I now have about 325 miles on my 05 d/a cc lb and i am looking for some input on break-in. I have a 26 ft tt approx. 7k lb and want to tow it NOW, however i don't want to mess up the truck. Any input greatly appreciated on how long i should wait

Manual says wait for 500 miles. Many here say go ahead and tow from day one. I did my first big tow at 300 miles. I say go ahead and tow - just take it easy for awhile until things break-in

I have always did a light breakin the 1st 2-300 miles then a light tow for 3-400 more then drive it like you stole it! Change fluids early and enjoy the truck.

Bought mine in Feb 03 and took first trip at 350 miles. Changed the rear dif fluid and towed the fiver for 3900 miles. Have 46k now with no problems.

I now have about 325 miles on my 05 d/a cc lb and i am looking for some input on break-in. I have a 26 ft tt approx. 7k lb and want to tow it NOW, however i don't want to mess up the truck. Any input greatly appreciated on how long i should wait
I'd say go for it! The rear diff is the only major concern, and the 325 miles that you've logged took care of that. Towing while respecting the powertrain, enhances the final break in/polishing process with increased cylinder pressure.

I'd suggest changing the engine oil immediately to flush out the dirt. My mileage/silicon content follows:

85 miles 44 ppm

325 miles 33 ppm

950 miles 29 ppm. I also changed filter here. MAN was that thing stuck on there!

metalhead - I would say hook it up too...I would, however, change both the front and rear differential oils very soon...You'll be quite amazed by the amount of trash on the drain plugs of both, I know I was.........

metalhead, started towin at 31 miles on the clock..kinda had too, bought the truck after my 02 died while enroute from MA to FL. Anyway, took it easy and changed rear fluids when I got home, all is great!!

I got this from another forum, hope I don't violate some rule here, but credit is given to author:



Written by "Shawn Spickler" of Off-Road.com The greatest damage to a new gear set results when it has been run for ten minutes or more during the first 500 miles and the oil is very hot. Any heavy use or overloading while the oil is extremely hot will cause it to break down and allow irreversible damage to the ring & pinion. In order to make them run cooler and quieter, new gears are lapped at the factory. However, they are not lapped under the same pressures that driving creates. These loads generated while driving, force any microscopic high spots on the gear teeth back into the surface of the metal. This is called "work hardening". Work hardening is similar to forging in the way that it compresses the metal molecules into a very compact and hard formation. This can only be accomplished if the metal surfaces are lubricated and the gear temperature stays cool enough that the molecular structure does not change. If the temperature of the metal gets hot enough to change the molecular structure, it will soften the surface instead of hardening it. This may seem like a balancing act but it all happens easily & passively as long as the oil keeps the gear cool while it is breaking in. Some of the synthetic oils on the market today can help a gear set live longer. Theses oils will continue to lubricate at temperatures where many crude oils break down. Even with synthetic oils, you should still follow the procedure for
BREAKING IN A NEW GEAR SET:
After driving the first 15 to 20 miles it is best to stop and let the differential cool before proceeding. Keep the vehicle at speeds below 60 mph for the first 100 miles. You should put at least 500 miles on the new gear set before heavy use or towing. During the first 45 miles of towing it helps to go about 15 miles at a time before stopping to let the differential cool for 15 minutes before continuing. This is necessary because not all of the gear tooth is making contact until it is heavily loaded. When towing, the teeth flex to contact completely, and cause the previously unloaded portion of the teeth to touch and work harden. All of this may seem like paranoia, but it is very easy to damage the ring & pinion by overloading before the teeth are broken in. It is a good idea to change the gear oil after the first 500 miles in order to remove any metal particles or phosphorus coating that has come from the new gear set. This is cheap insurance and a good time to discover any problems before they grow to disastrous proportions.

Judging by the last post, I would guess that I should still take it easy when I get my 5er even though I have 23k on my '04?

Our dealer didn't mention anything about a break-in period and knew more than we expected him to.

We got ours and three days later with just over 50 miles on it hauled a car back from CO to AZ (about 5k pounds). Now it has just over 1400 miles and has no issues except a squealing belt (brought up in another thread).

Good info oilburnr! $40k+ trucks, burn another tank of diesel and get some mileage on em before starting any significant towing. That reminds me, I need to change out the front differential fluid. God I love this site! JJ

My dealer recommended 5000mi before heavy towing...

I put about 500 miles on mine then started pulling with it...

I had about 250 miles on mine and towed a 10,000 lb 5ver and have had no problems with it. When I finally got my truck it was the day before I was leaving for Myrtle Beach.

Well, I don't know quite what to think. I'm an above average mechanic, and that is the first time I've ever come across anything about 'work-hardening' but it is plausable.

When I pick up my new Sierra here in a couple of weeks, I'll follow the instructions. I'll be real curious to see how warm that pumpkin is going to be after the first 15 miles etc. I just can't believe that unloaded, that much heat is going to be generated on a properly lashed gearset.

When I got my '99 Cummins, I took the advise of more or less easy varied driving for a couple of hundred miles, and then hook-her-up and head 4 z hills! Seemed to work well, at least for the engine.

Thanks for the quick input guys. I think i might try to sneak in a quick weekend camping before christmas hits. Woooooo Hooooooooooooo. Haven't been out to the hills for a while. My 02 gas burner only got "8" mpg towing to where we camp:eek: !

Yeah, well, let's say that this work hardening thing is true, for us 4x guys, how are we supposed to get the front pumpkin in shape? I'm so ignorant about the GM 4x system, is the front ring and pinion always turning?

On my Dodge with a central axle disconnect, the spiders were turning all the time, but that was it.

I had to start towing from new. Transmission went south in the old truck while on return from vacation. Got the new one to get home, only varied speed for first 500mi. At 2K changed front and rear diffs., after reading how they come low from the factory. Everything looked fine, ie fluid color, smell, and content (no big hunks). 13.6K everythings still fine, now running synthetic front and rear. Hope no long term damage. Time will tell.

Picked up my 04 back in May...500 miles later had 14,500lbs 5er hangin of her rear and movin down the road. 26,000 on her now and no problems. Changed the rear dif at 500, just put some significant time on the front dif so I'll change it this month. Other than that I'm pretty much following the manual on change intervals for everything else.

I'm new to the diesel game and I am not sure how to ask questions. I'll ask my question here anyway and see what happens! (Someone let me know the 'right' way.) My truck has almost 500 miles on it and I want to pull my approx. 8000lb trailer. The trip is approximately 250 miles one way. I'll keep the speed at 55 or less but should I stop often to allow the rear end to cool? Any other important issues?

Your '05 is supposed to come with synthetic oil in the diff (rear at least). I'd do the tow 1st to complete the "break-in", then you can think about changing the diff oil. I think the post about 1st tow may be extreme (IMHO), I'd stop at least once to check the diff temp, say after 50-75 miles and if it's not HOT, continue to your end point.

Frankly I think the whole diff break-in thang has gone over to the 4A club side of things at this point (again IMHO)... (or was it: at that point (old thread))

well, i bought my truck a couple of weeks ago, drove it "empty" for about 200 miles within a few days, then after i got my goosneck hitch in, dumped 12k Lbs on it and hauled off to work (still not pushing it hard, or for long) i now have just about 2k miles, and have yet to change anything, but will this weekend, if it has any problems, that what a warrenty is for....

According to the dealer & my own experiences with big rigs, there is no break-in period for the Duramax.

I'm really impressed with this site and all of its information...in fact I spent weeks reading it to learn about diesels and whether or not to purchase the dmax. So far, so good. Regarding the rear diff, how does one know if it is running HOT? Will I simply put my hand on the pumpkin and if I pull away screaming "Holy *&@*&@*" then I'll know that something is not right? Further, if that is the case, what do I do about it- turn around and go home?

Superdiesel states: I'll keep the speed at 55 or less but should I stop often to allow the rear end to cool? Any other important issues?"

Sounds like you are good to go. The truck will do fine, be sure to air up the tires, adjust the trailer brakes after you get them warm, and drive defensively. Enjoy! Welcome to the DP! :)

dan_diesel, you were doing so well until the "AAAA" jab. ):h You know the DP needs guys like us that run everything to ground, then to ground, then to ground! ;) Quad A's rule baby, yea! :ro)

JJ's out! :)

JJ: unfortunately I think I've been in that club since birth:) , infact, if you ask my wife, she'd vote for adding a 5th A to mine :p:

I just found myself rolling my eyes when I read about that extreme break-in procedure, and then immediatly thinking of how I'd soon be out doing it!):h

I was a machinist for more years than I like to think about. In my experiance with gears, I thought they were all "case hardened" That means, the outer metal faces of the gears are hardened with the inside metal being somewhat softer to adsorb all the bumping and banging they go through. I really didn't think you could work harden a gear face that is already so hard, that they will fracture and chip. I mean really....how much harder can the teeth get without being brittle?? Just my .02