Heat Cycling new gears?
07-30-2007, 10:53 PM
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Heat Cycling new gears?
Just got a new set of 3.73 installed and I forgot to ask the guy who put them in if I should heat cycle the new gears. I've heard different things from different people some say i should do 3 part heat cycle(50miles the cool down, 50 miles cool down, etc.) and others say it should be fine from the get go. Anyone know for sure one way or the other?
07-31-2007, 07:15 AM
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Re: Heat Cycling new gears?
You've been talking to off-roading people, haven't you...?
Most of the break in stuff I'm familiar with is for trucks with low gears and big tires, etc. that make a lot of heat from big loads (from big tires, low gearing torque, etc). The heat cycling isn't for the gears, it's to allow the oil to cool down. If the oil gets too hot before the gears mate and work harden, the oil will break down and the gears will burn. Once the gears mate and work harden, the oil won't get as hot and this isn't a problem. For cars you can usually drive normally (sanely) for a few hundred miles to keep the loads moderate during break in. The loads aren't as high, the heat generated isn't as much. I've heard that 15-50 miles is usually the rule of thumb for first time drive and cool down, but this is a big debate. This is another case of applications being different, so what is necessary for one isn't needed for something else. This has to do with how big your gears are, how much power, etc., also. A Ford 9 inch in a KA 240 won't get very hot, but a 1985 SUbaru diff in a Mustang would... Just off the wall examples to make a point, everyone simmer down.
Basically you're trying to get everything to work harden before putting full load on it. Then it's strong enough, and you're fine. If the gears aren't highly loaded, the temp is fine and fluid breakdown isn't a problem.
Most of the break in stuff I'm familiar with is for trucks with low gears and big tires, etc. that make a lot of heat from big loads (from big tires, low gearing torque, etc). The heat cycling isn't for the gears, it's to allow the oil to cool down. If the oil gets too hot before the gears mate and work harden, the oil will break down and the gears will burn. Once the gears mate and work harden, the oil won't get as hot and this isn't a problem. For cars you can usually drive normally (sanely) for a few hundred miles to keep the loads moderate during break in. The loads aren't as high, the heat generated isn't as much. I've heard that 15-50 miles is usually the rule of thumb for first time drive and cool down, but this is a big debate. This is another case of applications being different, so what is necessary for one isn't needed for something else. This has to do with how big your gears are, how much power, etc., also. A Ford 9 inch in a KA 240 won't get very hot, but a 1985 SUbaru diff in a Mustang would... Just off the wall examples to make a point, everyone simmer down.
Basically you're trying to get everything to work harden before putting full load on it. Then it's strong enough, and you're fine. If the gears aren't highly loaded, the temp is fine and fluid breakdown isn't a problem.
Last edited by Fabrik8; 07-31-2007 at 07:25 AM.
07-31-2007, 08:19 AM
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Re: Heat Cycling new gears?
every truck rear diff i build gets driven 100 miles before i release it to the customer, but that is cause the ones we build are for idiots that pull 20k behind an F350.
standard gears in a car dont need any break in as far as i am concerned, just the test drive to make sure that the gears are quiet and such. the main thing is to make several figure 8's in the parking lot, then come back in and reset the fluid level. i have had almost half a gallon have to be added after doing that (it sends the fluid to the outboard ends, namely the axle bearings and tube)
like anything else, break it in like you are going to drive it.
standard gears in a car dont need any break in as far as i am concerned, just the test drive to make sure that the gears are quiet and such. the main thing is to make several figure 8's in the parking lot, then come back in and reset the fluid level. i have had almost half a gallon have to be added after doing that (it sends the fluid to the outboard ends, namely the axle bearings and tube)
like anything else, break it in like you are going to drive it.