I am considering regearing the truck to offset my 35's. I would like to educate myself as much as possible before calling the shops around town, and at this point in time I'm pretty clueless on this subject.


I feel right now my truck pulls the 5th wheel ok, especially with the J/A on 2/2, but based on my friend's description of his stock truck pulling his 5er, I am thinking I might benefit from regearing. I have a few questions I am hoping you all can help me with.


1. Because I have the juice, is spending money regearing really going to give me that much more power and better fuel mileage? It does seem to need to shift into 4th quite a bit on even slight grades. Will regearing help get the truck back into it's power range?


2. My quick search on this forum says that 4.56's would be ideal for 35's. Does that sound right?


3. My build up sheet says I don't have the G80 locker, but I have heard it is basically standard with the D/A. Is there a way to tell just by looking, and if I don't have it, is it worth having one installed when and if I change the gears?


4. I figure I am towing about 10,000lbs fully loaded. Am I wearing anything out prematurely by not getting regeared, or is regearing strictly performance driven?


5. Finally, does regearing the truck throw off the speedometer? To me it seems the engine rpm's would be the same but the tires would be spinning at a different speed. If this is so, how do I figure what code to enter into the attitude?


Thanks for any info guys......


on edit: Reading another ongoing post here, I guess I will need to regear front and rear. Anybody know of experienced shops around the Reno/Sacramento area to get this done?Edited by: HD4fun

1. Because I have the juice, is spending money regearing really going to give me that much more power and better fuel mileage? It does seem to need to shift into 4th quite a bit on even*slight grades.*Will regearing help get the truck back into it's power range?


2. My quick search on this forum says that 4.56's would be ideal for 35's. Does that sound right?
To get right to the point don't expect your mileage to change much either way. In theory your mileage should increase but in reality it's usually a different story. You will get "out of the hole" a little quicker and it may shift a little better but it's still gonna run likes it's got big tires. You'll feel the gears alot more towing than you will around town. 4.56s are what I would recommend for 35s, some will tell you 4.10s but if you are going to drop down that kinda of money just go with 4.56s that way you don't have any regrets. The other thing about 4.56s is if it turns out to be to tall of a gear for your liking you could always bump up to 37s when your tires wear out. Edited by: y2kboti

To see if you have the G80, check the build label (in the glovebox?) on the truck. It will be listed. Or just get the right tire wet and nail the gas and look at the burnout.


For some reason, you can "feel" the G80 when you stab the gas at low speed in a corner. Mine acts unlike any posi I've had before. You can feel it turn on and off.


Normally you won't need a front posi unit unless you are doing serious off-roading. There is so much weight on the front tires, that it is hard to spin just one. It will spin both or none in most instances.

4.56 is minimum here with 35's if you tow a 10,000lb 5th wheel. A 4.10 would be marginal at best. Also if you are thinking about upgrade rear diff, do not put is a detroit locker type rear diff because they would not work well with towing.

HD4fun, I have heard good things about Folbeck on Glendale Ave. We need to hook up sometime just to chat.

1. yes...You will be very happy with the 4:56 gear.


2.yes 4:56 is the gear you want.


3. I would get a locker of some kind(Detroit would be a little over kill)


4.You are working your transmission pretty hard.


5. yes your speedo will need to be recalibrated.


I'm a bit of an offroad junky and I've been happy with the 4:56's I run in my jeeps and Chevy 1/2 ton. With the 35s and 4:56 gears in my 1/2 ton I pull a 5500lb travel trailer. This was before my Dmax.


http://www.dieselplace.com/forum/uploads/889_Z71_7.JPG

Trouthunt,


When you upgraded to 4.56s in your Z71 did you have any ABS issues? My brother went to 4.11s in his 1/2 ton and the ABS light stays on. He had the PCM retuned for the gear swap and when riding in the truck with a scanner attached, the rear sensor is right on with the odometer, but the two fronts sensors are reading different from the rear and from each other. Any insights?


JP

Trouthunt,


Awesome looking truck. I can't imagine that mileage would increase at all. You are increasing the RPM the engine is running for a given speed. That said, you could be increasing to a more efficient operating range, but you are still doing the same amount of work but increasing the rotational momentum of the engine. You should see an increase in vehicle performance but no way an increase in mileage.


Dennis

The G80 is not standard with a Duramax, but it does come as part of
the "Heavy Duty Power Package". The HDPP is a VERY common way to order a Duramax, since it lowers the cost by $1000. My guess is that at least 80% of the Dmax pickups sold this year were ordered with HDPP.

Re-gear to 4.56's for the sake of your tranny. I don't have any first hand experience with the Allisons, but I'm sure you're stressing it just as much as if it were a 4l80e or 700r4. Then again, maybe the Allisons can handle the extra stress.


A few years ago I lifted an old truck with a 700r4 tranny that had been on it's last leg for several years. About 20 miles after the new 35's were put on that old tranny finally croaked. Sure didn't take long once those new meats were on.

Heartbeat,


My 94 didn't come with ABS as an option. Sorry not much help..As far as mileage, pulling 35's pretty much shot that out the window but last year I found an LT1 from a wreaked corvette and did a engine swap. Now I get 26mpg with all kinds of horsepower. I had a custom chip burned for it with a few other goodies. She's a sleeper. With the 35's on her the dyno was 326hp.

I DONT THINK THEY MAKE 4.56S FOR THE AAM11.5 REAR END. IF THAT IS WHAT YOU HAVE.

Hey thanks for all the input guys....


Looks like I'll be calling up a few shops to check prices and experience levels. Appreciate the way knowledge is so forthcoming on this forum.

I DONT THINK THEY MAKE 4.56S FOR THE AAM11.5 REAR END. IF THAT IS WHAT YOU HAVE. If he has the Duramax, it has the 14 bolt 11.5" rear differential. And he states this in his user info, " 03 2500HDCC,SB, AFEStageII, Juice/Attitude, 4" Exhaust, 6" Fabtech "


So sense I see the Juice/attitude, I have to assume it is an Duramax. And yes, 4.56 gears are available for the 11.5" 14 bolt.


I would bet that mpg would increase by 1-1.5% on average. 4.30`s would probably be best, but I am not sure you will find them.

Yes they are made by Yukon for one at 4.10, 4.56, 4.88, 5.13 and 5.38 ratios. Same combos are availible for front axle as well.

Also a Dmax with 35's and 4.56's would be a very serious tow machine! Edited by: snoman

HD4fun and Heartbeat Hauler,


Here is some info I have found with the ABS/Brake Warning issue;


Since I'm at 8" with 37's and 4.56 gears it has put the speedo and overall power and feel back to stock....but I do have a ABS/Brake warrning chine and dash light caused from the above mods. I have made several calls but the LLY is still just too new at the moment. There is also the possiblity that it may not be resolvable due to the fact that the ABS rings are made and supplied to GM by more than one supplier, this has caused data programing issues with aftermarket chip makers etc..

HD4fun and Heartbeat Hauler,


Here is some info I have found with the ABS/Brake Warning issue;


Since I'm at 8" with 37's and 4.56 gears it has put the speedo and overall power and feel back to stock....but I do have a ABS/Brake warrning chine and dash light caused from the above mods. I have made several calls but the LLY is still just too new at the moment. There is also the possiblity that it may not be resolvable due to the fact that the ABS rings are made and supplied to GM by more than one supplier, this has caused data programing issues with aftermarket chip makers etc..


I would think that supplier would not be a issue here because they would have to maintain a standard spec to be of any value to GM because they cannot have different versions of ABS on same vehicals. This is a programming issue that need to be resolved and that can take some time with new firmware on a new engine.

I don't think the supplier is the problem since GM knows and has all the data at their finger tips and changes can be made very easy.


The aftermarket guys all have to look at and figure it out from a few trucks they can get a hold of.


Here is an example; My truck gets some rings made from mr "X" and then 3 month later GM gets a updated and better deal from Mr "Y". GM upgrades the firmware to allow both rings. So now the aftermarket chip makers have made a fix for the "X" rings but thay have no idea that GM has changed to "Y" rings. Now the guy with Mr "Y" rings still gets the ABS/ Brake light and Chine.


I'm no expert on what GM does or how this all plays out, this was only told to me by one of the chip makers.


I guess time will tell but for know I'll live with the ABS/ Brake light and Chinehttp://www.dieselplace.com/forum/smileys/Approve.gif

Still, I will bet that there is no difference on the rings. It counts pulses per second to determine wheel speed and that is then sent to ECM/ABS module. No matter who makes rings, I have little doubt that they are the same. GM uses more than one source to insure availibilty on item, not to have them different.

What % of the time do you tow with your truck? I doubt you would be happy after changing gear ratio's. Gas trucks really like or need a certain gear more than the broad tq range of the diesels. Your truck will never tow like your friends with stock tires since his truck isn't lifted and catching all the air your truck is.

What % of the time do you tow with your truck? I doubt you would be happy after changing gear ratio's. Gas trucks really like or need a certain gear more than the broad tq range of the diesels. Your truck will never tow like your friends with stock tires since his truck isn't lifted and catching all the air your truck is.

I doubt this seriously. It is like taking a truck with stock tires and raising the gear ratio to about 3.2 to 1 with as with 3.73's with 35's and that will make a big difference. Milage make improve as well because engine will run more effiecent and with a lighter load too with deeper gears. Also, I lifted truck is more that just body drag, there is more drag under truck from turbulance and extra drag and rolling resitance from tires to. There are no free rides here.

What % of the time do you tow with your truck? I doubt you would be happy after changing gear ratio's. Gas trucks really like or need a certain gear more than the broad tq range of the diesels. Your truck will never tow like your friends with stock tires since his truck isn't lifted and catching all the air your truck is.




I doubt this seriously. It is like taking a truck with stock tires and raising the gear ratio to about 3.2 to 1 with as with 3.73's with 35's and that will make a big difference. Milage make improve as well because engine will run more effiecent and with a lighter load too with deeper gears. Also, I lifted truck is more that just body drag, there is more drag under truck from turbulance and extra drag and rolling resitance from tires to. There are no free rides here.


I doubt you seriously, and I agree with CPMac. Gassers are not like diesels. If you were correct GM would offer DMax buyers a choice for gears. They don't because not necessary for these trucks that have so much torque.

Well guys, here's the deal. I am a summer tower with my 5th wheel, camping and seeing the sights with the family. It's usually winterized around October and brought back out in April.


I have the J/A and set it to 2/2 when towing, otherwise I'm in 4/4. My best time in 0-60 is 7.2 seconds on level 4, going by the Attitude monitor. Not great, but not bad for me, who has no experience whatsoever in racing anything, due to the fact I never owned anything fast, or that I thought would stay together long enough to finish the run.


My question basically came about because any way you choose to leave Reno, there are mountains. The constant changing of gears from 5 to 4 for every hill could be taken care of by locking out O/D, but then I am forced to slow down to about 60, not wanting to keep the revs up so high in 4th gear, not to mention lost fuel mileage. I like to get where I'm going fairly quickly. The constant button pushing for O/D and changing of cruise control speed just got me thinking, that's all.


I know that probably all sounds ridiculous, and I should just slow down and lock out through the mountains, but I like to drive the way I like to drive.http://www.dieselplace.com/forum/smileys/Ermm.gif I figure if I could get a good price on changing this stuff over and it would give me back some power, I could justify doing it. I originally thought it was a no brainer, but am now rethinking. Maybe I'll just keep it the way it is. Sound like there's a lot more to it than I originally thought. I still want to make sure the tranny will be ok the way I have it now.


Thanks again for all the feedback.

Take my word for it. Gears will not put the truck back to what it was stock. Your mileage isn't going to go up and due to the large tires it's still going to shift gears...just not as much. Yes it will run better than what it was, the biggest gain will be in low end power. No matter what you do a lifted truck is a lifted truck is a lifted truck. It will not run like it did stock.Edited by: y2kboti

Take my word for it. Gears will not put the truck back to what it was stock. Your mileage isn't going to go up and due to the large tires it's still going to shift gears...just not as much. Yes it will run better than what it was, the biggest gain will be in low end power. No matter what you do a lifted truck is a lifted truck is a lifted truck. It will not run like it did stock.

No, maybe even better yet if you gear it correctly. MPG may not be as good as stock but better than it is with stock gears and big tires.

snoman I wish that was the case. I have first hand knowledge granted it is with a 5.3L but I've hounded many Duramax owners about mileage and of those that have regeared nobody has seen an increase in mileage. I also think alot of it has to do with the weight of your tires. Some of the more aggressive tires, i.e. PJ Dirts Grips, weight alot more than comparable sized tires. Edited by: y2kboti

Aggressive tires consume a lot of power themselves and the action of your foot on the gas pedal plays a big roll in MPG as well but improper gearing makes it even worse. If you run big meats with a nasty tread you need to gear a bit deeper overall than stock to make the best of the situation and do not full yourself into thinking that you can cruise at 2000 RPM at 70 with big draggy tires and a lift and get best possible mileage doing it beacuse it takes more power to move truck and when RPM is held low it has to work even harder to do it and gas mileage goes south while doing it. You have to get that engine up in its sweet spot while cruising to get best mileage with big meats on it.

I have 35" tires and the OEM 3.73 gears. On the highway at 80mph I am at 2100RPM.


Looking at the Duramax torque curve, it sounds like the OEM gears will keep you in the sweet spot better than a 4.56 gear.


How are your EGTs now before the Allison downshifts into 4th? Perhaps you can turn up the J/A a little more to keep it in 5th.

I'll remain mute on the subj as I've my own opinion. However, have heard good things re West Coast Differentials in Rancho Cordova. Installed a limited slip differential for me w/o complications and at a fair price. Plus, differentials is all they do ~ ~

I have 35" tires and the OEM 3.73 gears. On the highway at 80mph I am at 2100RPM.


Looking at the Duramax torque curve, it sounds like the OEM gears will keep you in the sweet spot better than a 4.56 gear.


How are your EGTs now before the Allison downshifts into 4th? Perhaps you can turn up the J/A a little more to keep it in 5th.

Well, the speed limit is not 80 and the engine and tranny will have to handle about 20% more torque than stock to cruise and with any load attached to it as well. Kinda like towing a trailer before you even hook one up.

I have 35" tires and the OEM 3.73 gears. On the highway at 80mph I am at 2100RPM.



Looking at the Duramax torque curve, it sounds like the OEM gears will keep you in the sweet spot better than a 4.56 gear.



How are your EGTs now before the Allison downshifts into 4th? Perhaps you can turn up the J/A a little more to keep it in 5th.




Well, the speed limit is not 80 and the engine and tranny will have to handle about 20% more torque than stock to cruise and with any load attached to it as well. Kinda like towing a trailer before you even hook one up.



I guess I was not clear. I was not implying to tow at 80mph, I was only giving one point of reference. Here are a few more.


At 70mph I am at 1800rpm. This is the exact torque peak of the Duramax. Hard to get more ideal than that.


At 60mph pulling a steep hill, I can use 4th gear for a very powerfull 2200rpm. This rpm will still keep the RPM at a managable and sustainable level, and add some HP when pulling the hill.


I still feel that these are close to ideal gears, and although 4.10 gears would also be very nice, my personal opinion is that 4.56 gears would be lower than neccessary. JMO.

Every Dmax I have driven did not feel happy until at about 2000 RPM throttle responce wise and I do not really think that 1800RPM at 70 would be a good cruise with 35's as not far below that RPM the engine loses a lot of torque fast and not being able to effectively use OD at 60 in truck is just kinda plain silly.

I tow at 60mph in 5th gear all the time. I don't think it would drop to 4th unless the grade got rather steep. I guess even though I tow all the time, I must still be wronghttp://www.dieselplace.com/forum/smileys/Disapprove.gif. I bet there are at least 100 other members on this forum who also regularly tow with 35" tires and 3.73 gears. With the H2s almost being given away, they are a very popular size.

And you are really straining your tranny and engine and greatly reducing your towing ability as well. When that engine is loaded, it should be doing at least 2000 RPM or better for longer engine life and better effiency.

Amric,


I am right where you are when it comes to rpm's and speed. I'm at 1700rpm at 70mph. One thing is for sure, I ain't holding it in 5th gear at 60mph on an even small grade. It just won't hold the gear, plus the EGT's go through the roof. I thought 1700rpms was in the torque range as well, but my truck won't even shift into 5th until around 70mph if there is even a little load on the engine (i.e., even level roads). I like to tow in cruise, and every time the truck loses speed to just at 64mph, it goes into 4th on it's own.


Could the elevation have something to do with it? I have noticed that around town and in the mountains (5000-7000ft) when towing, level or grade, my EGT's would be consistent 1050-1200, and I will sound the attitude alarm at 1250 on a regular basis. At this point if the cruise doesn't automatically do it, I'll lock out O/D and can maintain speed with lower EGT's but engine temps hit 220+ pretty quick when running around 2200-2500rpm. Once I get down to 0-1500ft level, EGT's and engine temps aren't usually a problem, but I set the overboost alarm consistantly when I hit the go pedal pretty good. I have never once set the overboost alarm in town or mountains, towing or not.


If that's the case, maybe I'm just not getting enough air up here - sounds like a bigger turbo is in order. Somebody better get to crackin' on that!Edited by: HD4fun

EGT tends to raise at altitude and a bigger turbo with make it even worse. You stock turbo is compensating somewhat for altitude now adding to EGT proble with your incorrect gearing. Based on your RPM and EGT, you need to regear badly. 1700 rpm at 70 in not good any truck except maybe a OTR rig. Sounds like you need a 2 step jump in gearing because or RPM, tmeps and that you live at altitude. Many years ago, up until the late 70"s or so, Detriot used to equip cars delivered to high altitudes with deeper gearing than sea level units but stopped doing it a few years after emmisions and CATS set in.

SO what do you tach when in 4'th? Is 4'th with 35's the same as OD with stock tires?

Lets see, at 60 MPH
30"(stock) 35"
OD = 0.71 1753 1530
4'th = 1.00 2469 2155

at 70 MPH
OD = 0.71 2045 1785
4'th = 1.00 2880 2514

Not exactly. You do turn about the same revs at 70 w/35's as you do at 60 w/30's for what it's worth.

What does it all mean? At highway speeds, not much. 4'th gear is about as efficient as OD, maybe more since you are not driveing the OD gears. A little more strain on the drive line but only ~15%. Where you really notice the difference is starting out. You loose, again 15%, of your starting torque.

Where everyone gets fooled is most of these bigger tires are also wider. They run at lower pressures and have a fair bit more rolling resistance. You see that in your fuel economy.

I run 365/65R16's and they have a lot of rolling resistance. It is a compromise for me. I get off the highway a lot with the trailer and the smaller tires just couldn't keep a grip. I have no problems, but my starting torque is down a fair bit.

Any tranny and engine strainis up a fair bit too. New gearing is cheaper than a new tranny, especailly one the fails at the wrong time too.

EGT tends to raise at altitude and a bigger turbo with make it even worse.


Now I'm confused. I thought in theory, bigger turbo = more air in chamber = cleaner, more efficient burn = lower egt's. What am I missing?

At altitude, the turbo has to spin a lot faster to make a given boost. To spin faster, the backpresure in the exhaust pre-turbo must increase to push the compressor faster. The higher backpreasure increases the EGT. (PV=NRT) A bigger turbo does NOT exasperate this. For standard boosts, they both perform about the same. When you get into higher boosts, the bigger turbo is more effecient where the smaller will start maxing out. The oppisite is true too. At lower demands, the big turbo is not getting enough exhuast to work efficiently. Most of us don't run maxed out all the time.

Now, the only time drivetrain stress is an issue is getting the load moving. Going down the highway is nothing. If the load gets too high at speed, the tranny drops down a gear. End story.

Be warned that finding a sweetheart gear ratio for going over the mountains is a poke and hope proposition. It depends a huge amount on the load and the power your making at the time. If the shifting back and forth is a big problem for you then I suggest the following:

If the shifts to 4'th happen infrequently => 4.10
Constant 4'th OD 4'th OD => 4.56

As far as ABS problems with a gear change. Three ways to take care of it.
converter box on the spedo line to correct the counts to the computer
Reflash the ABS computer
Get the correct reluctors on the front wheels that match your new gear ratio.

Wow guys,


Thanks for taking the time to help me out on this, I appreciate all your input. That's what makes this forum great, you knowledgeable ones helping out us newcomers. I've definately learned a ton on this subject.http://www.dieselplace.com/forum/smileys/Clap.gifhttp://www.dieselplace.com/forum/smileys/Clap.gifhttp://www.dieselplace.com/forum/smileys/Clap.gif


So basically what I'm getting is that some of you feel a regearing is necessary, while other think the juice attitude should be enough, and regearing isn't really an issue. What nobody seems to dispute is that I am adding somewhat to the stress under load, but that comes with the territory of lifted trucks and bigger tires. I will gain back some power at the low end but no mileage increase, and maybe a little worse mileage. It comes down to how I feel the truck is performing based on my expectations. I must think about this for a while.......http://www.dieselplace.com/forum/smileys/Geek.gif

Great summary!

At altitude, the turbo has to spin a lot faster to make a given boost. To spin faster, the backpresure in the exhaust pre-turbo must increase to push the compressor faster. The higher backpreasure increases the EGT. (PV=NRT) A bigger turbo does NOT exasperate this. For standard boosts, they both perform about the same. When you get into higher boosts, the bigger turbo is more effecient where the smaller will start maxing out. The oppisite is true too. At lower demands, the big turbo is not getting enough exhuast to work efficiently. Most of us don't run maxed out all the time.

Now, the only time drivetrain stress is an issue is getting the load moving. Going down the highway is nothing. If the load gets too high at speed, the tranny drops down a gear. End story.

Be warned that finding a sweetheart gear ratio for going over the mountains is a poke and hope proposition. It depends a huge amount on the load and the power your making at the time. If the shifting back and forth is a big problem for you then I suggest the following:

If the shifts to 4'th happen infrequently => 4.10
Constant 4'th OD 4'th OD => 4.56

As far as ABS problems with a gear change. Three ways to take care of it.
converter box on the spedo line to correct the counts to the computer
Reflash the ABS computer
Get the correct reluctors on the front wheels that match your new gear ratio.

Two things, a bigger turbo will have more lag true but more boost will increase power and EGT, there is no escaping that. Keep back pressure as low as possible will help EGT temps. Also you are off on the added strain being only when starting out. It is there ALL THE TIME. Even when cruising it will take 15 to 29% more power to carry the load down the road with tall gearing. There are no free rides hear as you suggest. The Engine and tranny will carring a much higher torque load at all aspects of operation with tall gears for the tires in use. It is a shame to buy a nice tow vehical and ham string it with big tires without regearing it properly because any way you cut it you will have reduced towing power and added strain, boost or not vs stock tires and gearing. Yes you can boost power to try to make up for it but you also add unneeded strain as well just to get back to square one.

Main reason you are downshifting so much is that the ally is shift happy at that rpm, you are cruising at a rpm were it dosnt take much throttle to get it to downshift. If you forced it to remain in OD and lugged it EGT's would probably go through the roof though.


Turbos compensate and arnt as suseptibal to altitued as a NA motor, still the altitude aint helping but I dont its the root of the prob.


Gears will help, even though the stress once you get moving isnt anything an ally or your rear will care about. It will move you into a not so shift happy rpm and give you closer to stock gearing and operating rpm, a good thing.


Its pretty much impossible to have any idea what throttle response is bellow 2000rpm. The allison wont let you run there with anything other than lite throttle except in 1rst and then power is reduced.


More air will bring EGT's down. More boost will not raise EGT's. If you think otherwise go tell the dodge boys that they need to go to smaller chargers to keep down thier EGT's.http://www.dieselplace.com/forum/smileys/Ermm.gif

Oh....try running in T/H for grins once it shifts to 5th, I bet it will hold 5th a bit better. Just for grins though, the TH mode makes the ally not quite so shift happy.

Main reason you are downshifting so much is that the ally is shift happy at that rpm, you are cruising at a rpm were it dosnt take much throttle to get it to downshift. If you forced it to remain in OD and lugged it EGT's would probably go through the roof though.


Turbos compensate and arnt as suseptibal to altitued as a NA motor, still the altitude aint helping but I dont its the root of the prob.


Gears will help, even though the stress once you get moving isnt anything an ally or your rear will care about. It will move you into a not so shift happy rpm and give you closer to stock gearing and operating rpm, a good thing.


Its pretty much impossible to have any idea what throttle response is bellow 2000rpm. The allison wont let you run there with anything other than lite throttle except in 1rst and then power is reduced.


More air will bring EGT's down. More boost will not raise EGT's. If you think otherwise go tell the dodge boys that they need to go to smaller chargers to keep down thier EGT's.http://www.dieselplace.com/forum/smileys/Ermm.gif

You need lower back pressure and lower peak combustion temps to keep EGT temps down. If you use more air but not more fuel EGT will stay down too. A diesel burns as long as fuel is being injected and the longer the fuel injection cycle for more power, the higher the EGT. There is no mystery here. The more the gas is expanded and the quicker is does it also lowers EGT too.

And again as far as stress, it is still there and it will be like you are towing a 3 or 4000lb trailer when not towing with 35's and 3.73's and tow 10,000 pound and it will feel to the truck like 15,000 lbs or so with same combo. There is not escaping it. That is why big trucks have deeper gears to big with. Gear it proper and your tranny should give you a long trouble free life. Do not do so and you will shorten its life span. The big question is how much? Also, at higher RPMs by proper gearing the engine and tranny will cool better under load from better circulation of oil through engine oil cooler, water jacket and tranny fluid as well (and it will be cooler to because of reduced torque load) and reduced engine bearing oil film pressure loads as well with deeper vs stock gears at any given load with 35's. It is a win win situtation with proper gearing. There is a lot more than meets the eye here.

Main reason you are downshifting so much is that the ally is shift happy at that rpm, you are cruising at a rpm were it dosnt take much throttle to get it to downshift. If you forced it to remain in OD and lugged it EGT's would probably go through the roof though.


Turbos compensate and arnt as suseptibal to altitued as a NA motor, still the altitude aint helping but I dont its the root of the prob.


Gears will help, even though the stress once you get moving isnt anything an ally or your rear will care about. It will move you into a not so shift happy rpm and give you closer to stock gearing and operating rpm, a good thing.


Its pretty much impossible to have any idea what throttle response is bellow 2000rpm. The allison wont let you run there with anything other than lite throttle except in 1rst and then power is reduced.


More air will bring EGT's down. More boost will not raise EGT's. If you think otherwise go tell the dodge boys that they need to go to smaller chargers to keep down thier EGT's.http://www.dieselplace.com/forum/smileys/Ermm.gif

You need lower back pressure and lower peak combustion temps to keep EGT temps down. If you use more air but not more fuel EGT will stay down too. A diesel burns as long as fuel is being injected and the longer the fuel injection cycle for more power, the higher the EGT. There is no mystery here. The more the gas is expanded and the quicker is does it also lowers EGT too.

And again as far as stress, it is still there and it will be like you are towing a 3 or 4000lb trailer when not towing with 35's and 3.73's and tow 10,000 pound and it will feel to the truck like 15,000 lbs or so with same combo. There is not escaping it. That is why big trucks have deeper gears to big with. Gear it proper and your tranny should give you a long trouble free life. Do not do so and you will shorten its life span. The big question is how much? Also, at higher RPMs by proper gearing the engine and tranny will cool better under load from better circulation of oil through engine oil cooler, water jacket and tranny fluid as well (and it will be cooler to because of reduced torque load) and reduced engine bearing oil film pressure loads as well with deeper vs stock gears at any given load with 35's. It is a win win situtation with proper gearing. There is a lot more than meets the eye here.

Just adding boost will lower EGT's all else being equal and possibly increase power. Maybe not, depends if you are over or under fueled.


Yes big tires and stock gears will work the truck harder, didnt deny that, but is stock gearing going to make a noticable difference? I dont think so. But I also didnt say gearing wanst a good in this situation but I dont think he is going to kill anything one way or another. Gearing is more of a drivability thing here IMO.


I cant remember and am too lazy to look for it, how much and what does he want to tow???

Just adding boost will lower EGT's all else being equal and possibly increase power. Maybe not, depends if you are over or under fueled.


Yes big tires and stock gears will work the truck harder, didnt deny that, but is stock gearing going to make a noticable difference? I dont think so. But I also didnt say gearing wanst a good in this situation but I dont think he is going to kill anything one way or another. Gearing is more of a drivability thing here IMO.


I cant remember and am too lazy to look for it, how much and what does he want to tow???

I do agree that if you add more boost without any extra fuel you will gain a little more power and lower EGT temps as well.

Drivabilty? You buy a powerfull HD truck and turn it into a bit of a slug with derated towing abilty because of oversized tires without proper gears, I think this goes beyond drivabilty. As it sits now a 8.1 with 4.10 gears and stock tires would clean that trucks clock towing at any speed.

So what? What exactly is your point? He wants a lifted duramax, he bought a duramax and lifted it, he now has a lifted duramax to work with. Its all about driveability. That truck goes down the road just fine and to say otherwise is just plain silly. He isnt breaking anything and isnt going to break anything. Yes it could perform better but I'm sure he expected some driveability issues. I call lack of power and easy kick down outa OD while cruising a drivability issue. Its an annoyance. He can still function with his truck fine its just not optimum. He can still get by. Its his choice to have a truck that isnt as streetable or drive able or cruises or tows as nice or how ever the hell you want to say it. He wants the big tires, I wouldnt personaly run em because I dont want to live with the hedaches caused by em but to him they are worth it. If he wanted the ultimate towing rig I'm sure he would do things different but if he is putting 35's on his truck I would say his goal isnt to build the ultimated tow vehical. I'm sure even with his truck on 35's his truck will out pull quite a few vehicals on the road.....is there a point to that comment? NO!


And actually its been shown that just adding more boost on a duramax dosnt gain power in most cases, response yes but not peak power.

Been through the "stress" thing many times on rigs a hell of a lot bigger than a Dmax. They break things starting out. In the low gears. That is when the "stress" is the highest and is a limiting factor. So I repeat, "stress" is a factor when starting out, when the driveline torque is the highest and the tranny has no lower gear to go into. Once going down the Highway, the load on the drivetrain is fine.

That is my opinion and my experience. My .02 too.

Hd4fun, I agree with Ratlover that you are not hurting anything. And as he said, you have to choose what you are willing to accept in drivability compromises.

FWIW I have a 10 Ton dump that has just the opposite driveability problem. It is geared too low with 5.43's. Even in 9'th gear the thing rides the red line at 55 MPH! Drives me nuts. Been pissing and moaning about it now for over 7 years. The gear swap is very easy on this truck. Just swap the carrier. But for some reason, I have never done it. So I personally have simpathy for anyone who does not want to mess with the gearing on their truck if they don't have to.
Edited by: Fingers

Again, thanks for all the info....http://www.dieselplace.com/forum/smileys/Clap.gif


Ratlover is right, I knew exactly what was going to happen to my truck when I did it, and I was willing to deal with it. Still am, as it's really not that big a deal, and my truck still pulls 100 times better than my old 5.3 with only 5,000lbs behind it (remember 40mph @4,800rpm up the hill?). The reason for the post was to get some info from knowledgeable people on something I knew nothing about, which is exactly what happened, although maybe some got a little too into it. Differing opinions are what results in more knowledge in the end, in my opinion. I hope I didn't come off as being disappointed in the performance of my truck, I'm not, but like those who are always looking for that little extra, I just wondered if the regearing would help a little, and maybe take a little stress off the tranny. Plus, it makes for more conversation with friends in the garage over a beer.http://www.dieselplace.com/forum/smileys/Big Smile.gif


I absolutely love the look of my truck, and wouldn't trade it for anything. I have always wanted a lifted truck, but every truck I've owned I've decided to wait on a lift until I got my dream truck, as I knew I would keep selling what I had as I moved up the rungs. Now I finally got "The Truck", IMO, and its no holds barred. I've spent more on this truck in 6 months then I've spent on my last 3 vehicles combined with no second thoughts.


BTW, with my J/A on 2, towing 10,000lbs on a lifted truck and lifted 5th wheel, there's still not too much that passes me on the road. Aside from the serious grades, a lot of the time I'm in the fast lane with the rest of the crowd.http://www.dieselplace.com/forum/smileys/Cool.gif


So I may still go with the new gears, but if not, the least that happened is I learned still more from the people here that are in the "know".

100 time better? Come on now really, that logic means it "could" now pull 500,000 lbs the same as the 5.3 did with 5,000lbs. If the 5.3 sucked that bad it was poorly geared for the load it was handling not because it could not do it.

Oh boy, here we go again.......http://www.dieselplace.com/forum/smileys/Disapprove.gif

Oh boy, here we go again.......http://www.dieselplace.com/forum/smileys/Disapprove.gif

No, I am not the one making rediculous claims, I am only pointing them out.

you seriously crack me up at times. I mean really, I'm at work laughing out loud right now....I actually cant stop I find it so amusinghttp://www.dieselplace.com/forum/smileys/HiHi.gif

Can't find the emoticon shaking his head back and forth.http://www.dieselplace.com/forum/smileys/HiHi.gif

100 time better? Come on now really, that logic means it "could" now pull 500,000 lbs the same as the 5.3 did with 5,000lbs. If the 5.3 sucked that bad it was poorly geared for the load it was handling not because it could not do it.





Uhhhh........OK?http://www.dieselplace.com/forum/smileys/Confused.gif You have to be kidding, right?


I was giving you the benefit of the doubt with your aggressive stances and shots at the other posts, as thinking you were just very stubborn. To each his own, but..............COME ON!!!!!!! If you thought that was a serious and literal statement I made you got issues. Ever heard of a little thing called figurative language? I think the other guys got it, thank God.


Ok, follow me closely.......I.....like.....my......truck. It's.....better......than......my.......last...... .truck. That's it.

Ok, follow me closely.......I.....like.....my......truck. It's.....better......than......my.......last...... .truck. That's it.

My poor dog was under my desk, I was laughing so hard, I just kicked her accidently. http://www.dieselplace.com/forum/smileys/HiHi.gif http://www.dieselplace.com/forum/smileys/Clap.gif

Gotta go make it up to the pooch. She doesn't understand.