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

yYAw79386WI

[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.

[Souljah]

Google WaveTrac. The yanks seem to be getting good results out of them. Same principal as a truetrac however they will power both wheels under any throttle condition even if one is in the air unlike the truetrac however they drive like a total stocker.

[Tre-Cool]

i have a kaaz in my vy ute..

it's shit.

[Drizt]

i have a kaaz in my vy ute..

it's shit.

In what way exactly?

[IJ.]

Google WaveTrac. The yanks seem to be getting good results out of them. Same principal as a truetrac however they will power both wheels under any throttle condition even if one is in the air unlike the truetrac however they drive like a total stocker.
The Offroad version of the TrueTrac has a preload Bellville Spring and Plate arrangement to do the same thing, I used one in one of my previous cars when I built an IRS 9" for it, As they're set up for 33"+ Mud tyres it was hideous with low profile street rubber winding up and then letting loose with a SNAP when you tried to do tight turns, I ended up have custom springs made and it was really nice, Truetrac/Torsen are Torque biasing Diffs and if you have 100% slip at both wheels xx% of nothing is well nothing so no drive at all! (in case anyone was wondering why)

A nice "trick" I've used if I get stuck is to pull a couple of clicks of handbrake on and it'll usually motor out no probs with a non preload TT.

[HOLDAN]

Google WaveTrac. The yanks seem to be getting good results out of them. Same principal as a truetrac however they will power both wheels under any throttle condition even if one is in the air unlike the truetrac however they drive like a total stocker.

I have a Wavetrac and 3.5 gears in a 9" in my VESS A6 - works very well.

[07L98SS]

The diff specialist I asked about what to do with standard shit diff me the options: In price and toughness
standard diff(crap)< generic trutrac copy (as good as name brand) = $800 < eaton trutrac = $1300+ < wavetrac= $2000+
This was for the parts only and another $200 or so to fit them to a housing I supply re using the gears.
He recommended for regular street use a generic trutrac would be ok. For hitting the strip or competition use get the wavetrac.
Holdan what did you pay for that setup?.

[Jag530G]

The Offroad version of the TrueTrac has a preload Bellville Spring and Plate arrangement to do the same thing, I used one in one of my previous cars when I built an IRS 9" for it, As they're set up for 33"+ Mud tyres it was hideous with low profile street rubber winding up and then letting loose with a SNAP when you tried to do tight turns

Interesting what you say about the nature of Belleville springs/plates. My Jag 420G has a Thornton Powr Lok LSD which uses Belleville springs and plates. When I pulled the diff apart I was expecting an LSD set up similar to the Holden LSDs with the springs and clutch plates but not so.

Cheers, Matthew

[IJ.]

The diff specialist I asked about what to do with standard shit diff me the options: In price and toughness
standard diff(crap)< generic trutrac copy (as good as name brand) = $800 < eaton trutrac = $1300+ < wavetrac= $2000+
This was for the parts only and another $200 or so to fit them to a housing I supply re using the gears.
He recommended for regular street use a generic trutrac would be ok. For hitting the strip or competition use get the wavetrac.
Holdan what did you pay for that setup?.
Prices look to be one step out, $800 sounds close to an Eaton TrueTrac, $1300 is close for a Harrop TrueTrac.


Interesting what you say about the nature of Belleville springs/plates. My Jag 420G has a Thornton Powr Lok LSD which uses Belleville springs and plates. When I pulled the diff apart I was expecting an LSD set up similar to the Holden LSDs with the springs and clutch plates but not so.

Cheers, Matthew
Is the Thornton a Cone Style LSD Matt?

[IJ.]

^^ Did some reading and understand it's operation now ;)

[seldo]

Interesting what you say about the nature of Belleville springs/plates. My Jag 420G has a Thornton Powr Lok LSD which uses Belleville springs and plates. When I pulled the diff apart I was expecting an LSD set up similar to the Holden LSDs with the springs and clutch plates but not so.

Cheers, Matthew
I used these effectively 45 years ago! They work very simply by the torque forcing the sun-gear axle up a ramp in the diff-centre and thus clamping the dished clutch-plates tighter. We used to be able to buy sets of clutch plates in varying thicknesses thus allowing you set up whatever pre-load you wanted, and pre-determining the amount of slip to the point that I used to use them almost completely locked.

[QIKMIK]

Great vids and great info from all. Seldo, I didn't know you needed a diff to connect two horses :stick:

Mick

[Jag530G]

I used these effectively 45 years ago! They work very simply by the torque forcing the sun-gear axle up a ramp in the diff-centre and thus clamping the dished clutch-plates tighter. We used to be able to buy sets of clutch plates in varying thicknesses thus allowing you set up whatever pre-load you wanted, and pre-determining the amount of slip to the point that I used to use them almost completely locked.

What were you racing? E Types or MK 2s?

One thing I am curious about is that there are 10 bolts that hold the Crown gear on to the diff centre and in the UK they seem to refer to these Powr Loks as Salisbury units, I wonder if the Powr Lok centre could have been fitted to a GM 10 bolt Salisbury axle we have in V8 HK - HZ Holdens?

The Americans refer to these diffs as Dana units, Powr Loks were fitted to Jeeps over the years. @IJ, The Powr Lok might be where the idea of fitting Belleville springs/plates to a Trutrac to make the off road version came from, the Jeep guys were very familiar with Powr Loks.

Cheers, Matthew

[HOLDAN]

The diff specialist I asked about what to do with standard shit diff me the options: In price and toughness
standard diff(crap)< generic trutrac copy (as good as name brand) = $800 < eaton trutrac = $1300+ < wavetrac= $2000+
This was for the parts only and another $200 or so to fit them to a housing I supply re using the gears.
He recommended for regular street use a generic trutrac would be ok. For hitting the strip or competition use get the wavetrac.
Holdan what did you pay for that setup?.

I had a full rear end job done - included axles, tail shaft etc. Good for a 1,000 plus horsepower. Cost a shite load. I'll dig up the invoice and let you know what the diff-related costs were

[seldo]

Great vids and great info from all. Seldo, I didn't know you needed a diff to connect two horses :stick:

MickOf course you do Mick - otherwise you can't tell them apart and don't know what's the diff...

[seldo]

The Americans refer to these diffs as Dana units, Powr Loks were fitted to Jeeps over the years. @IJ, The Powr Lok might be where the idea of fitting Belleville springs/plates to a Trutrac to make the off road version came from, the Jeep guys were very familiar with Powr Loks.

Cheers, MatthewDana were/are the manufacturer, and PowrLok was the brand-name given to the unit which was supplied to many manufacturers as an OE fitment - Jag, Volvo, Willys, GM etc. Dana are/were very big in the US as a specialist drive-line components manufacturer and also made the unit fitted to the Holden CrossTrak which is also the same unit supplied to BMW for their X5. @IJ - there might be some other components there that may be of use to you...

[IJ.]

Dana were/are the manufacturer, and PowrLok was the brand-name given to the unit which was supplied to many manufacturers as an OE fitment - Jag, Volvo, Willys, GM etc. Dana are/were very big in the US as a specialist drive-line components manufacturer and also made the unit fitted to the Holden CrossTrak which is also the same unit supplied to BMW for their X5. @IJ - there might be some other components there that may be of use to you...
Nah it was New Venture/ New Process that made the Transfer cases Seldo, just upgraded mine to a Torsen T3 unit so frying front tyres is a thing of the past :D

[offshore]

One other thing I notice with the true track is it introduces a bit of torque vectoring you can see it in low speed corners or say a round about you get on the throttle a bit in the middle of the bend and because of weight transfer there is more torque going to the outside wheel with more traction and it tucks the front in slightly.

[IJ.]

One other thing I notice with the true track is it introduces a bit of torque vectoring you can see it in low speed corners or say a round about you get on the throttle a bit in the middle of the bend and because of weight transfer there is more torque going to the outside wheel with more traction and it tucks the front in slightly.

I love the fact they don't have the part throttle understeer of a tight enough to work conventional LSD ;)

[offshore]

I love the fact they don't have the part throttle understeer of a tight enough to work conventional LSD ;)

Yea exactly

[feistl]

Big thread dig i know, but just thought id share my opinion on LSD vs Trutrac...

I have a Manual VX (450rwkw) with a Harrop Trutrac and 3.91 gears.
I also have a Manual VY which had a Eaton Trutrac with 3.91 gears, but was recently swapped to a new LSD (still 3.91 gears).
I also just got an Auto VZ which has a tight LSD in standard 3.08 gears.

Now having driven all 3 of them in the last week (including the trutrac to LSD swap in the VY) i have noticed some subtle differences.

I should point out that there are obviously a lot of variables so this isnt fact, just my observations...

Firstly, Eaton vs Harrop trutrac...


Only noticeable difference was the eaton tended to have a little more "slop" or "give". As in there is a slight "clunk" when getting on/off power (Tailshaft has new donuts, driveshafts have no slop in CVs, all new suspension and bushes so the rest is tight). This wasn't as noticeable with the Harrop Unit. I also noticed the slop when physically playing with the input/output of the diffs by hand (before they were installed).


LSD vs trutrac

Pretty much in ever regard the trutrac is superior.
The LSDs tend to make the back feel spongy. EG, With a LSD when accelerating hard around a corner it feels like the inside wheel is getting more drive, causing the rear to move sideways and squirm a bit. Not a great feeling. The trutrac on the otherhand seems to drive both wheels more equally, which tends to pull the car into a straight line. Makes it feel a lot more planted, even under light load.
The only advantage to a LSD is it seems to be a little smoother in power delivery. This is most noticeable in the wet... The trutrac tends to be very sudden with its engagement which causes the rear wheels to break traction, whereas the LSD seemed to be a little smoother giving the tyre sidewall a chance to deform slightly and maintain grip. I know that seems counter intuitive, but having just got back from a drive in heavy rain and doing some pretty quick starts i was surprised at how well the LSD got the (relatively small amount) of power to the road.


Having just swapped from a trutrac to new LSD (with no other changes) gave real world "Back to back" feedback.

For big power (350rwkw+) id say go the Harrop, for anything less go the eaton.

Also, avoid the Trutrac diffs on ebay (Circa $1500). It took the diff "builder" 4 attempted to get mine working properly (With me having to pull/install the diff each time).

Spend a little more and get a quality workshop to install.

Cheers, Errol

[Camos]

Yes agree.

I tossed the standard LSD in my hilux for an Eaton Truetrac.
It's the best all round diff I have driven. Not as good as a locked diff off road but you don't have to engage and disengage all the time, the traction is always there so my vote is also for the trutrac.
It handles so much different now, especially since it now has 285kw punching through those gears. Sooo much fun that my cheeks hurt from grinning all the time.

I am running 4.3:1 which was standard and have 31in rubber. I am thinking of going a 4.7 to take a bit of load off the engine since the new rubber is quite a bit bigger than the commodores but that's a story for another day

[Red CV8 R]

Having just swapped from a trutrac to new LSD (with no other changes) gave real world "Back to back" feedback.

For big power (350rwkw+) id say go the Harrop, for anything less go the eaton.

Also, avoid the Trutrac diffs on ebay (Circa $1500). It took the diff "builder" 4 attempted to get mine working properly (With me having to pull/install the diff each time).

Spend a little more and get a quality workshop to install.

Cheers, Errol


Excellent post, thank you for sharing your experiences Errol.

Does anyone know if Harrop still sell their version of a Truetrac? I see they still have the standard Eaton version for $1,099.01 listed on their website plus a full made to order diff using their unit for $5,500.00 but no longer have the stand alone version listed that I can see?

[white lie]

Excellent post, thank you for sharing your experiences Errol.

Does anyone know if Harrop still sell their version of a Truetrac? I see they still have the standard Eaton version for $1,099.01 listed on their website plus a full made to order diff using their unit for $5,500.00 but no longer have the stand alone version listed that I can see?

That is the Harrop version...they're all made by Eaton (much like supercharger rotors), this is just to Harrop specs so its a Harrop Eaton. The lower rated one is just Eaton alone and won't have the Harrop logo stamped on it.
The regular Eaton is a fair bit cheaper, Tuff Car Parts and the like sell it locally for about $750-800, not sure what deal you'd get overseas at the current exchange but for 1100 its a pretty good deal IMO. Cheaper than they used to be.

[macca_779]

That is the Harrop version...they're all made by Eaton (much like supercharger rotors), this is just to Harrop specs so its a Harrop Eaton. The lower rated one is just Eaton alone and won't have the Harrop logo stamped on it.
The regular Eaton is a fair bit cheaper, Tuff Car Parts and the like sell it locally for about $750-800, not sure what deal you'd get overseas at the current exchange but for 1100 its a pretty good deal IMO. Cheaper than they used to be.

I was under the impression Harrop manufactured their own gear sets in house based on the Eaton design

[white lie]

You may be right there...for some reason I thought they were all done by Eaton

[SASLS1]

From Harrop FB page.


" Harrop Eaton Truetrac Facts

After 60 years of manufacturing quality products, we understand what it takes to produce a performance product that surpasses expectations. When it comes to driveline components for your vehicle, there is no room for inferior quality parts, so insist on the best.

All of our Harrop Eaton Truetracs are manufactured in Melbourne to the highest standards and have undergone extensive testing, from finite element analysis in the design stage through to lab durability testing and powering thousands of our beloved Holdens and Fords down the strip, and across our great country.

When purchasing your next Truetrac differential make sure to ask if it is a Harrop Eaton unit and look for these key signs to verify you are getting what you paid for; All Harrop Eaton differentials carry a unique serial number etched into the outer circumference of the Crown wheel mating flange, they will have both the Harrop and Eaton logo machined into the outer face of the casing along with the part number. If you find all of these elements you are good to go."

​
Some dodgy places are selling fake Eaton Truetrac's too, which are cheap chinese rubbish to watch out for...

Best way is to call them up direct.

[Red CV8 R]

That is the Harrop version...they're all made by Eaton (much like supercharger rotors), this is just to Harrop specs so its a Harrop Eaton. The lower rated one is just Eaton alone and won't have the Harrop logo stamped on it.
The regular Eaton is a fair bit cheaper, Tuff Car Parts and the like sell it locally for about $750-800, not sure what deal you'd get overseas at the current exchange but for 1100 its a pretty good deal IMO. Cheaper than they used to be.

As stated by other posters Harrop made their own version based on the Eaton. The link for the only M80 28 spline Eaton on their website ( https://www.harrop.com.au/shop/automotive-performance/performance-driveline/automotive-differential/truetrac-differential-m80-28-spline-eaton ) says down the bottom:

Note:

This part is the standard Eaton Detroit Truetrac part not the locally made Harrop/Eaton equivalent.

I'm sure they previously had their version on the website but I can't see it there now so they may not make that product any longer, perhaps other than made to order? I think the Harrop version was around $1500?

[white lie]

As stated by other posters Harrop made their own version based on the Eaton. The link for the only M80 28 spline Eaton on their website ( https://www.harrop.com.au/shop/automotive-performance/performance-driveline/automotive-differential/truetrac-differential-m80-28-spline-eaton ) says down the bottom:

Note:

This part is the standard Eaton Detroit Truetrac part not the locally made Harrop/Eaton equivalent.

I'm sure they previously had their version on the website but I can't see it there now so they may not make that product any longer, perhaps other than made to order? I think the Harrop version was around $1500?
Far out that's ridiculously over priced for the Eaton version then! They were half the price not so long ago

[Red CV8 R]

Far out that's ridiculously over priced for the Eaton version then! They were half the price not so long ago

It does seem expensive, I've seen the Eaton cheaper than even the Tuff car parts price so yeah, nearly double even now. I think you can get the superior WaveTrac for that kind of money too.

[macca_779]

Wavetrac is only any better if you have a zero load condition on one side; ie off road when you c0ck a leg. Other than that the added components add no benefit that i can think of in our applications

[Red CV8 R]

Wavetrac is only any better if you have a zero load condition on one side; ie off road when you c0ck a leg. Other than that the added components add no benefit that i can think of in our applications

Interesting, you may be right, although I thought the WaveTrac was also less clunky?

[macca_779]

I doubt it. The clunkiness you sometimes hear in a truetrac is the biasing engaging. That function is identical in the wavetrac so I can't imagine it would be any different in that regard

[ChrisCV8R]

I doubt it. The clunkiness you sometimes hear in a truetrac is the biasing engaging. That function is identical in the wavetrac so I can't imagine it would be any different in that regard

Hi, I've been reading up about this trutrac clunkiness a bit.

I drive a VY Monaro with a mild cam, full 3" exhaust and 3.9 + trutrac and experience a loading/unloading of the diff at freeway speed (100km/h in 6th, just below 2K revs) when going from no accelerator to touching the accelerator and vice versa. Is this the same thing you guys are talking about?

A similar thing happens in 1st gear when coasting with no accelerator in slow traffic, but causes the whole car to become unsettled. It starts lurching back and forth (and requires clutching)

So I'm wondering if swapping out the trutrac for a wavetrac will help keep the car more settled as low speed and get rid of the loading/unloading effect at high speed.

:) I guess I can always keep my foot in it and avoid the problem haha

[duke5700]

Wavetrac is only any better if you have a zero load condition on one side; ie off road when you c0ck a leg. Other than that the added components add no benefit that i can think of in our applications

A few of the more serious circuit guys used to prattle on about a KAAZ being better as if you hit a decent ripple strip with the Trutrack it would open up on the unloaded side.. I never managed to do it and I cooked more apexes than I care to remember. I'm only guessing that the unsprung weight/wheel weight/brakes kept mine locked.

I guess the Wavetrack would eliminate any possibility?

[duke5700]

Sounds more like a tune problem to me. Some kind of surging.

I never noticed my centre engage or disengage.


Hi, I've been reading up about this trutrac clunkiness a bit.

I drive a VY Monaro with a mild cam, full 3" exhaust and 3.9 + trutrac and experience a loading/unloading of the diff at freeway speed (100km/h in 6th, just below 2K revs) when going from no accelerator to touching the accelerator and vice versa. Is this the same thing you guys are talking about?

A similar thing happens in 1st gear when coasting with no accelerator in slow traffic, but causes the whole car to become unsettled. It starts lurching back and forth (and requires clutching)

So I'm wondering if swapping out the trutrac for a wavetrac will help keep the car more settled as low speed and get rid of the loading/unloading effect at high speed.

:) I guess I can always keep my foot in it and avoid the problem haha

[ChrisCV8R]

Sounds more like a tune problem to me. Some kind of surging.

I never noticed my centre engage or disengage.

I spent some time with a tuner in the passenger seat (fixing other idle/stalling issues) driving around a carpark while this was happening, and was told the fuel/air was stable. Just seems like there is some 'slack' in the drive line. There is a clear/mechanical sound to this engaging/disengaging.

[Smashfist]

I spent some time with a tuner in the passenger seat (fixing other idle/stalling issues) driving around a carpark while this was happening, and was told the fuel/air was stable. Just seems like there is some 'slack' in the drive line. There is a clear/mechanical sound to this engaging/disengaging.

You can't fix that. You're going from tight in one direction to tight in the other. My 10,000km old cammed VF does the same thing when I drive it the wrong way. Avoiding the surging is the only way to avoid clashing in the drivetrain.

You may be able to lessen it with a shorter set of gears though. Will increase the revs at lower speeds moving it out of the surge zone.

[ChrisCV8R]

You're going from tight in one direction to tight in the other

That's why I was wondering if a wavetrac centre could help in this situation.

[Smashfist]

That's why I was wondering if a wavetrac centre could help in this situation.

It won't make any difference. The lash will be in things like unis, gearbox output/diff input yoke splines etc. Even a tiny amount of play in each component will add up to a bit down the drivetrain.

[duke5700]

Yep, I'm with Smash on this. Changing the centre won't make a difference unless it hasn't been setup correctly to begin with.

When I did my centre, I had new Harrop CV's, changed to a single piece carbon driveshaft(moved to unis, no rubber) etc there isn't much slack in the drivetrain these days. Hasn't been driven much since then either sadly.

Cammed cars can and do surge a bit despite best intentions. For an auto, you just tune the parameters of the gearbox to avoid those areas in the map. In a manual, you are the loose nut that controls gear selection. Seeing as you have 3.9s, not much more you can do really other than drive around it.

[ChrisCV8R]

Yep, I'm with Smash on this. ... not much more you can do really other than drive around it.

Thanks for the replies. I might go back to APS, see if they can find and remove some of this drive line slack. There was no slack/slop issues like this before the trutrac went in. (cam went in at the same time as the diff)

[Micks]

Once you start the upgrade process, unfortunately you'll end up with a more aggressive/noisy drive train. A compromise may be too hard to achieve. ;)

[duke5700]

Luis has a pretty good reputation, I would think the tune would be spot on.


Thanks for the replies. I might go back to APS, see if they can find and remove some of this drive line slack. There was no slack/slop issues like this before the trutrac went in. (cam went in at the same time as the diff)

[SASLS1]

From Eaton Differential Owners Manual FAQ'S, link below...

Here... (http://www.eaton.com/ecm/idcplg?IdcService=GET_FILE&allowInterrupt=1&RevisionSelectionMethod=LatestReleased&noSaveAs=0&Rendition=Primary&dDocName=PCT_1087652)

"My Truetrac has more internal “lash” then an open
or plate style limited slip differential. Is this normal?

Eaton Detroit Truetrac differentials are a helical gear
style limited slip differential. At a high level system
view, the units are constructed similar to an open
differential – except all gears are helical and the
“pinion” gear is split into two intermeshed gears.
Because of the three gear tooth mesh interfaces, the
design must have lash. While all Truetracs (and helical
gear differentials in general) have internal lash, units
with preload are less noticeable. Typically, Truetracs
have a maximum lash of three to four degrees side to side
between gears. This is normal and required for the
superior torque transfer design of the product."


Same part number Eaton on Harrop page ($1099.01), "912A642" bit of a price difference...

https://www.summitracing.com/int/parts/dtl-912a642/overview/

$507.99 USD ($666.44AUD) plus $84.86USD shipping, total $777.77AUD...


The extra lash in the Truetrac compared to the std LSD, you can drive around it and avoid the clunk at low rpm from coasting to picking up the throttle in a manual, when driving like miss daisy.

Spirited driving, mine never makes any noises / clunks what so ever, can't get enough of how well it works, compared to the absolutely useless, POS OEM std lsd...

[blackvussii]

Hi, I've been reading up about this trutrac clunkiness a bit.

I drive a VY Monaro with a mild cam, full 3" exhaust and 3.9 + trutrac and experience a loading/unloading of the diff at freeway speed (100km/h in 6th, just below 2K revs) when going from no accelerator to touching the accelerator and vice versa. Is this the same thing you guys are talking about?

A similar thing happens in 1st gear when coasting with no accelerator in slow traffic, but causes the whole car to become unsettled. It starts lurching back and forth (and requires clutching)

So I'm wondering if swapping out the trutrac for a wavetrac will help keep the car more settled as low speed and get rid of the loading/unloading effect at high speed.

:) I guess I can always keep my foot in it and avoid the problem haha


I have similar mods in my vu, small cam, ls2 heads full exhaust 3.91s and trutrac and have the same symptoms...
I ordered the centre from summit when the dollar was good and bought a set of second hand genuine gears. I had a aftermarket warranty at the time so when the original diff started to go they paid for the install. The guy that did the work does diffs for Power Torque here in Brisbane so knew what he was doing.
He said I'd prob get a bit of a whine on decel due to using second hand gears because its impossible to set the pattern the same once they are worn a little. That didnt worry me cause new ones were $900 at the time and I could barely hear it over the exhaust.
He also changed the allen key bolts over to decent high tensile ones and locktighted them cause he said they can be a problem.

It did make a clunk when engaging 1st and on roll back on the highway and I read quiet a bit on here and US forums of the same issue.
Mine has progressively got worse and hops around at low speed in car parks at low rpm.
I have done plenty of high rpm launches at the drags on ETs which has definately caused it. There is quiet a bit of play in tail shaft when u grab it and rotate it back and forth. I going to get back under there today and put it in gear to do it to rule out the gearbox. Its not in axles/ cvs.

My theory is that the extra loading at the track has caused the pinion to move away from the ring and crush the sleeve further than its meant to be. I've never pulled a diff apart but now that we have a 3rd car and I can get away with having mine in the garage for a while I think I'm going to pull it out and have a go at rebuilding it with new seals and pinion sleeve to see if improves it. Have found some good DIY threads so keen to have a shot at it. Going to have a chat with a local diff place and see what they think but if I go down that path I'll put a thread up.

Overall its one of the best mods I've done and its never slipped with a fair bit of punishment but the clunkiness is pissing me off at the moment.