Mobil1 75W140 in a NP435?

[TheLoneRanger]

Hi all, just picked up some Mobil1 75W140 synthetic gear oil for my Bronco NP435 4-sp transmission. What are your thoughts on this lube?

My main concerns are cold weather performance, and yellow metal corrosion. I did look up the specs on Mobil's website, and they indicated this lube was formulated to be safe for copper based metals. Does this mean it's safe for brass syncros?

Thanks for your comments,
TLR

 

[HardbodyLoyalist]

Holy Schnoikies!

I don't think yellow metal corrosion will be nearly the concern that hard shifting will be.

I have the same transmission in my D-250. It seems to get along just fine with 75W-90 or even 80W-90 dino. Is there some problem you're trying to fix by using a 140?

 

[HardbodyLoyalist]

Wow. I didn't know any of these transmissions were spec'd for 140.

My manual actually calls for straight 90 GL-5.

By all means, if your manual calls for 140, then you should assume that's what the transmission was designed for. If you don't like the feel of 140, then you might consider draining 1/3-1/2 of the fluid and topping up with 75W-90 -- then you'll be an official "mixologist."

If Mobil says the fluid is safe for yellow metals, then it should be fine with brass synchros.

 

[MolaKule]

What's with this setup?

High viscosity lubes > 75W90 are used only when you have:

1. High loads and horsepower
2. large clearances
3. large gearing
4. Brass (sleeve) bearings

Before I would put a 75W140 in there I would check it and see if it is really that thick and look at the specs again.

 

[1040 WreckerMan]

My Ford book calls for "SAE 50 Engine Oil (ESE-M2c39-C)" This is for the NP435 and NP 542 in 1974. Later Ford may have superseded the spec to gear oil. If I'm not mistaken 50 wt engine oil would be close to a 90wt gear oil, so the 140 would be a little thick.

I think you could use that Mobil without a problem, but cold weather shifts might not be great. I'd probably be temped to run 75w90 instead, unless you have a lot of HP or really extreme loads. We run SAE 50 oil in the manual transmissions at work and they pull 200,000 pounds in some cases!

 

[TheLoneRanger]

I read that 140W spec for the NP435 out of a Haynes manual, and it does appear to be wrong. After some research, I've found that Ford did indeed spec 50W engine oil when the trans came out in the 60's, and then went to 90W gear oil in the late 70's.

Obviously the 75W90 is the correct choice, and my thanks to all (Loyalist, Mola, and Wrecker) for pointing this out.

Mola, very nice website for SF products; appears to be some good stuff.

Thanks again,
TLR

 

[TheLoneRanger]

Loyalist, thanks for the reply. There's no problem with the trans, it's just that the specs call for a 140W gear oil in this model. (I thought that was a little strange too.)

Now I'm wondering if I should use the 75W-90?