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immortality wrote:As I know it, the Holden M75 LSD centers don't have the groove machined inside the spider side gears to retain the stub shaft as used in the IRS diffs. This is where I believe the M76 came comes from as I believe it signifies the IRS centers.

ahhh hha! that might explain the grooves in the gears of mine! ... crewman LSD ..... but believed to have been rebuilt so who knows what parts are in it.

M75 and others are available in both IRS and live axle, as you say the only difference is the groove in the side gears for the circlip in the IRS version. I believe M76 is a different gearset, although with such a small difference perhaps it is interchangeable (Holdens never used it though, official listings are all M75).

Didn't really measure it but probably only took around 1mm off the end of the pinion. You can kind of see in the photos that I didn't bother going all the way to the centre since I couldn't get close enough to the tailstock, its really only at the outer edges where the teeth are that contacts. This is a 3.45:1 pinion, I was told that only 3.9+ needed modifying but that was wrong; possibly the higher ratios are longer again and may need more removed?

This should be handy for anybody rebuilding Holden IRS diff.
Interestingly, I was looking through some old Street Machine magazines and one had an article on doing a gear swap on the M80. The shop in question didn't use a collapsible spacer and they didn't show what they did (I'm certain it must have been a solid spacer) and them said the pinion nut was torqued to 220ft/lbs. They also later on mention torquing the center bearing carrier/hubs to 81Nm (with new bearings) which is a little more that what the factory info says above. Article also suggested .008" thou back lash for performance applications which is the same as what Motive recommend for their gear sets.

Perhaps they meant to say 81 ft-lb? (edit: oops, no that's backwards) I'd be a little concerned about over-tightening anything that threads into the cast housing, but the torque setting has more to do with the fasteners so maybe they were replaced? Street Machine doesn't get too hung up on facts or accuracy either. 220 ft-lb on the pinion nut also seems a bit over the top but its plenty big enough to handle that.

Plenty of room for a solid spacer in there, mine has one since I ran out of collapsible ones long enough and not willing to pay $30 each for new ones. I don't really buy into the idea that you need one for performance use, there's no force large enough acting in the right direction that could compress the collapsible spacers these diffs use, it takes ~100kg jumping up and down on a long bar on the pinion nut to squash them down to begin with!

81 Ft lbs is ~ 109 Nm, the above factory guide says to expect between 50-60 Nm on the hubs when setting carrier pre-load measured with spring scale.

It does seem odd they give one as a metric and the other imperial. Maybe they meant 220 Nm (which is 160 ft lbs)? It's not the first time however that I've heard numbers in the range of 200-300 nm (300 Nm been 220 ft lbs) on pinion nuts.

As a side post here guys.
How do I tell what centre my '95 model Live Axle VS Commodore has ?
You have all been throwing up M75,M76 & M78's numbers.
I gather the M80 is the VT on wards IRS centres ?

Asking for a future requirement to fit a LSD centre to the '95 VS sedan.

Any VS will have an M75. You may find people selling gears they claim to be M78 but if you query them closely enough the crownwheel will be marked 0575 which means M75.

Having said that as I mentioned above the centres for M75 and M78 are the same, you just can't interchange the gearsets.

M80 is no good to you at all, everything is a slightly different size.

VK_3800 wrote:Any VS will have an M75. You may find people selling gears they claim to be M78 but if you query them closely enough the crownwheel will be marked 0575 which means M75.

Having said that as I mentioned above the centres for M75 and M78 are the same, you just can't interchange the gearsets.

M80 is no good to you at all, everything is a slightly different size.

So just to be clear, you can mount a M78 centre in place of a M75 but ring gear and pinions from a M78 wont fit on a M75?

ejukated wrote:

VK_3800 wrote:Any VS will have an M75. You may find people selling gears they claim to be M78 but if you query them closely enough the crownwheel will be marked 0575 which means M75.

Having said that as I mentioned above the centres for M75 and M78 are the same, you just can't interchange the gearsets.

M80 is no good to you at all, everything is a slightly different size.

So just to be clear, you can mount a M78 centre in place of a M75 but ring gear and pinions from a M78 wont fit on a M75?

I believe that's the case. I understand its the gear set and the housing of the diff that's different.

Just to add to this (and add a little confusion), a M78 gear set can apparently be made to fit an M75 housing (by grinding clearances) however an M75 gear set can't be used in a M78 housing.

Point of interest, I'm just in the process of doing an M80 diff and it looks like the large pinion bearings have the same ID (pinion shaft)......

I'll take some proper measurements at a later stage.