How does manually shifting into OD at around 55 affect fuel milage? Because now you are going at higher rpms for longer than if you were to shift to OD at around 40 and from what I thought the longer the RPMs are high, the less milage.

 

I don't beleive it should affect your mileage that much either way if your just accelerating up to speed and then putting into overdrive. Although your RPM's are higher your engine isn't working as hard to get up to speed since the RPM's are more in the power band. Now it might be a different story if you are running a long time at the higher RPM. I've seen a lot of people running lower gear ratios and thus higher RPM's that get as good as or ususally better gas mileage than people with 3.55's get and I beleive it's because the engine is more in the power band, running more efficient than luggin at a lower RPM. At least that's my opinion and the reason I'm thinking of changing diff gears.

 

My post was in reference to improving shift quality, but you bring up an interesting point. Take the scenario where you are merging onto a highway or main road where you can accelerate up to 55 mph right away. In this case I would say the fuel mileage would suffer very little because of the short amount of time that you are staying in the lower gears. Of course, if you are taking two miles to get up to 55 mph, your mileage will suffer and I will either be on your bumper or passing you. [sm=gears.gif]

I used 55 mph as an example, but the speed to shift into OD is basically whatever your final cruising speed will be. If I'm getting on the interstate where I will be running 65 - 70 mph, I will wait until maybe 60 mph to shift into overdrive. At that speed, my engine rpm's are high enough to produce enough torque to bring the truck up to speed in OD with relative ease.

I started a discussion on this topic a few months ago. I can't say that any consensus was reached. I've been playing around with my vehicles since then and have found that it is best to keep the rpm's in a range where you are producing more torque. With my truck, that means keeping it out of OD until I hit cruising speed. The truck is running around 1600 rpm's at 55 mph (if I remember correctly), which is not a good range for developing torque. With my car, I lift the throttle when I get just above 40 mph and let the torque converter lock up, then use the engine torque to bring me up to speed. So really, I would say it is dependant on your vehicles motor and gearing.

 

i dont do any of that crap i just drive,if it aint going speed yet, dont let off the peddle just keep accelerating, also dont let off cause u lose your accelerative momentum and so its easier to just get up to speed no q's asked then to f' around trying to get there... lol its a truck drive it

EDITmg im sorry but i have to quote myself

accelerative momentum, WTF iS THAT!! haha guess im making new words

 

DeiselDemon, "The tranny shift points can be altered via software reprogramming."

Ooooh yeah, now THAT is what I wanted to hear.

Okay, how? Where do I plug the laptop in?

 

on a good working tranny,,, you should actually feel/see the tc lock up in 3rd and od.. right before it shifts into OD. youll see the RPM's drop down really quick and then you will feel it shift.. ... thats what my tranny guy told me at least..

that link for the TV cable adjustment also helps build up higher pressure in the fluid and helping in firmer shifts.. its possible but check the clip that hols the tv cable jacket onto the braket... not sur ehow but it could have slipped or something giving you the effects your talking about..

 

Yeah I do see the RPMs drop down when shifting to OD like you said.

And to correct myself earlier it idles around 600-700 RPM

 

UNless my memory fails me, which it often does, there was a TSB issued from Dodge for this shift problem. I had a 98 Sport model that did the exact same thing. IN my immediate area we have a crap load of 30-40 MPH speed limits and the truck would constantly shift back and forth between second and third gear. I would either have to slow down or break the speed limit to get it to stay in one gear. The dealer did a computer update and it solved the problem.