i have a 88 f250 with the 351w and a c6 thats leaking out of the rear seal.. i hate that it doesnt have overdrive so my question is what transmission options do i have that would give me od and not all that expensive and which out of all the transmissions is one of the better more reliable one or is it possible to add od to the c6. thanks in advance

 

You can add an OD unit to the C6, but it isnt just as simple as bolt on, that I am aware of.

Your best option would probably be a manual conversion. The C6 is a vacuum operated transmission, not computer controlled. The other automatics are computer controlled. With that, you will need a harness and an ECM for the transmissions.

 

I believe the aod is a non computer overdrive trans like everything some people have good luck with it some don't. Someone who knows more will chime in.

 

Chiming in! AOD, a 4-speed with O/D 4th. gear, is NOT electronically controlled, not connected to computer in any way. It is one of the most unique transmissions designed, in that it has 2 input shafts, but that is a good and bad point, weaker because of small inner shaft diameter. In 1st. and 2nd. gear, the trans. is driven by the torque converter turbine, like all transmissions used to be. However, in 3rd. and 4th. gears, the input to the transmission is taken from the shaft driven by the PUMP, as it's called, in the converter, which means the fluid no longer transmits the driving torque, but rather the engine flywheel (the TC drive member, or pump) provides the torque input to the trans. This eliminates the converter losses in 3rd. and 4th., but still allows normal converter operation in 1st. and 2nd.

This was how Ford eliminated the converter losses by mechanical means, rather than putting a CLUTCH in the converter, as most ALL transmissions do today. Certain drawbacks were present: today's clutched converters can be brought back into play in O/D gear, or any other, to gain more "oomph", which the AOD could only provide by downshifting to lower gears. AOD was used behind just about all of Ford's engines, is a fairly stout transmission. One problem early on was "hunting", shifting back and forth between 3rd. and O/D, if speed was kept at just the right level. This was eliminated by a change to control pressure regulation, sometime in the late '80s.

Overall length of AOD, at least as used in Mustangs, ca 1989 through mid-;90s, was quite similar, maybe identical to other autos, say, C6. If a non-overdrive trans. is replaced by AOD, if length and output shaft splines are same, bolt-in is possibly, with MAYBE some alteration at rear crossmember mount. Most were shifted by a CABLE reaching from the steering column to the trans., except Mustang, which had a floor shift set-up; this might be adaptable more easily if replacing say a C-6. Also, AOD had a MECHANICAL LINK from the throttle linkage to the transmission, which moved at all times with the throttle, to control shift points vs. throttle demand. Thus, that would have to be incorporated, to properly utilize an AOD. Earlier transmissions having a similar throttle-transmission mechanical link, used it solely to FORCE DOWNSHIFTS; usually, the link was motionless regardless of throttle movement, until very near full throttle, at which time the link came into motion.

I used a Mustang AOD when I put a 1992 5.0L HO in a '79 Ranchero. The very low numerical rear axle (2.69, or something like that), made the shift to 3rd. gear feel like a bog-down, since torque converter slip was eliminated. 9-inch rear axle made replacement with a 3.50 gear set easy; the vehicle ran super! impish

 

Thanks for chiming and the education hope it helps the original poster

 

If you want Overdrive you have 3 choices- The AOD as was mentioned, but it really is not heavy enough for a F250; convert to a manual,but that is alot of work; or go to an E4OD with an aftermarket controller. The early E4ODs had their share of problems, but a rebuilt one with ALL the upgrades and a GOOD torque convertor would be reliable- but you would have to drive the truck a long ways to save enough gas expense to cover the cost of the conversion.

 

thanks guys all the info was great i guess i have a whole lot to think about and have to look at my wallet

 

Probably the easiest and cheapest overall option would be to sell your truck and find another with a ZF5 or E4OD trans.

The AOD likely won't hold up in an F250, at least not in stock form if you're using the truck for it's intended purpose.

The E4OD is controlled by the ECM so you'd need one from a 351/E4OD combo or a stand-alone controller. I think the diesel trucks didn't need ECMs so they had stand-alone controllers for E4OD trannys. There would be some work involved in the swap and a significant expense unless you lucked into a cheap parts truck with a fresh tranny.

You can install a gear vendors or similar auxiliary OD unit and this would effectively give you 6 gears which would help out when pulling as load up a hill. This is probably the most expensive but least labor-intensive option.

The ZF5 would take some work but there's lots of write-ups just on this forum so you'll have plenty of info to get it done. And the ZF5 will probably last longer and need less maintenance and attention than an auto.