HQ Belmont Ute, 308, M21, Air all factory

[Innuendo]

Axle codes changed from HQ to HJ-Onwards and it catches people out!

[HK1837]

Axle codes changed from HQ to HJ-Onwards and it catches people out!

Spot on. It actually changes from LH (first vehicles around 11/73). The bulletin explaining it that I have is dated 24/5/72. It says the universal code system was established by GM Corporate and is in use for 1973-4 models in the USA. They basically aligned the rear axle into a code for the ratio, where previously it also included the rear axle design. It gives some examples too of what existing rear axle ratios are now and will be:

2.92:1 old GU3 new GX9.
3.08:1 old G93 new GU4.
3.23:1 old GU2 new GU5.
3.36:1 old G95 new GV4.
3.55:1 old G91 new GV7.