What Transmission for my 1971 F100 w/ 302?

[kcpat10]

I have a 1971 F100 with a 77 302. I have a C4 in it now but am wanting to upgrade for OD/MPG and towing capabilities. I was leaning towards a C6 but have learned that my engine it to small for the bolt pattern. The engine is new so sticking with it. Any suggestions?

[michael69]

There are small block C6 transmissions. I have one behind a 351w and a 302. But they don't have OD. You will have to go with another transmission if you want OD.

[kcpat10]

There are small block C6 transmissions. I have one behind a 351w and a 302. But they don't have OD. You will have to go with another transmission if you want OD.

Would that still be better for towing? I want to be able to tow a 19-22ft travel trailor with it.

[basketcase0302]

I have a C-6 behind my "little 302" (as some folks here call them). It holds it's own as far as hauling weight. But it sounds like you might want to look into your ring & pinion ratio versus transmission swap-economics wise. Maybe Dustin or someone more versed in the AOD's will pipe in here soon.

[kcpat10]

I have a C-6 behind my "little 302" (as some folks here call them). It holds it's own as far as hauling weight. But it sounds like you might want to look into your ring & pinion ratio versus transmission swap-economics wise. Maybe Dustin or someone more versed in the AOD's will pipe in here soon.

Thanks, any advice is welcome. I don't know much about the AOD's. Is your C6 w/o OD?

[Donnie]

The output shaft ratio is the same in 3rd gear in both C4 & C6...The C6 is larger thus stronger than the C4.
Both tranny's are 3 speeds.......The AOD is a 4 speed with 4th being OD. Your 302 / C4 will handle your towing if you are not in the mountains...The AOD is not a good choice for towing unless your rear end ratio is LOW.....Then your non towing mileage will suffer as well.....
The AOD trans is a bit unusual when in OD, there is no converter slip as the input shaft is splined directly into the front cover of the converter, which means that there is NO converter slip / RPM diff...That is why the AOD is a little jerky on the 3--4 shift....
3rd clutch burn out is common in the AOD---if you lose 3rd, you will lose 4th...
I tend to stray a bit, but to answer your question more directly, you can not have great pulling power & good mileage both.......How much towing vs. how much open road non towing are you doing.......This, only you can decide...Donnie

[dirtwrench]

I'm with Donnie on how much do you pull the trailer vs how much do you drive without the trailer?

If your 302 is basically stock, the C4 will handle whatever the engine will pull. If you plan to do a lot of towing, you may wnat to invest in a trans cooler and a thorough trans flush/tune up.

my

[kcpat10]

The output shaft ratio is the same in 3rd gear in both C4 & C6...The C6 is larger thus stronger than the C4.
Both tranny's are 3 speeds.......The AOD is a 4 speed with 4th being OD. Your 302 / C4 will handle your towing if you are not in the mountains...The AOD is not a good choice for towing unless your rear end ratio is LOW.....Then your non towing mileage will suffer as well.....
The AOD trans is a bit unusual when in OD, there is no converter slip as the input shaft is splined directly into the front cover of the converter, which means that there is NO converter slip / RPM diff...That is why the AOD is a little jerky on the 3--4 shift....
3rd clutch burn out is common in the AOD---if you lose 3rd, you will lose 4th...
I tend to stray a bit, but to answer your question more directly, you can not have great pulling power & good mileage both.......How much towing vs. how much open road non towing are you doing.......This, only you can decide...Donnie

That was very educational! You prabably just saved me a lot of $, Thanks! Is there anything I can do to my c4 other than a cooling system to improve on the good thats there?

[kcpat10]

I'm with Donnie on how much do you pull the trailer vs how much do you drive without the trailer?

If your 302 is basically stock, the C4 will handle whatever the engine will pull. If you plan to do a lot of towing, you may wnat to invest in a trans cooler and a thorough trans flush/tune up.

my

Thanks for adding your I do drive my truck everyday so that is just as important as towing. I don't suppose you know anything about gear ratio? The front 1/2 of the truck has been rebuilt but I haven't touched the rear end...

[kcpat10]

I'm with Donnie on how much do you pull the trailer vs how much do you drive without the trailer?

If your 302 is basically stock, the C4 will handle whatever the engine will pull. If you plan to do a lot of towing, you may wnat to invest in a trans cooler and a thorough trans flush/tune up.

my

OH! and any suggestions on a carb? Leaning towards Holley...2bb...I want to stick with something under 500cfm to save the MPG.

[Whateverman]

I'm with Donnie on how much do you pull the trailer vs how much do you drive without the trailer?

If your 302 is basically stock, the C4 will handle whatever the engine will pull. If you plan to do a lot of towing, you may wnat to invest in a trans cooler and a thorough trans flush/tune up.

my

get the biggest tranny cooler you can & bypass the one in the rad
a c6 will suck away more power than the c4,302's need all the torque they can muster up,they feel even softer with a c6 behind em
i used to haul a 30ft travel trailer and my c4 never seemed to mind- the brakes,well thats another story....


as for a carb,personally i'd go for small (450CFM) 4bbl over a 2bbl on a 302 anyday (i'm running a 600cfm edelbrock,but its a little too big ) ....... none the less they're better on fuel with a 4bbl

[kcpat10]

I'm with Donnie on how much do you pull the trailer vs how much do you drive without the trailer?

If your 302 is basically stock, the C4 will handle whatever the engine will pull. If you plan to do a lot of towing, you may wnat to invest in a trans cooler and a thorough trans flush/tune up.

my

get the biggest tranny cooler you can & bypass the one in the rad
a c6 will suck away more power than the c4,302's need all the torque they can muster up,they feel even softer with a c6 behind em
i used to haul a 30ft travel trailer and my c4 never seemed to mind- the brakes,well thats another story....


as for a carb,personally i'd go for small (450CFM) 4bbl over a 2bbl on a 302 anyday (i'm running a 600cfm edelbrock,but its a little too big ) ....... none the less they're better on fuel with a 4bbl

Thanks, will start looking at tranny coolers. I will alsocheck into the 450.

[dirtwrench]

Sorry I have been bogged down in the "real" world for several days. Donnie has answered all your questions except the gear ratio. Myself, I would check what is in the truck now. If I have to make a bet, Probably a 2.75 open. I have pulled a trailer more miles than I care to admit with a 302 or 351w, c4 or c6, and a 2.75 gear set. You feel like you need Fred Flintstone to help get a load moving. I swapped the gears in 1 truck to a set of 3.25 and WOW did that help. My mileage went down about 1 mpg and it was worth it. Getting a 6x16 bumper hitch stock trailer moving or a flatbed with another project became so much easier on everything.

Now I am lucky enough to drag those trailers with a V10 super duty. The mileage is scary bad, but set the cruise @ 70mph with a load of calves and lean back.

[j41385]

I know I'm kinda late in the game replying here, but thought I would put my in. You may have made your mind up to go with a C4, and that's fine if so. I have an AOD in my truck from a 1993 F150, so its non computer. The Shift pattern is P R N OD D 1, so when I tow up hills or in the mountains I just put it in D, then it acts like a c4 does because 3rd gear is 1:1. The Aod's 3rd gear however, is more efficient because 3rd gear is 60% lockup so it feels solid almost like a manual trans. On flat ground you can tow in OD just fine. Add to that better mpg when just driving. I would also add that all modern automatics lockup in overdrive, so it's not a bad thing.

I paid 275 dollars for my AOD at a wrecking yard, and 70 to my trans guy to inspect it. Turns out it was recently rebuilt and had a shift kit installed. The truck it was out of was really nice, so it was a Cash for Clunkers trade in.

Plus if you already have a C4, I will show you this picture for length comparison.



So if you wanted an aod you would need a Flex plate from an 85 F150 with a 351w that came with an AOD, which can be bought at napa. I say 351 because it has the same balance as your 77 302. 302 flex plates made for the AOD are after the 1981 balance change where they went from 28 ounce to 50 ounce. You will also need carburetor linkage corrector, and throttle valve cable bracket, both of which I got at summit. Less than 100 dollars if I recall correctly.

Anyway just a thought.

[kcpat10]

Sorry I have been bogged down in the "real" world for several days. Donnie has answered all your questions except the gear ratio. Myself, I would check what is in the truck now. If I have to make a bet, Probably a 2.75 open. I have pulled a trailer more miles than I care to admit with a 302 or 351w, c4 or c6, and a 2.75 gear set. You feel like you need Fred Flintstone to help get a load moving. I swapped the gears in 1 truck to a set of 3.25 and WOW did that help. My mileage went down about 1 mpg and it was worth it. Getting a 6x16 bumper hitch stock trailer moving or a flatbed with another project became so much easier on everything.

Now I am lucky enough to drag those trailers with a V10 super duty. The mileage is scary bad, but set the cruise @ 70mph with a load of calves and lean back.

Truthfully, I have worked on every part of the truck except the rearend so I haven't a clue about my gears yet. I can tell you that the truck does NOT like hills! Fred Flinstone is a good comparison. How do I find out the ratio?