Gears & Axles - How warm should a fully broken-in axle housing run?

I am breaking in my new gears and I have done 2 test runs so far. As expected the rear cover is quite hot to the touch. Once its broken-in I figure it will still warm up but how much? When is break-in over (by temperature), I know everyone says drive 500 miles.

Theres no set temperature to gauge this by. Many aspects affect temp heck even different lubes have different shear properties and viscosity that affect temp as well as the set up itself. If its on the tight side of clearances it will run a lot hotter than if its loose. This plays on many aspects;

-Pinion bearing preload
-carrier bearing preload
-backlash
-gear mesh

New bearings are very tight for the first while until they bed in. This makes the heat much higher so dont worry about it too much. If its not making horrid noise then drive it a thousand k and change the lube and you should be fine :)

I am breaking it in still and I noticed on my second trip out that I heard what sounded like a zipper sound when turning only once the differential was warmed up a lot. I am using cheap 75W90 oil right now, non-synthetic and its normal when cold. I figured that since the differential was extra warm the torsen might make some funny noises that it otherwise wouldn't. I plan to change to the GM synthetic once its time to swap oil and I would add the friction additive as well.

Ya a few initial moans and groans along the way are not uncommon. Grinding and loud clunks are more concerning. You dont need additive for a torsen although i have noticed some use it and claim it makes it quieter. Dunno. I run a Torsen and use Shell 75w90 full syn lube. Some guys run ATF with a Torsen. I'm not so certain how good that is for the gears but i bet it frees up a few ponies from less friction.

Ya a few initial moans and groans along the way are not uncommon. Grinding and loud clunks are more concerning. You dont need additive for a torsen although i have noticed some use it and claim it makes it quieter. Dunno. I run a Torsen and use Shell 75w90 full syn lube. Some guys run ATF with a Torsen. I'm not so certain how good that is for the gears but i bet it frees up a few ponies from less friction.

Thanks for the comments. I just returned from the dealer and bought GM synthetic fluid and some additive. I noticed that when I originally drained out the factory fluid, it reeked like fuel oil while the replacement oil did not smell much at all. I noticed that both the GM fluid and the additive stink a lot more in the container, especially the additive. So I know I will be putting in the same stuff it had before. I am pretty sure the factory fill had the additive in it, or someone put it in at some point. I know the differential was opened under warranty more than once.

Ya its the sulpher. Blech it reeks. Nasty stuff. Stock ten bolts are like russian roulette. Some guys take em to 11's... others ( like me ) blow them with 14 second dream machines on street radials. Still might as well run it til she blows


good luck