thaimonkee

Havent posted in awhile. Been out of the game and finally picked up another Dodge. Its a 2006 4x4 3500 DRW. G56 trans with 3.73 gearing. My question is when driving on the highway at 60 mph the rpms are at 2k. When at 65mph its spinning over 2500 rpm. Havent even gone over 70 mph cause it will spin over 3k rpm easily. Ive done some searching and everyone is running much lower rpms than what I am. What gives?

steelblitzkrieg

Is that in 5th or 6th?

I assume 6th, if so it sounds like someone changed the rear end.

Danderson

Your G-56 replicates an auto w/4.11's due to the very low 0.79 overdrive.
Mine does the same. Regearing(expensive) or taller tires will give you some rpm relief.
Starting with the latest 5.9's and continuing with the 6.7's the final drive ration was updated to 0.74 yielding lower rpm's.
It's typical to be reaching for a 7th gear.

steelblitzkrieg

Wow, that sucks.

I-5 must be redline, huh?

thaimonkee

Yes. Thats in 6th gear. I have the factory 235/80/R17 tires. Thinking about getting 255/80/R17. Hope that will drop the RPM down a bit

So most of the late 5.9 have this problem with the engine spinning this high? Im stuck driving at 60 mph tops.

thaimonkee

Did you get taller tires to fix this? I do not want to regear

BILTIT

I think you will need a taller tire than that to make much of a change. According to a calculator that change in tire size will net you 2.5mph difference in speedo, whats that in rpm? 100rpm?

Danderson

Yes. 285-75-17's gave me some relief. They're about 34" tall.
My next tires will be 35's which actually only yield a 1/2" increase in height. 18's have some taller,narrower sizes.
Regearing is super expensive and a $4K Gearvendor setup isn't recommended for towing or use with a exhaust break.
65 mph nets 2000 rpm on mine.
For hauling my 1800# camper around all the time the gears actually help with driveline wear. My stock dmf clutch was like new @ 37K when I upgraded to the SBC OKHD.

Danderson

The 6.7's had a higher geared final drive so they got some relief.

jumper

I've been researching Gearvendors units for my four speed automatic. GVs are expensive, but they are definitely recommended by the manufacturer for towing up to 30k pounds combined. They do say not to tow in double overdrive (OD in the transmission + OD in the GV).

The GV will also work with exhaust brakes, but, they want the GV in direct when the EBrake is in play. Don't use the EBrake with the GV unit in OD. The GV overdrive section doesn't like a large deceleration load applied. The overdrive section is designed to be driven by the unit's input shaft, not by its output shaft. When in direct, no issues with the EBrake.

thaimonkee

Im looking into the 285/75r17 Toyo AT 2. Doing some research and these tires will need a 2" spacer if I plan on hauling a toy hauler. Hoping this size will give me some RPM relief.

saggonwaggon91

Swap over to the NV5600, it will give you 70mph @ 2150ish RPM. Plus you get away from dualmass flywheel and get a stronger trans..

thaimonkee

The truck already has a dual disc clutch installed when I bought it. Not sure the brand whether its a South bend or Valair.
I think I will try larger tires first and see how it goes from there.
Thanks for all the replies.

nvrenuf

Is your tach working correctly? When my tach started going bad it would read high, eventually it became erratic over the entire scale. Now it stays around 1k all the time, it took about a year to reach this point.

I also have an 06 w/ G56 & 3.73's and have never experienced rpm's like that. Typically mine will turn around 2200-2300 at 70 w/ 33" tires. Unless you're experiencing some clutch slippage (and assuming you still have the 3.73 rear axle) you can't be turning that much rpm.

47Dodge

I agree! Something isn't right.




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