Diff Education Needed.

[Stevieboy34]

Pardon my stupidity but I cannot find a thread to explain what I am hoping to learn. I am wanting to get rid of my 2.92 diff gears in the Auto VE SS Ute and go to a 3.45 setup but the more I search the more confused I get. If I get just diff gears it means I have to open it up and put them in right. If I buy a whole diff I assume I just swap it over.

Now, my car has nearly 600hp at the wheels and I hear this talk of Truetrac diffs etc. In laymens terms do I really need that? If I just do the diff gears is my cars diff perhaps more tired than I know? I do know the LSD can be a bit dodgy under decent powerskids and is this where a Truetrac comes into its own?

ALso, when I ebay Truetrac diffs the list one without gearing for like 1600 and one with over 3k. I am utterly confused about how it all works. Anyone care to give me a laymens lesson and opinion on what is the go? I put 4.11's in my old VZ SS and it was unreal, but that was just with the std diff.

Really no idea what I have to buy or pro's and cons. Thanks in advance.

[Jag530G]

Well I've built a fair few Meccano model differentials over the years so heres my take.

FOr the purposes of this thread there are two parts of the diff to be concerned with: A) The Crown gear & pinion B) The diff centre

When you talk of ratios you are talking about different combinations of the crown gear and pinion, the diff centre doesn't change.

When you talk of the Trutrac, that is a type of "Diff Centre", you can have different types of diff centres irrespective of the diff ratio: open diff, limited slip diff, Trutrac etc, etc.

Basically the ratio is a seperate issue to the centre, you could have a 4.11 open or 4.11 LSD or 4.11 Trutrac or a 3.08 Trutrac or 3.08 open or 3.45 LSD or whatever you want.

Regarding the ad about the price of Trutracs. If you are happy with your ratio then that means you are happy with your crown gear and pinion, all you need to buy is the Trutrac diff centre. If you aren't happy with your ratio then you need to buy the Trutrac centre plus crown gear and pinion.

Hope this helps,

Cheers, Matthew

[Stevieboy34]

Ok cool thanks. Well I want to change the gear ratio for sure. Can someone tell me the biggest difference in going from a std Holden "diff centre" to a truetrac or locked type of diff to steer? I drive my ute every day circa 120km with the occasional "spirited driving".

[Micks]

Ok cool thanks. Well I want to change the gear ratio for sure. Can someone tell me the biggest difference in going from a std Holden "diff centre" to a truetrac or locked type of diff to steer? I drive my ute every day circa 120km with the occasional "spirited driving".

Basically peace of mind & reliability!

[VZ_V8]

Ok cool thanks. Well I want to change the gear ratio for sure. Can someone tell me the biggest difference in going from a std Holden "diff centre" to a truetrac or locked type of diff to steer? I drive my ute every day circa 120km with the occasional "spirited driving".

They are far more predictable as you know they will always drive both wheels so the car will behave the same every time. As soon as torque is applied and there is a resistance on both wheels it will be driving both wheels. I found especially at the track and also sometimes on wet roads, with the stock diff centre accelerating out of a corner it would sometimes spin both wheels then if the cone clutch slipped one wheel would stop and it would "grab" which really unsettles the car or sometimes it would only do one from the get go etc. The trutrack will never do this. Basically unless you remove the friction modifier from the stock diff which makes them sound like they are broken, they are shit.

If you can afford to do the gears and centre all at once you will save yourself a decent chunk of money in labour than if u decided to do the centre later. The trutrack is just as driveable as standard, it makes no noises or clunks. It is how they should have been from factory.

[offshore]

The stock LSD feels pretty slopy and sort of oscillates side to side where as the true track feels like the whole back end is a one piece and it gains quiet a bit more traction and this causes the traction control to be activated a lot less then the standard diff. If you get one though its important to really test out the diff behaviour though so you learn the different handling characteristics.

[Micks]

The stock LSD feels pretty slopy and sort of oscillates side to side where as the true track feels like the whole back end is a one piece and it gains quiet a bit more traction and this causes the traction control to be activated a lot less then the standard diff. If you get one though its important to really test out the diff behaviour though so you learn the different handling characteristics.

Most IRS diff centres will give that impression! Tightening of both rear suspension/all cradle bushings will help but will never beat the "Ultimate" being a solid axle!!!

[Jag530G]

Marginally off topic but might be of interest to the OP, what has happened to KAAZ diff centres? I remember on this forum years ago KAAZ diffs seemed to be fairly popular amongst the guys with heavily modified cars. Haven't heard much of them for a while.

Cheers, Matthew

[Gmfan]

I think because truetracs are mechanical and not clutch type lsd they have taken over as diff of choice. Described as maintenance free and no wearing parts so should last a lot longer than a kaaz. Being mechanical lsd the action is also alot smoother and not as clunky as clutch type diffs can be. I have been in my mates car with a 1.5 way nismo diff and being tight it still hops and clunks on tight turns. My truetrac is always silky smooth.

[seedyrom]

The trutrack arrived. No need to worry about diffs with clutches.
Dollar for dollar the best upgrade I've done.

Here's a modern video which might help

[BLACK 346]

Marginally off topic but might be of interest to the OP, what has happened to KAAZ diff centres? I remember on this forum years ago KAAZ diffs seemed to be fairly popular amongst the guys with heavily modified cars. Haven't heard much of them for a while.

Cheers, Matthew

When I was researching this for my old H+C VT2 SS, the KAAZ centres were getting bad reviews for not handling highish horsepower. The Eaton and Harrop Truetracs however were getting rave reviews. I ended up going the Eaton Truetrac with Harrop Sports cover and they performed beautifully whilst I owned the car.

[blackvussii]

They are a great mod, makes the car a lot more controllable when coming hard out of corners, stops it kicking around and leaves two straight black lines when u light them up. With that power and if you changing the gears anyway I would definitely throw one in. I'm not sure about the VEs but the older model ones could be had for around $600. The Harrop version is more expensive cause it has a harder case or something but plenty of people run the Eaton one with big power. Try and find a part number and maybe have a look at US prices.

I had one put in with 3.91s in a m6 and changed out the diff mount, cradle and crossmember bushes to pedders at the same time. Really changed the feel of the car, one of the best mods so far imo...

I think the Kaaz's lost popularity as the trutracs got cheaper and Ive read a couple threads of people breaking them with milder power levels.

[07L98SS]

Heres a vid that explain s the inner workings of the trutrac.
http://www.youtube.com/watch?v=lZmsY2YvVsc
I want to put the VE 3:45 diff in my A6 SS. If I supply the stock centre it would cost $1000 or there abouts to fit a trutrac to it.

[Jag530G]

Sorry wrong info. Mods please delete

[IJ.]

Pity they don't do a Torsen for our cars, much nicer to drive than a Truetrac, I have a Harrop in my car and it's basically a locker under power whereas a Torsen will send the power to the wheel with grip, nail it in a straight line on a cambered road and the car runs straight and true.