Break in on new ring and pinion

Mickey Bitsko · Feb 7, 2015

Just installed new Yukon R&P, break in instruction read , No towing or hard acceleration first 100 miles then change out gear oil @ 500 miles .
Will the gear oil be that contaminated after 500 mi ? Of course I will do as recommended , however I read in the new car owners manual it's recommended to replace factory gear oil @ 10-15k miles.

Why the difference ? Just curious :dunno:

Rowdy Fitzgerald · Feb 7, 2015

The oil will have lots of fine metal particles and the gears will have gotten very hot which will break down the viscosity.
The oil will become thinner and won't lubricate as well essentially. That causes the gears to fail due to being over heated.

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Mickey Bitsko · Feb 7, 2015

Thanks Rowdy, I'm leaving on a 250mi. one way trip this morning, going over a couple mountain passes, not hauling any weight, will this be a problem?

Captain Ledd · Feb 7, 2015

They do the initial break in at the factory.

Edit, I would consider the mountain passes counting as weight. It's going to be working that much harder against gravity. It will take more throttle, and therefore more power to the rear axle, just like pulling a trailer.

The gears will actually heat-treat themselves in the break in period, forming a thin layer of martensite (I think?) but a hard outer shell at the least. This is what gives your gears longevity, and if you don't take the steps to form that layer, your gears will wear out more quickly because it's rubbing against softer metal. Even with the very best and most precise manufacturing and installs, there is some mis-match, and it will result in increased friction, and with the amount of power and weight being transmitted through the rear axle, HEAT. Heat will kill even a properly broken in gearset.

I honestly would take another vehicle if mountains are involved, and that'a a long time to drive all at once. Short trips are better letting the gears heat up and then completely cool, forming a little bit better layer every time. Truthfully, even if you had just ~250-300 miles on the set I think you'd be ok, but not so much right after the initial break in.

Rowdy Fitzgerald · Feb 7, 2015

Ya like Ledd says I would take something different.

If you could drive for like 50 miles then stop for a hour, drive another 50 and stop for a hour, then drive 75 miles and stop for another hour, then drive the last 75 I don't think it would hurt them.

But imo it's absolutely gonna ruin the new gears driving that far through mountains without stopping to let them cool completely several times.

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Mickey Bitsko · Feb 7, 2015

Well guys, I made it , Rowdy, I followed your suggestion only kept it to 50-60 miles then a cooling period, never got so hot that I couldn't leave my hand on the cover for 5-10 seconds at least. Took the scenic route and did a little fishing on the Arkansas river.
I don't believe I overheated the rear diff, the front diff never got passed barely luke warm to the touch, Also I was able to keep my speed down to 50-55 max.
I suppose time will tell.
Also, I could have spared all my anxiety if I had another rig to drive.
Thank you again for your very good advice.

Rowdy Fitzgerald · Feb 7, 2015

Have you changed the oil yet? There should be a small amount of metal particles but it should be very minimal.

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scotts90ranger · Feb 8, 2015

I got the cheap Nitro (I think, whatever the cheaper version that Jim carries) gears when I did mine, I didn't go too careful with the breakin and the oil looked nasty when I changed it at the recommended 500 miles, the contact points of the gears didn't look great either, put it back together and tried my best to forget about it (and put a couple strong magnets in the diff cover) for about 4 years, last weekend I swapped to disc brakes and had to dig in, the contact areas were nice and smooth, and the backlash was even reasonable still

. I was hoping everything would be fine, and it was.

I don't think they're quite as picky as most people think, I'm pretty sure you are gonna be just fine.

Mickey Bitsko · Feb 8, 2015

I reread the break in instructions , first, drive 10-15 miles and let cool completely , second, do not "hard accelerate first 100 miles" , Three, change oil @500 miles

I have followed those instructions [ haven't changed the oil yet only 275 miles]
but I will @ 500.
But in retrospect I'm glad I followed Rowdy's recommendation just for piece of mind.
Curious to see the oil, I'm sure it'll be fugly..

Mickey Bitsko · Feb 8, 2015

scotts90ranger said:
I got the cheap Nitro (I think, whatever the cheaper version that Jim carries) gears when I did mine, I didn't go too careful with the breakin and the oil looked nasty when I changed it at the recommended 500 miles, the contact points of the gears didn't look great either, put it back together and tried my best to forget about it (and put a couple strong magnets in the diff cover) for about 4 years, last weekend I swapped to disc brakes and had to dig in, the contact areas were nice and smooth, and the backlash was even reasonable still . I was hoping everything would be fine, and it was.

I don't think they're quite as picky as most people think, I'm pretty sure you are gonna be just fine.

Are you running synthetic or does it matter one way or the other?

Captain Ledd · Feb 8, 2015

Synthetic is kind of an economic waste for 500 miles of use. I'd just use dino stuff. I put full synthetic in mine after the break in period though.

Mickey Bitsko · Feb 8, 2015

Thanks Captain Ledd, No my break in is regular Napa brand 80-90[ probably Valvoline] ,
Do you think synthetic is better than regular petroleum 80-90 , I doubt the cost is significant .

Captain Ledd · Feb 8, 2015

In most cases, no. Unless you see some really cold or extremely heavy duty use. If I did it again, I'd just put the regular Ford spec stuff in.

Mickey Bitsko · Feb 8, 2015

I 'm not sure what I'll put in yet, It gets cold here from time to time but haven't had a problem with viscosity , however I can feel the need for more power to get moving on those -20* mornings fairly rare now though with global warming and all. :icon_rofl:

Break in on new ring and pinion

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