Blew my TrueTrac - What Next? Help Please...

[MarcSpaz]

Well, I have had my TrueTrac in the car for less than 6 months. I drive the thing to work every day, so I prob put about 7000 - 8000 miles on it. I have only had the thing on the track 3 times for a total of maybe 23 passes. Only 10 of those with DR's.

Is this a complete fluke? Should I buy another one and make sure only non-synth oil goes in it? What is the next step as far as the diff goes, a locker?

The guys at Eaton swear that it broke because there is synth lube and friction modifier in the diff, but in the instructions it said I could put ANY fluid that would normally go in my diff. What is the real story? Are they trying to get out of fixing the thing for free or does synth oil really break these things?

Thanks,
Spaz

[2k05gt]

At least you dont need friction modifier since there are no clutches. I think you should run the oil that the open diff or gears requires.
I am going to Ask Chris what he used in mine when he installed the Truetrac

Standard Letter From Eaton.
"We appreciate your interest in our product.
We recommend that you use any good mineral based multi-weight gear oil. Synthetics are not recommended. While many people have used synthetics in Truetracs without issue, there have been times that synthetics have caused the unit to be very noisy. Additionally, many of our resellers do not recommend synthetics for high performance applications. In fact, most will void their warranty if synthetics are used.
Friction modifier should not be used in a Truetrac as it has no benefit. As for Moly additives, these products are similar to synthetic gear oils and should be avoided with the Truetrac."



One reason Eaton does not want synthetics or slippery additives used with the Trutrac is that it affects the bias ratio of the limited slip. The gear type limited slips rely on a certain amount of gear friction to operate. If you reduce friction with various base oils or additives, it reduces the effectiveness of the unit to a degree. I've not heard of any noise issues using synthetics, but the Eaton guy would probably know better than me.


From Eatons Site
The Truetrac has three sets of element gears (a.k.a. pinion gears) in mesh around side gears that are splined to the axle shafts. There may be more or fewer element gears depending on the torque capacity of the unit and the desired bias ratio. Both the side and element gears are helical, though the gears are specially cut to provide more resistance and friction. The element gears are also in mesh with the element gears on the other side.

They operate partly on the one-way worm gear principle, meaning that when they are "powered" from one direction (e.g. the outside wheel speeding up as the car turns) they rotate freely but they resist turning in the other direction (when driven by the ring gear thru the carrier). The other friction comes from the axial thrust of the element gears into the housing. Torque tends to wedge the gears into their pockets and create extra resistance. In both these situations, decreasing friction would tend to decrease the bias ratio of the unit. The friction is carefully calculated and the lubricant is part of that equation.

In use, the gear type limited slips are very smooth and have a generally constant bias ratio, meaning that they do not gain much extra braking force from increases in input torque, as do the plate or cone type limited slip types, but they react faster to changing traction conditions. The clutch type limited slips need a fraction of a second to “ramp up,” i.e. allow the gear separation forces a chance to increase clamping force on the clutch packs beyond the preload. The gear type limited slips also maintain their bias ratios over a longer period. As the clutches wear in plate or cone type limited slips, their bias ratio decreases and they revert back to open diffs. Most plate types are practically open diffs by the time they hit 80K miles. Some go sooner. The bias ratios of gear type limited slips do degrade over time but the drop is very small and very gradual... slow enough that you can call them "life-of-the-car" limited slips.

The side and element gears allow for speed differential in turns, according to the gear ratios of the tooth counts, but do so while applying torque to both tires. This makes them popular on road race courses because they offer a smooth and predictable action. In simple terms, a driver can power through a turn and power out of a turn more aggressively without the danger of losing control.

They are also better in ice than plate type limited slips, because they do not need tire grip in a turn to "break away" the clutch pack to let the unit differentiate in a turn. It's almost seamless, even on ice. In four-wheeling, they can be overcome by wide variances in traction side to side, more so than a preloaded clutch type LS, but with brake pedal modulation, the bias ratio can be controlled by the driver. Ditto when they are combined with electronic traction control systems that use the ABS brake system.

[MarcSpaz]

Yea, I talked to him on the phone. He basicly said I was screwed. I wonder if chris changes the fluid to a non-synth heavy gear oil if I can buy some more time with it.

[2k05gt]

Whats it doing? why do you think it's gone?

[MarcSpaz]

It grinds really bad almost all the time and it has a horrible vibration.

I know it is not the trans cuz it did it with both. I know it's not the drive shaft, cuz it does it with both. I am 99% sure it's not the gears cuz the pinion is nice an snug and the Gear God did the install.

[2k05gt]

Here is a Post from an guy on another Mustang Site and a response from an Eaton Engineer.


The Truetrac will sometimes make screeching and grinding noises with some synthetics. It goes away with a refill of dino oil. He can't give me any specifics on which oils, but it occurs reasonably often with factory fill syns. The Truetrac is used in several OE trucks, Ford for one, and it's a little bit of a warranty issue right now. He doesn't know exactly why. Some syns seem to be fine (or at least people aren't calling back to complain). I suspect it could be a quality issue between some brands. I'm not sure if Eaton has even really studied why. It's much simpler to shotgun it and just recommend a dino oil. I guess a guy could try a synthetic and if there was no screeching, drive off happily into the sunset. If she makes noise, I guess you'd have to do an oil change. I've got a few other feelers out on this and if they bear fruit, I'll pass it along. All I know for sure at this point is that LE-607 doesn't make mine screech and grind for mercy!


Then another response
Heard back again from Eaton, I asked a few more questions such as: What was the gear oil in the R&D stage of the unit and why they were pushing dino over a synthetic. Here is the answer that I received:

"The oil used in developing the Truetrac was always mineral based and usually a multi-weight product like a 75w-140 Valvoline.
Although synthetics provide better wear under a cruise type situation, they don't provide 'shear' or 'crush' strength required during high performance applications. Synthetics are mainly used for fuel economy purposes, not performance. One of our big customers, Drive Train Specialists in Michigan, did testing with GM regarding gear oil temp and wear. They tested 3 different setups; 1 with straight synthetics, 1 with straight synthetics and a finned alum cover and 1 with straight 90 weight mineral based gear oil. There tests showed that although the oil in the synthetics was cooler, the differential itself was hotter. The oil shed the heat but it had nowhere to go but sink into the diff and housing. Overall, the mineral oil based differential was cooler than the other 2 synthetic units. The tests placed the oil based unit 1st, the finned synthetic unit 2nd and the synthetic with a standard cover 3rd.
The testing above is why we recommend standard gear oil over synthetics. The Truetrac operates on gear separation forces and clearances are very important. The additional heat and less oil 'cushion' caused by synthetics can prevent the Truetrac from operating properly.
Our dealers have also mentioned how the industry has changed in the last 20 years. 20 years ago they rarely did differential work unless it was to do a gear change or a differential upgrade. Today, they work on rearends everyday, replacing gears and differentials with less than 100,000 miles. In their opinion, the difference between yesterday and today, is the widespread use of synthetic oils."

When you swap out the transmission to the 6060 have chris look at it since you have to swap out the adapter on the rear, I think it might be a simple fix, those Truetrac units look like tanks and I would be amazed if you killed it with shy of 400 RWHP.

[2k05gt]

Why would a helical diff not be able to use synthetics?

Here's some interesting Torsen/helical info
http://www.torsen.com/fsae/fsaefaq.htm (http://www.torsen.com/fsae/fsaefaq.htm)

# 19 - Using less viscous oil will also raise TBR. A more viscous fluid will lower it. If you are changing the oil, be sure that you still use a GL-5 specification lubricant.

# 8 - A GL-4 or GL-5 gear oil is required by Torsen Type 1 units. This oil provides high-pressure additives needed to prevent the oil from breaking down under the extreme conditions generated by the tooth mesh. A 75W-90 is recommended, but higher or lower viscosities can be used if they meet GL-4 or GL-5 specification.

[chad05gt]

SD steered me clear of the synthetics w/ mine, drained and filled w/ dino and no problems thus far :dr1:

[MarcSpaz]

I have had a few people tell me to swap the fluid and it will be ok. I'll give it a shot and see what happens.

[chad05gt]

WAIT!!!


What you and your Tru Trak do in the privacy of your own garage, is not anyones business...:pileon:



































...what, too late? yea... but couldnt resist!

[MarcSpaz]

Man, I can't believe it! I couldn't find the Valvoline 75-140, but I did find the 80-140. The grinding sound is completely gone, there is no more vibration, and I can clearly feel a major improvement in traction. I think I was one a single drive wheel for some time.

Damn Synth oil. I hope this is a long-term solution.

Thanks for the feedback guys.
Spaz

[2k05gt]

Did you replace it or Chris?
He was not sure if the synthetic would cause the issue, but would give it a try

He said he puts the Ford Recommended in the rear when he does the work. The ford product is a synthetic

See Here http://fiveguysracing.com/SERVICE_MANUAL/2-Chasis/%5bDifferential-8.8In%5d/8.8-SPECIFICATIONS.pdf.