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Hi everyone...first of all, let me tell everyone how excited I am that I finally have the 351C in my 1973 convertible running like a deer. I was having fits with hot starts, and after talking to people on this forum, etc, replaced the Holley street dominator single plane intake manifold with the Edelbrock performer (dual plane designed for idle to 5500rpm) along with a Holley street avenger 670cfm carb to replace the Edelbrock under series carb. The difference is impressive with how well it runs. But now I have another issue. The transmission is slipping. For quite some time the car will go into reverse when it is cold but not drive. You have to let the car warm up for about five minutes before it will go into gear. A local recommended trying some stop slip to see if it would help, and it did a little, but not much. The local shop thinks it is an FMX transmission, but I can't find the ID tag which would tell me. Would anyone mind letting me know where I could hunt it down?

Besides that, does anyone have strong feelings about rebuilding the transmission versus an alternative, such as putting in an AOD transmission. I talked to Broader transmission in Texas after seeing them mention in several places, and he made it sound like quite a bit of modification to make it fit. The local shop that I deal with seems to think a rebuild of the existing transmission (be it the FMX, C4 or C6) along with new gears in the rear end would be all I would need. I'm not building a race car. I want something that is fun to drive and will get up and run from a stop. As always, any input would be a great help! Thanks again, Tyson
 

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If your car was originally a 351C-2V (2-barrel), chances are it has an FMX (Trans code 'X' on door tag). The optional 'heavy-duty' trans was the C-6 (door code 'U'). C-4s were not factory in 71-73s. If your pan is pretty deep and square (actually a bit wider than it is front-to-back), that is a FMX. The C-6 trans pan shape is more like Utah...


May guys here have done an AOD swap into their classic Cat.
 

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Got an AOD in my 69 to replace the FMX that was there (originally a 4 spd car though) - not hard to do. Your looking at similar costs to rebuild yours or go ahead and get a rebuilt AOD. (If you leave it stock) You'll have to get a different crossmeber for it (mustangs plus sells them among others) and possibly shorten the driveshaft 1".....it depends on what application the AOD came from I think. You'll also need a TV cable kit (Lokar makes one) and don't forget the spacer plate when you get the trans (assuming you get it from a junk yard) the best ones seem to be post 1988 ones out of truck/van's. BE SURE TO CHECK THAT THE SHIFT LEVER IS ROTATED 180 if it came out of a column shifted vehicle!....ask me how I know. (It's not possible to do it when it's in the car) The biggest factor for doing it may be that you will get better mileage and you can cruise more comfortably. Don't expect race car like gains though! That isn't going to make much if any diff - depending on what your final ratio ends up being. There are a few weak points in AOD's to consider - the input shaft is known for weakness and you should have a hardened one put in (if you go lockup style). The earlier pre 1988 ones had problems that the later ones don't so try to avoid them. There are lots of options to modify them - but it gets expensive quick if you go down that road....better clutch packs or AODE guts into the AOD case....etc
 
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