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Discussion Starter #1
What kind of gear oil are most guys using in their trucks? I put a detroit locker in the rear a few years back and put in valvoline 75-140 full synthetic(limited slip) gear oil and was gonna service the rear and the front axles cause i got a front mag-hytech diff cover and thought i'd also service the rearend while i'm doing the front. Thanks
 

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I purchase the Royal Purple it comes with the friction additive already in it.
 

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+1 on the royal purple synthetic - its easily obtain at pepboys/orielys and many others.
and you dont have to go screwing w/ the extra friction modifier...its already in the
royal purple !
 

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Discussion Starter #4
+1 on the royal purple synthetic - its easily obtain at pepboys/orielys and many others.
and you dont have to go screwing w/ the extra friction modifier...its already in the
royal purple !
But do you really need the friction modifier if you're not running the factory differential? I'm running a detroit locker in the rear...it's not like the factory limited slip that has the clutches that need the friction modifier in the gear oil.
 

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But do you really need the friction modifier if you're not running the factory differential? I'm running a detroit locker in the rear...it's not like the factory limited slip that has the clutches that need the friction modifier in the gear oil.
no you wouldnt need it - but the royal purple is still fine for you to use.
 

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I have tried Royal P...it's ok, most 100% synthetics are, but since I have had this Dually it's been AMSOIL from end to end and I'm much more satisfied with their extended drain intervals! Lab testing proves it stands up better over the long haul and I'm at 480,000+ Km. plus you can become preferred customer for like 30 dollars a year and get it delivered to your door at full dealer wholesale price...
 

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Sorry, got on a tangent haha, Bush pilot is correct you do not need friction modifiers in a Detroit Locker for sure...no clutches.
FYI the AMSOIL 75w140 Severe gear has the FM built in like the Royal Purple.
 
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It's all great oil, I just like the color of the "purple" bottles.LOL
 

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Discussion Starter #10
thanks guys for the feed back. The differential in the frontend doesn't have frictions like the factory rearend does it?
 

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thanks guys for the feed back. The differential in the frontend doesn't have frictions like the factory rearend does it?
the rear may not have friction plates/clutches in it either - there were TWO
3.73's offered (at least when i bought my truck) one that was open & one
that was limited slip.

the front does NOT have clutches its a "locker" (which is why you cant turn
"well" when your in 4x4, w/ the hubs locked)

check your manual, but i know on MY truck the gear lube weight thats
called for is different front to rear.
 
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Discussion Starter #12
my factory rearend had an open diff. I'll check the manual and see what is recommended for oil weight. Thanks
 

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iirc at some point ford revised the manual and went to same weight front/rear, but
again im not certain of that.

i highly recommend installation of the '08 rear cover - its aluminum and finned - the
factory stamped steal rusts because it bakes the paint off the cover.

the cover is about 50 bucks w/ the new bolts, its pretty too :D
the 08 cover has the weight of the required gear lube cast into the cover !
 

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Discussion Starter #14
iirc at some point ford revised the manual and went to same weight front/rear, but
again im not certain of that.

i highly recommend installation of the '08 rear cover - its aluminum and finned - the
factory stamped steal rusts because it bakes the paint off the cover.

the cover is about 50 bucks w/ the new bolts, its pretty too :D
the 08 cover has the weight of the required gear lube cast into the cover !
I have both front and rear mag-hytec covers. Just checked the manual for front and rear oil specs. It says front axle-hypoid gear oil SAE 90, rear axle-75w-140 gear oil. What is hypoid gear oil SAE 90...is that the same as 75w-90?
 

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Discussion Starter #15
I was just at carquest and they stock 75w-90 and 75w-140 gear oil in royal purple, mobil 1, and valvoline.
 

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yup id go w/ the "multi" viscosity 75-90 & 75-140
 
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I second that, and of those 3 choices I would go with Royal purple if I couldn't have AMSOIL.
The term "hypoid" has more to do with the construction of gears than it does with oil. Early automotive engineering involved gears that meshed with each other straight on. When you think of gears, this flat face-to-face gear teeth approach is what we learned as kids in cartoons and marketing images of big machinery. However, automotive design soon figured out this gear approach was inefficient and also very loud when running. Thus, the "hypoid" design was invented which basically has two gears shaped like Christmas trees mesh with each other at 90 degree angles or similar.
The hypoid approach reduced gear-meshing noise and it allowed greater torque pressure for stronger drive. The design was so successful every car and vehicle today uses it as a standard transmission design. Due to the higher pressure on gears as a result, the lubrication needed has to include ingredients to provide more protection for the gears. This special gear oil is designed not to deconstruct under higher pressure.
 
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Discussion Starter #18
thanks guys....i'll go with the royal purple. I'll put the 75w-90 synthetic in the front and the 75w-140 synthetic in the rear.
 

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iirc at some point ford revised the manual and went to same weight front/rear, but
again im not certain of that.

i highly recommend installation of the '08 rear cover - its aluminum and finned - the
factory stamped steal rusts because it bakes the paint off the cover.

the cover is about 50 bucks w/ the new bolts, its pretty too :D
the 08 cover has the weight of the required gear lube cast into the cover !
What's the PN for the '08 cover? I'm interested! I'm assuming it will fit an '06?

I'll go with Strokin6L conclusion - 75w-90 synthetic in the front and the 75w-140 synthetic in the rear.
 

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the front does NOT have clutches its a "locker".
I thought it was open??????

At one time I had my front drive shaft off because I was painting it black. When it was off I wanted to see it it had a locker in the front or if it was a live axle. So I drove around in 4X4 High and took a tight turn and I had no hop. Then I put the drive shaft back on and it hopped.

I think the hop is from the front wheels spinning faster than the rear.
 
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