FMX to C6....Final Decision

[351carlo]

Well guys, had the FMX running great, but I think I blew the torque convertor and/or 1st gear. I'm going to rebuild it, but need some input. I can pick up a C6 for 75 dollars with convertor, but I would have it rebuilt. I could also just rebuild my FMX.

Problem is, I need to know if it would be necessary to cut the driveshaft on my 70 Stang. Could I use the current crossmember? How about linkages? If it would only cost me approx. 100 dollars to convert to the C6, I'm doing it. If you think I would have to cut my driveshaft, fab up a new cross member, get a new flywheel (I'm pretty sure the one in a 351c mates up with a c6 or an FMX), and do any other additions, I'm not going with the C6.

Anyone done this and know what it entails?

THANKS FOR ANY INFO. I'm gonna try and tell the trans guy by tomorrow.

 

[mak6363]

The C-6 should be a direct swap for the FMX. I just changed from a C-4 to FMX and had to change everything. I have a small block C-6 but it needs rebuilt and I found a good FMX for $100 so I put the FMX in my car. I found out that the C-6 and FMX are the same length so driveshaft used is the same. The crossmember is the same. The only things that might be different are the oil cooler lines and maybe the shift linkage but these are minor problems.

 

[Snail50]

off-topic, but is the FMX a much heavier unit than the C4 or C6?

 

[Ronstang]

The FMX is pretty heavy considering that it has a cast iron case. It is simply the big brother of the original Ford-O-Matic that was used in the 50s. I think it is heavier than a C-6 but don't quote me on that one.

I would build a C-4 and say screw the other two heavy beasts but as someone already said you would pretty much be replacing everything. The FMX/C-6 crossmember will work but the driveshaft will not. Your call. If you already have the FMX and do not have aspirations for a 10 second street car then I say stick with the FMX....I think (but may be wrong) that the C-6 has the most parasitic loss of any of the Ford automatic transmissions.

 

[nosaj122081]

I don't have a small block C6 to judge, but I have a BB one, and it weighs ALOT more than my FMX by the ouch-my-back-o-meter. The slip yoke is the same for both trannies, however, thats the only thing I can verify.

I agree with Ronstang though, I wouldn't swap from a FMX to a C6, I saw a comparison somewhere on the web and the C6 ate the most HP PERIOD (that's including Mopars and GM's). If you don't want to use the FMX, go with a C4, but IME the FMX is a reliable, solid tranny, I have one that works perfectly occupying a corner of my shop, never did kill the damn thing and ran it outta fluid twice when cooler lines broke. Just kept on tickin'.

 

[351carlo]

So stick with the FMX? All I'm looking for is 13 seconds, maybe high 12's with some stickys. I'm assuming driveshaft would be too long for a C6?

I thought the FMX ate the most power....but I've been wrong numerous times before. As for a C4, that's way out of the question. I'll shorten the driveshaft, but I won't buy a new one yet. As for shift linkages and cooler lines, aftermarket on both so it wouldn't matter. I don't know why everyone wants me to do the C6 conversion....any positives to it? I hear the FMX is pretty bullit proof unless I want to race it. I'm gonna get a Trans Go shift kit for the FMX and the guy rebuilding it for me knows a few tricks to making it shift hard. I really want it to snap my neck back during shifts.

 

[GaPonyFarm]

Stick with the FMX. Its a much more solid tranny than a C6 and can take a lot of heat. If you don't get into the 13's... the FMX won't be the reason why.

 

[351carlo]

Thanks guys. The decision is made. C6 wouldn't be worth the guesswork on my part. Sticking with the simple swap in and out. Any idea if it would be possible to drop it in the driveway? I don't have a truck that has tags anymore to tow it, and I don't like the idea of it sitting up at my shop for a few days with the new interior. Lots of theft.

 

[nosaj122081]

Dropping the tranny is a pretty easy procedure, I've done it many times in my garage with basic tools... Just take out the driveshaft, unbolt the bell from the motor and the crossmember, unbolt the converter, disconnect the cooler lines and the shifter linkage (along with the kickdown/steering lockout if you have them), and pull the sucker out. The only issue I ever have is getting the car high enough. I'm a little guy and can lug an FMX+bell around, so I would wager anyone can.

 

[D.Hearne]

You can actually drop an FMX from the car easier than the C-4 or 6. Just unbolt the main case from the bell likeyou would a std transmission. Then pull it out, Then you can unbolt the bellhousing,torque converter and flexplate. I'd keep the FMX too, unless I was short of cash and had the C-6 on hand.

 

[D.Hearne]

Oh and when you go to reinstall the FMX, just reverse the procedure, but stabbing it back in will be a lot easier if you take at least 2 ( 4 would be better) long small block head bolts and cut the heads off, then screw them into the bolt holes in the bell so they'll act as guides when stabbbing the main case back in

 

[1973mach1]

From what I have been told you dont need to change the driveshaft for a FMX to c4 swap just the yoke and crossmemember? I seen one guy that builds them to handle 450HP for like 700 dollars which includes a 2 year warrenty. I'll probally go c4 and keep my FMX parts in case I ever want to switch back.

Jim

 

[Mach1steve]

FMX isn't known for taking lotsa rpm's
they tend to puke over 5,800
They're fine for torque but not for High Rpm's
been there, done that 3 times, blew the engine once due to tranny puke
could never get the 2nd to 3rd shift to click in hard, had to release the gas pedal and let it drop in. Not fun on the Drag track.
Lost lotsa time but still turned mid 12's (between tranny rebuilds).
Suggest a properly prepared C4