4th Gen Rear Diff Fluid Discrepancy?

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leafsby2

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To start off I live in a small town where everyone knows everyone, I am good friends with the salesman whom sold me the truck and he is great friends with the owner. I never get up sold or even try to, everyone at the dealership knows me etc.



I hit 100,000km and my rear diff fluid looks new and I wanted to change it, I went and purchased 75w140 as that’s what the manual states to use, I went over to visit the salesman (as he is a friend of ours) and my child poses for dealership pictures when the new owners don’t want to, it started as a joke and has taken off he asked if I called the dealer to check the price, I stated no because the dealer is always more expensive. He talked with the parts manager and they ran my vin, as per my vin my rear takes 75w90 and if my truck was in getting work done and they needed to add fluid it would be 75w90. So this got me to digging, the same owner owns a tirecraft (a tire shop that also does mechanic work) and has their own software for instructions on fluids, mechanical work, the time jobs should take and the amounts of fluids needed in all different makes and models. According to their system by inputting my make and model it tells them to use 75w90 and 2.2 litres.



Now I am confused, the manual calls for 75w140 but all other places I’ve contacted including the dealer call for 75w90 I don’t have the limited slip and just the “conventional rear end” 3.21 gears which fluid should I use? Or just leave it alone?
 

Wild one

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Use the 75W-140,they only started reconmending using 75W-90 when they went after milege numbers.I've never seen a diff blow up from to heavy a fluid,but have seen them blow up from to light a fluid.Plus it's a multi-viscosity fluid that isn't any heavier then the 75W-90 till the rear-end gets hot,which is when you want a heavier duty fluid.
 
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leafsby2

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Thanks, I was also told by the dealership that there is some sort of “additive” in their 75w90 that my diff needs? Snake oil?
 

Wild one

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Thanks, I was also told by the dealership that there is some sort of “additive” in their 75w90 that my diff needs? Snake oil?
If you have the open/conventional diff,you don't need the limited slip additive,that'll be what they're trying to upsell you to,the additive doesn't hurt,but it's not needed in the one wheel peeler diffs,which is what you have,no limited slip.I'd run either Redline or Amsoil 75W-140 fluid if it was me,but Ma Mopars 75W-140 fluid will work also
 

pacofortacos

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You would think 75w-90 and 75w-140 would perform the same cold, but I can feel the difference between the two - more so when cold than when warm.

They were 2 different brands though, so maybe that was it.

I personally am a Redline 75w-110 fan, but I also change it every 10,000 miles or so. ie. every 2 years.
I do tow and at high speed, but it is a boat (about 5-6k lbs.) which is a little easier than a camper - though the boat hull sits higher than the bed of the truck and the windshield is about even with the top of the cab.
If pulling 8000+ and a camper, I would probably opt for the 75W-140. And change it for winter and summer use hahaha.

I actually enjoy changing the rear diff. gear oil - much more than the engine oil. Slide under, pull the drain plug, let drain, pull the pan out, slide under put the plug in, slap 2 bottles or so in and call it a day.
 
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leafsby2

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You would think 75w-90 and 75w-140 would perform the same cold, but I can feel the difference between the two - more so when cold than when warm.
That’s what I was worried about here in eastern Canada we can get down to -35C to -40C (-31F to -40F)
 

HEMIMANN

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I'd run 75W-90 if I weren't towing capacity in the summer, if I were you.

I even run 75W-90 in my Ram 2500 with huge 11.5" AAM axle ring gear. Of course, that's the same axle in the 3500 so I'm not using it anywhere near load capacity. Living in mid-Minnesota, we get temperature swings from -30F to +100F. It's just friggin' utopia here.
 

Wild one

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That’s what I was worried about here in eastern Canada we can get down to -35C to -40C (-31F to -40F)
I'm in Alberta,and have no issues with 75W-140. I swapped the wifes ZF diff from 75W-85 to 75W-140 to combat the infamous howling ZF diffs in the cars,and haven't seen any differance in the cars times at the track.Best with 75W-85 was 11.44,best with 75W-140 Redline is 11.43,if anything the car is faster with the Redline 75W-140 then it was with the factory 75W-85 fill. But i did notice a hell'va change in the howl it used to have,it's virtually silent now,compared to the factory fluid. Spent to many years around right angle gearbox drives to be a fan of light duty fluids.Your manual specifies 75W-140 that's what i would stick with,but it's your call
 

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"They" have determined adding friction modifier doesnt hurt open diffs, so literally every gear fluid except special order will have additive in it, so just use that. It is in every single gl-5 spec, so go with the flow. Only old stuff like 60's and 70's and earlier would have specific spec for slippery clutches. Mind you by chance if you get shudder after doing what the book says, please pm me and update the thread.

75w90 has been pretty universal for gear fluids until fca pulled an okey doke and spec'd 140 for their rear diffs but only in 1500's. I don't really know why, nobody has that info except fca, I'm rolling with rich and say use what the book says. If you want better cold performance, then use a gear fluid that is pao or pao/ester as opposed to going thinner. It's your truck your choice, that is just some info maybe you find helpful.
 

Wild one

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"They" have determined adding friction modifier doesnt hurt open diffs, so literally every gear fluid except special order will have additive in it, so just use that. It is in every single gl-5 spec, so go with the flow. Only old stuff like 60's and 70's and earlier would have specific spec for slippery clutches. Mind you by chance if you get shudder after doing what the book says, please pm me and update the thread.

75w90 has been pretty universal for gear fluids until fca pulled an okey doke and spec'd 140 for their rear diffs but only in 1500's. I don't really know why, nobody has that info except fca, I'm rolling with rich and say use what the book says. If you want better cold performance, then use a gear fluid that is pao or pao/ester as opposed to going thinner. It's your truck your choice, that is just some info maybe you find helpful.
They used to call for 75W-140 in the cars before 2010,then between 2010 and 2014 they called for 75W-140 in the V6 and 5.7 cars,but spec'd 75W-90 in the 6.4 cars,then in 2015 they started spec'ing 75W-85 in the cars,and that's when guys started yelling about the diffs howling in the cars,so you can draw your own conculisions,lol
 

Wild one

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To start off I live in a small town where everyone knows everyone, I am good friends with the salesman whom sold me the truck and he is great friends with the owner. I never get up sold or even try to, everyone at the dealership knows me etc.



I hit 100,000km and my rear diff fluid looks new and I wanted to change it, I went and purchased 75w140 as that’s what the manual states to use, I went over to visit the salesman (as he is a friend of ours) and my child poses for dealership pictures when the new owners don’t want to, it started as a joke and has taken off he asked if I called the dealer to check the price, I stated no because the dealer is always more expensive. He talked with the parts manager and they ran my vin, as per my vin my rear takes 75w90 and if my truck was in getting work done and they needed to add fluid it would be 75w90. So this got me to digging, the same owner owns a tirecraft (a tire shop that also does mechanic work) and has their own software for instructions on fluids, mechanical work, the time jobs should take and the amounts of fluids needed in all different makes and models. According to their system by inputting my make and model it tells them to use 75w90 and 2.2 litres.



Now I am confused, the manual calls for 75w140 but all other places I’ve contacted including the dealer call for 75w90 I don’t have the limited slip and just the “conventional rear end” 3.21 gears which fluid should I use? Or just leave it alone?
 

HEMIMANN

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They used to call for 75W-140 in the cars before 2010,then between 2010 and 2014 they called for 75W-140 in the V6 and 5.7 cars,but spec'd 75W-90 in the 6.4 cars,then in 2015 they started spec'ing 75W-85 in the cars,and that's when guys started yelling about the diffs howling in the cars,so you can draw your own conculisions,lol

I'd never heard of a 140 gear oil spec in a light duty vehicle until I came over from Chevy to Mopar. Car companies don't make their own axles anymore, so what gives?

140 always and only went into the heavy duty trucks. And bulldozers, and such.
 

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the 75W is for winter compatibility so either 75W90 and 75W140 should be the same in cold weather. 140 gives a bit better shock absorption vs 85 or 90. If a lot of miles or towing I would run 75W140 I doubt the average person will not see any real mpg difference maybe 0.2 mpg at most.
 

Andersoncma

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2011 Ram 2500 6.7L Cummins. I don’t do any heavy towing, and run valvoline Full Syn 75W90. 137K miles, No problems, no issues, removed Diff cover last spring and everything looked brand new and all tolerances appeared to be factory spec
 
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leafsby2

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2011 Ram 2500 6.7L Cummins. I don’t do any heavy towing, and run valvoline Full Syn 75W90. 137K miles, No problems, no issues, removed Diff cover last spring and everything looked brand new and all tolerances appeared to be factory spec
I do tow a 6,500Lbs 36’ camper, don’t go too far though.
 

Wild one

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I'd never heard of a 140 gear oil spec in a light duty vehicle until I came over from Chevy to Mopar. Car companies don't make their own axles anymore, so what gives?

140 always and only went into the heavy duty trucks. And bulldozers, and such.
Alot of the earlier trucks spec'd straight 90 weight hypoid gear fluid,which is probably about the equilevent of a multi-viscosity 75W-140 now.Up till i think late 2017 they spec'd 75W-140 in the 1500's in the owners manuals.
Ford spec 's 75W-140 in their 05+ diffs.

 
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After my truck go re-geared, the shop that did it said to only go with 4.5 quarts of 85-140 because of the 4.88 gears and the larger and heavier wheel and tire combo ... does that sound right ?
 

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This makes me wonder if they've cost-reduced the gears to marginal capacity.
 

zogg

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I just changed both differentials on my 2019 classic. I used Royal Purple 75/90 in both. My manual calls for GL5 and 75/90.
 
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