Locking Rear Break-in

[gmhunter]

A quick question about breaking in a locking rear end. I have a 2003 2500HD with D/A. I have read and understand what is said in both the owners manual and from these message boards concerning taking it easy the 1st 500 miles and only going 50 or so miles and then taking a break. My quesiton is, what justifies an appropriate weight for break-in. I have two boats, one that weighs about 6,000 lbs and one that weighs about 2,000 lbs. Is towing the 2,000lb boat enough to justify a "break-in tow" or do I have to have tow something bigger? I was going to pull it around this weekend for maintenance and fishing and wondering if it can be part of my 500 break-in. Thanks for the help.

[RyanbabZ71]

for the 1st 500 miles you arent supposed to tow anything

 

then after that tow away but after 500 miles of towing you SHOULD change out the rear differential fluid

[gmhunter]

Sorry, my mistake, I already have about 3,000 miles on the truck, just never towed anything yet. Thanks for the critique.

[RyanbabZ71]

oh ok tow away then but after 500 miles it is suggested (in the manual) to change the rear diff fluid

[BlackSilver]

You're good to go with any tow you want.  My manual says nothing about changing the rear diff, and I specifically asked the dealer who said "what for?"  (Maybe if you had a 1500 you should     )

[Shaners]

I think on the 2001 HD's and newer, just drive it like you stole it.

 

They switched the rear gears over to full synthetic in '01, and my dealer says not to replace it ( my manual says nothing either).  Just check levels and add some if needed.

 

My '00 said to change after 500 miles of towing...

[mr_jafo]

My 2001 K2500HD states in the manual to change after 500 miles of towing. Takes synthetic and it is expensive from dealer. Page 7-9 in my owners book.

[Bob G.]

I don't remember reading anything in the manual about changing the rear diff fluid at 500 miles. Seems a little excessive to me, since I'm already at 16000 miles! I don't have my manual with me, but I think it calls for rear diff fluid change at 50k miles.

 

Bob G.

[Shaners]

My 2001 K2500HD states in the manual to change after 500 miles of towing. Takes synthetic and it is expensive from dealer. Page 7-9 in my owners book.

We must have different manuals.  Page 7-9 in my manual is the beginning of the scheduled maintenance section.  It says at 7500 miles, to "Check rear/front axle fluid and add fluid as needed".  It tells you to do that every 7500 miles, but never mentions anything about changing it.

[Budz]

As RyanbabZ71 said change the fluid after 500 miles of towing. Also when you start towing, heat cycle your rear a few times. After the 50 mph and less inititial breakin, the ring and pinion are seated and worn in at the contact patches of the gears. When you tow a heavy load, the contact surfaces of the ring and pinion will be differrent. Time to break in again.  Once again keep the towing speed 55 mph and below. After towing for 20 minutes, the gears will be heated up and it's time to stop and let  the rear end cool down. Do this a couple of times before continuing your tow. After a few heat cycles your gears are ready to complete the towing breakin period uninterupted. After 500 miles of towing, change out the differential lube. Shaners, you really trust your dealer?

[RyanbabZ71]

i didnt tow anywhere near 500 miles but at 18K miles i changed my rear diff fluid and there were alot of metal shavings around the magnet.  Sure glad i spent the $$$ and time to change the fluid.

 

However just remember a few of us warned you.  Hindsight is 20/20

 

[Shaners]

Shaners, you really trust your dealer?

Budz,  I actually do trust the service dept at my dealership.  They are top notch!!!  Also since I had a '00 1500 and a '01 HD, there is definatly a difference in the procedure for rear gear maintenance.  I read it in the manual myself!!!

[Gunruner]

I'm puzzled.  I had a 2000 1500 2X4 4.8 V8 with a locker and 3.73 gears.  I put about 1000 miles on it and towed a 5,000lb trailer for 40,000 miles and not a problem.  Didn't change or add any fluid to the rear locker ever.  Now I have a '03 K2500 4.10 locker and 6.0L V8.  I've read every page in the owners manual and there isn't ANY suggested change time for the front or read diffs.  All that is mentioned is check and add if low. 500 mile change?  I put 98,000 hard towing miles on a '94 Chevy K1500 and front or rear never got changed, when checked they were always full.  Maybe these new synthetic lubes are the problem(excessesive cost and maintenance).  Regular gear oil never gave me a problem or malfunction in 38 years and over 750,000 miles of driving.  Let's use me as a test bed.  I will not change mine and I'll report any problems here on the forum.  I do my first tow today at 3,200 miles on the new truck.  It will be less than 200 miles to adjust hitch, brake controller, and will be small rolling hills, 65 degrees.  I do change my engine oil at 3,000 miles or less without fail.  I use Havoline 5W30 and AC-Delco PF-44.  Oil change cost is $9 and my time.  Here we go.................

[Budz]

There may be different breakin recommendations for 1500 and the 2500 HD. I've had some problems in the past with not breaking in the rear (ran hot got noisy with age) of the 1500 series axles.  I have taken all precautions in breaking in the axle with my 2500HD. I'm a believer in doing what I can for preventive maintenance.

 

Sorry, I don't remember the source but from a post that I saved from (?) forum:

 

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.

"From Mr. Ralph Holmquist of Eaton, the maker of the locking differential:

"The maintenance schedule for the rear axle was developed by American Axle &

Manufacturing and GM truck based on multiple tests. The Eaton locker does

not require additional maintenance nor does it add heat to the lube. The

lube will darken due to the carbon wear on the clutch surfaces, much the

same as a disc brake pad & rotor. This does not damage axle components such

as seals or bearings. However, a new axle can produce excessive

temperatures (plus 350 degrees F) due to the ring & pinion breaking in that

will break the lube additives down. Avoid high loads, trailer towing and

high speed extended driving during the initial break in of the vehicle.

After the break in period axle temps will level at a much lower figure.

Lube changes are a good idea because the additives are replenished and

contaminates such as casting sand are eliminated. The axle is filled at the

factory with a synthetic 75w90 GL5 rating made by Texaco under part # 2276.

The GM service # is 12378261. This is the only lube we have done extensive

testing with to insure locker compatibility. The only negative to using one

of these other lubes is an increased potential for clutch chatter. This

really doesn't hurt anything and can be corrected by changing the lube. I

noticed in the latest GM owners manual the term "or equivalent" when

referring to the lube specification. Look for a GL5 rating on the bottle to

make sure the ring & pinion, seals & bearings are protected. Limited slip

additive is not needed."

 

 

Make your own call. It sounds reasonable to me no matter what I read or hear. Keep in mind that TSBs are issued when problems crop up and engineers find the cure.

 

Budz

'03 2500 HD D/D CC SB

[BDBWTE]

Phhh break in....blah blah blah... I broke in my truck with 227 miles with a 10,000lb Bobcat... Rear end fluid??? Yeah we have three full time mechanics at work and we don't change rear-end fluid until the rear ends are out.  We have a K1500 Chevy my work truck that has 279,000 miles with the original rear-end fluid in it.  We check the level and make sure it doesn't have any water in it then let it rock.  If the HD lets me down and doesn't perform that same way I won't buy a new chevy for the rest of my life.  Changing all these fluids is just a pain in the ass.  I'm surrounded by fixing equipment all day and I have all the equipment at the shop to tear the truck down to a frame and rebuild it but I don't do the little stuff.  You guys have a garage and Craftsmen tools and do this..  I'm not knocking you guys at all I just think it's funny that I don't take the time to put the truck on the lift and do the little stuff...as a matter of fact none of us do... We make sure the Oil and Tranny is changed and full but that's it... Whoo hoo go us..