I need to switch my gear oil from 75w-140 to 75w-90 and Peak has some cheap synthetic gear oil. Made in USA, cheaper than Valvoline and Mobile1. The reason for the switch is my rear end chatters on turns when cold and once warmed up, it's just fine. I'm thinking a thinner gear oil could help this situation. Limited slip rear, yes I used Mopar friction modifier. 

Absolutely... I always suggest using 80w-90 weights in the axle. 140 is way too thick and even cold it barely even moves it like tar. Even towing I still use 80w-90 you want a lubricant that will flow out to the hubs in a quick fashion as well. Ask JL_Welding about his experience with 140 weight synthetics. As long as the gear lube is a GL5 lubricant its good to go.

I was running 75-140 and mopar friction modifier without issues for about 15k miles. Then recently I was coming home from a 100 mile run with a loaded car trailer and it started chattering/binding really bad on tighter corners. Sounded like bowling balls rolling around and slamming into the bedside. Took the rear end apart expecting the worst but everything was perfect.... So threw it back together with some cheap 80-90 I had laying around and it's been fine ever since.

80w 90 is the original and still the best. If that's not working you need to go with a medium duty truck.

Dumb question why is it that anyone talks about engine oil they look for the quickest flowing oil. Then when doing axle lubricants they get the thickest tar to put in the axles? Why is that? If I could find a GL-5 lube that was lower in the winter (W) side I would jump on it.  Like 75W-90 or simular in a GL-5 petroleum base.

Ill report back. Hoping to weld a bung instead of paying $200 for an aftermarket diff cover with a drain plug. I think I put 75w140 because thats what the cummins manual said. Lesson learned. I seem to remember using amsoil 75w90 on my 03' hemi with no issues.

75w110 amsoil no issues.

lubricants usage.

FRONT AXLE

² The lubricant should have MIL-L-2105C and

API GL 5 quality specifications.

² Lubricant is SAE 75W-140 SYNTHETIC gear

lubricant.

REAR AXLE

² The lubricant should have MIL-L-2105C and

API GL 5 quality specifications.

² Lubricant is a thermally stable SAE 80W-90

gear lubricant.

² Lubricant for axles intended for heavy-duty or

trailer tow use is SAE 75W-140 SYNTHETIC gear

lubricant.

NOTE: Trac-lokY and Vari-lokY equipped

 

lubricants usage.

FRONT AXLE

² The lubricant should have MIL-L-2105C and

API GL 5 quality specifications.

² Lubricant is SAE 75W-140 SYNTHETIC gear

lubricant.

REAR AXLE

² The lubricant should have MIL-L-2105C and

API GL 5 quality specifications.

² Lubricant is a thermally stable SAE 80W-90

gear lubricant.

² Lubricant for axles intended for heavy-duty or

trailer tow use is SAE 75W-140 SYNTHETIC gear

lubricant.

NOTE: Trac-lokY and Vari-lokY equipped

 

 

 

Seems pretty cut and dried... if you tow use 75w-140. AFIK that has always been the recommendation for the Dana axles. 

 

75w-90 and 75w-140 should have the same cold flow properties but I am not sure what cold is. At -40°C the -140 is 84% thicker, looking at Amsoil products.  

 

As far as gear lube vs engine oil it's because gear lube is splash lubed and not pumped thru very small clearances; additionally, a 75w gear lube and a 75w engine oil would not have the same viscosity. 

 

Lets look at Amsoil 75w-90 gear lube and AME 15w-40 engine oil. Using the 40°C Kinematic Viscosity test the two oils are very close and the gear lube is only 10.8% thicker than the engine oil. Now if you look at the 75w-140 it is 96% thicker. Unfortunately that is the coldest test that is conducted on both fluids. 40°C is 104°F so not exactly cold fluid.

I have been running the 80W-90 in mine for a while now. I do tow heavy but very seldom, about 2k to 3k a year. I move it about every 4 months. There seems to be no ill effect. No noises or leaky seals, the LS seems to be working properly. Think I am doing any harm to anything? 353k on it right now.

Dumb question why is it that anyone talks about engine oil they look for the quickest flowing oil. Then when doing axle lubricants they get the thickest tar to put in the axles? Why is that? If I could find a GL-5 lube that was lower in the winter (W) side I would jump on it. Like 75W-90 or simular in a GL-5 petroleum base.

Haha very true. 75W-90 is perfect for the axles. I run that all year round with no issues. I will be changing it out in December and adding in some fresh oil. I will be using Mobil 1 synthetic for sure since it's easy to find and of high quality.

Now if only I could remember how many quarts of oil to buy.

Anyone ever drill and tap the differential housing for a drain plug? I'm thinking of tapping the bottom to actually drain all the fluid. Disadvantages? 

Anyone ever drill and tap the differential housing for a drain plug? I'm thinking of tapping the bottom to actually drain all the fluid. Disadvantages? 

Its simpler just to buy another differential cover that has a drain at the bottom. 

 

Also you will not get all the fluid out either way because of the viscosity and the axle tubes will always hold some residual.

Ya, but I'm not spending $200 on a cover. I was originally thinking welding a nut at the bottom of the cover, but there a lip at the bottom of the housing that traps a decent amount of fluid.

Ya, but I'm not spending $200 on a cover. I was originally thinking welding a nut at the bottom of the cover, but there a lip at the bottom of the housing that traps a decent amount of fluid.

You could weld a bung to the back of the cover that uses a flange type bolt similar to what is used on the oil pan. I would not worry about a few ounces at the bottom that does not pour out. Just be sure whatever plug you intend to use has a magnet. 

I never understood why there's not a drain plug on all differentials. Seems like Toyota is one of the few smart enough to put one there. I can't imagine adding one would cause any structural issues but maybe a stress fracture could start there if you really abuse it.

I know all the factory drains I've seen have a raised shoulder surrounding the plug but I assume that's more to prevent the plug from getting ripped off than added structural support. I'd go smallish on the hole like 1/4" pipe thread. If your willing to play guinea pig I say go for it.

I never understood why there's not a drain plug on all differentials. Seems like Toyota is one of the few smart enough to put one there. I can't imagine adding one would cause any structural issues but maybe a stress fracture could start there if you really abuse it.

I know all the factory drains I've seen have a raised shoulder surrounding the plug but I assume that's more to prevent the plug from getting ripped off than added structural support. I'd go smallish on the hole like 1/4" pipe thread. If your willing to play guinea pig I say go for it.

Yes. Toyota does do that but so does different Meritor axles that do not have removable differential covers. 

 

I would weld in a bung otherwise risk a leak. I would not pipe thread any structural piece. You can weld to iron with a nickel welding rod.

Seems like Toyota is one of the few smart enough to put one there.

Toyota doesn't have a removable diff cover so they have to. Toyota have the 3rd member pop out and you can do gears on the bench vs in the axle.

Yes. Toyota does do that but so does different Meritor axles that do not have removable differential covers. 

Yes Toyota is one of the manufactures smart enough to put a drain in.

 

I would weld in a bung otherwise risk a leak. I would not pipe thread any structural piece. You can weld to iron with a nickel welding rod.

Could you elaborate on this because pipe thread is more or less self sealing and an improperly welded bung can also leak. Are you saying don't pipe thread structure or don't thread structure? I was leaning towards threading it because welding cast iron overhead can be a real bugger.

Toyota doesn't have a removable diff cover so they have to. Toyota have the 3rd member pop out and you can do gears on the bench vs in the axle.

Yes well understood I have a few yota axles sitting in the weeds right now. I guess you could say a convenience stemming from a necessity. Just saying there's no reason every manufacturer couldn't put a drain plug on the diff.

My concern is structural integrity if I tap the housing. I think I'll just weld a bung on the cover