Considering changing out the gears in the 83 F100. My biggest issue is that, at highway speeds, I feel like the engine is working it's **** off...as in it's turning such a high RPM, I worry about longevity. I have 3.73 gears with a 300 I6/C6 trans. Last time I took it on a short trip about an hour away, I was pulling a maybe 1200 pound boat/trailer setup, at 55mph, and it returned 15mpg. Not too shabby. This is the only "work" the truck ever sees. Other than that, it just gets driven around unloaded or to move boxes when I move.

I think the biggest thing I need to balance is pulling the light boat out of the water. It has no issues now doing it. But driving down the interstate, its running 2800-3000 just going 65-70. I'd like to step it down to a 3.08 or similar, but looking for input. I also don't want to cut the legs out from under the truck. I just know 3.73 is not ideal for me considering the trucks usual operating environment. I think 2.73 may take it out of it's comfort zone, but I'm not too sure.

Thoughts? 2.73? 3.08?

If I stick with the 3.73s, I'll likely try to find an AOD and boot the C6 (save it away for the future). I want to be able to run interstate speeds (which is everywhere I drive) without killing gas mileage or an engine.

 

I would look at installing the AOD if you are 3000 RPM at 70 the AOD would drop it to 2010 RPM at 70 in 4th.. keeping the 3.73's in the rear will still allow you to have the pulling power and off the line acceleration.

 

I vote some sort of overdrive trans also. That's what all the newer trucks are running to try and get the best of both worlds.

 

Fair, gents. I was trying to consider ease of swap and cost. But I think my dad may have an AOD mated to a 351 in an 87ish truck he’d sell me. That may be the route...

 

run the numbers. calculate driving 10K miles per year. Calculate current mileage estimated at 15 mpg, then recalculate at 18 mpg, and see how long it takes to financially break even for the amount it's going to cost. If this is strictly to get better mileage, you'll find it takes quite awhile to get back the money you invest in a new transmission. You can buy a lot of gas for what an AOD might cost, but sure, if you've got a free one laying around.....

 

I don't have a free one, my dad has a salvage yard, I could probably have it cheap though...and it isn't necessarily just the gas mileage. I am worried about running the engine at 3000 RPM everywhere I go. I feel like an AOD or a higher gear would turn the RPMs less and not work the engine as hard...

Maybe someone can tell me this though: should I be concerned about turning 3K on every trip? Am I realistically gonna hurt anything? I had always thought 300s shouldn't be run that high. But a lot of 4 cylinders and V6s turn that RPM on the interstate daily.

By the way, this engine has always had good oil pressure according to the gauge in the truck. It does have a part throttle rattle that is cured by either lifting off the pedal or pressing harder on it. Never figured out the reason. Probably gonna unhook vacuum canister and see if it goes away. I am wondering if it's over advance and I am hearing it ping. I don't think it is...but I should probably check.

 

The 300's don't like to be rev'd but 3K is not going to hurt anything but it will shorten the life span of everything including the engine, your part throttle rattle is likely a lean detonation. try pulling the vac from the vac advance and see if it goes away.

 

I have been through this with my diesel. It had a c6 originally with 4.10 gears. I swapped in a 5 speed overdrive. I got a donor truck and sold some of the stuff off it to recoup my costs. But I found out after I did the swap there are so many benefits other than fuel mileage. Like you said there is less wear on the engine, and it's so much quieter at cruising speed.

 

You could just slow down :-)
In 1983 the speed limit was 55 so the trucks didn't need to run 65 and 70
I could not drive 55 and California made a lot of money from me.
-HH

 

my 82 F100 (RIP) had a ridiculously low numerically gear ratio. with a C6 and a four wheeler in the bed starting up an overpass was like hitting quicksand.

now my 1980 Bronco is much better but it raps out a bit on the interstate. It has a square around the 55 on the speedometer.

 

AOD not available with 351W

 

So I read that after I posted this...what auto trans would an 87-90ish truck have had with a 351w?

 

I'm 22 and I want to keep up with traffic...plus make the hour drive to the lake in an actual hour. You're right that I could slow down, but that's not the point. I don't want to

Dumb old, podunk Weleetka, OK made their money from me for 35 in a 25 as I accelerated after I saw the sign, but before my car had actually passed it...anytime I go through there from here on, it'll be with a middle finger up as I carefully drive the speed limit

Ironically I have 3 cars and have gotten 3 tickets, but only one of them was in one of my cars. The others were on trips hauling or driving cars for my dad not a great business model for me.

 

I understand

 

You can put the AOD behind the 351W that is not an issue and was used behind them in the CVPI's till 91 and with the 5000 lbs tow package.