G'day FC427,
Got me stumped.
.
To the best of my knowledge (and I could be wrong), GMH only made three types of manual 3 speeds:
a) The grey motor crashbox, used from FX through EK Holdens. The grey motor crashbox has a bottom transmission cover (sump) and integral casing/bellhousing. The gearbox had synchromesh on second and third gears only,
b) The red motor crashbox, used from EJ through HK Holdens. Like it’s predecessor, the red motor crashbox still had synchromesh on second and third gears only, with the internal gear and shaft layout and operation very similar to the grey motor crashbox. However, the gear selector process was changed significantly, as was the construction – red motor crashboxes have a side transmission cover and separate casing/bellhousings, and
c) The Aussie three-speed, used from HK through HZ Holdens as well as LC-LX Toranas. The external construction of the Aussie three-speed gearbox is similar to the red motor crashbox, having a side transmission cover and separate casing/bellhousing. However, the Aussie three-speed was fitted with synchromesh on first, second and third gears (often referred to as an all-synchro box), and the gear selector process was changed again.
The bellhousing engine-end pattern looks to be Holden grey motor:
Grey on the right, Red on the left. Red and grey bolt/dowel pattern are near identical, with some differences on starter bolting and the lower mounts. So I'm guessing its from something that Holden supplied grey motors for. I'm not sure what other companies GMH supplied to... possibility it could also be an industrial box.
If I'm reading the photo right, there is no mounting position for a clutch slave cylinder. This would probably date it to pre-FE Holden (pre-mid 1956), assuming that the original car got hydraulics about the same time as GMH.
The photo also shows holes at the 4/8 o'clock position for a dust cover. Early casings have these, whilst later casings (apparently around the FC model) only have four holes tapped, deleting the two holes at the 4/8 o’clock position. This again probably dates the casing to FE or earlier.
There looks to be a GMH part number cast into the passengers side of the main casing. Looks to be 7137.... (can't read the rest). There are however no 7137 numbers in the 20 Beers Master Old Farts Dogologue. 7134... is for FC, with the Dogologue then jumping to 7139... for EH/HD. I guess GMH may have assigned the 7135..., 7136... 7137... and 7138... numbers to whoever they supplied parts to. This would imply the box is around FC (ish). Post the number and I'll cross-check it against the 20 Beers Master Old Farts Dogologue.
Cheers,
Harv (deputy apprentice gearbox fiddler).