wrong gears in the differential?

[MMFinkel]

I have a 2006 Dodge 2500 Mega Cab (diesel) with a manual transmission, stock tires and per the order, window sticker and specs, a 3. 73, limited slip rear end (the 4. 11s aren’t even an option for the manual transmission). I noticed how high my rpms were at highway speeds (about 2,000 rpm at 60 mph in 6th). I started comparing them with other similar trucks my friends had and they were turning less rpms at the same speed. I then checked my ratio by jacking up the rear end, marking the drive shaft and rear tire and with the truck in neutral, the drive shaft turned a little more than 4 times for one revolution of the tire! This should mean that it is a 4. 11 rear – right?



When I took it to the dealer they confirmed the truck was speced with the 3. 73 and claimed they compared it to other trucks on the lot and had the same results I did. Their explanation was that “for some technical reason they couldn’t explain” those differentials (implying the limited slip ones) just did that but it was still a 3. 73 rear. Since then, I did the same test on a friend’s 2006 2500 quad cab with an automatic transmission and 3. 73 NON limited slip rear and the drive shaft turned the expected 3. 73 times for one rotation of the tire. I find it hard to believe the fact that mine is a limited slip makes it behave exactly like a 4. 11 but I am not sure of the next step I need to take with the dealer since it is basically my word against his unless I can find an identical truck with the limited slip that does the same.



Also, my same friends truck turns about 300 less rpms at 60 mph than I do. Now, he has the automatic transmission but the final drive in an auto is not as tall as 6th gear in the manual so all other things being equal, mine should be turning less than his!



I am looking for any thoughts or comparison on this from others with an identical truck. By the way, the truck is a 4x4 and it performs fine in four wheel drive so I assume the front and rear gears match.



Thanks!

 

[JFaughn]

I agree with you , to find out for the dealer battle , take the diff. cover off , rotate till you can see the stampings on the ring gear , that will be the absollute , then I wouldn't feal comfertable with out looking at the front diff. if you have one .
Go back to the user control pannel and fill in as much info as you can get , so we can know how to answer , also get a build sheet , heres a link , haven't tryed yet ,

Contact Dodge

 

[nickleinonen]

Now, he has the automatic transmission but the final drive in an auto is not as tall as 6th gear in the manual so all other things being equal, mine should be turning less than his!

g56 6th gear is not as tall as the nv5600 or 48re. . 3. 73 gears + g56 in 6th = same rpm as 4. 10 gears & nv5600 in 6th...



did you have both tires in the air turning when you did your count? if one is stalled, the count goes wacky [double what it should be if there is 0 movement on the other wheel, lower if the other turns slower than the one you are turning to count turns]

 

[JHardwick]

The G-56 isn't offered with a 4:11, but it's geared to make a 3:73 turn the same R's as a NV5600 with 4:11's.

 

[JHardwick]

g56 6th gear is not as tall as the nv5600 or 48re. . 3. 73 gears + g56 in 6th = same rpm as 4. 10 gears & nv5600 in 6th...

ya beat me to it, lol

 

[MMFinkel]

g56 6th gear is not as tall as the nv5600 or 48re. . 3. 73 gears + g56 in 6th = same rpm as 4. 10 gears & nv5600 in 6th...



did you have both tires in the air turning when you did your count? if one is stalled, the count goes wacky [double what it should be if there is 0 movement on the other wheel, lower if the other turns slower than the one you are turning to count turns]

I did have both tires in the air turning when I did the count (I tried it the other way and noticed the wackyness!). but are you saying that the gearing on the auto trans in an 06 2500 is geared taller than the manual? I thought it was the other way around when I read the gear ratios in the catalogs?

 

[Prairie Dog]

As I remember the auto is higher geared but that still doens't explain your counting the revs of the drive shaft and wheels and then coming up 4:11 gearing.

 

[oneshotkyle]

YES auto's have a taller O/D gear. they should turn a hair less RPM's at the same speed. .

 

[nickleinonen]

g56 = 0. 79 od

nv5600 = 0. 73 od

48re = 0. 69 od

 

[cojhl2]

I did have both tires in the air turning when I did the count (I tried it the other way and noticed the wackyness!). but are you saying that the gearing on the auto trans in an 06 2500 is geared taller than the manual? I thought it was the other way around when I read the gear ratios in the catalogs?

How were you sure the spiders wern't working a little. It would not take much to show the difference you are talking about.





edit:

Oops,, if that were the case the observed ratio would be less than 3. 73 wouln't it!!!



edit again:

Waitaminit I was right the first time wasn't I?? Brain hurts!!

 

[MMFinkel]

OK, I appreciate the replies about the difference in ratios of the 4th gear auto vs the 6th gear manual and apparently I was incorrect there (although at . 10 difference I find it hard to believe that makes 300 rpm difference - must be the lockout torque converter?). However, I still am interested in how my drive shaft could be turning 4. 11 times per tire rotation and still be a 3. 73 gear?



Thanks for everyone's help!

 

[sag2]

Just pull the cover and count the teeth. Takes all the guessing and speculation out of it.

 

[klenger]

Assuming that you have stock tires, go to the 2nd page of this document and compare RPM's and speeds.



http://www.klenger.net/dodge/general-reference/gear-speed-calculator.pdf



You can also download this worksheet and enter your own numbers.



http://www.klenger.net/dodge/general-reference/gear-speed-calculator.xls



I'm sure you will find that you have 3. 73 gears. The limited slip was probably messing up your test.

 

[Matthysse]

My 06 DCTD is running the same mph & rpm as Mr MMFINKEL, had the diff covers of to change the oil & rotate tires, done by Hemlock transmissions today, rotated the assembly on the rear diff and found the stampings on the ring gear, 11 - 41, 41 for the ring gear divided into 11 for the pinion gear = 3. 72727 (3. 73). Hope this helps. If anybody in the West Palm Beach & surrounding area or anybody coming in for a visit and are in need of a good shop the folks at Hemlock are outstanding always there to help.

 

[AMink]

When I was looking to get an 06, I drove both G56 and 48re. Both were 3. 73's and the G56 ran quite a bit higher at the same speed. If you do a search, you'll find quite a bit of reading regarding the issue. BTW, welcome to the TDR!

 

[HNelson]

Your RPM vs. MPH you see on the instruments has nothing to do with your gears, it displays whatever it's programmed to display. So figure out if your speedometer and odometer are accurate by setting the cruise on the highway and counting mile markers. If your cluster is correct you can do some easy math (or use the readily available calculators on the internet) to figure out what gear ratio you have.



More than likely when you were turning the tires to count driveshaft revolutions the two tires were not during at the same speed, which would screw up your measurement. I'm not sure how the gear driven limited slips work as far as the tire backdriving the driveshaft... but it very well could not be a 1:1 ratio.

 

[RustyJC]

My truck has an NV5600 with 4. 10 rear axle. It runs 2000 RPM @ 60 MPH and 2350 RPM @ 70 MPH - GPS verified. Your G56 truck with 3. 73 axle should be about the same.



Rusty

 

[CUMMINZ]

Leave the vehicle on the flat surface and mark the bottom of the rear tire and bottom of the shaft. Roll the vehicle forward till shaft makes one complete turn see where the tire mark is. It don't make any difference as to the type transmission you have. :-laf

 

[DJennings]

Leave the vehicle on the flat surface and mark the bottom of the rear tire and bottom of the shaft. Roll the vehicle forward till shaft makes one complete turn see where the tire mark is. It don't make any difference as to the type transmission you have. :-laf

The driveshaft will turn 3. 73 times for each revolution of the tire. That means that for one revolution of the driveshaft the wheel will only turn about 97 degrees of a full circle.



He did it right. You mark the shaft at the pinion. You raise the rearend, rotate the tire one complete turn, and count the revolutions at the driveshaft. It's a lot easier doing that, than rolling a truck around.

 

[J.BURCHFIELD]

When it comes to telling the truth Dealers and Politicians have a lot in common