Hey there, was checking my vehicles settings when I noticed it has my axle ratio at 3.21 . . . I could have sworn 2008 4.7L auto 2wd was 3.55 stock . . . if so and I hear back from you guys, I'll be fixing that immediately.

Thanks.

 

There were 3 ratios available from the factory, 3.21, 3.55, and 3.92. 3.55 was the most common, most of the trucks with the factory tow package got 3.92s. I can't imagine having 3.21s in a quad-cab, that thing must be a dog. Take that thing to a gear shop, you should be able to put in new gears for $800 or less, and as long as you've got it there, put in a good LSD and save yourself the exploding diff headache.

 

Thanks for the quick reply Pyro, I actually have Motive 4.56 gears waiting to be installed. But haven't had a day off to get to the shop. Isn't there a way to check the axle ratio ? I coulda swore when I first joined I read up you can jack up the back end, mark the tire, rotate it one full rotation and see how many turns something made ? If so I think I'll do that.

Oh and I didn't get a LSD to go with my 4.56's I could draw out a bit more money for that but if I couldn't, would it still be ok w/o ? I haven't been doing too much riding this season but I may soon. So will I be fine for now ?

 

There should be a sticker in the glove box with your axle ratio on it, or you can jack up the back end, mark the drive shaft, rotate the tire and count the driveshaft rotations. 3 1/2 driveshaft rotations = 3.55 gear ratio.

To answer your question, yes you'll be fine with the stock LSD for awhile, I just noticed your truck is an 08. Just fair warning that the stock LSD is known for disintegrating after 60k miles or more. Mine lasted until 115k miles, but it's a fairly common problem. I bought an Auburn LSD for $425, shouldn't cost you anymore in labor since they have to pull the diff to swap gears.

If you do have 3.21s and are switching to 4.56s, it'll feel like a whole new truck! I swapped from 3.92s to 4.56s and it was night and day. You'll run at higher RPM and pull through the revs quicker, you'll notice a change in gas mileage. I picked up about 1.5 mpg in town, and lost about 0.5 mpg highway, I expect you'll loose a bit more highway. It's still a great mod. Whether or not you change diffs, follow the break-in procedure! I can't stress that enough, you'll be tempted to stuff your foot in the throttle when you leave the shop, but don't, you'll ruin the gears and be back to square one a lot poorer.

That is the break in guide from Randy's Ring and Pinion, but from person experience and the guy that did my gears, the first 100 miles, you need to really baby it. Drive for 20 or so minutes, then stop and let the diff cool for 10 minutes, repeat. 100-300 mile mark, still baby it, no hard acceleration, don't run for extended periods of time at highway speeds where the RPMs are above 2000. 300-500 miles, you can drive normally, and just before you take it in to have the diff fluid changed, you can hammer on it. This lets the gear surface harden and cure properly, which is essential.

 

Well, I really couldn't have asked for a better response to my (or so I thought) noob thread.

Thanks Pyro.

http://moesperformance.com/index.php...roducts_id=358

This the one you got ? If I do go this route, this may be the last thing I do for a year or two . . . seeing I'm only 20 and not yet made of money (yet hopefully haha) But seeing how I only have 6800mi on the truck, I should be safe to hold off on this right ? The heaviest towing I'd be doing would be a utility trailer with 1-2 bikes/quads on it and a quad or bike in the bed . . .

As for the break in period, I bowl every wed. and have to drive highway for about 4.5mi then onto side streets again . . . is this all right if I stay around 55-65mph ? (I'll keep an eye on the RPM's and if they go too high I'll hop off and take site streets from there, but we'd be cutting really close on our arrival time) I'm sure I'd be fine with what you've provided seeing how it's only a 5-15min highway drive then a 5-10min street drive with a 1.5-3hr cool down period as I try for more 600 series haha

 

Yep, that's the diff I've got. If you can't comfortably spend the extra $400+ for the LSD, don't. It's well worth doing, but you shouldn't have to worry about the stock LSD failing for quite some time. And you'll be find for short highway hops, just don't go on a two hour road trip.

Just a side note, I don't know what your RPMs are at now for highway speeds, but with 33 inch tires and 3.92 gears I was running about 2200rpm at 70mph. With 4.56s I'm running just shy of 2500 at 70mph. Expect to loose some highway mileage. I'm not even sure the 08 4.7s have the same transmission my 02 does, so this may be irrelevant to you.

 

I don't think the 08 has a sticker in the glove box. I never have noticed one in mine.
'
My 08 with 3.92's runs right at 2000rpm @ 70mph in 5th gear. 33" on 20's.

 

With my 31.5" tires atm, I'm running highway RPMs of about 1500-1700 at around 65-70 . . . so I should be roughly in the prime rpms after the gear swap, as per the "Better mpg with 4.56 gears???" thread I read a few weeks ago, putting me around 2100-2250 rpm at 65-70.

Seeing these rpms I'm curious how my muffler will hold up with droning, so far at current highway rpms, absolutely no obnoxious droning (delta 50 FM). If it becomes bothersome the classifieds may see a new item LoL.

Only thing I'll need to keep an eye on is the drive back from the shop is about a 20mi highway so I'll be sure to make a stop and let'r' cool off. Or hah, just do it all street and happily sacrifice the gas this go around.

Once again, thank you Pyro, this has enlightened me to quite a bit about my choice in going with 4.56 gears and properly breaking them in.

 

lxman your truck has a hemi right?

I know the Hemi Rams all shipped with 545RFE transmissions, but 4.7s are a different story, my truck has the 45RFE, and a .75 overdrive gear, the 545RFEs have a .67 overdrive. The 4.7s shipped with both transmissions depending on the year and options.

I used to have a Flowmaster, it was absolutely miserable at highway speeds, so I bought a Cherry Bomb. It's loud, but not headache inducing drone. And you're quite welcome, it's nice to see a thread that isn't "hai guyz can i fit 35s with a level kit?"

 

Well Pyro instead of wheeling out the jack, I set'r' in Neutral, marked the Drive-shaft and pushed her one full tire rotation, looked to me like a 3&1/4 turn ~_~ 3.21 gears it would seem.

This makes me oh so more curious what she's gona be like with the 4.56's
And instead of waiting for a day off to go watch the install, I might drop her off after work tomorrow and pick'r' up the next day. But I could always request Tuesday off and do it then. Drive it a bit before Wed. Bowling.

Again, thanks for all the info. Now to start saving up for the distant future headers to be available.