Why does my rear differential require 75W-85 GL5?

I started hearing a clicking/tapping noise coming from my rear when I'm driving at low speeds and the drivetrain is unloaded. It almost sounds like what a differential would sound like if you had it open, sitting on a bench, and were turning the input shaft by hand. It's like the sound of the gears meshing, but louder than it should be. It's not a "bad" sound, not a grinding sound, it's just there.

I'm wondering if the gear oil is low. I'm going to change it. The manual calls for 3.12 quarts of 75W-85 GL5.

To me, that seems like kinda an oddball oil for this diff. Why the friction modifier? It's not a limited slip. It does have the electric locker.

It's also hard to find. Amazon has

$39 Red Line 50104 75W85 GL-5 Full Synthetic Gear Oil for Hypoid Limited Slip Differentials - 2 Quarts

Red Line 50104. Is that OK?

75W-90 is a lot easier to find locally. Is it an acceptable substitute?

Thanks for any replies.

 

75w90 is fine.
you don't need LS mod. no harm if you buy one that already has it.

If you can find Mobil Delvac 75w90 for a good price, it's a full synthetic gear oil that does not have LS mod in it. But if you need to save money, Walmart Supertech 75w90 is usually the cheapest full synthetic you can buy in any city and it's more than adequate.

 

Thanks.

I wonder why the Toyota engineers spec’d 75W-85 GL5.

I really hope the oil level is just low and this fixes my problem. I don’t even want to know what a rear rebuild would cost.

 

fuel efficiency is why they spec'd 75w85

 

The pinion bearing(s) is usually the first victim of low diff oil.

 

At the expense of lubricity and ultimately, longevity, I’m inclined to assume.

 

Is the pinion bearing an expensive fix?

 

This is the exact sound it’s making:

https://youtube.com/shorts/Yvp4msK4Rls?si=PehRrWvGo2c5YyxF

 

Check the fluid level. If it's low look for gear oil leaking into the drum brakes

You could have a rotational sound coming from the brakes, look for broken hardware or debris in there

Check the driveshaft u-joints

Hell you could have a rock stuck in the tire tread

Just because you found a YouTube video that sounds like your noise doesn't mean you need a diff

Toyota isn't "sacrificing longevity for the sake of mpgs" with their choice of gear oil. We're talking about a tiny difference in viscosity between 75w-85 and

$28 75w-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75w-90. these diffs aren't delicate flowers.

 

Nobody has addressed the "GL-5" requirement. GL-5 is for all hypo gears - it is not for limited slip purposes - that is a different additive. It would be hard to find axel/gear oil without it being GL-5.

As for the weight; straight 90W would be fine for most climates. I will be moving to 90W140 when I next change mine. Currently at ~95,000 miles.

No comment on your noise. It is not going to be good.

EDIT: Yes, your first post link to the Redline product is fine.

 

Wait until people realize the 2005-2007 manuals said to use 90w in the rear.

Like you said, the diffs in these trucks aren't that sensitive.

 

It sounds an AWFUL lot like that video. I mean, it's an exact match.

I ordered 4 quarts of Valvoline 889785 full synthetic

$28 75W-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75W-90 for in-store pickup tomorrow morning. I'm crossing my fingers that the oil is low and filling the case will be an instant fix, but man, I'm skeptical. My crystal ball shows a $2,500 rebuild in my near future.

...

Would I have oil on my garage floor if it were leaking through the drum brakes? My floor is bone dry. Absolutely zero oil.

 

I wouldn't buy anything until I know what the problem is

Lift the rear of the truck and run the wheels, listen around with a stethoscope

 

If I open the fill plug and she's full, I'll return the oil.

I just want to be ready tomorrow morning.

 

Park on level ground. Remove the fill plug. Stick your finger in the fill port. If oil is within 1/2” of the fill port, it’s full.

The important part here is that you are on level ground.

You can be at least a half quart low an no noise from the diff. Mine was that low when my axle seal blew.

 

Thanks for the reply.

Have you ever heard a case where simply adding oil eliminated a noise and the differential lived happily ever after?

 

If the oil level got low enough to cause a noticeable noise then the damage is already done. Adding oil likely won't fix the noise

If there was a big enough leak to cause damage you probably would have seen something dripping in the driveway or soaking the drum brakes and wheels

 

Not exactly, No.
Not adding oil.

Changing the oil, Yes.
But only on older mechanical LSD differentials.

In your case. I seriously doubt adding or changing oil is going to help the noise.
It can't hurt anything. And it's relatively cheap. Worth a try.

Also, FWIW. I'm not one to get caught up in oil brands and type.
When I say cheap, I mean "Not some fancy super synthetic oil".

The cheap Valvoline stuff works for me.

 

As stated, if the back of your brake backing plates aren't wet, your pinion seal isnt dripping wet, chances are its not low at all....
Figured you would have mentioned you have a leak, if you did...

 

I could smell the leak.
Then I found the leak.....