M78 Diff Qn and basic info please.

[colourmesilver]

Hi guys,
have a 98 vt ss 5L with an M78 Diff, 3.04 ratio? or 4.07? not sure, but it's standard Limit Slip. Can anyone suggest or help me find diff gears to suit an M78 and the cheapest, say 3.9 gears for the M78, can only seem to find stuff for the M80...
thanks guys

 

[colourmesilver]

Also, just curious where to buy 3.9 diff gears for the M78, I know the M80 diff gears need to have an inch cut off one end, but any help would be great thanks, I'm in brisbane btw thanks guys

 

[colourmesilver]

Actually, and update, i found something on eBay, but wanted to confirm what actual diff is in the vt1 ss. Its a 3.04 LSD. So would that take a btr78 3.91 gearset the eBay listing also says M75, argh, confusing, lol. thanks any help appreciated.

 

[Immortality]

M78 will also fit in the earlier M75 housings.

you'll want to double check that diff ratio. M78 would be 3.08, M80 would be 3.07

 

[TI3VOM]

Yep and the M78 is an open diff and the M80 is the LSD.

 

[Immortality]

M78 and M80 can both be open and LSD.

 

[colourmesilver]

Thanks for the replies, it's a series 1 Vt SS 304, the sticker on the diff barely can see cos it's dirty and scratched a bit, can see an EH and the tag says LSD, it must be the m78 style before the m80

 

[TI3VOM]

M78 and M80 can both be open and LSD.

Is that standard from the factory in the Holden's? This is the first time I've heard of it.

 

[Immortality]

Thanks for the replies, it's a series 1 Vt SS 304, the sticker on the diff barely can see cos it's dirty and scratched a bit, can see an EH and the tag says LSD, it must be the m78 style before the m80

VT was the change over model for the diffs. LSD was available in both the M78 and M80 so that is not definitive either. From my info, VT series one still had the M78 diffs in all models and VT series 2 received the M80 with the new LS1 V8 engines coming with 3.07 ratio for Auto and 3.46 for manual cars.

Try and give the label a wipe with a cloth to clean it off. It should have the actual ratio on it. It should be 3.08 being an M78 diff.

Is that standard from the factory in the Holden's? This is the first time I've heard of it.

M78 and M80 come standard (from Holden for models like Executive, Berlina and Calais) with an open diff and optional LSD although some models like SS tend get an LSD as standard equipment.

 

[_R_J_K_]

Is that standard from the factory in the Holden's? This is the first time I've heard of it.

Yup. M78 had cup & cone LSDs, pretty crappy now after all these years and aren't really worth the rebuild with the cup & cone setup. Not sure what the M80 LSDs had from factory.