9" Ford Gear Oil Weight

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Jun 17, 2008 | 01:26 PM

IcemanV8

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9" Ford Gear Oil Weight

What weight is recommended for the Ford 9". Mine is in an 86 F-150. I'm wanting to go synthetic. Was thinking Lucas or Mobil 75w-90...

UNTIL I started seeing people also say they take an 80w-140. QUITE the difference.

Just what do they call for? I'm going synthetic, so I don't care to go thick, but what's the best for longevity?

Jun 18, 2008 | 05:20 AM

ford390gashog

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From: Brentwood,CA

75w90 seems to be the best. the 80w140 was known for bearing race scuffing.

Jun 18, 2008 | 08:51 AM

IcemanV8

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THANKS. So, I guess I'll just go with Mobil1 75W-90 in the rear end as well as the NP435 (which I'm doing today). I hope this doesn't waste money and shift like crap. I'm torn between full synthetic Mobil1 75W-90 or Valvoline Durablend Sythetic BLEND 80W-90 for either OR both. Any recommendations?

Jun 18, 2008 | 11:59 AM

jimandmandy

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From: Running Springs CA

Both will work, but synthetic can find leaks that you may not know you have. Yes, Ive heard the argument that syn does not CAUSE leaks hundreds of times. When I switched a GM 8.875 axle over to syn at about 50,000 miles, the pinion seal started seeping, and the housing was completely dry before the change. You dont have to believe it, but you have been warned. I would only change equipment over to syn if it was still under warranty or freshly rebuilt, or didnt care, like putting Redline in the BMW that was already seeping a bit.

Jim

Jun 18, 2008 | 10:09 PM

IcemanV8

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I'm changing only the tranny and rear end to synthetic. Already done my NP435 to Mobil1 75W-90, and man, I'm loving it . Only been in for one day, but I've drove it a lot. Done good. I dunno what was in it... looks red. Probably ATF fluid.. fine for a new truck.. don't think so for an NP435.

Thinking of Mobil1 85W-140.... or is is 75W-140, for my rear end...

What do you guys think?

Jun 19, 2008 | 10:11 AM

IcemanV8

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^Umm... I posted that **** faced drunk last night. That's why I practically asked the same question again. Thoughts...weren't...clear.

I'll try not to make this take longer than needed. It appears the 9" called for 80W-90. Then, the 8.8" took it's place, and ORIGINALLY in the light duty trucks, it also called for 80W-90, only later to be changed to 85W-140.

So, that's why I'm even asking anything. I just want whats best for it. But, I'm leaning towards 75W-140 Mobil1, since my truck turns 2200-2300RPM at 55mph, it may need that little extra thickness.

Jun 20, 2008 | 10:49 AM

jimandmandy

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From: Running Springs CA

Ford, GM and Toyota all use 75W-140 syn as factory fill today, so you probably cant go completely wrong with it, but unless you are towing, 75W-90 should give you better gas mileage and still protect as well or better than the 80W-90 that was original fill when yours was new.

Jim