Break In & Changing the rear Differential ?

[cowboywildbill]

Do we still have to change the rear gear oil after break in, now that they come from the factory filled with synthetic ? I was under the impression that you don't have to change it anymore. Just not to tow for the first 500 miles.

[DmaxMaverick]

Same rear end, same lube, same break in, since the 2001 M/Y. The key is to heat/cool in graduating cycles to work harden the gears w/o overheating. If you do it wrong, you will see the paint on the cover peel off. The synthetic lube will tolerate the heat well, but it can do only so much. Gleen the best you can from previous recommendations, and do what you think is right. The key is to prevent overheating, and change out the lube as soon as it settles down. The GM lube is costly, but there are alternative synthetics that work as well for much less $$. In any case, I do not recommend keeping the OEM lube past 10K. Cheap insurance if you plan on keeping the truck is to change the lube (as well as the engine oil) soon and often through a reasonable break in period. How soon, and how often isn't so much as important as is just doing it. There are too many variables between climates, driving habits, loads, etc, to state a specific interval for every vehicle.

[cowboywildbill]

Thanks for the reply. I will probably change it at about 3,500 miles then.
I changed the 02's at 1,500 miles. I always run a good synthetic lubricant in everything on the truck. That is except for the engine until it gets enough miles on it to make the switch.

[Docklobster]

Any suggestions on a good syntheic to run for heavy towing??? Dealer wants $35 a quart for GM stuff....

[DmaxMaverick]

Any suggestions on a good syntheic to run for heavy towing??? Dealer wants $35 a quart for GM stuff....

I've been using Amsoil Severe Gear 75/140 for heavy towing (previously Series 2000, but they changed the formula and the name). Mobil 1 and Redline also have good lubes. I can get a case of the Amsoil for 1/2 the cost of one change with the GM lube. I also use Amsoil Severe Gear 75/90 in the front diff, which most people just plain forget about (if they have one).

[David Proske]

Some dealers will go through a truck and top off all fluids as part of the prep. Most do not.

Both of my 2500HD's bought a different dealers were almost 2 quarts low on gear oil. Not good for the rear end due to all the heat generated during break in. Guess GM is trying to save money on gear oil.

[cowboywildbill]

Our 06 rear diff was 2 qts low also, I'm glad I checked it before I towed with it. I did drive it about 300 miles like that. I hope it had enough fluid to get the wheel bearings wet and keep them lubed. The tranny was 1 1/2 qts low also.
The strange thing is when I pulled the "top" fill plug, not the bottom one on the transfer case out, it was way over the fill hole? I let it drain to the right level. I guess it would have vented if it built up too much pressure. I had to do a double take I thought I was geezing and pulled the drain plug for a nano second. I wonder if they put the Dexron VI in there also or still fill that with the Dexron III? OH Well you know what they say, If you want it done right, Do it yourself!

[FBJR]

Some dealers will go through a truck and top off all fluids as part of the prep. Most do not.

Both of my 2500HD's bought a different dealers were almost 2 quarts low on gear oil. Not good for the rear end due to all the heat generated during break in. Guess GM is trying to save money on gear oil.

Better check mine soon :eek: Done the other changes at 1200 mi but haven't checked the rear yet. Good thing I have not towed yet :)

Figure 2 quarts for all the 1000's of trucks sold would be a pretty penny. Probally just within specs so they can they nothing was wrong.

FB

[SoTxPollock]

COWBOYWILDBILL, did you check level with the differential cold? If you filled it to the top cold, it may be too full. I usually like to top mine off when towing a good grade and pulling into a rest area while its still hot and sliding under and checking the fill level hot, just to be really sure its right. Of course you need to check the levels on your trailer and truck to be sure your're sitting fairly level when checking. I'm probably over cautious. I used Mobil 1 in mine, no problems yet 86,000 miles.

[cowboywildbill]

It was cold when I checked it, it came from the factory with too much fluid. I will get it up to operating temp and check it again, I'll let it drain some more if it is still above the fill plug. I am going to put transynd in it soon. Thanks.

[Chevy2DMAX]

How much grease is required for the change? Seems like it used to be four qts, but was revised to 3.2 or something?

[68Nova]

Some dealers will go through a truck and top off all fluids as part of the prep. Most do not.

I have been a mechanic for about 25 years, all at dealerships and have done more PDI's than can remember. Whether it be GM, Ford or Dodge or an import, an inspection sheet is filled out. On that inspection sheet it states "Check and top up all fluids" I have seen low fluids on new vehicles. Even though I shouldn't have to as a customer, I check all the fluids on a new vehicle I have purchased. I have been lucky enough not to find any low but if I did, I would be contacting the service manager and the owner of the dealership and confront them on this.

[Turbo Al]

I brought an old post back to the top of forum that has a pretty good explaination on what is happening back there -rear end break in procedures