I just finished my first good break-in run with my new truck. 1750 miles total. 900 of it towing 9000#. I did the first 500 towing miles at 50 mph and got 13.4 mpg. On the empty run out to get the 5ver I got 21.5 at 65-70mph.

I've heard I should tow heavy and drive it like I stole it to break it it. On a few 6% grades in OD I hit 750+ EGT post turbo and I think I gave it a workout.

...ok, to my question. My buddy with a GMC warned me that he had to change his diff fluids after only 1000miles of towing?? My manual says I'm ready to tow, already have a synth fluid, and don't need to think about a change until 15,000 miles.

Is that OK??? I don't mind crawling under there and changing out the diff fluid if it's helpfull... but I will skip it if it's over kill.

Opinions?

 

I just replaced my diff lube @10,000km. I must say for that little mileage it sure was dirty and a little milky looking. So i don't think it's over kill to change it soon. I used 75w-140w syn. my truck does most of it's mileage pulling a 33ft 5th wheel.

 

I'm at 5k miles now... maybe I'll do it early.

how much is in there? I think that stuff runs $8/quart?

 

I did mine by the book at 15,000 and mine was very milky looking as well. Subsequent changes have not had the peculiar milky tint. I used Mobil One 75W-90. Any GL-5 rated synthetic 75W-90 will do. The third gen trucks do not have the requirement of 75W-140 for towing that the second gen trucks have. The third gen trucks also do not require friction modifier.

 

Go ahead and change it out. You won't regret it. I changed mine out at about 1000 miles and I'm glad I did, it was milky and nasty as all heck.
Mine now has AMSOIL from head to toe and loves it.

 

I have just over 500 miles on mine and will be changing it this weekend. The first 500 to 1000 miles produces the most heat and initial wear.

I like to get that crap out of there fairly early. I believe GM recommends 500 miles before towing and an early change interval with the 11.5 AAM unit.

Especially with the geared anti-spin unit.

 

I changed mine at 14K miles,- was real dirty. I did not like the 75W-90 'thin as water' lube in it so I put 75W-140 Royal Purple syn. lube in it. Others have complained about gear wear/scoreing and rear end whine . I feel much better useing the 75W-140, more so if you tow. Redline Syn. is another excellent brand lube that you can get in the heavier weight, or 75W-90.

I totally do not agree with those who say you should "drive it like you stole it". That is abuse and you can destroy anything if you try hard enough. I say drive it hard, work it hard, don't baby it, the mighty Cummins is the best built, most reliable engine available but I would never abuse it. JMHO

 

sounds like a good project. I'll go shopping for some lube.

What's the capacity of the axle?

 

[QUOTE]Originally posted by CAKUZ
[B] I totally do not agree with those who say you should "drive it like you stole it". That is abuse and you can destroy anything if you try hard enough.

Come on get a grip. The expression "Drive it Like you stole it" means exactly that. Don't BABY it and drive it hard because that's what its designed to do
Of course this is MY OPINION

 

I see you have a 4 x 4, if memory serves it takes just under 8 quarts to do both axles.

 

I changed my rear diff fluid last night. Found a thread on here that said the rear takes 4 qts and the front 3 qts and to tighten the bolts to 30 ft-lbs. My 11.5 rear was about 1/4" below the fill line with 4 qts (am planning to do the front axle this weekend).

As a note, the fluid smelled like the "grape juice" fluid that was in my Duramax's rear axle. That stuff is dark looking even when new. The fluid that came out of the diff looked perfect, and the gears of the axle look great. This is with 1200 mls of towing and 1000 mls of no load driving. The fluid could definitely gone longer before the change. Oh well, at least I have peace of mind knowing nothing appears to be wrong.

By the way, I liked how GM speced the axle to have the drain hole on the bottom of the axle. Made changes a lot easier.

 

MY neighbor has a 03 2500 4x4 3.73 gears 6speed.He tows a 3 horse trailer as a part tiime job.Long and short it has 105k on the odometer.Changed his diffs and tranny fliuds FIRST time in the 90k range.FLIUD looked GREAT.Got 90k out of factory tires and hardly on wear bars and brakes front have 60% or more left on them.Anyhow I wouldn't change diff fliuds any eariler then 15k.Just my 02 worth.30kwith little or no towing.

 

Must be clean because of the lack of clutch packs.

 

Did my front diff last night (the rear was done the day before). 3 quarts is too much for the front! The fluid started leaking out the fill hole at about 2.6 quarts.

 

Miles towed means less than where it was towed. Long steep hills mean heat. I stopped at the top of Cajon summit once to get gas. As I was filling, I could hear the oil in the rearend boiling. Whi knew you could not tow 9k with a 1500?