75w-140

[Fasttimez]

Originally Posted By: mlatour
Coincidence or not,

my brand new in 2004 Dodge RAM 1500 4.7l 2WD was specced for 75W-140 in the "9-1/4" rear axle w/3.55 gears
as I live in a rather cool climate (Montreal) and never towed or hauled anything I figured a quality synthetic 75W-90 would
suffice and help with the lousy gas mileage and cold weather flow.
Diff. got a fresh fill of RedLine every 3 years.

After 10 years-120K miles, the rear axle started whinning badly at speed / at operating temp. as the pinion bearing went south.

By this point I tried switching to a mineral 80W-140 to delay repairs but it was still as noisy.

My new 2014 base model F-150 XL 3.7V6 specs 75W-140 and you can bet I won't 'experiment' with using a thinner gear lube in it.

I understand your point completely. Using the chart & doing calculations, my rear differential barely specs in the lower region of the 75w-110 category at low speeds, at high speeds it's at the bottom of the 90w range, almost a 85w. I returned the 75w-90 Valvoline oil & got some Amsoil Severe Gear 75w-110. This is what my axle specs out to be, not 75w-140. Ford just went up to the 75w-140 because the 110w is so odd ball nobody really makes it. The 110 range my axle falls in, used to be included in the old 90w category before it split into 110w & 90w. So that answers my question about why 90w was spec'd for years & then the change to 75w-140.

 

[rslifkin]

Based on that, the 75W-110 should work fine. The 140 was likely spec-ed for a combination of a little extra safety margin and better availability. There's not really a downside to using it over the 110 though. I'd be amazed if you can detect a difference in mpg from that change in diff fluid with a truck.

 

[FastLane]

My Mustang says on the diff cover tab...."75W-140 SYNTHETIC ONLY".

 

[Shannow]

Originally Posted By: zeng
Originally Posted By: Fasttimez
He said they formulated a 80w-90 full synthetic fluid that did fine, but Ford backed away from it instead keeping the 75w-140.


Allow me to further elaborate on my previous workings above,where it says that in relations to desired gear oil KV@40C (from 213 cSt to 161 cSt) at varying road speeds of 40 - 70 mph :

KV@40C of following gear oils, in increasing order of viscosity are :-

a) Mobil 1 LS 75W-90; Synthetic; GL5; 106 cSt --- Inadequate

b) Mobilube® HD 80W-90; Dino; GL5; 136 cSt ------ Barely adequate

c) Mobil 1 LS 75W-140; Synthetic; GL5; 179 cSt ---Quite adequate

d) Mobilube® HD 85W-140; Dino; GL5; 377 cSt ------More than adequate.Caveat:ambient not below -10 C

e) Mobilube GX SAE 140; Dino; GL4; 447 cSt--------Over-the-top adequate.Ambient not below 0 C


Ford's final selection of synthetic 75W-140 at approximate KV@40C of 179 cSt makes perfect sense in this market where it's ambient does get below -10 C.

In my tropical climate of minimum 24 C year round, 85W-140 of KV@40C of 377 cSt would provide wear protection in a wider range of road speeds well below 40 mph.

Note: In a way, the selection of Synpower 75W-90 of KV@40C of 100 cSt above, would likely cap power output per differential at about 50-60 hp .

JMO.


zeng,
I've really enjoyed your contribution to this thread, as it's pertinent to me.

The 85W140s that I've seen locally all have a VI that's typically monograde...the 75W140s are all obviously very highly VIIed.

My old engineering texts were pretty well developed in the Newtonian gear oils, and my recent industrial experience has had VIII doped ISO 1000s become 400s in a month service (heavily loaded roller bearings).

Do you have some good resource that you can point me to on non Newtonian hypoid protection/EHD ?

 

[widman]

I would recommend against most 85W-140 oils as they are too thick to lubricate the smaller shafts/bushings/bearings. You will cover the gears but wear out the rest.

 

[zeng]

Originally Posted By: Shannow
[/quote]zeng,
I've really enjoyed your contribution to this thread, as it's pertinent to me.

The 85W140s that I've seen locally all have a VI that's typically monograde...the 75W140s are all obviously very highly VIIed.

My old engineering texts were pretty well developed in the Newtonian gear oils, and my recent industrial experience has had VIII doped ISO 1000s become 400s in a month service (heavily loaded roller bearings).

Do you have some good resource that you can point me to on non Newtonian hypoid protection/EHD ?


Check machinerylubrication.com for valuable tips.
Probably off topic here , I'm of the opinion that in the context of differential lubrication, use of highly VII'ed oils is a bad choice due to its propensity to viscosity shearing.

 

[zeng]

Originally Posted By: widman
I would recommend against most 85W-140 oils as they are too thick to lubricate the smaller shafts/bushings/bearings. You will cover the gears but wear out the rest.



Widman , I can understand where you are coming from,in terms of 'probability' of shafts/bushings/bearings not getting adequate lubrication, especially at initial motion of moving from a prolonged complete stop.

At fill hole lube level, the two roller bearings on the input pinion shaft and the other two roller bearings on the two output spider gears (LHS and RHS outputs) are all 'properly' submerged in gear oil as per axle manufacturer design.

However ,'unfortunate as it may be', out of the 4 spider bush bearings in a typical differential spider assembly, at least 1 to 2 units are fully above fill hole lube level ..... thus your concern.
Now, in normal straight line driving there is no relative rotating movement between the 4 spider bearings and its journals, thus negating concerns of lack of lubrication at initial rotation of tire wheels generally.