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Old May 18th, 2007, 05:33 PM   #21
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exellent topic, just what i needed.........

i am going to miffy spring fling next weekend and i will be installing new gears frt/rr on tues nite (knock on wood that they come in) so this was right up my alley

and the question on frt gear break in, not everybody has engaged frt axle while driving in 2wd, i have hubs to lock unlock--so should i drive it with the hubs locked in to break those in?
It should be locked with the hubs and driven as straight as possible being in hilock. If that is to scary just drive with the hubs locked. It is better than nothing.
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Old May 19th, 2007, 11:25 PM   #22
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I see Jesus covered it . manufacture recommends break in period .

Metal will change is molecular structure as it warms and cools , Some types of metal actually harden in this manner . Im not sure about the steel gear sets are made of .

Also they do as some one stated wear together , I also recommend changing diff fluid after 500 to 1,000 miles . There will be metal frags in it . Not enough to see unless something is wrong but none the less the gears will scuff off a small amount of metal wearing into each other .
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Old May 20th, 2007, 05:41 AM   #23
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Interesting topic. To add some information though, a hardened gear will not lose it's hardness till getting into the 700-800 degree F. range. At 450 degrees, the problem is not hardness failure but rather a start of oil breakdown. I highly doubt that it is getting to that range either because a standard buna oil seal is only good for up to about 350 degrees and I don't think you see a failed oil seal if a gearset fails right away. Has anyone had this happen?

Yes, there is higher heat generated right at the contact point just like in the cumbustion chamber of an engine.

I have been involved in designing gearboxes for machinery for years. The concept for runin there is that the manufacturing process is not perfect and the runin allows for small high spots and imperfections to "self lap". As stated before, that is where the smooth shiny pattern shows up after some running.

It was mentioned that factory gears are run in as sets together. Is this really true? When I have been in the assembly plants it seems to me (a little foggy here) that they just match mark them as best as possible & throw them in.

Ironically, I have bought 2 new trucks in the past 7 years that I literally picked them up and hit the highway out of town on business. Once a straight drive to Cincinatti and once to Cleveland. Never a probelm.
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Old May 20th, 2007, 06:44 AM   #24
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Interesting topic. To add some information though, a hardened gear will not lose it's hardness till getting into the 700-800 degree F. range. At 450 degrees, the problem is not hardness failure but rather a start of oil breakdown. I highly doubt that it is getting to that range either because a standard buna oil seal is only good for up to about 350 degrees and I don't think you see a failed oil seal if a gearset fails right away. Has anyone had this happen?

Yes, there is higher heat generated right at the contact point just like in the cumbustion chamber of an engine.

I have been involved in designing gearboxes for machinery for years. The concept for runin there is that the manufacturing process is not perfect and the runin allows for small high spots and imperfections to "self lap". As stated before, that is where the smooth shiny pattern shows up after some running.

It was mentioned that factory gears are run in as sets together. Is this really true? When I have been in the assembly plants it seems to me (a little foggy here) that they just match mark them as best as possible & throw them in.

Ironically, I have bought 2 new trucks in the past 7 years that I literally picked them up and hit the highway out of town on business. Once a straight drive to Cincinatti and once to Cleveland. Never a probelm.

Yes they are matched .. The pinion is machined to match the ring gear it is mated with. That is why they stamp each set with a Identifying number.

Again OEM gears are run together as a set for a standard amount of time. So brak in falls under the whole vehicle break in procedure that is printed in the owners manual.

Jim you would have not made it to the ohio border if they were aftermarket gears they would be a molten mess by then.
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Old May 20th, 2007, 07:07 AM   #25
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Bill,
I was not sure about the ring and pinion. When I worked at the Pontiac Motor engine assembly, I know they matched various ring sizes based upon the high or low limit of the cylinder bores. I thought they may have done the same with the ring and pinions.

Thanks for the clarification.
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