Breaking In New Gears

[Blue88Comanche]

I hopefully will be getting my Jeep back this sometime in the next day or so.  I have read on several forums how to break in new gears, just want to triple check.

 

This is what i have gathered:

• The first several trips must not be longer than 20 min.
• After the first several trips the diff must cool down for at least 45 min.
• No heavy acceleration
• Vary speed (if possible)
• Change diff oil after first 500 miles
• No towing during the first 1,000 miles
• After towing for the first time let the diff cool down for 45 min.

Anything i missed or should add?

 

Thanks,

[Jeep Driver]

Never heard of any of that.

[nitroxsteve]

The only thing I would do on that list is change the oil at 500miles. The gears are heat treated so no need to worry about heat cycles or a break in period. If everything is setup properly you are good to go. But that's just my opinion, I would follow the advice of the person who ibstalled the gears.

[Blue88Comanche]

most of those precautions where from a vendor from another site.. wish i saved the link for reference.

 

but good to know i may not need to follow it to the letter

[Comanchemodder]

From "Ford Differentials", 2013, (CarTech series) by Joseph Palazzolo, Page 115, Break-n procedure:

 

(I will type this the best I can since i don't have the scanner at the moment)

 

"Keep in mind that the higher offset of the 9-inch axle makes it prone to more heat generation than the 8.8 axle"

 

"The first 100 miles is the most critical.  Use the axle at street speeds of 30-45 mph and stay below 60 mph for the fist trip, which is usually less than 15 miles.  Then allow the axle to cool for 30 minutes. Repeat this process for the first 100 miles on the new gears.  Never subject the axle to full throttle or aggressive throttle accelerations in the first 500 miles because this exposes the components to excessive heat and can cause premature failure.  Also never go to the race track with the first 500 miles because the axle is not prepared to withstand extreme loads."

 

"Change the axle oil after the first 500 miles.  This removes any metal debris that was generated during the break-in and if the oil was partially overheated, it is replaced."

[Jeep Driver]

The rear end in my Ranger went out at 37K miles, 1000 mile past the warranty. At the time I was afraid to tear into it, not to mention it was my only transportation.

I took it to a speed shop in town that specialized in building racing differentials.........not cheap.

 

Anyhow, the guy never mentioned anything about a 'break in' period........I drove the S--- out of it for another 210K miles and never even change the gear oil.

[jeepsouth]

When I had my gears done on my mustang I beat on it right outta the shops parking lot! Three+ years later ,and no issues (ford 8.8 trac loc)

[nitroxsteve]

I have not built alot of small axles but I have built several very large axles and I never had to "break them in". Rebuild a rear end in a log truck and load it down and go. Rebuild an axle in a log skidder and send it to the woods. IMO you shouldnt be able to tell the difference between a ring gear and pinion with 50 miles or 50k miles. If its wearing something is not adjusted correctly. But who knows I have been know to do stuff wrong before. LOL

[cruiser54]

New cars don't need a "break-in" on their axles......

[Lurch]

I always heard no towing or heavy off-roading for the first 500 miles and change the gear oil at that mark as well. This is from two different gear specialists.

[nitroxsteve]

New cars don't need a "break-in" on their axles......

x2

[Blue88Comanche]

 

New cars don't need a "break-in" on their axles......

x2

its not a new Jeep lol.

 

while it may not be needed i am going to play it safe anyway.  I will just use the jeep to make short trips in town till i hit 150 miles then take it to work (30 min drive) 2 days a week till i hit 500 miles. the change the oil.  and may change the oil again with the next oil change to make sure the roll pin is not working out again....

[nitroxsteve]

 

 

 

New cars don't need a "break-in" on their axles......

 

x2

its not a new Jeep lol.

 

while it may not be needed i am going to play it safe anyway.  I will just use the jeep to make short trips in town till i hit 150 miles then take it to work (30 min drive) 2 days a week till i hit 500 miles. the change the oil.  and may change the oil again with the next oil change to make sure the roll pin is not working out again....

it definitely won't hurt anything to take it easy for a while.

 

I have a theory about motorcycle break in periods too. I don't think they are for the bikes but more for the rider.

[MrSimon]

Agreed, it might not be necessary, but following those break in procedures sure can't hurt anything.

 

Although I don't think the cooling down stuff makes any sense.

[Blue88Comanche]

Agreed, it might not be necessary, but following those break in procedures sure can't hurt anything.

 

Although I don't think the cooling down stuff makes any sense.

 

from what i read, newly machined parts are not perfectly smooth, they have tiny "mountains" and pores.  when new gears are "broken in" the rubbing surfaces cause these tiny "mountains" to be warn down, and leafing tiny metal particles in the oil.  the added friction from wearing those mountains down in addition to the new gears not having the oil soaked into those microscopic pores (creating a protective film) generates more heat than normal.  the metal particles in the oil can also increase wear on the bearing.  the article i was reading also said the friction heat can get hot enough to destroy new bearings and or gears.  Thus the cool down time for the first few trips..

 

That's how i understand it anyway.  It makes sense to me...

[sloride]

That does make sense.  But what machine parts used in production cars/trucks are perfectly smooth?  Machine it and kick it to the curb as quick as they can has been my experience. 

 

The machine finish can't be any smoother for after market parts can it?  Would the factory, lets say, use 125rms finish to machine their gears and the after market do theirs say at 63rms which would be smoother than factory?  Or is it the opposite, thus requiring a break in period for aftermarket parts that would be rougher instead of the smoother factory parts?

 

Either way you slice it, the truck is your baby.  Treat it like such if you want.  No one will fault you for that.

[skidoo_j]

I treat gears like an engine. If you just did a rebuild on an engine unless it's for racing only you are easy on it. I would follow what you found. I've witnessed new gears in, filled the diff and took off for a 200 mile run. Somewhere between where they were installed an my place the gear oil drained. Needless to say we drug the vehicle onto the trailer because the gears had welded. When i asked the owner of the vehicle if he drove easy he replied like others have on here... "the mechanic didn't say anything about taking it easy ". Needless to say he played with his new high ratio gears, and had smoked his tires right out of the shop. He bragged about being able to spin his 33". Had he taken it easy done a cool down and checked his fluid he wouldn't have had to replace his gears in less than 200 miles.

 

The mechanic didn't cover it because they were used gears.

 

Bottom line Nothing you listed would cause any negative issues. Would it benefit the gears I would say it's more than likely going to prolong their life rather then negate. But it's not likely anyone can quantitatively prove or disprove a "break in period" because someone would have to test a set of gears and pull them at each step to compare and contrast to a set that was not babied. And even that test would be inconclusive because the gears are not identical and the backlash would not be identical from install to install etc. Bottom line is if the manufacture warranty says anything about it, follow it to a tee and document it in some way.

 

I'd relate it to breaking in a gun. Some people get a gun and just shoot the $#!& out of it and never clean it and argue that a dirty rifle shoots better. If I get a new rifle I shoot it twice, clean it, shoot it thrice clean it, shoot it 5 times, clean it, and each of the rounds are shot making sure I never heat the barrel. From there on out I clean the rifle after every trip to the range typically 5-10 rounds. For my long range rifles i clean at range often after every 3 rounds. A new handgun I'll clean after 5 rounds, then after that it gets cleaned every couple hundred rounds.

This is what i have gathered:

• The first several trips must not be longer than 20 min.
• After the first several trips the diff must cool down for at least 45 min.
• No heavy acceleration
• Vary speed (if possible)
• Change diff oil after first 500 miles
• No towing during the first 1,000 miles
• After towing for the first time let the diff cool down for 45 min.

 

 

I'd add check fluid level several times during first 500 miles. Then atleast twice after the change. $20 worth of fluid isn't worth destroying 2500 worth of gears, bearings, locker.

[xjrev10]

New cars don't need a "break-in" on their axles......

When I bought my new 2012 Ram 2500, they did tell me at the dealer that heavy towing is not recommended within 1000 miles.

 

I have a friend that bought a brand new super duty, less then 500 miles on the truck, loaded up 3 HEMI JKs and headed to the Black Hills. (About 900 miles away) No issues besides not be able to keep up to a similarly loaded 5.9 Cummins!

 

Changing gear oil isn't going to hurt anything. I would change it once with new gears and I have been told in the past if a locker is installed, you should change it 3 times. ARB was the locker we where talking about. Changes after trail rides or every few hundred miles.