Changing Gear Oil -- Close enough?

[Bean Counter]

As a bean counter I can say, mathematically speaking, the difference of 20 to 30 in say the viscosity weight of your motor oil is a much bigger difference than 80 to 90 in your differentials. So my truck wants 5w30 in the engine and that's what it always gets. Does it matter as much in the gear oil? It isn't as plentiful insofar as supply goes and there's a well priced synthetic 75w90 that hasn't caused my truck to fall apart yet. I put it in last go around, but am wondering if I'd be better off getting to 400,000 miles from 300,000 miles if I stick to the SAE 80w in the front and transfer case and 90w in the rear as I think the specs call for. 75w90 good enough all around or need to be exact?

thank.

[Dan-o]

Tagging.......   because I've always wondered the same thing.

[Magnum_Willys]

Synthetic in engines and transfer case is good.  Stay away from synthetics in differentials.  Mfg's and racers will tell you this.  Synthetic just does not cling or cushion like you need in differentials. 

75w-90w is the same as 90w as soon as it warms to operating temp.

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"Q23. What kind of oil should be used with an Auburn limited-slip differential/ Auburn ECTED Max differential?
A23. Non-synthetic 80w90 GL-5 oil treated with Auburn Gear friction additive, part #504102 (also known as a friction modifier). See Catalog page 32. Three (3) ounces of additive will treat one quart of oil. GM or Ford limited-slip additive may be used. We do not recommend synthetic oil. Auburn limited-slip additive is packed in every box with the differential."
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[Bean Counter]

Thanks Willy.
I'm doing some research and starting to remember things from a few years ago when I last did this and stuff sounds vaguely familiar. According to my back-of-the-napkin maintenance records I used the same gear oil all around and didn't add the friction modifier to the differential. I haven't had any problems in my Tundra in the last few years. Maybe its for people who tow?

[Woodchuck]

Synthetic in engines and transfer case is good.  Stay away from synthetics in differentials.  Mfg's and racers will tell you this.  Synthetic just does not cling or cushion like you need in differentials. 

75w-90w is the same as 90w as soon as it warms to operating temp.

----------------------
"Q23. What kind of oil should be used with an Auburn limited-slip differential/ Auburn ECTED Max differential?
A23. Non-synthetic 80w90 GL-5 oil treated with Auburn Gear friction additive, part #504102 (also known as a friction modifier). See Catalog page 32. Three (3) ounces of additive will treat one quart of oil. GM or Ford limited-slip additive may be used. We do not recommend synthetic oil. Auburn limited-slip additive is packed in every box with the differential."
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Um, I run synthetic in the race car in EVERYTHING. Well except for the water in the radiator  . We break in with conventional and after that it goes synthetic. 
I highly suggest using the manufacturer's spec. Some pretty smart people put that out there for a reason, even if we don't know what that reason is.

[jackelope]

I agree with Woodchuck. They put those specific fluids in for a reason.

[Bean Counter]

Um, I run synthetic in the race car in EVERYTHING. Well except for the water in the radiator  . We break in with conventional and after that it goes synthetic. 
I highly suggest using the manufacturer's spec. Some pretty smart people put that out there for a reason, even if we don't know what that reason is.

Well fine then. I'll use the 80w90. But, they also say to use conventional, not synthetic. 

[Woodchuck]

Um, I run synthetic in the race car in EVERYTHING. Well except for the water in the radiator  . We break in with conventional and after that it goes synthetic. 
I highly suggest using the manufacturer's spec. Some pretty smart people put that out there for a reason, even if we don't know what that reason is.

Well fine then. I'll use the 80w90. But, they also say to use conventional, not synthetic. 

That would be the route I suggest.

[thinkingman]

Synthetic in engines and transfer case is good.  Stay away from synthetics in differentials.  Mfg's and racers will tell you this.  Synthetic just does not cling or cushion like you need in differentials. 

75w-90w is the same as 90w as soon as it warms to operating temp.

----------------------
"Q23. What kind of oil should be used with an Auburn limited-slip differential/ Auburn ECTED Max differential?
A23. Non-synthetic 80w90 GL-5 oil treated with Auburn Gear friction additive, part #504102 (also known as a friction modifier). See Catalog page 32. Three (3) ounces of additive will treat one quart of oil. GM or Ford limited-slip additive may be used. We do not recommend synthetic oil. Auburn limited-slip additive is packed in every box with the differential."
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Good advice here.
Use dino oil and buy the TOYOTA friction modifier.

[Woodchuck]

Synthetic in engines and transfer case is good.  Stay away from synthetics in differentials.  Mfg's and racers will tell you this.  Synthetic just does not cling or cushion like you need in differentials. 

75w-90w is the same as 90w as soon as it warms to operating temp.

----------------------
"Q23. What kind of oil should be used with an Auburn limited-slip differential/ Auburn ECTED Max differential?
A23. Non-synthetic 80w90 GL-5 oil treated with Auburn Gear friction additive, part #504102 (also known as a friction modifier). See Catalog page 32. Three (3) ounces of additive will treat one quart of oil. GM or Ford limited-slip additive may be used. We do not recommend synthetic oil. Auburn limited-slip additive is packed in every box with the differential."
---------------------------

Good advice here.
Use dino oil and buy the TOYOTA friction modifier.

Just like the manufacturer of that part suggests. 

[jackelope]

Synthetic in engines and transfer case is good.  Stay away from synthetics in differentials.  Mfg's and racers will tell you this.  Synthetic just does not cling or cushion like you need in differentials. 

75w-90w is the same as 90w as soon as it warms to operating temp.

----------------------
"Q23. What kind of oil should be used with an Auburn limited-slip differential/ Auburn ECTED Max differential?
A23. Non-synthetic 80w90 GL-5 oil treated with Auburn Gear friction additive, part #504102 (also known as a friction modifier). See Catalog page 32. Three (3) ounces of additive will treat one quart of oil. GM or Ford limited-slip additive may be used. We do not recommend synthetic oil. Auburn limited-slip additive is packed in every box with the differential."
---------------------------

Good advice here.
Use dino oil and buy the TOYOTA friction modifier.

Just like the manufacturer of that part suggests. 

[Bean Counter]

Thanks hive mind. Trad gear oil it is.

The rocket scientists and brain surgeons that wrote the owners manual don't have the torque specs in there. But, there's instructions on how to lock the doors.  Time to call Toyota.

[jackelope]

Thanks hive mind. Trad gear oil it is.

The rocket scientists and brain surgeons that wrote the owners manual don't have the torque specs in there. But, there's instructions on how to lock the doors.  Time to call Toyota.

You need a service manual, not an owner's manual. Google is your friend.

[jackelope]

What do you need?
I used my mad rocket science skills to find them online.

[Bofire]

  I get my truck serviced when the book says to and I use the stuff the book says. I also use a dealership for my work.
Carl