Gear Break In???

[Chevyboy96]

I have a question on the break in. I know 20 miles the let it cool for about 60 minutes. My question is what speeds or loads should this be at? 20 miles at 40 mph with out stoplights, 60 mph on the highway, or 35 mph in town with stoplights, etc.?
And the rest of the 500 miles does it matter like the first 20 miles?? Say 50 miles to Portland to visit my sister at 70 mph? Or should it be kept to a certain type of driving? I know not to tow with it already but what type of driving for the4 break in period?

Thanks as usual, you guys are always a huge help.

[HalfFastFord]

Second part to this question is : why is it needed?
I've never seen anyone do this to a new vehicle. They buy it and drive it and never have r&p problems. What's the justification of break in?

[Dhmoto111]

Originally Posted by Chevyboy96

I have a question on the break in. I know 20 miles the let it cool for about 60 minutes. My question is what speeds or loads should this be at? 20 miles at 40 mph with out stoplights, 60 mph on the highway, or 35 mph in town with stoplights, etc.?
And the rest of the 500 miles does it matter like the first 20 miles?? Say 50 miles to Portland to visit my sister at 70 mph? Or should it be kept to a certain type of driving? I know not to tow with it already but what type of driving for the4 break in period?

Thanks as usual, you guys are always a huge help.

i always just break it in with normal driving


just drive it around for a little while, let the diff cool then your are done just dont tow for 500 miles thats the main concern. you dont want to overload it before its broken in


its also recommended you change the diff fluid after 500 miles to remove metal particles or phosphorus coating from the new gears

[4x4junkie]

Originally Posted by HalfFastFord

Second part to this question is : why is it needed?
I've never seen anyone do this to a new vehicle. They buy it and drive it and never have r&p problems. What's the justification of break in?

Maybe I'm wrong, but I'm pretty sure vehicle manufacturers "break in" things like axles, gearboxes and engines to some extent during production. This would remove most of the need for the consumer to do it.
Such is not the case if new gears are installed afterward by the owner.


As for the break-in, I would avoid the freeway until you get at least 50 miles on it, in-town stop -&-go driving works real good during break-in.

[dirtoyboy]

for new vehicles there is an engine break in period for the first few hundred miles...the gear break in is included in this. Stock vehicles with stock tires typically put less stress on the components. Break in is VERY important for off road (typically larger tires) 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. The 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 seen like a balancing act but it all happens easily & passively as long as the oil keeps the gear cool while it is breaking in.
After driving the first 15 to 20 miles it is best to stop and let the differential cool before proceeding. Personally, I like to repeat this process a few times. Keep the vehicle at speeds below 60 mph for the first 100 miles. Do not tow or heavy use (read: off road) for 500 miles. If you take it easy on a new ring & pinion and keep it full of high quality oil, it should last a lot longer. and yes, change fluid after break in.

[KILLER"B"3]

OEM gears don't need the "break in" procedure that most after market gears sets need. You have to wear the sulphide finish off the gear hence the break in. They get really hot during the break in as it wears the finish off(just like breaking in a cam in a motor). That is why you keep it at a low load value. I do 3 20 minutes drives at 55 constant speed. No load shock load for 200 miles, no towing until 500 miles.

[Chevyboy96]

What about the front gears?? How do you break them in???

[4x4junkie]

Originally Posted by Chevyboy96

What about the front gears?? How do you break them in???

Stick it in 4x4 and drive it about 20-30 miles or so on dirt or gravel roads. After that, you can start putting more load on it, although try not to shock-load it (bouncing while on the throttle) for at least another 100 miles.

BTW, you HAVE to have a load on it for it to break in (work-harden) the gear teeth. The common suggestion of just locking the hubs in and leaving the t-case in 2WD (or vice-versa) won't work for this.

[Chevyboy96]

Originally Posted by HalfFastFord

Second part to this question is : why is it needed?
I've never seen anyone do this to a new vehicle. They buy it and drive it and never have r&p problems. What's the justification of break in?

Here is Randy's R&P say on the issue:

Do we really need to break in a new gear set? I have heard many people say "When I bought my new truck, no one ever told me to break in the ring & pinion." Whenever we are blessed enough to afford a new vehicle, we take it easy on the engine for the first few hundred miles. While we are pampering the engine (probably for the last time ever), the ring & pinion set goes along for the ride and gets a chance to break in before we hammer the throttle.
In most stock vehicles with stock tires there is seldom a risk of a burned gear set.

[Chevyboy96]

:biggrin:
Gears are in and I got the truck back about an hour and 1/2 ago. Took her for ashort drive and letting her cool down now. Meanwhile I reprogramed for the new gears. All set now The shop put about 20 miles on it before I got it back to check everything out and I just put on another 15 or so.
I am going to put on another 20 or so before work and some more in the morning for a total of about 85 miles. Think it would be ok to go on a 48 mile drive each way to my sisters tommorrow before work? 2 lane highway 50-55 miles an hour and a couple towns in between at 35 mph. About 2 1/2 hours cool off time while I'm there.

[4x4junkie]

Should be OK.

If you have the little 10bolt rearend in there with those 315s (35s), you might pull off halfway through the 1st 48 mile trip going there and let it cool once just to be safe.

[ljschnel]

Originally Posted by 4x4junkie

Should be OK.

If you have the little 10bolt rearend in there with those 315s (35s), you might pull off halfway through the 1st 48 mile trip going there and let it cool once just to be safe.

x2

Just to understand why you have to let them cool between drives while first breaking them in, touch the diff after your 48 mile ride. I guarentee it will be pretty damn hot!

[Chevyboy96]

Originally Posted by ljschnel

x2

Just to understand why you have to let them cool between drives while first breaking them in, touch the diff after your 48 mile ride. I guarentee it will be pretty damn hot!

Actually it was quite cool after. Warm but not hot.

[ljschnel]

Originally Posted by Chevyboy96

Actually it was quite cool after. Warm but not hot.

Wow. When I was breaking in gears on my truck the diffs would get SO hot after thirty or fourty miles! I could tell when they were broken in. It took about 2 or 3 hundred miles before the rear stopped getting so hot. The front I don't know so well. Just took it easy on it the first couple times off road, did some fire road driving to heat 'em up a few times and called it good.

[Chevyboy96]

Yea, by the end of the drive yesterday I had about 200 miles on them. I have taken it out about 3 times to work the front gears.

[4x4junkie]

Probably the winter ambient temps keeping it cool. You should be fine then.

I did the gears on the 8.8" in my Bronco II (5.13 and 35s) and 1st trip out (August summer day) I felt it after only about 20 miles and almost burned my hand on it.