C6 Croaked, need advice

[Sazman]

I haven't posted in a long while, but I do check up on the forums regularly, always learning something. Here's my dilemma, my 72 f250, 390 with C6 has never got better than 10-11 mpg (empty), in the appx. 3 years I've had it. Nothing really too unusual about that. However, the tranny has been showing signs of dying, and now apparently has. I have been reading about some of the different ways that guys have installed OD trannies behind FE's and am not sure I want to do that. I do have an Np 435 tranny,(thanks JOR) that I could put in, I have an older 62/63ish brake/clutch pedal set laying around, and here's what I really need advice on. My rearend in there now is the Dana 60, 4.10 gears. I have a 69 parts truck with a slightly better(higher) ratio, 3.89 I think. Is there much chance of any significant mpg gains if I put in the np 435 and swap out the Dana 60's? Can a relatively handy guy fab up the adapter needed to go from the FE bellhousing to a AOD or similar OD automatic? Any and all thoughts are welcome.

[ToughOldFord]

FWIW, I had 4.10s and got 8mpg in my '69 F-250. I went to the next set up, 3.73, and although my RPMs on freeway driving dropped 200, my mileage did not improve one bit.

However I did recently ditch my C6 for a NP 435 and gained about 2mpg.

[Sazman]

Glad you got an improvement, 2 mpg is pretty good on these old gas suckers. Wonder why you didn't make any gains on the Dana ratio change? Oh, I went and looked at the 69 Dana, and you are correct, it is a 3.73. I also have a t-18 in the 69, but since the NP 435 is already out, I don't think there is any potential gain in using the T-18, at least none I know of. I recall it and the NP are pretty similar gear wise pretty much. What height tires are you running on your F250 ? I still have 16.5 wheels on this one but also have some 16's I could use, but don't know what height tire to use for maximum gains in the mileage department.

[ToughOldFord]

I know, I was surprised I had no gains with the gear change either. You'd think 200 less rpms would add up to something.

You're correct, the T-18 and NP both have a 1 to 1 ratio in high so they'd be the same on fuel economy.

I 'm running 235/85/16s on newer stock Ford wheels. They measure out to 31".

[Clarko]

I recommend AOD all the way. The OD is a .67:1 ratio (3000RPM on the highway becomes 2000RPM in OD) Here's a part of my last post on the matter:

From a company called Bendtsen’s Transmission Center.
http://www.transmissionadapters.com/ford_fe.htm
It'll make ANY small block trans fit behind an FE! (they make an FE to chev trans adapter too, if you're into unnatural combos and want to spend more)
They also make a bunch of different trans adapters too.
I'm completely impressed with the quality of this kit so far.

The Throttle Valve Cable (kickdown/modulator in one basically) that I'm going to use is from Lokar (pn KD-2AODHT) http://www.lokar.com/product-descriptio ... d-kits.htm. It works with most Holley/Edelbrock carbs for sure. I'm not sure about Autolites or anything else.

Now let me say this about the TV cable. Not only does it control shift points but also changes the line pressure in the valve body. If the TV cable is misadjusted, it could cause damage to the trans. The factory adjustment process involves two pressure gauges installed on the side of the trans to get it perfect. TCI has come up with a valve body that keeps a constant pressure in the valve body and makes the TV adjustment do nothing but change the shift points. I'm going with this in my AOD. http://www.tciauto.com/Products/Ford/ford_aod.asp

[cdherman]

You will be very lucky to get the same mileage with an AOD as with the T-18 or NP-435. Probably will be better with the manual tranny, and a lot tougher tranny to boot. But if you like automatics and really hate shifting, then by all means, consider the AOD. Since you already have a C6, some of the setup is already in place. Part about the kickdown is correct, but you may be able to use your existing C6 linkage. But as noted, the adjustments MUST be correct.

The early 60's clutch/brake assembly will NOT interchange with the later truck.

[Sazman]

Thanks for the heads up that the brake/clutch assembly from the 62/63 won't fit. I can take the assembly out of the 69, no problem there. Just curious why you think the AOD would not be an improvement mileage wise. Conventional wisdom would hold that anything less that 1to 1 final drive out of the tranny would have to be more economical, no? I realize that there are some parasitic losses running the pump on an automatic trans and a C6 is said to be a real hog in that department, but I haven't heard that in particular about the AOD, so please explain your theory. Anyone else with experience with the AOD please chime in.

[cdherman]

The AOD is still creating parasitic losses, just less. Even at highway speeds. Perhaps if the rear end gearing were really messed up, then the AOD would beat a 4 speed. But with a sensible happy medium, or even better, a pretty high rear, then 1:1 top end of the 4 speed will be just fine to beat the AOD in terms of mileage.

The AOD is a nicer, more driveable tranny. But I don't think it will beat the 4 speed.

Of course, the 390 is a foreign beast for me, so take what I say with some salt -- perhaps the 390 drinks so much gas and has such spare power that the AOD would be just the ticket.....

[Sazman]

Well, I see what you are saying, and real world economics being what they are, since I already have the NP 435 and the main components of the swap to the manual tranny, the AOD will probably remain theoretical at least for the time being. I heard today that gas might be back down to 3 dollars again before too long. We all know that won't last too long though, greedy bast%$@s. The Bendtsen? adapter , while it looks to be a well made item, is a significant chunk of change, and pretty hard to justify on a truck I just don't drive that much. I know with that granny tranny it's capable of about anything I need to do with it and where I live and what I do with it, it likely will never see 65 miles an hour. And if I swap the 4.10 rearend for the 3.73, that should be a pretty good dual purpose gear I would think, maybe even get a little bit better economy, no?