I'm in the process of rebuilding the 351W in my 69 Mach and I'd like suggestions on a Transmission replacement. It currently has the "weak" stock FMX and I'd like to upgrade. Any suggestion on a "clean" replacement that I can drop in without a lot of other modifications? Thanks, in advance for the help.
Auto Transmission Question
- Thread starter hh3
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Stang_1973
Founding Member
I agree the C4 in its stock form can handle about 350 HP easily. If you beef it up it can handle alot more. It is also alot lighter than the FMX or C6 and has less power loss. You can put a shift kit in to make it have nice crisp or hard shifts, or turn it into a full manual. This costs less than converting a A/T car into a manual car.
302 coupe
Founding Member
there's nothing weak about an FMX, they're good trannies. The only problem is the lack of aftermarket support. If you just plan on a mild rebuild, or a shift kit and converter upgrade, the FMX will be just fine. Its heavy, but thats the only real downside. I'd stick with it if I were you. Strengthwise, its between a C4 and a C6, ditto for parasitic loss. Save yourself the hassle of changing parts and stick with it.
I second that, there was nothing weak about the FMX. I've heard numerous cases where for somereason or other they had been run dry to the point where they quit pulling, then refilled and run some more. try that with a C4. As for a C4 handling 350 horses, I've gotta disagree, I had a heavy duty one in a 69 van behind a 200 horse 302 and in the ten years we had it, we had it rebuilt 5 times.
D.Hearne said:
i also agree witht he fmx being a strong tranny, but heavy.
as far as a C4, i have run one very close to dry, and still was able to tow a car and not have the C4 break. a C4 will handle about 300hp without upgrades and more when properly upgraded. one more thing, the fmx was the basis for the aod which is also a strong, but misunderstood tranny. if you have a 164 tooth flexplate with the right converter bolt pattern you can swap an aod in place real easy.
DarkBuddha
Founding Member
Well I'm glad other folks chimed in about the FMX being a good tranny... It is heavy, but it's a good performer. It's the evolution of the old original Ford Cruise-omatic, and was used as the basis for the late model AOD & AODE. The FMX is a great performer, stronger tranny than a stock C4 and will hold up as well as a stock C6. The iron belhousing is what makes it heavy, but it also provides better protection should something let go. The only thing that sucks is that it is a serious power robber. Still, if I hadn't upgraded to the AOD, I would've gladly stuck with my FMX forever.
Go FMX!
Go FMX!
DarkBuddha
Founding Member
Damn, I knew that... iron case, not bellhousing. I gotsD.Hearne said:Iron bellhousing? Where'd you find that antique?Most FMX's Ive seen had aluminum bells,
most had aluminum tailshaft housings too. only the main case was always iron.
. Damn, imagine how heavy it'd be with a damn iron bellhousing! 
302 coupe
Founding Member
a C4 would be preferred in that particular scenario. However, if the car already had an FMX, I'd leave it in place as it should hold up fairly well behind a 350 hp engine.
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