Importance of "Breaking in" new Gears?

Conrad B

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Hey Guys,

I'm new to the forum, and didn't see anything on this, so I have a question... I just put 3.73s in my car, and I know that you're supposed to have a break in period of 500 miles. I've been doing some reading up on this (mostly on truck forums) and they say to keep the trips shorter(To keep the fluid cool) to promote work hardening. Now, these short trips are supposed to be around 20 miles, but I have a 55 mile commute I have to take 3x a week that is getting tiring in my '96 Nissan Truck. If I were to take my car on this commute before the 500 mile "break in period", would I pay for it later, and if so, how?

Thanks for any info.

Conrad
 

Shepp1691

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I put Richmond 3.73s in my car, drove "normal" for 60 miles and then started laying into it, no problems yet.... knock on wood
 

zPipes

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Dude I love comments from these type threads. OP you will get a few mixed responses, but you will see plenty of people saying shit like they beat the dick off the car straight from the shop with no problems lol.
 

Stanger00

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Had a few sets of gears put in my car and drove like an asshole right after install. The first time I had motive gears that howled like a friggin shot dog. Replaced those with FRPP's and never had an issue after that.
 

P49Y-CY

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most of the info i have seen recommends just one or two cool down cycles, then drive normally.
 

Conrad B

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Hey, thanks everyone for the quick responses. I'm going to take the car on the commute Thursday, so we'll see how it goes.

Thanks again!
Conrad
 

VirtualSVT

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I did a burnout in mine on the street outside the shop that installed them. Backed out the bay and bam.
 

BreBar21

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Had a few sets of gears put in my car and drove like an asshole right after install. The first time I had motive gears that howled like a friggin shot dog. Replaced those with FRPP's and never had an issue after that.

Out of curiosity, how long ago did you swap? Motive has been making FRPP gears for years now.

FWIW, my first set of gears was genuine FRPP version before Motive started making them. They howled like a mother****er because the guy that installed them did a terrible job. My current set is Motive and they are silent because they were installed properly. Moral: make sure to find someone who knows how to install gears in an IRS carrier and you'll be noise-free.
 

Stanger00

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Out of curiosity, how long ago did you swap? Motive has been making FRPP gears for years now.

FWIW, my first set of gears was genuine FRPP version before Motive started making them. They howled like a mother****er because the guy that installed them did a terrible job. My current set is Motive and they are silent because they were installed properly. Moral: make sure to find someone who knows how to install gears in an IRS carrier and you'll be noise-free.

Motives were put in back in 2004. Removed for FRPP's in 2009. Its pretty hard to screw up backlash and pinion depth. I will contribute bad parts and bad install. The pinion seal blew and when I found the blown seal the pinion nut was loose as well. This was found 3 years later. I retightned everything and torqued with a new seal. Had everything replaced along with carrier in 2009.

My roommate at the time used the same shop to install FRPP gears. No noise.
 

quick01snake

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Its pretty hard to screw up backlash and pinion depth.
This may be true, but if you don't preload the side bearings (you basically have to spread the case apart to get enough shims in), it will whine or howl, depending in how loose you left it. You can't just go with enough side shims until its a tight fit putting the carrier in like a solid axle 8.8, if you do that it will make noise every time.
 

Stanger00

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This may be true, but if you don't preload the side bearings (you basically have to spread the case apart to get enough shims in), it will whine or howl, depending in how loose you left it. You can't just go with enough side shims until its a tight fit putting the carrier in like a solid axle 8.8, if you do that it will make noise every time.

I'm sure that if anyone knows how to read a dial indicator and has good judgement with reading contact on the ring gear then I still stand by my original thought. It is pretty hard to screw up an install.

To add. My car was at the shop for 3 days as they reset the gears backlash to different settings. The gears made a howl on decel between 35-45mph and didnt make much noise besides there...Could of been a runout problem who knows. That set of gears sucked.
 

quick01snake

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I'm sure that if anyone knows how to read a dial indicator and has good judgement with reading contact on the ring gear then I still stand by my original thought. It is pretty hard to screw up an install.

To add. My car was at the shop for 3 days as they reset the gears backlash to different settings. The gears made a howl on decel between 35-45mph and didnt make much noise besides there...Could of been a runout problem who knows. That set of gears sucked.

You missed my point. What I was talking about with the shims has nothing to do with pinion depth or backlash. The aluminum case flexes significantly under load unlike the cast iron housing on a solid axle. If you don't set it up tight enough you will get a howl especially on deceleration. It can also cause rear end failure on hard, sticky tire launches.
 

Stanger00

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I don't have an IRS.

So you are saying it's ok to use more shims then required to minimize flex underload. Got it.

Edit: the shims that go between the carrier and axle housing do affect backlash...Have you looked up the install instructions and have you seen how thick the shims need to be to correct back lash that is .001" out of spec? If you are getting that much movement from housing flex then something else is wrong, IMO.
 
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Conrad B

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So before I go drive my new gears 55 miles one way (mostly hwy), should I not exceed a specific speed? (besides the speed limit... of course...:whine: )
 

quick01snake

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I don't have an IRS.

So you are saying it's ok to use more shims then required to minimize flex underload. Got it.

Edit: the shims that go between the carrier and axle housing do affect backlash...Have you looked up the install instructions and have you seen how thick the shims need to be to correct back lash that is .001" out of spec? If you are getting that much movement from housing flex then something else is wrong, IMO.

Yes the relative difference in thickness of the shims on one side of the carrier vs the other do change the backlash. I was saying the even if you get your backlash set correctly, on an IRS pumpkin you have to spread the case and add more shims to get the side preload correct. Otherwise, yes, when it flexes under load the backlash can change and cause noise or in extreme cases failure. I didn't realize you had a solid axle, that would negate my point for your instance.

It's one of those things that I feel there are probably a lot people not doing correctly, kind of like the whole squeaking throw out bearing deal, if you take a couple seconds to center the outer race of the TOB on the center if it, it won't start chirping after only a few thousand miles.
 
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Stanger00

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Yes the relative difference in thickness of the shims on one side of the carrier vs the other do change the backlash. I was saying the even if you get your backlash set correctly, on an IRS pumpkin you have to spread the case and add more shims to get the side preload correct. Otherwise, yes, when it flexes under load the backlash can change and cause noise or in extreme cases failure. I didn't realize you had a solid axle, that would negate my point for your instance.

It's one of those things that I feel there are probably a lot people not doing correctly, kind of like the whole squeaking throw out bearing deal, if you take a couple seconds to center the outer race of the TOB on the center if it, it won't start chirping after only a few thousand miles.

I was just making sure I was on the same page.

Do you just use a big ass pry bar to spread the case a little to slide in an extra .001"-.002" shim on the right side? Or did you fabricate some sort of turnbuckle with plates on the ends to bolt to the case to help spread? I'm curious.

OP, I would first take it around the block a couple times and see if they make any noise first before you drive it all the way home.
 

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