Hey guys, is it me or is 75w-140 rear diff fluid overkill for an everyday driver F150 that doesn't tow anything ? The rear is not a limited slip, so no clutch packs. It does have the electronic locker. I'm going to be changing out my diff fluid & was going to put 75w-90 full synthetic back in it. I was planning on using something readily available off the shelf such as Valvoline SynPower, which has some great reviews & carries a lot of certifications. Is there any disadvantage to using a synthetic 75w-90 vs 75w-140 ? Like I said, I never tow hardly at all, I don't beat on my truck such as racing down the road or anything. I know my manual specs for 75w-140, but it just seems like overkill for my application.
75w-140
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If the owners manual specs 75w-140, go for it. It's going to be at minimum a synblend and won't affect cold performance too much.
Plus, if you do tow with it, you won't have any problem.
85w-140 ... that stuff is too heavy.
Plus, if you do tow with it, you won't have any problem.
85w-140 ... that stuff is too heavy.
Not overkill IMO. Its what Ford specs and its what should be run. AAP has the Mobil 1 75w-140 if I remember correctly. Its what's in my 99 E-150 and seems to be doing great.
I hear you, it's just weird that for Ford's bigger F250's & 350's with Dana axles it only calls for 80w-90. You would think a 75w-140 would be needed for those applications. I'm guessing all the issues Ford had with noise in the rears & shuddering concerns due to LS clutch packs they just decided to spec an oil that would cover everything. I've actually put a sample of 75w-140 & 75w-90 in my freezer for 24hrs, the 75w-90 was MUCH MORE free flowing than the 75w-140. I know this isn't a scientific test but it was noticably thicker. Thanks for the replies so far.
In my mind the fact that Ford has spec'd so many other axles for 80w-90 then all of the sudden spec'd these for 75w-140 is reason enough to use it. They had a reason I'm sure.
Its not like this is a new fluid in that application either. My '99 F150 specified 75w140 in the rear axle, and that was 16+ years ago.
My '04 F150 called for 75w90 from the factory, but was changed by 75w140 not to long after, and even had a new tag installed when the service was done by Ford.
In my mind, just use what is specified.
My '04 F150 called for 75w90 from the factory, but was changed by 75w140 not to long after, and even had a new tag installed when the service was done by Ford.
In my mind, just use what is specified.
Originally Posted By: MNgopher
My '04 F150 called for 75w90 from the factory, but was changed by 75w140 not to long after, and even had a new tag installed when the service was done by Ford.
2004 was about the time you started seeing all the "shudders on take off" & "rear gear whine" concerns from Ford on the F150's & Explorers only. Almost 100% of the shudder concerns were pinion angle or clutch pack related, & the gear whine was either backlash or just a metallurgy problem. Just courious if they spec'd this fluid to try & cover up subpar components in their rears, but since have fixed the issues, but just kept the 75w-140 spec because they have boat loads of the stuff to use up.
My '04 F150 called for 75w90 from the factory, but was changed by 75w140 not to long after, and even had a new tag installed when the service was done by Ford.
2004 was about the time you started seeing all the "shudders on take off" & "rear gear whine" concerns from Ford on the F150's & Explorers only. Almost 100% of the shudder concerns were pinion angle or clutch pack related, & the gear whine was either backlash or just a metallurgy problem. Just courious if they spec'd this fluid to try & cover up subpar components in their rears, but since have fixed the issues, but just kept the 75w-140 spec because they have boat loads of the stuff to use up.
Originally Posted By: Fasttimez
Hey guys, is it me or is 75w-140 rear diff fluid overkill for an everyday driver F150 that doesn't tow anything ?
Gear oil viscosity selection is heavily influenced and determined by linear speed at gear tooth (of differential in this case) .
No towing plus high road speed, lower viscosity gear oil is preferred.
At low road speed,higher viscosity gear oil is preferred.
Originally Posted By: Fasttimez
The rear is not a limited slip, so no clutch packs. It does have the electronic locker. I'm going to be changing out my diff fluid & was going to put 75w-90 full synthetic back in it. I was planning on using something readily available off the shelf such as Valvoline SynPower, which has some great reviews & carries a lot of certifications. Is there any disadvantage to using a synthetic 75w-90 vs 75w-140 ?
At gear tooth linear speed of say, 750 fpm and below, I would abandon xxW-90 gear oil viscosity.
In a differential, generally xxW-140 offers far superior wear protection than a xxW-90.
I tend to believe xxW-90's frictional heat reduction is of no significance.
Originally Posted By: Fasttimez
Like I said, I never tow hardly at all, I don't beat on my truck such as racing down the road or anything. I know my manual specs for 75w-140, but it just seems like overkill for my application.
I see no reason why you are not selecting xxW-140 as recommended. Having said this, I would select xxW-90 if gear tooth linear speed consistently exceeds say , 1000 fpm.
JMO.
Hey guys, is it me or is 75w-140 rear diff fluid overkill for an everyday driver F150 that doesn't tow anything ?
Gear oil viscosity selection is heavily influenced and determined by linear speed at gear tooth (of differential in this case) .
No towing plus high road speed, lower viscosity gear oil is preferred.
At low road speed,higher viscosity gear oil is preferred.
Originally Posted By: Fasttimez
The rear is not a limited slip, so no clutch packs. It does have the electronic locker. I'm going to be changing out my diff fluid & was going to put 75w-90 full synthetic back in it. I was planning on using something readily available off the shelf such as Valvoline SynPower, which has some great reviews & carries a lot of certifications. Is there any disadvantage to using a synthetic 75w-90 vs 75w-140 ?
At gear tooth linear speed of say, 750 fpm and below, I would abandon xxW-90 gear oil viscosity.
In a differential, generally xxW-140 offers far superior wear protection than a xxW-90.
I tend to believe xxW-90's frictional heat reduction is of no significance.
Originally Posted By: Fasttimez
Like I said, I never tow hardly at all, I don't beat on my truck such as racing down the road or anything. I know my manual specs for 75w-140, but it just seems like overkill for my application.
I see no reason why you are not selecting xxW-140 as recommended. Having said this, I would select xxW-90 if gear tooth linear speed consistently exceeds say , 1000 fpm.
JMO.
Originally Posted By: zeng
Originally Posted By: Fasttimez
Hey guys, is it me or is 75w-140 rear diff fluid overkill for an everyday driver F150 that doesn't tow anything ?
Gear oil viscosity selection is heavily influenced and determined by linear speed at gear tooth (of differential in this case) .
No towing plus high road speed, lower viscosity gear oil is preferred.
At low road speed,higher viscosity gear oil is preferred.
Originally Posted By: Fasttimez
The rear is not a limited slip, so no clutch packs. It does have the electronic locker. I'm going to be changing out my diff fluid & was going to put 75w-90 full synthetic back in it. I was planning on using something readily available off the shelf such as Valvoline SynPower, which has some great reviews & carries a lot of certifications. Is there any disadvantage to using a synthetic 75w-90 vs 75w-140 ?
At gear tooth linear speed of say, 750 fpm and below, I would abandon xxW-90 gear oil viscosity.
In a differential, generally xxW-140 offers far superior wear protection than a xxW-90.
I tend to believe xxW-90's frictional heat reduction is of no significance.
Originally Posted By: Fasttimez
Like I said, I never tow hardly at all, I don't beat on my truck such as racing down the road or anything. I know my manual specs for 75w-140, but it just seems like overkill for my application.
I see no reason why you are not selecting xxW-140 as recommended. Having said this, I would select xxW-90 if gear tooth linear speed consistently exceeds say , 1000 fpm.
JMO.
So my differential gearing is 3.73:1, I generally travel at speeds of 45mph-70mph. My transmission ratios are as follows 4.17:1(1st gear) 2.34:1(2nd gear) 1.52:1(3rd gear) 1.14:1(4th gear) 0.86:1(5th gear) 0.69:1(6th gear) with 90% of driving spent in 6th gear. Given this information what would be my gear tooth linear speed (aproximate) ? Does it warrant more of a 75w-140 or a 75w-90 ? I'm always curious about things like this.
Originally Posted By: Fasttimez
Hey guys, is it me or is 75w-140 rear diff fluid overkill for an everyday driver F150 that doesn't tow anything ?
Gear oil viscosity selection is heavily influenced and determined by linear speed at gear tooth (of differential in this case) .
No towing plus high road speed, lower viscosity gear oil is preferred.
At low road speed,higher viscosity gear oil is preferred.
Originally Posted By: Fasttimez
The rear is not a limited slip, so no clutch packs. It does have the electronic locker. I'm going to be changing out my diff fluid & was going to put 75w-90 full synthetic back in it. I was planning on using something readily available off the shelf such as Valvoline SynPower, which has some great reviews & carries a lot of certifications. Is there any disadvantage to using a synthetic 75w-90 vs 75w-140 ?
At gear tooth linear speed of say, 750 fpm and below, I would abandon xxW-90 gear oil viscosity.
In a differential, generally xxW-140 offers far superior wear protection than a xxW-90.
I tend to believe xxW-90's frictional heat reduction is of no significance.
Originally Posted By: Fasttimez
Like I said, I never tow hardly at all, I don't beat on my truck such as racing down the road or anything. I know my manual specs for 75w-140, but it just seems like overkill for my application.
I see no reason why you are not selecting xxW-140 as recommended. Having said this, I would select xxW-90 if gear tooth linear speed consistently exceeds say , 1000 fpm.
JMO.
So my differential gearing is 3.73:1, I generally travel at speeds of 45mph-70mph. My transmission ratios are as follows 4.17:1(1st gear) 2.34:1(2nd gear) 1.52:1(3rd gear) 1.14:1(4th gear) 0.86:1(5th gear) 0.69:1(6th gear) with 90% of driving spent in 6th gear. Given this information what would be my gear tooth linear speed (aproximate) ? Does it warrant more of a 75w-140 or a 75w-90 ? I'm always curious about things like this.
Basic point is the idea that Ford has a boatload of the stuff to use up is bunk. The issues you noted were on 2004 trucks, and we are 11 years later. More than ample time to "use the stuff up" if that was the idea.
Given the price of 75w140 vs common 75w90 oils, you can bet if they could cost engineer it out of being needed to save a few pennies, it would have been done long ago.
Given the price of 75w140 vs common 75w90 oils, you can bet if they could cost engineer it out of being needed to save a few pennies, it would have been done long ago.
It seems to me you are overthinking the problem. Ford wants 75W-140, there were issues with the diff when they briefly spec'd 75W-90, and there is no significant difference in cost, ease of use, etc.
As mentioned it could be pinion angle issues; that is most certainly a design issue but that does not necessarily mean a design deficiency.
Just taking the one possible reason mentioned so far here, the non-ideal pinion angle may be required due to other factors (pinion angle almost always is) that are chassis-geometry related.
In other words they may not be able to change the pinion angle to the optimum one because of space available for fitment, length from tailshaft to diff (OD planetary gearset is typically added as a unit to the rear of a non-OD transmission case, increasing it's length), and flexibility required to handle load variation, necessary suspension stiffness versus tow or box load, I suppose I could go on. But I won't.
Just use the 75W-140.
As mentioned it could be pinion angle issues; that is most certainly a design issue but that does not necessarily mean a design deficiency.
Just taking the one possible reason mentioned so far here, the non-ideal pinion angle may be required due to other factors (pinion angle almost always is) that are chassis-geometry related.
In other words they may not be able to change the pinion angle to the optimum one because of space available for fitment, length from tailshaft to diff (OD planetary gearset is typically added as a unit to the rear of a non-OD transmission case, increasing it's length), and flexibility required to handle load variation, necessary suspension stiffness versus tow or box load, I suppose I could go on. But I won't.
Just use the 75W-140.
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Well , is it all right to make the following assumptions on :-
a) Tire size is 265/60R18 and 245/70R17 (Outer Diameter of 30.5 inches) ; or
tire size is of 2785/55R20 (Outer Diameter of 32 inches) .......... and,
b) Pitch Circle Diameter of bevel(big) gear of say 8 inches ?
Note: Major and Minor diameters of bevel gear heel/toe would help too.
a) Tire size is 265/60R18 and 245/70R17 (Outer Diameter of 30.5 inches) ; or
tire size is of 2785/55R20 (Outer Diameter of 32 inches) .......... and,
b) Pitch Circle Diameter of bevel(big) gear of say 8 inches ?
Note: Major and Minor diameters of bevel gear heel/toe would help too.
If Ford specs 75W-140 in the rear differential, then that is what you should use.
As far as the fluid, either Mobil 1 LS 75W-140 or Amsoil 75W-140 Severe Gear. I am sure Valvoline SynPower 75W-140 would work just as well.
As far as the fluid, either Mobil 1 LS 75W-140 or Amsoil 75W-140 Severe Gear. I am sure Valvoline SynPower 75W-140 would work just as well.
Originally Posted By: zeng
Well , is it all right to make the following assumptions on :-
a) Tire size is 265/60R18 and 245/70R17 (Outer Diameter of 30.5 inches) ; or
tire size is of 2785/55R20 (Outer Diameter of 32 inches) .......... and,
b) Pitch Circle Diameter of bevel(big) gear of say 8 inches ?
Note: Major and Minor diameters of bevel gear heel/toe would help too.
Tire size is 275/55R20, ring gear is 9.75". Thanks
I get what everyone is saying about "just used what's spec'd". The reasons I've heard as to why it's needed haven't made sense to me. If it's because of wear prevention & longevity of parts, then why don't they use it in their F250-350 trucks that see more load & heavy duty work than my truck ? It would make sense to use the more "heavy duty/severe duty" fluid in a truck that sees heavy loads continuously. Wouldn't a more robust fluid be better on parts for high load, low rpm use like towing heavy (exactly what the F250-350 were made for). Yet they use 80w-90....weird right. I'm willing to bet the only reason they spec 75w-140 is their fear of rear end gear whine that they were so famous for starting in 2004 with the F150 & Explorer's. But that's just my opinion.
Well , is it all right to make the following assumptions on :-
a) Tire size is 265/60R18 and 245/70R17 (Outer Diameter of 30.5 inches) ; or
tire size is of 2785/55R20 (Outer Diameter of 32 inches) .......... and,
b) Pitch Circle Diameter of bevel(big) gear of say 8 inches ?
Note: Major and Minor diameters of bevel gear heel/toe would help too.
Tire size is 275/55R20, ring gear is 9.75". Thanks
I get what everyone is saying about "just used what's spec'd". The reasons I've heard as to why it's needed haven't made sense to me. If it's because of wear prevention & longevity of parts, then why don't they use it in their F250-350 trucks that see more load & heavy duty work than my truck ? It would make sense to use the more "heavy duty/severe duty" fluid in a truck that sees heavy loads continuously. Wouldn't a more robust fluid be better on parts for high load, low rpm use like towing heavy (exactly what the F250-350 were made for). Yet they use 80w-90....weird right. I'm willing to bet the only reason they spec 75w-140 is their fear of rear end gear whine that they were so famous for starting in 2004 with the F150 & Explorer's. But that's just my opinion.
Basing on tire size of 275/55R20 and bevel PCD of 9.75 inches , calculated parameters are:-
MPH Bevel rpm Bevel FPM Desired KV@40,cSt
70 737 1882 161
60 632 1614 174
50 527 1345 191
40 421 1076 213
KV@40C of following gear oils, in increasing order of viscosity are :-
a) Mobil 1 LS 75W-90; Synthetic; GL5; 106 cSt
b) Mobilube® HD 80W-90; Dino; GL5; 136 cSt
c) Mobil 1 LS 75W-140; Synthetic; GL5; 179 cSt
d) Mobilube® HD 85W-140; Dino; GL5; 377 cSt
e) Mobilube GX SAE 140; Dino; GL4; 447 cSt
Take your picks,
Note: thousand apologies for inaccurate off-the-cuff quote on gear speed in previous posts.
MPH Bevel rpm Bevel FPM Desired KV@40,cSt
70 737 1882 161
60 632 1614 174
50 527 1345 191
40 421 1076 213
KV@40C of following gear oils, in increasing order of viscosity are :-
a) Mobil 1 LS 75W-90; Synthetic; GL5; 106 cSt
b) Mobilube® HD 80W-90; Dino; GL5; 136 cSt
c) Mobil 1 LS 75W-140; Synthetic; GL5; 179 cSt
d) Mobilube® HD 85W-140; Dino; GL5; 377 cSt
e) Mobilube GX SAE 140; Dino; GL4; 447 cSt
Take your picks,
Note: thousand apologies for inaccurate off-the-cuff quote on gear speed in previous posts.
I have and have had owned Ford trucks for over 30 years (F350/F550) and all have speced with 75w-140 in the rear ends. My current truck is an '15 srw F350 which is a Ford rear end, the duallys use the dana rear end and I'm not familiar with that spec. I do know the 4wd trucks spec 75w-90 in the front axle, but it only moves when 4wd is engaged.
Why are you changing your fluid? The F250/F350 srw is lifetime fill unless submerged. A good rule of thumb is you can't go wrong following the owners manual.
Why are you changing your fluid? The F250/F350 srw is lifetime fill unless submerged. A good rule of thumb is you can't go wrong following the owners manual.
Originally Posted By: roadrunner1
I have and have had owned Ford trucks for over 30 years (F350/F550) and all have speced with 75w-140 in the rear ends. My current truck is an '15 srw F350 which is a Ford rear end, the duallys use the dana rear end and I'm not familiar with that spec. I do know the 4wd trucks spec 75w-90 in the front axle, but it only moves when 4wd is engaged.
Why are you changing your fluid? The F250/F350 srw is lifetime fill unless submerged. A good rule of thumb is you can't go wrong following the owners manual.
Filled for life seems like a great marketing pitch to me. They took all the external fuel filters off of Ford vehicles, nothing to chnage....it's considered a "lifetime" filter which sits inside your gas tank....because I'm sure fuel quality has evolved to the point of cleanliness to never have to change out a filter....it's kinda like motor oil, your manual spec's a viscosity grade, yet web forums like BITOG expose all sorts of reasons as to why you should run a specific grade whether it's what your manual calls for or not....& people post up data to back up their claims & findings. I'm sure 75w-140 is MORE than enough for my axle, but ask yourself this....why is Ford just about the only other OEM the uses the gear lube grade for normal duty service, every GM I've ever seen calls for 80w-90, every Dodge is the same. They will say use 75w-140 for severe duty applications. I guess Ford has made the choice for you & opted on the side of caution so they specify severe duty gear lube weight from the start.
I have and have had owned Ford trucks for over 30 years (F350/F550) and all have speced with 75w-140 in the rear ends. My current truck is an '15 srw F350 which is a Ford rear end, the duallys use the dana rear end and I'm not familiar with that spec. I do know the 4wd trucks spec 75w-90 in the front axle, but it only moves when 4wd is engaged.
Why are you changing your fluid? The F250/F350 srw is lifetime fill unless submerged. A good rule of thumb is you can't go wrong following the owners manual.
Filled for life seems like a great marketing pitch to me. They took all the external fuel filters off of Ford vehicles, nothing to chnage....it's considered a "lifetime" filter which sits inside your gas tank....because I'm sure fuel quality has evolved to the point of cleanliness to never have to change out a filter....it's kinda like motor oil, your manual spec's a viscosity grade, yet web forums like BITOG expose all sorts of reasons as to why you should run a specific grade whether it's what your manual calls for or not....& people post up data to back up their claims & findings. I'm sure 75w-140 is MORE than enough for my axle, but ask yourself this....why is Ford just about the only other OEM the uses the gear lube grade for normal duty service, every GM I've ever seen calls for 80w-90, every Dodge is the same. They will say use 75w-140 for severe duty applications. I guess Ford has made the choice for you & opted on the side of caution so they specify severe duty gear lube weight from the start.
You're the one who posted here asking for advice, you're getting it and not liking what you're hearing, so it seems as if you've already made your mind up to use a lighter fluid than spec in owners manual.
Its your truck and you can do whatever you like.
Its your truck and you can do whatever you like.
Originally Posted By: roadrunner1
You're the one who posted here asking for advice, you're getting it and not liking what you're hearing, so it seems as if you've already made your mind up to use a lighter fluid than spec in owners manual.
Its your truck and you can do whatever you like.
I wasn't asking for advice, I was asking for solid information or data to back up why 75w-140 was any advantage over 75w-90 in an application that doesn't need it based on usage of the vehicle. So far advice is all I've gotten & not facts or data (save for one poster). Because the manual "says so" isn't very scientific in nature, don't you agree....if the manual was the bible & the end all be all of the automotive world, why do we even have a forum like BITOG that has disproven many "manual recommended or spec'd" fluids or services. I keep asking the same question because all I've gotten is opinions with nothing to back it up. Nothing wrong with opinions, I'm just not wired in the way of accepting opinions in place of data or facts.
You're the one who posted here asking for advice, you're getting it and not liking what you're hearing, so it seems as if you've already made your mind up to use a lighter fluid than spec in owners manual.
Its your truck and you can do whatever you like.
I wasn't asking for advice, I was asking for solid information or data to back up why 75w-140 was any advantage over 75w-90 in an application that doesn't need it based on usage of the vehicle. So far advice is all I've gotten & not facts or data (save for one poster). Because the manual "says so" isn't very scientific in nature, don't you agree....if the manual was the bible & the end all be all of the automotive world, why do we even have a forum like BITOG that has disproven many "manual recommended or spec'd" fluids or services. I keep asking the same question because all I've gotten is opinions with nothing to back it up. Nothing wrong with opinions, I'm just not wired in the way of accepting opinions in place of data or facts.
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