Overdrive or Taller Gears for Fuel Savings

[Bernie]

What would an exhaust brake have to do with a manual transmission. Wouldn't the brake be connected so it applies back pressure when you are off the throttle at speed?

 

[J.BURCHFIELD]

I can't see how an overdrive unit could interfere with an exhaust brake. Sounds like the competition trying to spread a rumor to their advantage. When you look at it, it is just another gear. It is like saying if you had a 7 speed tran your exhaust break would not work in 7th gear. Knocking the RPM down 500 RPM at 70 MPH is a nice noise reduction and I like mine. They are expensive and maybe not worth the money. It is an individual choice.

 

[ENafziger]

Actually, it's not the competition that says you can't use an exhaust brake. I emailed Gear Vendor directly yesterday, and here was THEIR response:



"We require the Gear Vendors overdrive to be off when you are using your exhaust brake, and using your factory 6-speed transmission ratios to control road speed when deaccelerating. Early exhaust brakes would have a separate switch that would activate the system into a standby mode, then you would either activate the brake with a switch on the shifter, or accelerator pedal, to control speed under deacceleration. We would attach a "lockout" wire to that underdash control switch to lock out the Gear Vendors unit. With the newer Dodge applications, since the vehicles computer is the control for the brake, there is not a separate dash switch that controls the initial operation. These late model Dodge vehicles are unable to use our lockout system. So, we instruct the owners that they must turn the Gear Vendors system off first, before activation of the exhaust brake. "



The gear vendor unit appears similar to a miniature automatic transmission. If you remember, it wasn't until '06 that dodge even developed an auto trans that allowed an exhaust brake to be used on an engine. There is a lot of "reverse" torque being applied when the exhaust brake hits. When downshifting quickly into 3rd gear, my Jacob's exhaust brake will break both back tires loose on dry pavement and leave some pretty good patches of rubber



If I were to get an overdrive unit, it would be to keep the rpm high to assist in braking as much as for the advantages in acceleration. To keep track of what gear you were in, whether it was a split gear or direct, turning on/off the exhaust brake, and then turning on/off the overdrive unit would be a little cumbersome to say the least... especially when traffic stops quickly on the interstate and you've got 16,000 lbs on your back.



Both an exhaust brake and an overdrive unit have their advantages when towing heavy. Not being able to use them together to me would be a big disadvantage!



Hope this helps clear things up... Eric

 

[Bernie]

E-mailed AAM

I dropped AAM's sales department an e-mail about getting taller gears for my axles. I got an "out of office" auto response. I'll post if/when I hear back from them about something taller than a 3. 73.

 

[geusterman]

Speaking from experience (ahem ), I went to all the frigging trouble to GV (the best) my 02 6spd 3:73. Why... same reason... seemed like I needed another gear on freeway... A lot of money later... I was cruising about 1650 at 70 (with 33" tires... which were 19. 5's). I would just go with tall skinny tires if I were to do it again. I cannot tell you I saved fuel... but liked the quieter motor. It was right at peak torque... so not too hard to accelerate. I have an auto now with higher top gear. Taller tires is easy way out especially with your mileage. GV's are tough. George

 

[TAbbott]

For whatever it's worth, 265-70 R19. 5's on steel Ricksons (34. 5 in diameter) will fit on 3rd gen 4x4 trucks w/no lift w/o interference. These tires/wheels are 602 revs per mile, compared to 656 revs per mile for the Michelins in 265-70 R17. That equates to approximately an 8. 3% reduction in engine rpm at any given speed. Where you were turning 2400, you'd be turning 2202 or roughly 200 rpms less at whatever speed 2400 rpms delivered before. These are heavy tires and wheels and eat some power getting up to speed, but for long distance cruising they'll just work like a bigger flywheel helping you maintain speed over overpasses and the like. They also require slightly greater brake pedal effort when it comes time to slow down. They're relatively narrow, w/ a 10. 2" section width and 8. 1" tread width. They fit inside the wheel wells (at least they are inside OEM Power Wagon fender Flares, which aren't very wide) and roll pretty freely at 55 psi or so. They also look really nice on the truck, filling up the wheel wells w/o protruding outside the stock vehicle lines and they should wear like iron, probably getting at least double if not more than the stock tires and wheels before needing replacement. Just one more alternative and about 1/2 the price of a Gear Vendors unit.

 

[Bernie]

Thanks, but there are a few things I don't like about taller tires:

-Taller truck! I don't go offroad anymore, so the stock height is overkill. It is already difficult for some (shorter) people to get in and out of it.

-Taller truck! More wind resistance .

-Taller tires are heaver and need more power to get them moving.

-Even though I'll be at less RPMs, the additional fuel consumption because of the above items will probably negate the advantage.



Also:

-Taller trucks don't handle as well (not that I bought this truck for its handling). In an emergency maneuver they are more likely to roll over. I was in a 4xi4 rollover years ago, and don't want to take that ride again.

-Taller tires are wider, and worse in wet conditions and really bad in snow conditions.

-Taller tires cost more than stock sizes. You buy new gears or an overdrive once, but have to keep buying more expensive taller tires for the time you own the truck.

-I run dedicated snow tires. If I got to 19. 5" wheels with taller tires, the snows that I use (Hakkappellita) are not available.

-Taller tires wear suspension/wheel bearing parts faster.

 

[geusterman]

Then figure $2800 installed by others for GV. Lots of fuel there... but if you are really gonna keep your ride to 500K... what the heck! George

 

[Bernie]

Then figure $2800 installed by others for GV. Lots of fuel there... but if you are really gonna keep your ride to 500K... what the heck! George

Thanks, but I haven't given up on finding some taller gears for the diffs. That would be cheaper, although I would loose some pulling power all of the time, where with an overdrive I would only loose it when it is engaged.

 

[Bernie]

but if you are really gonna keep your ride to 500K... what the heck! George

Probably 300K for this truck. I'm sure I will get board with it, but it is the most I've ever spent on a vehicle. I'm no stranger to high mileage:



-I got my 85 Toyota 4 Runner at 80K and kept it to 250K

-I got my 95 Dodge Ram Sport at 120K and got rid of it 10 months later at 174K

-I had my 03 Toyota Tundra for 90K in two years.

 

[ilovetrains]

best of luck

This question has been asked many, many times. I have an 05 with the G56, and was surprised at the highway RPM. I think the estimates of 1. 0 MPG improvement or more are dead on.



BTW- there is NO other axle ratio available. Again, beat to death. People have been pleading with AAM to make another ratio for almost two years. They haven't. There was talk that they would for the 07, but since DC changed the auto to a 6 speed and expect to sell alot more auto trucks than manual, we are left out in the cold.

 

[Ross]

BTW- there is NO other axle ratio available. Again, beat to death. People have been pleading with AAM to make another ratio for almost two years. They haven't.

Check out this link: AAM



It looks like the 11. 5 AAM is available with anything from a 3. 54 on up to a 5. xx? I checked out Richmond Gear, and couldn't find anything, but AAM may? I haven't called them, but it's worth a try. I too have a new G56 w/3. 73's and want som more room on top... .

 

[JHardwick]

When are ou guys gonna get the REVs down to the point that you HURT mileage due to lugging??

 

[J.BURCHFIELD]

On the old 12 valves peak torque is at 1300 RPM. I understand it is a much higher RPM for the 24 valves. I seriously doubt 1500 RPM at 70 MPH is lugging my 12v. Mileage did not change when I installed the GV unit. Towing or otherwise. The only thing that helped mileage was when I put in Marine injectors but only when towing. EGT and water temp. would indicate lugging but the temp. stays the same towing or not towing. Also before the GV was installed the temp. was no different. It is my opinion that Dodge used the Auto tran that they use in the gas powered Rams when in reality they should have used a tran with more speeds as I hear they are doing now. -- email address removed --

 

[CBorzoni]

I have a nv5600 trans with 3. 73 gears and you are absolutly correct about needing another gear. I installed a Gear vendors unit and would not ever turn back since the install. With out the gear vendors unit 6th gear seemed to top out at 70 mph not that i couldn't go 85mph if i didn't want to but the engine was turnig alot of rpm's. The gear vendor unit made my truck a joy to drive as now i can go 85mph and still be cruising, heck i can't even shift into 6 od until i am going 70 mph then i cruis at like 75-80 mph and get great mileadge of course this is when i am not towing. If i am towing i run 5th od and it is like running in 6th gear normally. i saw an increase of 1-2 mpg depending on towing or not and my right foot but if i drive normally it will get you better mileage. Gear vendor rates their units at 30,000 gvw and are supposed to go 250,000 miles before an overhaul.



good luck, CB

 

[RollOver_Pete]

Had a 6 x 4 in a 1978 Pete. Those were the days. I wonder if Spicer makes or made a 2,3 or 4 speed brownie that one could fit behind our 6 speed trannys? Think about it... A set of sticks in a 3500 Ram

Too cool!

 

[cojhl2]

I loved those transmission setups. You had to understand gear shifting in htose days. None of this pansey syncro stuff and air shifts!!!





But when you grew up with early Ford transmissions that had gears big as bricks and just as square you learned at an early age what "Match the gears" meant.

 

[J.BURCHFIELD]

Drove semis 1966 to 1982 so based on my experience I would if I could like to have a 9 speed road ranger (Fuller) which is your standard 5 speed with a high range/low range air shift by a pull up push down lever/button that you use to repeat 2nd 3rd 4th and 5th while in high range giving you 9 speeds forward. First/low you would not need so you would only use 8 speeds. There were a lot of 13 speed trans which was a 9 speed with a direct and overdrive that was used in the top 4 of the 9. There could be an 8 speed out there. I have heard of them but never drove one so hesitate to say they exist. Spicer had a two stick affair, a 5 speed with a 3 speed bolted up behind the 5 speed called a 15 speed. If a 3 speed could be still obtained today I would think that would be ideal to put behind. Some of the old Mac's had 10 speeds by using a 5 with a 2 bolted on behind (2 sticks) but that was so long ago they have probably all been melted down by now. While I was still driving I heard about an Allison 16 speed automatic. Don't know how they worked out. GM built an automatic for semis and I heard one trip and they self destructed. I really think the ratios would be all wrong. We used 4:11 rear ends and 20 or 22 inch wheels. There were other ratio rear ends but close to the standard 4:11 or what seemed to be standard. -- email address removed --

 

[Jong]

There was an add-on transmission for sale a couple of years ago called a Brabnod Mountain Gear for off-road rigs built by some guy out in Colorado that gave you four extra air-shifted gears. They were usually set up for deeper low range 4x4's for better crawling ability, but I'm sure it wouldn't be too hard to refit one for overdrive. They were built out of semi parts with straight-cut gears for strength, somewhere around 2000+ lb/ft. They were only about 8" long as well, and obviously you were able to use 4wd with it. Not quite sure what happened to them, but something like that would solve a lot of our problems without having to regear the axles.

 

[Bernie]

I think the estimates of 1. 0 MPG improvement or more are dead on.

Thanks. I'm hoping to find owners with a G56 that have done this to see what their real world increases were to see if it was worth it.