O.K. forget fixing the FMX. Will a C4 bolt up the same?

70MustangGrande · Jun 17, 2004

I ran a post yesterday about my FMX troubles. I have a mildly worked up 351w with the original FMX and it seems to be slipping. Can a C4 simply bolt up in the same place as the FMX without any changes or modifications? If not, what's required?

ForceFed70 · Jun 17, 2004

As long as you've got the propper flywheel balancing, it should be fine. I think the driveshaft length will chance as well.

If your going to do it...why not go AOD?

mak6363 · Jun 17, 2004

I just changed from a C-4 to FMX in my 70 MACH1. They both bolt up to the engine with no problems but there are some things that are different.

1) C-4 is shorter so it takes a different length driveshaft.
2) output shaft on the C-4 is smaller so it takes a different yoke on the driveshaft
3) C-4 uses a different crossmember than the FMX
4) cooler lines are different
5) Shifter linkage rod is shorter for the C-4

Hope this helps.
Mark

D.Hearne · Jun 17, 2004

mak6363 said:
I just changed from a C-4 to FMX in my 70 MACH1. They both bolt up to the engine with no problems but there are some things that are different.

1) C-4 is shorter so it takes a different length driveshaft.
2) output shaft on the C-4 is smaller so it takes a different yoke on the driveshaft
3) C-4 uses a different crossmember than the FMX
4) cooler lines are different
5) Shifter linkage rod is shorter for the C-4

Hope this helps.
Mark

Hey, sounds like you could sell him your C-4. And then later on when it craters, he'll wish he'd kept the FMX.

ratio411 · Jun 17, 2004

Strange...
I removed a C4 and put in an FMX, I bolted it right in.
I used the C4 flexplate, mount, driveshaft, starter, crossmember, speedo cable, etc...
It was years ago, but I was on a budget and would remember changing the driveshaft. It was my first car and I know the driveshaft and yoke were not changed until I put a C6 in place of the FMX. The car was a 71 model that came from the factory with FMX, C4, or C6... so it had the adjustable crossmember. I just moved it back one set of holes each time I swapped to a larger tranny. A 70 would surely have the same adjustment... right?
Dave

65fsbkhipo · Jun 17, 2004

ratio411 said:
Strange...
I removed a C4 and put in an FMX, I bolted it right in.
I used the C4 flexplate, mount, driveshaft, starter, crossmember, speedo cable, etc...
It was years ago, but I was on a budget and would remember changing the driveshaft. It was my first car and I know the driveshaft and yoke were not changed until I put a C6 in place of the FMX. The car was a 71 model that came from the factory with FMX, C4, or C6... so it had the adjustable crossmember. I just moved it back one set of holes each time I swapped to a larger tranny. A 69 would surely have the same adjustment... right?
Dave

Drive shaft must be changed to a shorter one and the shifter rods, as well as the trans mounting bracket are different. C4 bracket will not fit on the FMX. Just did the same change-over on a 69.

ratio411 · Jun 17, 2004

Okay... Maybe the driveshaft/yoke will swap from a C4, but not vise-versa.
When you say trans mounting bracket, I am not sure what you mean, it must be the year difference. My mount and crossmember was a direct swap. Even when I went to the C6.
I had an aftermarket shifter, so I won't argue that one...
Dave

65fsbkhipo · Jun 17, 2004

Trans mount bracket (cross member) for a FMX has two bolt pilot holes on one side (driver) and one bolt pilot hole on the other (passaenger). The C4 has two on each side. The FMX mount actually angles back toward the rear (passenger side) tunnel mounting position.

70MustangGrande · Jun 17, 2004

Bah, scrub the C4 idea then. Maybe i'll get lucky at the junkyard and find an old F-150 with 60,000 miles wrecked, although finding a transmission like that with under 150,000 miles won't be easy to dig up.

Im guessing the FMX runs along the lines of a C6 huh? I thought that there wasn't much to offer for an FMX and a C4/6 would be preferred over it due to better parts availability and shift kits.

D.Hearne · Jun 18, 2004

70MustangGrande said:
Bah, scrub the C4 idea then. Maybe i'll get lucky at the junkyard and find an old F-150 with 60,000 miles wrecked, although finding a transmission like that with under 150,000 miles won't be easy to dig up.

Im guessing the FMX runs along the lines of a C6 huh? I thought that there wasn't much to offer for an FMX and a C4/6 would be preferred over it due to better parts availability and shift kits.

I've got a low miles FMX but the shipping would kill you from here to California

70MustangGrande · Jun 18, 2004

D.Hearne said:
I've got a low miles FMX but the shipping would kill you from here to California

I'd only need the transmission itself and not the bellhousing and the extension housing. That would help reduce weight unless you would rather get rid of the unit as a whole.

What kind of mileage would it happen to have? I'd pay what it's worth to you if I have no other options finding a replacement.

D.Hearne · Jun 18, 2004

I don't know the actual mileage, but it came from a low mileage 71 LTD that was parked due to the timing set wearing out ( ain't nylon coated aluminum gears wonderful)on the 351W under the hood. I pulled the 351 and FMX and the block had very little wear in the bores and was still std size. ngine had never been rebuilt either. The FMX that was behind it looks to have been rebuilt at some point. The FMX should still work, but I cannot guarantee it 100%. I was going to keep it as a spare, but I don't really need it. Make me an offer. I can ship it without the bell and torque converter.

1973mach1 · Jun 18, 2004

I was told on my 1973 going from a FMX to a built c4 I would need a new yoke, crossmember, cooler lines, linkage. I was told the driveshaft will work, I seen a webpage that said the difference between a FMX and c4 was FMX=30 3/4" C4=30 1/4"
I havn't done it yet but im building a built c4 when I get my Cleveland done.

Jim

70MustangGrande · Jun 18, 2004

D.Hearne said:
I don't know the actual mileage, but it came from a low mileage 71 LTD that was parked due to the timing set wearing out ( ain't nylon coated aluminum gears wonderful)on the 351W under the hood. I pulled the 351 and FMX and the block had very little wear in the bores and was still std size. ngine had never been rebuilt either. The FMX that was behind it looks to have been rebuilt at some point. The FMX should still work, but I cannot guarantee it 100%. I was going to keep it as a spare, but I don't really need it. Make me an offer. I can ship it without the bell and torque converter.

Ah, lemme think.....

If the coolant passages are good and clear, the cast iron case doesn't have broken bolt holes and the casing isn't excessivly rusted (salt roads and humid climates tend to do that) then how about..........100 plus cost of shipping W.O. the housing/converter/and exit shaft?

mak6363 · Jun 19, 2004

D.Hearne said:
Hey, sounds like you could sell him your C-4. And then later on when it craters, he'll wish he'd kept the FMX.

I bought my car with a bad C-4 in it. The C-4 can't handle a cleveland in stock form. It has to be built up inside. THen they will handle about 400 to 450 horsepower reliably. The one advantage is that the C-4 is smaller and lighter with less internal mass to turn so there is a gain in rear wheel horsepower as opposed to running an FMX or C-6. For me though I would rather have the bigger, stronger transmissions than to chance a C-4. Especially since I'm building up my cleveland.

O.K. forget fixing the FMX. Will a C4 bolt up the same?

70MustangGrande

ForceFed70

That's why they call it "dope"

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