Rear Differential Fluid

[crouse]

What gear oil do you run in your rear differential? I know the owners manual says 75w140, but I think now we're supposed to run 80w90.

Looking on Rock Auto, the Motorcraft 80w90 shows Premium Rear Axle Lubricant. The Motorcraft 75W140 shows Synthetic.

I think we supposed to use full Synthetic?

Rock Auto has a Mobil 1 75w90 that is Synthetic.

[offroadkarter]

you have that backwards, the 80W90 call was superseded by 75W140

run a 75w140 synthetic that has limited slip additives (most should)

[crouse]

Ahhh. Thanks for the help.

[crouse]

Holy crap it's expensive. Rock Auto has it at $22.89 per quart, whereas 80W90 is only $7.59 per quart.

[fastblackmerc]

Use 75W140 synthetic, Using synthetic negates the need for friction modifier.

[offroadkarter]

Holy crap it's expensive. Rock Auto has it at $22.89 per quart, whereas 80W90 is only $7.59 per quart.


Go to Walmart, they have tons of 75w140 in stock. No reason to mail order that unless you're going to use something more boutique like Amsoil. Most are around $15 at Walmart.

[BLACKMARAUDER04]

How much fluid do we need to change the gear oil?


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[JVD]

Whats the reason for the switch to 75w140? I think thats what the police vics use.

[offroadkarter]

How much fluid do we need to change the gear oil?


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2.5 quarts, although 2 quarts is usually enough if you're not pulling the axles and getting ALL of the fluid out


Whats the reason for the switch to 75w140? I think thats what the police vics use.

don't know, ask Ford

[BLACKMARAUDER04]

So had the differential serviced.
Replaced the girdle with a Finned one from Amazon’s brand A+. Very reasonably priced. It doesn’t include screws. The seal is RTV. No gasket needed. You just need the RTV to dry enough to finish sealing. The repair person got the screws from O’Reily’s.

Now for some reason. the alignment is way off. The steering wheel is facing 8 o’clock. It’s on the rack being fixed as I type this.


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[Comin' in Hot]

Was the steering wheel straight when you drove it to the shop?

[fastblackmerc]

So had the differential serviced.
Replaced the girdle with a Finned one from Amazon’s brand A+. Very reasonably priced. It doesn’t include screws. The seal is RTV. No gasket needed. You just need the RTV to dry enough to finish sealing. The repair person got the screws from O’Reily’s.

Now for some reason. the alignment is way off. The steering wheel is facing 8 o’clock. It’s on the rack being fixed as I type this.


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Changing the fluid and replacing the differential cover has NOTHING to do with the front end.

[BLACKMARAUDER04]

Obviously, the alignment has nothing to do with the differential. That’s why it was mysterious. The steering wheel was not straight. I had to drive with it pointing left. It’s all fixed now.
They also fixed a flat tire( for free)
Off one of the other Marauders


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