Gear break in

[70barracuda]

So just got my rear axle back. Full rebuild, new gears, and new limited slip. Currently breaking it all in. Bunch of different but similar ways to do it. So far I've done 3 short 15 minute drives keeping it under 40 but mainly 25 to 30. Tomorrow I'm going to my buddies which is about 60 miles away, all highway. Is it safe to take it on that drive? It'll have a full day to cool down and ill keep it at 65. I have my big road trip next weekend and I need to do the 500 mile break in before that and this drive will definitely help. Thanks. 

 

[Jeep Driver]

500 miles of normal mixed driving. 

 

Don't even think about it. 

The only restriction is pulling a trailer which doesn't apply to you anyway. 

[gogmorgo]

I would change out the oil just before leaving on your road trip, then again when you get back, as a precaution. Otherwise I wouldn’t think too much about it. I broke in my new gears in my zj by putting maybe 20 miles on it around town, draining and refilling the oil to make sure there was no serious glitter, driving 250 miles down the highway to the city in one shot, turned around and came back the following day, and changed the oil again when I got home. Probably more precautious than necessary. New trucks in my work fleet go straight to work after delivery (usually a 50 mile drive) and no one worries about them. Out of 200 vehicles we’ve only lost one set of ring and pinion gears, and that truck had over 250,000 miles on it.

Break-in is less about heat cycling and more about wearing in the contact pattern in a non-violent way. Basically you’re grinding off any microscopic high point that could become a hot spot, and that happens pretty quickly. You just don’t want to overheat those microscopic points or you risk screwing with the heat treat on the surface of the gear teeth, hence being relatively gentle for the first little bit.

 

My thoughts on changing out the oil are to reduce the amount of steel dust floating around in the diff that is totally normal to have during break-in, and any possible contaminants that weren’t cleaned out properly during the install… there were actual rocks inside the axle I rebuilt for my zj. I cleaned it out as best as I possibly could, but again, there were rocks in it when I tore it down.

[Eagle]

It's not the speed that cause damage during break-in it's load. Drive it like there's an egg between your foot and the gas peddle. No jack rabbit starts or heavy acceleration.

 

[derf]

Drive it.  Take it easy.  Drain and refill when you hit 500 miles.  Check the fluid for excessive glitter.

[70barracuda]

Man driving this thing like a grandma was tough. Jersey driving is bad enough as it is, but not trying to really load it out of toll plazas and merging was rough. I took it insanely easy the for the 60 mile drive.