mullishacrew

is fuel milage worse with a 3 speed auto? or do you get a better fuel milage with a 5 speed manual? im debating on installing a manual tranny in my automatic, but it's a big job but id like the choice of me picking what gears and towing.

Chrisreyn

While a big part of that is probably in the gearing and the weight of your foot,
I have had two 5speeds and now have the auto., all with 3:54 rearends, one of the 5 spds was a 4WD and the other a 2WD. I just replaced my 93 D350 clubcab 5 speed with a 93 D350 clubcab auto.......

in both 5 speeds I was getting an average of 18-20mpg mixed driving and 16-18mpg towing the horse trailer fully loaded. The auto( A518) is averaging about 16mpg mixed driving and I havent towed with it enough to get a average on it yet.

I would LOVE to have this current truck with teh 5 speed in it!!

mullishacrew

ohh ok, well mines a 4x4 extended cab long box with 354 gears and modded injector jump fuel screw turned 3 times and smoke screw and fuel pin spun 180

flyingd

If your auto has the slush bucket TC it will get worse fuel mileage than the 5 speed. The slush bucket is always having higer rpm to get going especially when towing and going up and down hills. But with a good TC or the exhange to the 47RH the fuel mileage will be about the same. IMHO of course.

tomd

How does one determine if one has a slush bucket transfer case?

Thank you!
TD

wannadiesel

A 5 speed truck with 3.54's will always do better than a 727 auto truck assuming they are otherwise identical. The trucks with 518's do better than the 5 speed trucks on the highway lightly loaded due to the taller OD gearing.

G1625S

slush bucket torque converter, not transfer case

leper

I think that the main difference will be how you drive it(skinney pedal, weight of load, speed, type of road, etc)

mhuppertz

Manual transmissions are a direct link to the rest of the power train all of the time (with the clutch engaged). Automatic's are only directly connected only when the torque converter is locked (if so equiped) but still suffer from frictional losses because of the greater rotating mass of the internals and during shifting (overlap).

Fred Swanson

Loaded question, certain criteria will net a better result with the auto vs the manual. You mentioned you want to pick the gear, then switch to a 5 speed.

As Dave stated, the OD gearing in the Auto w/OD, will net lower RPMs crusing down the road. And with the right TC(Converter, not Case), an auto can provide decent mileage, which could rival any manual truck.

But, given a load, and picking the right speed, I would say the manual should do better.

dpuckett

IN THEORY, the taller gearing of the OD tranny (non-lockup, anyway) would give lower RPM. In prectice, it can be quite different. I hooked my tach up to my mom's pickup (identical to mine, only auto with a p/u bed) and went for a spin. I turned 2100rpm at 55 in OD; 2150rpm in 3rd I also turned about 2200-2250 in OD at 70. (For comparison, I turn 2050-2100 @ 50 in 4th; 2080 @ 70 in 5th.) The convertor is so sloppy, it actually gets better MPGs at 70+ than at 55-60. I know, it needs, work, it has needed work since she bought it from me. I sold it cause it needed work, and tried to talk her into looking on........

I also know guys who have seen 25mpg with a 2wd auto/ 3.07 truck. I have one of the 18-19mpg hwy manuals guzzlers.

Daniel

mhuppertz

If there is an automatic out there that gets the same mileage (all other things being equal) as a 5 speed, it'll be the first I ever heard of. Just look at the EPA mileage ratings of ANY vehicle line. The auto is always 2 to 5% less efficient.

tomd

oh I see! thank you!
lol

Fred Swanson

With the right Converter, it is possible to get very close if not the same as a manual in certain scenarios, like cruising down the highway. I'm not comparing a stock auto to a manual for the same generation truck.

And I stated, pulling a load, it would favor the manual. Ask me how I know, I've setup a few to know it can be done.

mullishacrew

you have put in a manual tranny into a automatic truck?, how did you go about doing this?