I was with Toyota Industrial Trucks from almost the very beginning in the USA.

As someone said in a previous post, in the 70's Toyota had a lot of transmission problems and poor radiator design.

In the early 1979 thr 4 series made many improvements with larger clutch drums and improved radiator design and air flow through the counterweight but had a lot of problems with the differential.

The 5 series was introduced in late 1986 and many, many improvements. What a great tuck. Such good quality, the some dealers complained they were not selling enough parts for the series, and yes, parts were expensive. Some were aprehensive of the 4Y engine because of the aluminum head. It has proven to be almost bullet proof.

In 1995 came the 6 series, and a step backwards. Thin side panels, relocated tilt cylinders, etc. Mid series improvements were made but it never was the quality of the 5 series. Proof is the short production life of the series.

Then in 1999 (I think) the 7 series with the new SAS. A lot of glitches at first but was overall a good truck.

A severe accident put me on the disabled list in 2001 and cannot comment on the 8 series, but I assume Toyota has continued with their tradition of producing the best quality product in the industry.