Synthetic Diff. Lube???

[BLANK21]

everyone praises synthetic fluids for everything in the truck. I recently bought 4.10's and an Aurburn Gear Hi-Performance LS unti with cone clutches. Both the tranny mech. who is doing the install and the paperwork that came with the LS unit say to use dyno oil and not synthetic. The tranny mech actually told me not to waste my money on the syn. in the rear end. This is a very reputable shop that only does tranny, transfer case and rear end work. They also build a lot of race application stuff, dragsters etc. My brother had a highly modified Buick Grand National back in the day and the previous owner owned a company that built racing suspensions..the car came with "whale sperm" in the rear end. Is that actually what it is or just what it is called. if it is real.....how does one get it from the whale???? I am going with the dyno oil as advised and will use dyno oil after the break in period. has anyone else heard of not using syn. oil in the rear end.? Is anyone else using syn. with the LS units? I am just looking for comparison info. Thanks guys

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[dirtyd0g]

Well getting the whale sperm is tricky, here's a hint don't swallow
I don't bother with synthetic fluid becuase I service mine every 2 years. If you don't want to service so often use the synthetic fluid.
Alan

[DDan1967]

Actually it had Sperm Whale Oil in it.

Sperm Whale Oil used to be used as a base for lots of lubricants before the 1972 ban on whaling.

Though dirtyd0g's post is good for a

As far as what to put in your new Diff I'd go with what the paperwork says.

Doug

[WLF]

When I installed my Eaton LS I put in Mobil synthetic gear lube along with two friction modifiers. One day on ice I had the misfortune to get stuck with only ONE wheel spinning.
I called Eaton and they said NO synthetics in the rear. Seems the Synthetics are so good the LS could not make friction. The clutch plates require friction to work.
Replaced the fluid; added good dino with one friction modifier and it got real jerky. Then added a second friction modifier and it is now working smooth.

[Bluegrass]

I believe there are some points to be made here.
First a limited slip with no modifier will make the clutches grab and act rough.
The modifier is to actually make some slip in the lube to allow the clutched not to grab. That's why it is put in. Think about it.
If one put to much in then your defeating the LS clutch action.
The Owners manuel says that synthetic lube in the rear normally does not have to be changed.
I know there will be disaggrement but take some time to research it before you debate the points.
It is common practice for drag racers to NOT use friction modifier in there traction lock 8.8 rears for this reason.
For 02, the owners manuel pages 287 and 289 spec 75-140 sysn with foot note on change interval.
Don't know how many years spec it this way.

[kgvickers]

Bluegrass, you stated that there was some sort of reference to the replacement interval for the diff lube in the '02 manual. Can you elaborate?

I just bought a '99 with 156K. My manual states that the diff lube is good for life and never needs to be changed . . . I'm not too happy with that recommendation, so it would be nice to see if Ford has changed its mind on that.

Thanks,

Keith

[cliles55]

kgvickers,

I don't think Ford means, "Don't change the fluid"; I read it as, "Not required unless ...."

Certainly, if you are uncomfortable with lifetime lubrication (I don't believe anything has unlimited, lifetime anything), change it. Just make sure you comply with the Owner's Manual lube requirements.

Take care,
Curt