I finished up the '88 Town Car engine/tranny swap into my '76 Ford F-100, and I love it so far. The only thing that I didn't account for is the highway speed gearing with the AOD. I don't know what gear the truck currently has, but I do know that it is not the original gear. The RPM was of course pretty high at 65 mph with the original transmission, and now when I 'm cruising down the road with the AOD I feel like the gearing is way too high once it kicks into overdrive. I feel like I'm losing gas mileage because it is having to kick down to 3rd half the time because it's like the weight of the truck is almost too much to go down a level road once it hits overdrive.

I'll try to see if I can figure out the rear axle ratio, but I'm wondering if anyone out there has an AOD, and with what gear ratio do they have mated with it, and does the truck still pull slightly at 55-65 mph without having to repeatedly kick down into passing gear ever 30 seconds.

Thanks!

 

Give us some more info, please. tire sizes and what you do with the truck would be a start. In general, with stock 29-30" tires, I'd say a 3.55 or 3.73 is an all purpose rear with a 3.27 or 3.31 as an option if you do a lot of highway driving and 4.10s if you do a lot of towing. Don't see much use for a 3.08,2.73 or 2.47 in a truck, although Ford has built enough of them that way and gears bigger than 4.10 really only make sense with bigger tires. The next 17 replies will all disagree with me though.

 

Well, I'm running a 275/60-15. If I had to describe my overall driving needs, I would say I would want to have it be a highway driver. I don't do much hauling or anything, but I would like to be able to hook up a trailer and pull my lawnmower or something very, very occasional. I will use the truck mainly 90% highway driving.

I agree with you and say that a 3.31 OR 3.55 would be a good all purpose gear. Right now I feel like it has a 2.73 in it or something. When it hits overdrive it drops to about 1100 rpm on the highway. I don't really know the EXACT speed currently, but as soon as I can get some friends around I will try and get the 60 mph speed/rpm point figured.

I think that I should start looking at a 3.55 gear because that AOD has like, a .67 final ratio I think. I would like to be at about 1600 rpm at 60 mph I think. When you are at highway speeds and it's around 1100 rpm there's not alot of power there without kicking down. I just want to keep it from having to kick down all the time when it's on the slightest of inclines.

 

4.11 is the best gear to run IMHO.

 

Sounds like 3.55 would do it for you, with 3.73 still worthy of consideratoin since you do have overdrive. I wouldn't go any higher (numerically lower) than 3.55.