KBunny

Hey, I was wondering how I can figure out what transmission I have.

I recently replaced my U-Joints and I replaced the tail shaft seal at the same time, but the only seal that would fit was one thats made for a C6 transmission. I thought I was just a tail shaft from a C6 but I have been haveing problems with the speedomiter gear. I put a 16 tooth left rotation gear in and it was the wrong roation gear (wich I was told was the right gear for a C4 trany) So if you could point me in the way to figure out what I have that would be great.

69mach1377

Find the casting number and report it here. Someone should be able to help...

caballo66

wheres the casting number located?

KBunny

yeah, is it somewhere that I can get to it without haveing to take stuff apart? are the casting numbers in the same place for the C4 and C6? (I would assume yes because you said to report them to find out)

69FECoupe

What engine do you have? If the bell housing and body are one piece it's a C6. If the bell is removable and the body is aluminum, it's a C4. If the bell is removable and the body of the tranny is cast iron, it's an FMX. In Mustangs, C6's were only used on big blocks. C4's were used on small blocks and FMX's were sometimes used on 69/70 small blocks but were most commonly used on 71-73 Clevelands. Hope this helps.

69mach1377

My FMX number is on the driver's side above the linkage, may be hard to see though. The pans and gaskets also may have different shapes and patterns that could be used to figure it out. FMXs were used mostly on 351s IIRC.

caballo66

i think i have a c4 w/ 24 spline input shaft.

pootscratch89

Here's one way to decipher trannies:

FMX has 15 bolts on the trans pan
C4 has 11 bolts on the trans pan
C6 has 14 bolts on the trans pan

Vern

KBunny

ok, I guess its just a C4 trany with a C6 tail shaft because I checked a cupple of the ways you guys told me and they all came up as a C4.

Thanks for all your help guys.