C4 or FMX? (pics)

[Black Thunder]

Is this an FMX or a C4 transmission? I really don't know how to tell the difference. I know it isn't a C6.

 

[D.Hearne]

I can't tell from those pics. But I can tell you this, the FMX pan is wider than it is longer. A C-4 pan is about as square as you can get. The FMX also has a cast iron main case. The C-4 is all aluminum

 

[Dark Knight]

FMX
View attachment 524481

 

[Black Thunder]

Well here is a picture of the pan. Funny, doesn't look like either one of the diagrams.

 

[D.Hearne]

You've got a C-6 in there, that's why. You've flunked transmission ID 101 class. Time for summer school

 

[Black Thunder]

You've got a C-6 in there, that's why.

Funny, I had just started to come to that conclusion. Found a diagram of pans and that's what it looks like for a C6. Why they would put a C6 in car with a 351-2V is beyond me unless it was done by a previous owner.

 

[D.Hearne]

May have been done by the previous owner(s) or by Ford , anything can happen under there in 30 years. Most 351's I've seen had FMX's from the factory, but with Ford, you never know. They have been known to switch components when other components were in short supply. They're also known for using up components ( like Hi-Performance parts) rather than store them.

 

[Black Thunder]

You've flunked transmission ID 101 class. Time for summer school

LOL.. Yeah I need some schoolin

 

[Black Thunder]

So lets say I have a C6. I want to put in a 408 eventually that will put out 490HP at the crank. My transmission is leaking right now so I was just going to take it in to have it rebuilt to hold up to that much HP, but will the C6 hold up to that much HP to where I wouldn't need to get it rebuilt? It shifts just fine and the leak is just a seal. So if I don't need to rebuild it, I will just have the seal replaced and maybe add a shift kit. Hell, for all I know it has been rebuilt and had a shfit kit installed. It shifts pretty quick as it is. That's the bad part about buying a car where the previous owner didn't know what was done before.

 

[66SilverStar]

a stock c6 will hold up to a 408 with no problem. majority of the C6's went behind big blocks, if that tells you anything. but yeah a shift will make it more fun. To tell you the truth the C6 will slow you down compared to a C4. However you will have to BUILD a C4 to hold the Tq. Its just that the C6 is so big and has a heavy rotational mass which slows you down in racing. Replace the seal and let it ride. Just my 2 cents.

Jimmie

 

[D.Hearne]

So lets say I have a C6. I want to put in a 408 eventually that will put out 490HP at the crank. My transmission is leaking right now

Leak, what leak? Looked pretty damn clean to me. I'd just change the front seal ( that's the one leaking, right? ) and leave it be. A C-6 will handle anything a 408 can dish out. Just ask the one in my 34 year old 68 Merc. 34 years old, never been rebuilt, but has only 62K miles on it, but still works great behind the 390 in there. As for them being a drain on hp, this car weighs in at 4200lbs and runs mid 14's, the only mods to the motor are a Crane 272 degree cam, FPA headers and a 428PI intake topped with a Holley 750. short block and heads are as stock as they were when it left the factory.

 

[Black Thunder]

Thanks for the input guys. I've always had 5-speeds so I'm new to the automatic transmissions.

As for the leak, this is what leaked in less than a week. Sometimes it leaks a little and then other times it drops about 1/4 of a quart. It is in the front so most likely just a seal that has dried out from sitting so long. It was out of commission for over a year getting restored. It looks clean because it was repainted.

 

[D.Hearne]

The front seal is easy to change, the hard part is removing the transmission

 

[69Rcode_Mach1]

I have a 1969 Mach 1 that was a 351 2-v and it also has a c-6 under there. Exactly like yours.

 

[mustang2]

I am also under-educated with auto., or basically all mechanic work, but I'm learning. My trans. is currently sitting in the garage, you said it's easy to change the front seal, can you tell me how to do it so I don't damage anything. And also is there anything else I should do to it while it's out of the car. It's a C4. Thanks

 

[D.Hearne]

Just pull the torque converter out, you'll see the front seal that the collar on the rear of the converter fits into. Use a seal puller to remove it ( available from most parts houses along with the seal) install the new seal using a hammer and wood block. Drive the seal in gently , tapping the block over the seal with the hammer. Take note how the old seal fits before removing it, you'll want the new one to fit the same. when it's in, just stab the converter back in, but make sure the flat sides on the rear collar( of the converter) fit into the front pump gear, this is what powers the front pump. If you'll look into the front pump while the seal is out, you'll see the flats that the flats on the converter collar fit into. What ever you do , do NOT force the converter into the front pump. It's very easy to break the gear in the pump doing this. Just stab it in gently and rotate the converter to "feel" for the collar to engage the pump gear.Might also be a good idea to change the output shaft seal while you're at it.