Differential Fluid for Detriot Truetrac Ford 8.8

JTGrant · Jan 1, 2008

I am getting ready to install a Detriot Truetrac differential with FRPP 4.10 gears. The factory fluid is a Synthetic 75w-140 with 4oz friction modifier. Some have said that I would need to run a thinner gear oil. I have tried to contact Eaton about the gear oil recommendation, they still haven't responded (I guess the holidays). The Truetrac doesn't use clutches, it uses a set of gears to split the torque. I don't think that I would need any sort of friction modifier, but I have heard that it is good for break-in and lowering operating temps. Any recommendation or advice for fluid type or additives would be much appreciated.

walter · Jan 1, 2008

I'm not sure about the Truetrac but I used to run Redline Heavy Shockproof without any friction modifier on my Helical R200 LSD Diffs back in my Nissan days and they ran like a swiss time piece. Considering this doesn't have clutches it should be the same I would think.

JTGrant · Jan 2, 2008

Here is the response from Eaton:

Mr. Grant-
"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."

I wonder why they don't recommend synthetic?

walter · Jan 2, 2008

Someone is stuck in the dino age.... that's what it sounds like to me.

Here's why I love the heavy shockproof. It is a regular heavy gear oil weighing at 75w-90 when conditions are normal but it has the same throwoff resistance and viscosity that a 75w-250 in heavy use. In other words it's light enough for daily usage, but when you get serious about driving it can handle the most extreme types of driving. I used it successfully on my Daily Driver / Auto-X / Drift 240SX and never had a problem.

I'd immagine the noise some synthetics "create" comes from not properly warming up the oils in the car. I can't stress enough how necessary this is. I had a stubborn gearbox on my 240 and I refilled it with this stuff. If i shifted too hard when cold it would grind like a broken garbage disposal, but if I took it easy for a couple of miles then most of the issues (read bad synchros so constant grinding) the car had went away.

Differential Fluid for Detriot Truetrac Ford 8.8

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