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Rear end gear

Kain

Kain

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Seen a shop put gears and a posi unit in rear diff then get it assembled and while on the lift let it run in gear with no weight on it.
what is the point of that? I thought once your pattern is right and you follow break in your golden.
 
never heard of that, was always told just drive like granny for 500 mile then check your pattern change the fluid
Does it help?
 
just seams like a waist of time, i can see putting on a dyno under its own wait but this is silly to me
 
I knew a guy who rebuilt automatics back in the 80's ,he wouldn't stand behind any of his work if the customer installed the transmission themselves , and didn't let it spin the rear wheels while jacked up for at least 10 minutes and made sure the fluid level was correct before putting a load on it by driving it..

Maybe he was just weird that way,but he had a good reputation for rebuilding and modifying automatics..very few customers had any issues with ones they had rebuilt or swapped from him..

I remember he said he worked at an AMMACO transmission shop for 25 years,but got fired because he liked to drink,and one day his boss caught him imbibing during lunch hour--he was in his truck eating a brown bag lunch and they got in an argument,so he told his boss where to go,and started working out of his garage at home..
He said his boss called him several times,begging him to come back to work,but he said no thanks..
 
It is a heat and cool process. So spinning with no load is useless.

Street Driving
Drive normally on streets for approximately 15-20 minutes, stop, and then let the rearend cool down for 30-minutes. The process should be repeated 2-to-3 times. The oil should be changed at 500 miles, don't be alarmed if this first oil change comes out much darker than when it went in as the black phosphate coating is wearing off the gears, along with a minimal amount of steel from the bearings, gears, and differential wearing-in.

Towing Vehicles
Drive at low-loads for a total of approximately 300 to 500 miles of mixed street driving (see above) and highway driving before towing any load.
 
That’s what I though without the heat just a waist of time and gas^^^
 
And yet GM and all the other manufacturers sold brand new cars and trucks without doing any "break in" ,yet the diffs lasted well over 100,000 miles ..:dunno:

How many people got their gear oil changed after 500 miles ?..probably close to zero..

Not saying it's OK to set up a diff and just run it,but it does make one wonder...I'd follow the above recommendations ..
 
Like I said it was basically used as something to do while you ate lunch but looked busy.
 
diesel4me said:
And yet GM and all the other manufacturers sold brand new cars and trucks without doing any "break in" ,yet the diffs lasted well over 100,000 miles ..:dunno:

How many people got their gear oil changed after 500 miles ?..probably close to zero..

Not saying it's OK to set up a diff and just run it,but it does make one wonder...I'd follow the above recommendations ..
Click to expand...
I have no source to quote, but I was always told the original gears had a break-in cycle done in the factory.

Similarly when you install used gears there's really no break-in period or similar darkening of the oil.
 
The 500 mile requirement probably isn't necessary, but it's cheap insurance and probably not a bad idea to pull off the cover and make sure everything is working properly.
 
I mean how many guys change gears then immediately go down the drag strip?
 
Well a drag racer may never get driven 500 miles, so you need a different kind of break-in. But back in the muscle car era some cars would get test driven down the drag strip, which is just one of the reasons new cars come with gears already broken in.
 
Plus, almost every drag racer will jack up the rear end and warm up the drivetrain before rolling into the staging lanes....
 
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