Any ideas? I want a new transmission for '71 F100

[RWVNRAL]

Been through quite a bit with a '71 F100 Sport Custom (manual everything...sometimes even have to push). Picked it up 2 years ago from a couple of fellows who were in the process of "restoring it"...which apparently meant pulling together a compilation of working systems from just about any place they could find them. For the longest time, thought I had a 307. Turns out its a 351 Windsor from a 1979 LTD/Bronco (not certain which)....but it was running the firing order (and distributor) from the stock 307.

Anyways... We've rebuilt the whole darned thing at this point. Engine rebuild went well...and now I've got electronic distributor with the correct 351 firing order. Disconnected anything having to do with emissions or EGR valves. Rebuilt the back end as well. Pulled the tranny out with the engine to have it rebuilt. It's an automatic C4. Everything was fine for about a month. Then, on the way back from a job, tranny started to bind and, within seconds, I lost 1st, 2nd, 3rd...all my forward gears are plum gone. Still have Park, Reverse, and Neutral though. Pulled the pan and there's nothing remarkable inside (except for one of the screws from the valve body casing....apparently the threads are stripped---at least that's what the tranny guy says). But, there was nothing in the pan to indicate damage to anything inside the transmission. At this point, not sure what to do. I got a REALLY GOOD DEAL on the rebuild (which, perhaps, is why the damned thing don't work).

So, here's my thinking. I don't want to screw around with this C4 anymore. I believe a bigger, stronger transmission would be preferable to rebuilding (or continuing to throw time and money at) the C4. What would you fellows recommend for an alternative transmission? I should add that I'm not racing this baby nor am I planning at this point to do a full restoration of the body. This is a work truck, and I just want her to hold up to the task of hauling her capacity.

Thanks for any input!

[9t3svt]

I would go for a C6. Small block C6s are common in late 70s-mid 80s vans and in early to mid 80s 2wd pickups, shouldn't be too hard to find.

[MaxKlinger]

You can't go wrong with a C6. Very reliable. Like 9t3svt said, an early 80s pickup version would be great. I had a C6 in my '83, which I assume had the smallblock V8 bellhousing to work behind my 300 straight six. Since you're using a smallblock 351W, you have other options for a 4-speed overdrive transmission, namely the AOD, AODE, or 4R70W (I believe the 4R70W was available in late 1990s Explorers with 302W's in them).

[71fordkid]

A 351 windsor cam factory in alot of broncos and f150 pickups in the 80s and 90s. I am using an AOD from a 80s bronco in my stepside with a 302 (same bell housing pattern). its a 3 speed with overdrive (4 speed).

4r70w and AOD-E transmissions have electronic imputs that need to be fed to make the shift solenoids work. however, you can build a hybrid AOD/4R70W and get the lower first and second gear from the 4R70w in the AOD non-electronic transmission.

[9t3svt]

AOD would be good if you are on the highway a lot, but if not worried about that, or if pulling most of the time, go c6. If you were anywhere close to me I would sell you a good one for $150