Dually w/ 70HD diff, temp warm at pinion question

[JellyBeanDriver]

Working on the ranch truck today - inspecting rear brakes.

Drove it from cold 8 miles from the ranch to my house. Crawled under the truck and inspected the drivetrain, feeling the u-joints, diff, etc and surprisingly found the diff was warm on the pinion shaft end. Axle at the wheels was stone cold. Rear cover was a little warmer but not much. Diff at pinion end was definitely the warmest part.

Surprised that only 8 miles would do this.

Normal? Can pinion preload account for this or is there something more sinister going on?

Thanks

[speedmachine]

did you check the fluid level?

[INSIDIOUS '86]

The pinion gets the most direct heat and friction from everything. You could prob go 20 miles and it shouldn't be any warmer. Check the fluid level just to be safe while your poking around down there
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[wraprail]

Have you had it apart? Change the seal lately or remove the yoke for any reason? If not then I wouldn't worry about it. As long as it has fluid,

[JellyBeanDriver]

Going to chalk this up to being normal.

The fluid level was low, but only like 1/4". Fluid condition wasn't so great though - dark and waxy buildup on the axle shafts, rear cover, etc.

Removed the cover, pinion and ring gear teeth look great. Changed fluid and took the truck back to the ranch. Crawled under and the differential was warmer this time than the trip from the ranch to my house. Granted it's a mild uphill to the ranch.

Drove home in my 93' Ford Ranger pickup, parked and then crawled under to feel it's differential. Quite a bit WARMER than the C30!

So I guess this is just how differentials are. Never in all my years have I bothered to feel one after a short drive. Would never have guessed!

[LONGHAIR]

Never seen a semi truck bob-tailing in the rain? Yes that is steam.
There is a lot of friction going on there, plus the force against the pinion. That is why I always recommend synthetic gear lube, whenever you have the cover off.