Diffs, FAQ

[Kung-Foo-Kamel]

You will need the 8 inch gears from a super 6 or ls1. The NA 6 is a smaller diff (I think 7.5 inch is right), the early diff on the VN-VT S1) is 7.8 inch

Oh crap so theres a 7.8" diff to, this is crazy

Im gonna throw my car on the hoist today and get all the numbers of my diff and see if I can establish what I have, it will probably be easier to buy a whole diff I think

 

[Immortality]

the BW78 does refer to 7.8" crownwheel. the BW80 refers to 8.0" crownwheel. unfortunatly i'm not familiar with the BW75 i'll see what i can find out.

holden did change the driveshaft configuration in later models, i figure they did this to eliminate the driveline shudder that so common with the VN to (and especially) VS models.

i honestly can't see why holden went to a smaller diff with later model V6 engines when they are making more power and the BW78 certainly more then capable of handling what ever a V6 can throw at it.

 

[greenfoam]

I read the later NA 6's use "M76" 7.6 inch diff. Why they went to a smaller diff, well the VN diff had to hang onto some more grunt than the V6's with the likes of the 5 litres, HSV specials/5.7 litres. I guess it was over kill if they were going to seperate V8 diffs, Less is better when you are selling cars for a profit.

I also re read the first post and see you want V6 gears. So well good luck I have no idea what models you would get them from, perhaps a SV6 but do they use the small gear or the V8 one....... Who knows

 

[vnv8driver]

so what model did they start using the smaller diff??? all i know is stock from vy onwards the rartios changed anything from 2.79-3.08-3.23...

 

[yZoH]

I still dont understand in a way... Is it possible to put the insides from a vq v8 irs diff into a vn live axel v6 diff... if so what do i need to know?

 

[Immortality]

early model IRS should have identical centers to live axle diffs. i have heard stories that say later model IRS has a different offset center (where the crown wheel bolts onto the center) but a quick visual inspection will tell you if they are the same offset (as they should be). V6 and V8's use the same diffs although the V8's got shot peened gears. not an issue either.

if you do swap the centers you need to make sure the crwonwheel to pinion backlash is ok otherwise your going to stuff the gears quick

 

[yZoH]

thankyou very much!

 

[Immortality]

for anyone interested, there is a really good tech article about the BW78 diffs and upgrades in this months (june 08) street machine with great pics. shows a split LSD center (showing spider gears/cones etc) and also a split open center with minispool fitted:thumbsup:

 

[XRUFFX]

small diff question..
got myself set of 3.45's (i have a vr irs calais) inquired bout gettin them fitted, some bloke quoted me $550 cos i need a bit of stuff...im lost?? how so? wat could i possibly need..its the same diff...??
got another quote from pedders to do fitting gears, and mini spool for $330...can i trust pedders to rig it all up properly? they couldnt even align my wheel properly...
lol thats 2 seperate questions... =/

 

[Immortality]

sounds excessive unless he wants to also supply the gears for that price. the only thing that will need doing is checking the backlash and wear patern to make sure you don't stuff the gears.


don't know about pedders. some other members may be able to recommend a decent diff shop depending on where you are?