Diffs, FAQ

[Immortality]

I wouldn't think so, with the larger gear diameter it needs to be spaced out further to get the correct gear mesh.

Nothing wrong with the smaller M78 anyway. Plenty of big HP cars using them. The only down side is the cost of after market centres is higher

 

[Jaba]

Hey guys, wondering if you could help me out with a bit of a problem here.

Currently in the process of fitting a set of VS control arms into my VZ Senator. I've swapped the handbrake mechanisms from a VZ to the VS arms.

Everythings ready to go, the only problem is the VS driveshafts are too short and the VZ ones are too long. I figured the rear subframes from both VS + VZ were the same, therefore changing to VS arms should mean VS driveshafts would be the correct length.

The only thing I can think of is if the VZ diff is narrower than the VS unit? Anyone able to shed some light?

 

[Immortality]

Can I ask why the change (are you looking to alter the wheel track width possibly or rear chamber)?

Not sure on your predicament TBH. VZ would have a wider wheel track than the VS. Maybe you need to compare the VS and VZ arms side by side and see where the difference may possibly be.

By the VZ model there had been a number of revisions of the IRS system, I wouldn't think that using the VS arms in the VZ subframe would be a good idea.

I've not measured the width of a BW78 and BW80 unit but I wouldn't be surprised if the later unit is wider. People have however fitted BW80 diffs in early model Commodores so it must be possible.

How much to short are the shafts? You are aware that the C.V. do have a little lateral movement in them?

 

[Jaba]

Looking to alter the rear track, to allow for wider wheels / tyres at a more commonly available BMW offset. I also have large 6/4 brake setup limiting my wheel choice due to clearance, something with a high offset to fit a 275/285 isn't possible.

The only difference I can see is the cast section where the hub / handbrake setup / shock mounting point etc is. The rest of the arms look near identical.

The VS shafts are now a good 15-20mm too short, I can only just get the bolts to thread, with a large gap between the end of the shaft and the axle hat.

 

[Immortality]

Fairly sure from VT onward the subframe is wider.

Also fairly sure by VZ the angle of one of the mounting points as well the matching arm mount are at lightly different angles to improve the wheel camber during the full range of travel so the VS arm probably won't be a good match.

VP to VR/VS had a different offset but used the same arm, the difference in track came from the different hubs used in the arms. It may be better to try and source a couple of VP hubs to achieve a narrower wheel track.

 

[HQH]

Does anyone know if the 7.5" Detroit Truetrac Centre 28 spline (part #912A317) will fit into a VK borg warner (m78) housing? A lot cheaper than a Harrop

 

[teocali76]

3.45 0575 gears in a VS IRS diff?

Does anyone know if the 7.5" Detroit Truetrac Centre 28 spline (part #912A317) will fit into a VK borg warner (m78) housing? A lot cheaper than a Harrop

Can 3.45 0575 gears fit into a VS IRS diff centre? I cant seem to find the information I appreciate anyone if you can tell me thanks

 

[Immortality]

Does anyone know if the 7.5" Detroit Truetrac Centre 28 spline (part #912A317) will fit into a VK borg warner (m78) housing? A lot cheaper than a Harrop

No idea TBH but most likely not.

Can 3.45 0575 gears fit into a VS IRS diff centre? I cant seem to find the information I appreciate anyone if you can tell me thanks

Yes.

 

[Deuce]

Does anyone know if the 7.5" Detroit Truetrac Centre 28 spline (part #912A317) will fit into a VK borg warner (m78) housing? A lot cheaper than a Harrop

I agree with immortality. I think I read once of someone bringing in the usa truetracks and MODIFYING them to work with the commodore diffs.

 

[Sandman]

I was always of the under the impression thats what the Harrops were.