i wanted to change my fluid in my differentials. i have a 01 ram 1500 4x4 with limited slip diff. i looked in the service manual and it says it's 75w90 in the corporate. i wanted to switch to synthetic and i was told that it would cause problems and 6 months later i would have to replace seals cause it would leak. is this true?


thanks

 

I changed over to Mobil 1 75W-90 synthetic in mine about 8 months ago and have had no problems. I put a tube of "friction modifier" in the rear one first, then filled it to spec with 75W-90. The friction modifier stuff is usually with the gear lube at parts stores. Some people say you don't have to use it with synthetic, but I did anyway. Just in case you don't know, there is no gasket on the diff covers. Get a tube of red gasket maker while you are at the parts store and use that to form the gasket on the cover.......
I don't have any idea why someone would have told you that synthetic would cause the seals to leak. The "weight" of the oil is the same - so it's gonna leak if the seal is bad no matter what you have in there.

 

Fiction. I agree with racefan, just put the friction addative in.

 

you ad the friction addative because it's a friction plate limited slip differential right?

 

Yes, if your seals are not in great shape, a synthetic lube will usually leak where a conventional lube might not (due to the molecular properties of synthetics, molecules being much more consistent in size and shape, etc..., basically the things that make synthetics so good to begin with). This applyies to synthetic motor oil as well. That's why you often hear that switching to synthetic on a high mileage engines could result in new leaks. People often inaccuratly think the synthetic oil caused the leak, but in fact it was just that your old seals were in poor shape and could not contain the synthetic lube like it can conventional lube.

But, it's not really seals you have to worry about when switching to synthetic in a limited slip differential. Synthetics can cause chatter, which can damage the unit. There are some exceptions to this. If your limited slip unit is a gear type unit, synthetic lube is ok, and probably even called for (like in many new Rams with factory gear-type limited slips). If it is a cone assembly type or clutch pack type, it is definelty better to use standard lube with a friction modifier recommended by the manufacturer of the limited slip unit.

If you have an Auburn limited slip (for example, and since that's what I have), do NOT use synthetic lube. Also, only use Ford or GM friction additives with an Auburn limited slip. There is a warning that comes with the Auburn unit. Mines at home, but found this one on another forum. Same thing mine said as I recall.

Hope this clears it up.

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I use" Royal Purple Max Gear" diff fluid, anygood ?it says that it doesnt need an additive, am i good to go? or still put additive in?