Transmission and Rear End Gearing

[dorkweed]

OK guys, I've been thinking of this thread now for a while.Why do our trucks have an "over-drive"??? The strongest gearing in our transmissions is direct or 1:1. It would seem to me that for a truck that's designed to tow........that's what you would want cruising. Add a gear or two in front of first......remember Granny gear??...........and change the differential gearing to 3.27:1 or 3.07:1 or higher. See where I'm going here???Why aren't our trucks geared that way?? Am I misssing something???

[dripley]

from my view point my 1st gear has the engine turning 2k rpm at 7 mph which seems to be plenty low enough to pull my 13.5k 5th wheel. i just let the clutch out and it goes. i dont think i need anything lower than that. as far as od, my truck will pull the trailer in 6th on flat ground and slight inclines with no problem at half throttle though egt's get alittle high. i probably should have been using 5th instead. learned that here. od is great on the highway when you are not towing and want good fuel economy. if we change our diffs to what you suggest would that not cause us to loose the granny gear you speak of? the 1 to 1 in 5th would be gone also. i spend more time driving than towing so that does make a differance and i am glad i did not get a 4:10 rear end on mine. for my money i would rather have double over drive than one more lower gear. one more lower gear in reverse would not hurt my feelings though. just my .

[dorkweed]

I think you're missing my point. You can essentially achieve the same gear reductions via the differential gearing. Over-drive is great, don't get me wrong.......I love the low RPM's, but you could achieve the same engine RPM's in direct drive with a "taller" rear end.

[Mopar1973Man]

Kind of reminds me of the Chevy 1 ton fire truck we have in the fire dept here. Its a 3 speed manual transmission with 3.27 gears. It so tall legged than 3rd gear is worthless come to any hill or grade. and Your stuck in 2nd... I thing what would happen it you'd reach the same gear ratio but the overlap of gear would be lost...

[dripley]

it would not take alot for me to miss the point. i dont know alot about gearing, but if i am seeing it right by adding another gear in front of first and a taller gear in the rear end the transmission would be physically stronger.

[flagmanruss]

Well I had a gas GMC (305 cid) with 3.07s & it was horrible. I lowered the ratio as far as I could with that carrier. My 68 Plymouth Road Runner 383/727 auto, 3.23 (14" rims) was a a fine well balanced car. My Chevy C30/454/auto/3.73s/16.5 was a towing fool... at 11mpg (loaded or empty).

I do agree a multispeed transmission, with a 3.23 or 3.55 (big wheels) would be a better combination. OD is fine for running empty...

edit

When I got this truck, it was my first full sized diesel (Ranger 2.2 & JD backhoe preceded it). I didn't realize that the diesel engine really made little difference to the effects of the ratios (my opinion, now). The stock ratio is much better than the 4.10s I got unless one is going to run much bigger wheels. I'd be much happier if this truck had 3.23s or 3.55s. I relied on the f*cking salesman & he wanted to sell the unit on his lot.