Diakron was the name under which Diaclones were sold in the US. The Diakron toys entered the stores late 1983 or early 1984, and disappeared again only a few months after that. It was then followed by Kronoform. This was probably because by that time, Hasbro had bought the rights to sell these toys as Transformers, so Takara had to drop the Diakron line.

DK-1  - The red Diaclone version of Sunstreaker. Besides Multi-Force 14, this is the most common pre-Transformer.
DK-2  - The black Diaclone version of Ironhide.
DK-3  - The blue Diaclone version of Trailbreaker.

ARAGON  - Powerdasher car
ZETAR     - Powerdasher drill
CROMAR  - Powerdasher plane

MULTI-FORCE 14  - This is the Diakron version of the Diaclone Gats Blocker. It was also released as part of Kronoform in the
                              US under the name Multiforce. The Diakron version and even more the Kronoform version have been
                              sold in large numbers in the US, and is therefore the most common pre-Transformer.

DIATRAIN          - Also sold both as Diakron and as Kronoform.
COSMO ROLLER  - I'm not certain if this one was sold as Diakron. It was sold as Kronoform toy though.

Toy Pictures
 

MULTI-FORCE 14  (box inside, robot, robot close-up, vehicles) Multi-Force 14 is one of the most common pre-Transformers and also a very unique toy. It consists of 14 vehicles and a launching platform. The vehicles combine to form a robot. I prefer the Diakron version over the Kronoform version, as it comes with 5 figures and the Kronoform version only has 2.