Is the factory 4.88 third different from the others (4:10)?

[elripster]

That's understandable. I'm not looking to get rich off the the stockers either, just offset the costs of gears and tires.

Frank

[RobG]

So what size tires are you putting on your IFS that you need 5.71's? 37's?

Just Curious.

[slosurfer]

So what size tires are you putting on your IFS that you need 5.71's? 37's?

Just Curious.

The autos are really geared too high from the factory. Stock with 4.88's and 31's it is already behind and will hardly hold overdrive. I've got 33's and the 4.88's and it is really a dog. I was going to 5.29's but now I'm pretty sure I'm going to 5.71's also.

[RobG]

Yeah, The 3.0 Auto is a little sluggish but I thought 33's with 5.29's were OK. I'm a little skittish on 5.71's with all the bad press they used to get.

I've run 33's on 4.88's and 5.29's with my V6-Auto. 5.29's are better but still can't hold a grade on the Freeway, 4.88's + 33's are definitely drivable. If I didn't need a new front diff I wouldn't have regeared the 4.88's. I tend to think more of the long range plan these days so I don't wind up paying for things twice. If you plan to do a 3.4 or 5spd swap with 5.71's you may be geared too high. Many Pirate guys have stepped back from 5.29's to 4.88's for strength reasons, granted alot of those rigs never see the street, much less the freeway.

[blknblu]

I'm a little skittish on 5.71's with all the bad press they used to get.

For anyones consideration that shares that concern. Sounds like it's not an issue for RobG anymore.
http://www.gearinstalls.com/410suck.htm

[elripster]

The pinion on the 5.71's is the same as the 5.29's so there is no added risk between the two. Now the set up is very critical on each so it's good that you either have the right tools and know what you are doing or have a shop that does. The shop I intend to use will have the rear gears cryo treated for $65 for some added strength. Also, they will only do the job with the high end gears, I would not use the cheap ones where they use 4 cyl gears with a spacer.

Our engines are not terribly powerful so a good setup with quality gears will last.

Frank

[Robinhood4x4]

The sizes might be the same, but the reaction forces are not. Put 100 ft-lbs of torque into a 5.29 and you get 529 ft-lbs back. Put 100 ft-lbs into a 5.71 and you get 571 ft-lbs back. Thats a 7.3% increase in stress.

[blknblu]

It will be interesting to see Zuk's re-write on this.

[elripster]

I would think the reaction forces in the gear teeth themselves will be the same since that is a function of the torque applied to the drive shaft. For example, if I were to perform FEA on the gears I'd assume the rear wheels were magically locked and someone dumped the clutch (which I don't have so that could be good). I would then take a look at the resulting tangential force from the combination of static and dynamic torque acted on the ring gear tooth and reacted by the pinion tooth.(or vice versa,doesn't matter) At that point, the ratio is not an issue beyond converting the tangential loads based on the radius of the pinion.

Now beyond the gears in , for example, the carrier and splines, a greater torque/stress will be felt due to the increased leverage from the lower ratio gears. That translates into a high tangential force at the wheels for greater acceleration.

To take this one step further(I'm glad we are having this thought exercise, I'm realizing somethings), if me the driver is targeting a given rate of acceleration to match that of traffic, it will take less torque and the drive shaft to produce that rate which translates to less torque/stress on the gears for typical partial throttle driving.

Frank

[elripster]

One thing I should add is that my truck holds overdrive rather well. For example (for those of you familiar with San Diego) if I leave our place in Mission Valley and head to Vista to see my folks, I can set my cruise control at say 75 and my truck will shift out of OD two times. One is climbing 163 out of the valley. The next is cresting the top half of that last hill before 78. Those are fairly steep climbs. I really want to preserve the drive quality as much as possible. I don't have to get my foot in it all the time like I hear others having to do and I think that will go a long way towards engine and transmission life both of which are not easy or cheap to rebuild.

Frank