4.56 Gears - Correct parts before pulling the trigger

[whyzed]

I already have a 11.5 Yukon R&P for the rear and I'm about to get the other 3 missing pieces. Before I push "buy", I wanted to run these by anyone here that may have advice/experience. The bearing kits change 2010+ and I want to make sure the 9.25" front R&P is reverse rotation.

I've done quite a bit of looking and I think I'm going to settle w/ the precision front R&P rather than Yukon due to the limited use my 4x4 gets. The overhaul kits also come with Koyo bearings rather than Timken and even though I feel terrible about not ordering Timken (due to living only 5 miles from a large plant they have in Canton), I've heard nothing but good results w/ Koyo's and the price is more attractive.

http://bumpersuperstore.com/i-11537838-precision-gear-gm9f456-gm-9-1-4-4-56-ring-pinion-ifs.html

http://www.mudnrocks.com/master-overhaul-kit-ifs-gm-9-by-precision-gear/

http://thejeephut.com/master-overhaul-kit-gm-by-precision-gear-p-27881.html#.UenDDI21GAk

I also may lower my truck a couple inches in the future & run 35" tires, but from the calculations I've done, I don't believe I'll be overgeared on the highway. There should only be about a 100 rpm difference at highway speeds if I drop my tires diameter in the future, as these 4.56 will get my effective gear ratio pretty close to the stock 3.73s on a 30.5" tire.

Any input would be greatly appreciated. Thanks in advance guys.

 

[whyzed]

Bump.

 

[cwylie]

Where are you located? I have a set of axles with 4.56 gears in them already we could swap.

 

[radvans]

4.56 is too high for 35's, I tried them. You'll like the 4.10's better, and they were ok with 37's. If you're staying w/37's go with 4.56's.

 

[Hot COCOAL]

If you have a 5sp, IMHO, 4.56 gears will be too high of a gear ratio, I am running 4.11 with 35's, I feel like the gear could handle 37's pretty easy, better than 3.73 with 35's, if you plan to go with 35's in the future I would highly suggest 4.11/4.10 gears

I debated my gear swap long and hard, I actually bought the 4.56 and swapped them with the 4.11 at the last minute, I'm glad I did too, 4.56 gears would be way to short and would've been turning too many rpm on the freeway even with the 6sp, running a 35. I dont think the 4.56 gears would even let the turbo get into full swing.

I bet they would be great if the truck was a dedicated pulling truck(running a 35)

 

[whyzed]

Where are you located? I have a set of axles with 4.56 gears in them already we could swap.

I'm in Akron, Ohio (NE Ohio)

4.56 is too high for 35's, I tried them. You'll like the 4.10's better, and they were ok with 37's. If you're staying w/37's go with 4.56's.

The biggest thing about my decision on the gears was if I'm going to do it, I'm going to go with a big change. By that, I mean going up 2 sizes to the 4.56 rather than 1 step up w/ the 4.11. 4.56 will be a little over geared with a 35", so I'm still up in the air about that. The reasoning on 35s is to simply lower my truck just a bit. I wanted to perhaps cut my bottom bump-stop bracket 1.5", lower the keys, & put a smaller block/remove the add-a-leaf in the rear.

The fabtech 8" is so hard to lower, because your stock geometry stays pretty well intact from what I understand. You really don't have much adjustment other than playing with the torsion on the front, which may only get me about 1-2" at the very most. The 35s would get me another 1".

If I could somehow figure out how to squeeze 37s in there while lowering it, even better, but that would definitely involve more cutting than what has already been done.

If you have a 5sp, IMHO, 4.56 gears will be too high of a gear ratio, I am running 4.11 with 35's, I feel like the gear could handle 37's pretty easy, better than 3.73 with 35's, if you plan to go with 35's in the future I would highly suggest 4.11/4.10 gears

I debated my gear swap long and hard, I actually bought the 4.56 and swapped them with the 4.11 at the last minute, I'm glad I did too, 4.56 gears would be way to short and would've been turning too many rpm on the freeway even with the 6sp, running a 35. I dont think the 4.56 gears would even let the turbo get into full swing.

I bet they would be great if the truck was a dedicated pulling truck(running a 35)

I've put so much thought into this as well. I always do; on everything that I do. It's one of my best and worst traits at times, because I start to over think things.

From what I've put together, this is what I've found with RPMs @ 60, 70, & 80 mph respectively with a .71 final drive ratio (5-speed):
30.5" Tire @ 3.73: 1750,2042,2334
36.5" Tire @ 3.73: 1463,1707,1950
35" Tire @ 4.56: 1865,2176,2486
36.5" Tire @ 4.56: 1788,2086,2384

This puts my current tires in a 4.56 as obviously the best fit for reaching stock figures. That extra ~100-150 RPM on the highway if I do choose to downsize to 35s kind of scares me though. Is this enough of a gap to cause much of a concern?

This is why I've also had thoughts of spending the extra $600? (unsure on prices off the top of my head) on a valvebody modification in order to get me that .61 final drive 6th gear.

 

[mackthehack]

4.56's and 35's no go... Go with 4.11's or stockers. Why go with fagtech if there is not much adjustability? There are other and better ifs lifts out there.

 

[Hot COCOAL]

I've put so much thought into this as well. I always do; on everything that I do. It's one of my best and worst traits at times, because I start to over think things.

From what I've put together, this is what I've found with RPMs @ 60, 70, & 80 mph respectively with a .71 final drive ratio (5-speed):
30.5" Tire @ 3.73: 1750,2042,2334
36.5" Tire @ 3.73: 1463,1707,1950
35" Tire @ 4.56: 1865,2176,2486
36.5" Tire @ 4.56: 1788,2086,2384

This puts my current tires in a 4.56 as obviously the best fit for reaching stock figures. That extra ~100-150 RPM on the highway if I do choose to downsize to 35s kind of scares me though. Is this enough of a gap to cause much of a concern?

This is why I've also had thoughts of spending the extra $600? (unsure on prices off the top of my head) on a valvebody modification in order to get me that .61 final drive 6th gear.

Meeee toooo, I over think and dwell on every mod till its practically a negative attribute but you have to, I mean there's so many variables to consider. Like, how often do you really do the exact speed limit? Me either, so you will wind up turning high R's all the time, I would be concerned that it would get bothersome, and expensive burning more fuel n all. My truck on 35's with 4.11 gears and the 6sp(don't remember final drive) turns 1650rpm's at exactly 60mph, I wish it were a bit lower as the truck has the torque to push it no problem, but with the 3.73's I would be turning like 1350 or less, and that was too low and resulted in being under the turbo(lag) and excessive egt's when towing and all around really, my egt's have dropped all around since the swap.

Idk what's gonna be best for you, what your willing to give up and sacrifice v.s what you are looking to gain. I do know that a 4.11/4.10 gear will handle a 37" tire, and going that route would be more "user friendly" in the long run. Tough decisions fer sure, I'm glad I'm through it

 

[whyzed]

4.56's and 35's no go... Go with 4.11's or stockers. Why go with fagtech if there is not much adjustability? There are other and better ifs lifts out there.

The lift was on the truck when I purchased it.

Meeee toooo, I over think and dwell on every mod till its practically a negative attribute but you have to, I mean there's so many variables to consider. Like, how often do you really do the exact speed limit? Me either, so you will wind up turning high R's all the time, I would be concerned that it would get bothersome, and expensive burning more fuel n all. My truck on 35's with 4.11 gears and the 6sp(don't remember final drive) turns 1650rpm's at exactly 60mph, I wish it were a bit lower as the truck has the torque to push it no problem, but with the 3.73's I would be turning like 1350 or less, and that was too low and resulted in being under the turbo(lag) and excessive egt's when towing and all around really, my egt's have dropped all around since the swap.

Idk what's gonna be best for you, what your willing to give up and sacrifice v.s what you are looking to gain. I do know that a 4.11/4.10 gear will handle a 37" tire, and going that route would be more "user friendly" in the long run. Tough decisions fer sure, I'm glad I'm through it

Thanks for your insight. I went ahead with the 4.56 and they are on their way. I have somewhat of buyers' remorse, but I know that once I have them on, I will love them regardless if they're 4.11 or 4.56. Either will make such a dramatic change from what I have gotten used to. Its such a dog right now. :rofl: