C4 C6 questions...FMX

[gt45rpm]

which is the stronger trans? Am I correct to asume that the C4 backed up pintos, small block Fords, 302 351, 400 and the c6 backed up the big block Fords? And will early 80's four speed auto ( do'nt know the code name ) fit a early 70's windsor engine,, 351. a side from the bell housing being larger or smaller betwean the c6 and a c4, can the guts be interchanged, and I have heard of a FMX version of the Ford auto, what dose a FMX mean? I'm asking For a Ford Friend whith a 72 GranTorino ( being a Chevy Guy I know a hell of a lot more abought Fords Than he, ) that is cooked, but the body is mint. All I need to do is paint it red with a white stripe and crash over garbage cans in back alley's...

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[Klitch]

well if my dad was home i'd ask him, i know he has all of those listed. what i do remember was the FMX was a heavier trans, took the abuse better from the 351C than his other auto's. think it was slower shifting though?
if you dont get a definate answer before i go to bed, i should be able to ask him what he knows.

[Klitch]

ok heres what i found out from him.
C4, meant for small blocks, C6 meant for big blocks.
FMX was an older cast iron center section, mostly meant for pickups?

[keith97xlt]

i hear the c6 is one of the best trannys ford ever made.

[glc]

The C4 is a medium duty trans, the C6 is heavy duty. The FMX is old technology based on the original "Cruise-o-Matic" which is a Borg-Warner design. I would say its strength is somewhere between the C4 and C6.

The early 80's overdrive was the AOD, which was based on the FMX.

[Bluejay]

There was/is a small block C6. It bolts to the smaller bell housing same as a C4 but the transmission itself is larger and heavier. I ran a 351 C in a 54 Ford drag truck for several years and the best transmission I had was a beefed up C4. You can make them as strong as the C6. I ran a small block C6 for awhile and was just never happy with it. The FMX will bolt up to the small block, but as stated it is less desirable. If I remember correctly, it has a cast iron housing rather than aluminum.

[Klitch]

bluejay, yeah FMX is a heavy pig, cast iron housing.

[Bluejay]

Wow, it's been nearly 18 or so years since I'v thought about any of this stuff, but if memory serves correctly, the small block C6s came behind the 351Ms and the 400s.

[Rock Krusher]

For most applications I'd pick a well built c4 over a c6. A decent c4 can hold almost as much power as a stock c6 but it has 1 major advantage, it doesn't waste nearly as much power. My numbers are prolly off but IIRC the c4 uses something like 25-40 hp, and a c6 is in the neighborhood of 60-75hp. That's a hell of alot of power wasted.

[Bluejay]

Originally Posted by Rock Krusher

For most applications I'd pick a well built c4 over a c6. A decent c4 can hold almost as much power as a stock c6 but it has 1 major advantage, it doesn't waste nearly as much power. My numbers are prolly off but IIRC the c4 uses something like 25-40 hp, and a c6 is in the neighborhood of 60-75hp. That's a hell of alot of power wasted.

Yep, and I assure you, it's noticeable when racing. I loved that little C4. Also, it is so much easier to handle when you have to remove it or stab it. After we built it up, it lasted 3 years of racing, in a heavy truck body, with about 375 HP plus 150 HP nitrous, 4.88 gears, slicks, and a 2400 stall converter. I'm talking nearly every weekend.

[93 Rust]

Had a '70 Mach 1 w/ 351C 4V with FMX. Shifted HARD. Barked 2nd consistently,
occasionally 3rd. Downshifted RIGHT NOW. GLC is correct. Old B-W unit. Ate 2nd gear servos,though. Wished every car I had since then shifted like that.