leafspring

Mostly they want the gears in the rear end to get the proper lashing wear pattern started otherwise noises could develop.

spdmpo

Ring and pinion gears are mostly broken in within 50 miles.

leafspring

Bearings yes, as far as gears developing the proper wear pattern, not even close.

techrep

iTrader: (1)

looks like nobody really knows...

Loki 5.0

Ford does and they say 1000 miles, yet some want to second guess them.

mister_d

Did a quick search and these popped up in other forums. I'm not sure how accurate they are but it was interesting to me.

Ram:
Engine break-in procedures Caution:
During the first 805 km (500 miles) a new vehicle is
driven, do not tow a trailer. Doing so may damage the
vehicle.
Limit speed to (80 km/h) 50 mph during the first 805
km (500 miles) of towing.

Toyota:
Your vehicle does not need an elaborate break-in. But following a few simple tips for the first 1600 km (1000 miles) can add to the future economy and long life of your vehicle:

~Avoid full throttle acceleration when starting and driving
~Avoid racing the engine
~Try to avoid hard stops during the first 300 km (200 miles).
~Do not drive slowly with the manual transmission in a high gear.
~Do not drive for a long time at any single speed, either fast or slow.
~Do not tow a trailer during the first 800 km (500 miles).

GM:
Notice: Your vehicle does not need an elaborate
break-in. But it will perform better in the long run if
you follow these guidelines:

• Keep your speed at 55 mph (88 km/h) or less for
the first 500 miles (805 km).

• Do not drive at any one constant speed, fast or
slow, for the first 500 miles (805 km). Do not
make full-throttle starts. Avoid downshifting to
brake, or slow, the vehicle.

• Avoid making hard stops for the first 200 miles
(322 km) or so. During this time your new brake
linings are not yet broken in. Hard stops with new
linings can mean premature wear and earlier
replacement. Follow this breaking-in guideline
every time you get new brake linings.

• Do not tow a trailer during break-in. See Towing a
Trailer on page 4-51 for the trailer towing
capabilities of your vehicle and more
information.

Following break-in, engine speed and load can be
gradually increased.

swiffer

Not to get off track here, but according to the break-in periods for all models it seems you can't even take a trip as soon as you get the truck. I have 500 mile round trip "get-away" planned 4 days after my new truck is supposed to be delivered. Assuming the truck arrives in time, it seems that, according to the manual, driving 70 mph for 200 miles is discouraged. Hmmmm.....

Bill G

The owners manuel says a 1000 miles for a reason... A good friend of mine a few years back bought a new GMC and hauled a loaded racing trailer right off the get go to a race about 300 miles away, not paying no mind to GM warning about the same subject. He had to have his rear end replaced within 3000 miles and he played hell convinsing GM he did not pull anything within the limits they stated in the manuel, he almost had to pay for the repair himself.. He is now a believer in following what the manual says.Better to be safe than sorry..

Take Care,
Bill G

blackknight87

1000k, is a million miles, it doesnt take that long to break in. :P

eclark53520

He should have paid for it himself. He, and people like him, is the reason everyone else has to fight for warranty work.

Always gotta screw the system.