I've driven lifted gas trucks with different gears to go along with taller tires. The dealer said that the only gear option with the Duramax is 3.73s (was going for 4.10s). Is there a reason for this and is there any problem going with 4.56 gears to compliment a set of 37" tires with this motor?


Thank you!

Nothing wrong at all with deeper gears to match tires and keep overall
ratio about the same. (it is actually a very smart move) A 4.56 would just about be right for 37's and a
D-Max. For the record Yukon makes them as low as 5.38 for the
front and rear of that truck. Also for what it is worth, here are the
part numbers for the gears in Yukon brand, front is YG GM9.25-456R and
the rear is YG GM11.5-456.






Edited by: snoman

I didn't think there would be a problem but just wanted to make sure. I wonder whey GM doesn't offer 4.10s as an option?


After thinking about it some more I might go with 4.88s but have found that the bigger ratios are hard to find for the truck. I have a friend that couldn't locate 4.56s for the front of his HD. Nobody had them.

GM does it I think to keep engine RPM down with stock tires because
4.10's with 31's would be close to redline at 70 in drive for a Dmax
(not OD). Yukon is a good gear brand and your friend must have
looked the wrong places as even 4.88's are not hard to find for that
truck. In your case it would be a tossup between 4.88 and 4.56.
If it is mostly a cruiser, 4.56 would be the way to go with 37's but it
you plan on some serious towing you might consider 4.88's
too. Click on the link below for a link to Yukon sales



Click here (http://www.ring-pinion.com/)

This is one of the places that he tried. Alot of manufacturers and vendors listed them but didn't have anything.

This is one of the places that he tried. Alot of
manufacturers and vendors listed them but didn't have anything.



Curious, I was told some time ago that they would be avaible in the
fall. Did you try Precision Gear and is the front or rear gearset
that is the problem?

You will have to do more than just change the gears. You will also have
to change the reluctors on the front wheels to satisfy the ABS.
Reluctors that match the 4.10's are available from the dealer since
4.10's were and option with the 8.1 gasser and the allison.. I don't
know where you would come up with a set for the higher ratios.



GM only offers 3.70's because they are the correct choice for getting
the most out of the diesel and the low end torque it provides with the
stock tire offerings. 4.10's were and are available through the dealer,
but I would look in the junkyard first and see if I could come up with
whole axle set. It would be cheaper than buying from the dealer. I
would call Precision first. Make sure you ID the axle correctly.



Changing gear ratios in these trucks is not to be taken lightly.

I didn't think there would be a problem but just wanted to make sure. I wonder whey GM doesn't offer 4.10s as an option?


After thinking about it some more I might go with 4.88s but have found that the bigger ratios are hard to find for the truck. I have a friend that couldn't locate 4.56s for the front of his HD. Nobody had them.





Davesmax,


If I were you I would probably think about 4.88s again, unless you don't do much highway driving. I have 37's and am considering around 4.28's I think the ratio is or something around there, 4.10's think are to high for 37's and don't make much of a difference (experience on buddy's hd w/37's) I'd go with Yukon gears aswell like snoman, they don't whine like some other lesser quality gears do. Just my .02

I was wrong. GM changed a few thing since last I did this. http://www.dieselplace.com/forum/smileys/smiley5.gif
There is only one wheel sensor or tranny speed sensor available. I am
not sure which module, ABS, TCM, or ECM scales the vehicle speed
signal.

What is the average cost of swapping gears? I assume a dealer wouldn't be willing to do this modification....

I was wrong. GM changed a few thing since last I did this. http://www.dieselplace.com/forum/smileys/smiley5.gif
There is only one wheel sensor or tranny speed sensor available. I am
not sure which module, ABS, TCM, or ECM scales the vehicle speed
signal.








With a gasser if you reprogram the ECM properly, it will fix the ABS too with a gear swap.

What is the average cost of swapping gears? I assume a dealer wouldn't be willing to do this modification....



A set of gears on line (front and rear) for a HD is about $425 to $450
on line plus what ever shipping may be. The install part would be
expensive and a dealer would be my last choice to do it. I would
think you should be able to get them installed done for in the $500 to
$800 (depending on where you are) or so.

I've been following alot of these gear threads for awhile now. Seems like the smart way to get some longevity and driveability back out of the truck. I'm running 35's and have read that 4.30 would be about the best ratio to fool the truck into thinking it was stock again. Only problem is nobody I know makes them. Would going to 4.10's from 3.73's be worth it or what?


I'm sure some of you have done a gear change ie, voodoo. Guys that have done it please chime in. I'm interested aswell.


Rich.http://www.dieselplace.com/forum/smileys/smiley4.gif

Well a 4.30 does not exist for a GM 10.5 or 11.5 14 bolt axle so you
have either a 4.10 or a 4.56. With 35's a 4.10 would make a
difference and take drive line strain off truck too across operating
envelope too. If you did some very serious towing (above 10,000 lbs
regularly) a 4.56 might be a better deal. Even Dodge offer a 4.10 as a
factory option with its diesel and Cummins are not know to be shy on
torque either.

Gear changes are not for the layman. Don't even try it if you don't have good mechanical and machine shop measuring skills.



I did a front and rear years ago on a GM 1/2 ton. You need a hydraulic
press to remove the bearing from the pinion and/or press the new one
on. You need a gear seperator to grab the pinion bearing to press it
out.



The good thing is both the front and rear have threaded side adjusters so there is no shimming for backlash required.



You need to be able to measure pinion head depth with a special tool or
figure out how to do it the machinist method.. which I did. First you
install the new pinion with the old shim if there was one and compress
the crush
sleeve, taking it to proper preload. Once the pinion preload is set,
I used a
dial indicator and a surface gauge base off the pinion head to the
bottom of the bearing bores. Used joe blocks to find where the
indicator zeroed. Added half the bearing bore to find the center. This
gave me pinion height. Pinion height spec is either marked on the head
of the pinion or in your package documentation. This is the
relationship of the top of the pinion to the center of the side bearing
bores. Than you adjust the
pinion bearing by removing
it again on the press and changing the shim. Sometimes you get lucky
and the original shim is right.



Set side bearing preload with the threaded adjusting sleeves making
sure you don't bind the gears in the process. Than set backlash.



Check pattern.


Edited by: hoot

....and repeat. I've never hit the pinion right the first time. Been real close a few times though.



In my opinion, the only reason to change is starting torque. I'm
running WIDE 35's and don't have any problems what so ever. AND I
tow heavy.

I'm running 37" tires on my '02 HD. They were ok with the factory 4.10s but the truck felt like it needed more. Going to 4.56s wasn't a night and day difference but it gave it some more RPMs while crusing down the highway. The jump from 3.73s to 4.56 will be more noticeable with 37s. I used the Superlift speedometer corrector on that truck and will probably do the same with my new truck when it comes in.

....and repeat. I've never hit the pinion right the first time. Been real close a few times though.



In my opinion, the only reason to change is starting torque. I'm
running WIDE 35's and don't have any problems what so ever. AND I
tow heavy.






I did it once (hit it on the button) using the marking on the pinion
heads and adjusting the shims accordingly. You can do just fine without
a depth gauge (though it is kinda nice it is not a must have) You MUST
check gear mesh/pattern with gear paint though and adjust shims as
needed and you need to set backlash and preload too.



Also, it changes more than starting torque, it changes availble torque
thru whole envelope of operation in every gear and reduces driveline and tranny
stress at any give tractive effort load as well.

Edited by: snoman

I'm running 37" tires on my '02 HD. They were ok
with the factory 4.10s but the truck felt like it needed more. Going to
4.56s wasn't a night and day difference but it gave it some more RPMs
while crusing down the highway. The jump from 3.73s to 4.56 will be
more noticeable with 37s. I used the Superlift speedometer corrector on
that truck and will probably do the same with my new
truck when it comes in.



With 37's and a gas engine (small block) in a big truck your are in
4.88 to 5.13 territory. A 4.56 with 37's is about the same over all as
31's with 3.73's PLUS the extra rolling resitance and drag of the
bigger tires and higher truck profile as well.

Good reasons why I was 9-10 MPG with my 8.1 HD :)

My thoughts were that with a lower gear the truck would shift to 2nd quicker thus allowing more power. With that in mind would my truck benefit greatly going from 3.73's to 4.10's if price weren't a limiting factor.


Rich.

I've driven lifted gas trucks with different gears to go along with taller tires. The dealer said that the only gear option with the Duramax is 3.73s (was going for 4.10s). Is there a reason for this and is there any problem going with 4.56 gears to compliment a set of 37" tires with this motor?


Thank you!





I have had no problems with my 4.56 and 37" other than the ABS/Brake Warning issue. I say make the change if you want.

Voodoo: That is a bad ass truck! :)


I guess you are getting the ABS/Brake light all the time? I'm using a Superlft callibration box and only get those lights when I come to a stop. They shut off as I pull away. I hope to get rid of that issue with the next truck.

I have made the change from 3:73 to 4:10. It cost me a lot, around $2000 installed. But the speedo is right on with 35 inchers. It towed alot better too as the tranny did not go out of overdrive as much. Towing and speedo wise it was great put the price was hard to swallow. I have not had any ABS/Brake light warning issues associated with the change at all. The only time I had a brake light issue is when one of my front wheel bearing went bad and it heated up the ABS switch on the hub and ruined it.Edited by: BassinRVer

The lights usually only come on when you get to 4.56s. I don't remember the details but it's something about the way the computer is calibrated.

Voodoo: That is a bad ass truck! :)


I guess you are getting the ABS/Brake light all the time? I'm using a Superlft callibration box and only get those lights when I come to a stop. They shut off as I pull away. I hope to get rid of that issue with the next truck.





Thanks for the kind words, and yes 99% time I get the warning.. one time and then it's just the lights on the dash. I can live with it, I guess it's the price you pay to play.http://www.dieselplace.com/forum/smileys/smiley2.gif

I have a 6" lift with 315/75r16 (35's) on 10" wheels and run the stock 3.73's.


I installed a programmer to compensate instead of the gears. I was also concerned with the tires size but it isn't as much of an issue with the diesel and programmer, there is way more torque then a gasser. If you didn't use a programmer I would say that the 4.10's would be perfect. I know the 4.56 puts it closer to stock but it seemed a little tall to start with, but that is only my opinion.


I have friends that run 37's, with the same programmer and there is a noticable differnce in lack of power delivery to mine, and also it really puts the rpm's lower at speed, around 1500. For mine I run about 1650 at 65mph, instead of the 1950 with the stock tires.


I think with 37's you would be good with the 4.56's if you don't do a programmer. If you do a programmer, then the 4.10's would be good.


The price for the programmer is around $350-$400, (there are more expensive ones around $800-1000 also) so it is quite a bit cheaper then gears. The programmer also, really makes the truck a completely different animal.


Also, even with 8" lift I think you will have to trim the front bumper and possibly to bottom of the fenderwell, unless you turn up the torsion bars. I don't care for the pre-runner look so mine is level and until it was trimmed I would rub on the from fender and air damn (plastic piece).


Don't forget to factor in a nerf bar or step of some type. (I am still waiting for mine to arrive) With mine I can pull myself up but the wife and 6yr need help if you are not on level ground.

http://www.tbyrne.com/Silverado/Silverado2004side.jpg


I had to trim the plastic under the front bumper a little to run the 37s. That will be a little more work on the Sierra's front bumper.


I get kind of greedy so I'd way the added performance of the steeper gears along with the increase from the upgraded programming. The Duramax tends to be a little soft on the bottom end until the turbo spools up so I'd like to compensate for that.

All you guys smarter than me, don't be afraid to chime in if I have this wrong......so I can erase all this. http://www.dieselplace.com/forum/smileys/smiley2.gif


The way I figure it, if you "upsize" your tires, the reduction in your gear ratio (numerically) is inversely proportional to the difference of the tire diameters.
Sure, the actual ratio is the same, but since the larger tires take fewer revs to make the same distance, the "effective" gear ratio (numerically) decreases.
(old tire diameter x old gear ratio) / new tire diameter = new "effective gear ratio"
Using that logic, if I upsize to H2's (315/70/17), then my "effective" ratio will be reduced to the equivalent of 2.90 gears.
(245 x 3.73) / 315 = 2.90111111


The rim diameter and sidewall ratio shouldn't matter, since the tire diameters themselves should be constant.


Using this same logic, you could figure out the ratio you would need to get back the same performance as stock.
(new tire diameter x old gear ratio) / old tire diameter = new gear ratio needed.
(315 x 3.73) / 245 = 4.7957
So....if I'm right, using 4.56's would get you almost back to stock performance levels when using 315 size tires.


Does this hold water?


Tom http://www.dieselplace.com/forum/smileys/smiley30.gif

The percentage method works. Whatever percentage you increase tire
diameter, thats the percentage you increase gear ratio. Comes out
pretty close.

Well Tom, Here goes:



You're close. the 315 and 245 you are using is not the same as
the tire diameter. To figure out the actual tire diameter, you
have to take the tire width (the 315 or 245 or whatever), and multiply
by twice the sidewall ratio (70 or 75 or whatever), and add that to the
diameter of the wheel (but you have to convert either the wheel to
metric or the sidewall dimensions to inches).



Examples: <span style="color: rgb(0, 0, 255);">315</span>/<span style="color: rgb(0, 255, 0);">70</span>-R<span style="color: rgb(153, 153, 153);">17</span>



<span style="color: rgb(0, 0, 255);">315</span>*<span style="color: rgb(0, 255, 0);">0.70</span>*2/(25.4 mm/in)+<span style="color: rgb(153, 153, 153);">17</span>=<span style="color: rgb(255, 0, 0);">34.6</span> inches



<span style="color: rgb(0, 255, 255);">245</span>/<span style="color: rgb(255, 153, 0);">75</span>-R<span style="color: rgb(0, 204, 153);">16</span>



<span style="color: rgb(0, 255, 255);">245</span>*<span style="color: rgb(255, 153, 0);">0.75</span>*2/(25.4 mm/in)+<span style="color: rgb(0, 204, 153);">16</span>=<span style="color: rgb(255, 0, 255);">30.5</span> inches



Now, once you have the actual diameter of your wheels, you can figure out the effective ratio as you described:



(<span style="color: rgb(255, 0, 255);">30.5</span>/<span style="color: rgb(255, 0, 0);">34.6</span>)*3.73=3.28



To find out what ratio you need to return to stock effective ratio, flip the ratio:



(<span style="color: rgb(255, 0, 0);">34.6</span>/<span style="color: rgb(255, 0, 255);">30.5</span>)*3.73=4.23



If this doesn't make sense, let me know,

Dennis

Hey Dennis! Makes sense, but.....


Isn't the first number the circumference of the tire in cm? If so, why not compare those?


Thanks for the info.....


Tom http://www.dieselplace.com/forum/smileys/smiley30.gif

The first number is the tire width in mm. The second number is
the ratio of sidewall to width as a percentage, and the third number is
rim diameter in inches. . . makes as much sense as teats on a boar hog,
but that's what we're stuck with.http://www.dieselplace.com/forum/smileys/hihi.gif



Dennis

This is the thread I was looking forward tohttp://www.dieselplace.com/forum/smileys/smiley32.gif. My Pro Comp 6" lift has been in for a while and now my wheels and BFG 37's are now in too. I still want to drag my truck and therefore was wondering what ratio should I go to. I use the truck daily on the highway so I really want something so I can have the best of both worlds. Thanks, Nick

All you guys smarter than me, don't be afraid to chime in if I have this wrong......so I can erase all this. http://www.dieselplace.com/forum/smileys/smiley2.gif


The way I figure it, if you "upsize" your tires, the reduction in your gear ratio (numerically) is inversely proportional to the difference of the tire diameters.
Sure, the actual ratio is the same, but since the larger tires take fewer revs to make the same distance, the "effective" gear ratio (numerically) decreases.
(old tire diameter x old gear ratio) / new tire diameter = new "effective gear ratio"
Using that logic, if I upsize to H2's (315/70/17), then my "effective" ratio will be reduced to the equivalent of 2.90 gears.
(245 x 3.73) / 315 = 2.90111111


The rim diameter and sidewall ratio shouldn't matter, since the tire diameters themselves should be constant.


Using this same logic, you could figure out the ratio you would need to get back the same performance as stock.
(new tire diameter x old gear ratio) / old tire diameter = new gear ratio needed.
(315 x 3.73) / 245 = 4.7957
So....if I'm right, using 4.56's would get you almost back to stock performance levels when using 315 size tires.


Does this hold water?


Tom http://www.dieselplace.com/forum/smileys/smiley30.gif
Old post I know. Im dealing with this now. I figured it about as you did Tom. Dennis hit it dead on. With 35's we fall right in the middle. I think Im going with the 4.56's Im going to err on the side of more RPM in hopes of helping egts. (if that even works lol) I hadnt heard about the abs issues tho?