My Au forte v8 1998 has live axle LSD unsure of diff ratio. however the diff is moaning and whining time for recondition...

any advice or rough price's people have paid on there diff rebuilds? am thinking if i going that far going 3.7 gear ratio. should be nice.

good question

just to completely clarify, what woudl be the ideal model car for me to get a diff centre from? 1999 au1 fairmont ghia with irs, pretty sure its a 3.23 or 3.45 single spinner.
would it be wiser just to get an lsd centre? or just to buy the whole housing + centre off a certain model xr6?

what would the price of it roughly be?
cheers

The housings are all identical... 3.08 ratio gives the best final drive for the best fuel efficiency... Remember all cars are designed to be most fuel efficient at around 100 to 110km/hr so knowing this, the manufacturer knows which rpm it must be... Knows the final ratio of the gearbox, and hence picks the diff to suit...

3.08 to 3.45 is not that many more teeth... I have never counted the teeth, and you can't have .08 of a tooth, it must be a whole number... so if you do the maths... the ratio 3.08:1 as two integers is 77:25 at the smallest... So I'd near say there would be 77 on the crown and 25 on the pinion... and 3.45:1 as integers is 69:20 at smallest... Therefore all in all there is actually less teeth in a 3.45 ratio diff This doesn't make the crown smaller, it makes the teeth wider to take up more space... So 8 teeth less on the crown and 5 less on the pinion...

For the sake of it, 4.11:1 doesn't simplify any further than 411:100 and this can't be right... Whereas 4.10:1 is 41:10 which doesn't seem enough teeth, so go one step back and you get 82:20 which might be close...?



If you handy and can change the diff yourself... Get the whole thing... Your fairly limited with regard to model choices... You can only get a diff from AUI with IRS, AUII or AUIII... I somehow doubt it would be a 3.45 ss, never seen a factory ones of these before... It could be a 3.23 or something, but if auto, most likely a 3.08 due to the lower output shaft speed than the manual...

If you just buy a centre you have to a diff place to fit it... It requires a full set of shims to get it sitting right... and the collapsible washer on the pinion... A diff spreader, various scales and tools to set the face/flank, toe/heel, preload, and backlash in the diff... If you have the tools and the know how on how to set these up then get a centre, much cheaper and smaller to post... Otherwise a diff place is likely to change upwards of 500 bucks due to the time involved with chopping and changing shims to get the settings right......

At the end of the day its your call... I live 6hours from Sydney and LSD's are rare out here... I wasn't buying a centre due to not being confident enough to fit it and not having all the proper tools... So I went with a Lokka which goes inside a ss carrier (replaces the hemisphere in the centre), as such the carrier and the ratio don't change and no re-setting of those above mentioned settings needed... Just put it back together exactly as it came to bits...

Goodluck...

alright, are you positive about only being able to get it from an auI/II/III? e series have the same diffs as au's apparantly, the centres will just go straight in. does the donor car have to have irs for it to fit in mine or is that just completely disregarded?

Brett would be more help here...

My understanding... If your swapping a whole diff... You will require a IRS diff (only in AU's)... If your only swapping the centre, then yes I do believe a centre from an E series will go into a AUI IRS diff...

E series (other than same centre) are live axle and not IRS and the whole diff will not be a direct swap...

But again a centre will require a diff place to put in...

I'm here.

If you have a live axle AU diff, the only difference between an EF/L diff is the length. With an IRS diff, the centres out of a live axle WILL FIT. If anyone tells you they do not, they are full of s**t.

Doing a hemisphere swap on an IRS diff is easy. I have a spare at home, so I'll do a tech doc on hemisphere swap in an IRS.

Hi while you's were talking about diffs, i gotta ask, if a car with an open ended 3.23 geared diff went down a 1/4mile in 15sec, how much faster would it be in a car with 3.45 LSD? or alterativly same senario but 0-100kph? is the diff gears really that different, or important in take off? or speed over distance of a 1/4 mile

Also another point not covered (atleast as far in this thread as I covered)
The existence of so called 'High Performance' Single Spinner diffs...

Don't laugh, I hadn't heard of anything like this before, I asked a wrecker to supply me with a 3.45:1 LSD diff, full hub to hub, and on the 3rd attempt I gave up and accepted what he sent me, which turns out to be a single spinner diff, but it has a ford tag over the diff oil hole that says 'HIGH PERFORMANCE DIFF OIL ONLY'

Its been some time since I've looked it over, but from memory the conclusion that I came to was that it is an open wheeling 3.45 diff from an ED era Fairlane ghia, I think it would have been an NC?...
(I Base that on that I went to the wreckers and watched them remove it from a boxcar Fairlane ghia, Stuffs me why its not an LSD like it should be...)
Don't think these were covered?
I still never understood what was supposed to be so high performance about this diff, and it certainly isn't the LSD I asked/paid for (EDIT: I should probably not mention where I got it..)

(Either that or they poached the LSD centre out before they sold me the full hub to hub LSD... hmm)

Last edited by Ace on Fri Apr 30, 2010 7:57 pm, edited 1 time in total.

or the clutches have completely s**t themselves?

A high performance diff is a 4 pinion centre, an LSD will have Spin Resistant diff on the tag.

3.45 ss diffs are in AUs.

anything VCT got IRS, which standard was 3.45ss, LSD was an option, so yes, AU got 3.45ss

Yes that's right, its a 4-pinion single spinner...
Advantages over normal s/s ??

4 pinion diffs were in EB-AU. Some EB1's and all EA's got 2 pinion diffs which are weaker.