is like a lottery. Maybe one in five or 10 owners will have problems and they will suffer from high repair costs. Sometimes, even the diagnosis can be time consuming and expensive.
Bill McNamee(From a presentation to the Nov 2005 PAC meeting)