What's the best Differential Gear Oil?

[TexasTruck72]

I am looking to flush the old gear oil from my 9" Ford rear end and replace with new gear oil. My truck has 4.11 gears in the rear. What would be the best weight and or brand of gear oil to use for this application? Appreciate any input. Thanks.

[Busboy]

You will get 100 different opinions based on nothing. Just go by the owners manual recommendations as to weight and any name brand will work. I use the house brand at Wal-Mart.

[BobbyFord]

Valvoline EP 90-140

[TexasTruck72]

Thank you both.

[radioactivelarry]

I am looking to flush the old gear oil from my 9" Ford rear end and replace with new gear oil. My truck has 4.11 gears in the rear. What would be the best weight and or brand of gear oil to use for this application? Appreciate any input. Thanks.

Use synthetic! I use AMSOIL, reduces wear and will last a long time. Use the same weight recommended 80-140 etc.

[ThinLizzy13]

You will get 100 different opinions based on nothing. Just go by the owners manual recommendations as to weight and any name brand will work. I use the house brand at Wal-Mart.

X2. House brands work fine.

[Busboy]

When people recommend a certain brand of whatever, they are merely expressing their feelings of how the product performed. I submit that nobody is speaking from a position of actually having conducted scientific tests of said product. If I spent 10 times more for something with expectations of getting more for my money, human nature guarantees that I'll will "feel" like it works better. It's just like when you get your car washed it seems to just run better! People that claim great success from Amsoil, Slick 50, Royal Purple etc. are just repeating what they are told in the advertising. This type of marketing is the second oldest profession on the planet. P.T. Barnum was exactly correct.

[Ranchero50]

I am looking to flush the old gear oil from my 9" Ford rear end and replace with new gear oil. My truck has 4.11 gears in the rear. What would be the best weight and or brand of gear oil to use for this application? Appreciate any input. Thanks.

Use synthetic! I use AMSOIL, reduces wear and will last a long time. Use the same weight recommended 80-140 etc.

Be wary of synthetics as they tend to leak around old seals much easier than dyno oils. Walmart house brand meets the manufacturers specs. Run Rotella if you want something 'better' or at least in a different bottle.

[HIO Silver]

I use Lucas 85w-140 and Valvoline 80w-90.

[radioactivelarry]

When people recommend a certain brand of whatever, they are merely expressing their feelings of how the product performed. I submit that nobody is speaking from a position of actually having conducted scientific tests of said product. If I spent 10 times more for something with expectations of getting more for my money, human nature guarantees that I'll will "feel" like it works better. It's just like when you get your car washed it seems to just run better! People that claim great success from Amsoil, Slick 50, Royal Purple etc. are just repeating what they are told in the advertising. This type of marketing is the second oldest profession on the planet. P.T. Barnum was exactly correct.

Wrong, wrong, wrong.... I have used AMSOIL in everything from my chainsaw to all my vehicles. When you use a chainsaw for years then remove the muffler to inspect the piston and the original hone marks are still on the cylinder walls you know there is no wear. When you get well over 500K miles on an engine and it still has great compression and runs like new where's the gimmick?
Anyone that says synthetics are not worth the money has never tried them. There are several brands of synthetics and all are not the same. Just because it says synthetic doesn't mean it is a quality product. AMSOIL is at the top of the list along with Lucas, Red Line and Royal Purple . All other synthetics are below, some are way below even Mobile One.
AMSOIL is everything they say it is, period. I use it and many other friends of mine use it and we swear by it instead of at it. If you think it is a marketing gimmick keep using those old petroleum products and keep the parts suppliers rich by replacing worn out parts that synthetics would allow to last longer, much longer.
243,538 miles on my V6 Monte Carlo and the same on the transmission running AMSOIL and not so much as a problem with either. Same thing on my other vehicles, high miles, n problems, no blow-by or low compression. Do you have any idea how much money I have saved over the years????? A LOT......HIGH QUALITY SYNTHETICS ARE NOT A GIMMICK AT ALL BUT A MONEY SAVER. Ask any guy why he runs AMSOIL in his race car, off road vehicle or his 2 stroke anything.....

DON'T KNOCK THEM IF YOU HAVE NEVER TRIED THEM...............

[Busboy]

The latest example of my point exactly.

[radioactivelarry]

The latest example of my point exactly.

Your POINT is pretty dull. Hopefully no one believes you.........

[LANCE65]

For that "SCIENTIFIC" explanation, see "Bob is the oil guy"....he's done tests on oils and filters....you'll be shocked.

[TexasTruck72]

Wow, this thread has become quite the debate room. Thanks everyone for your responses.

[BobbyFord]

My '63 Uni has over 500,000 miles on it. 4 motors, one transmission with 2 rebuilds and one rearend all on dinosaur oil.
Flat tappet cams aren't going to benefit from synthetic oil unless zinc is involved.