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1973 FMX transmission conversion
I'm based in the UK and have a '73 Mach1 351 Cleveland with FMX transmission. I have ongoing problems with the FMX that despite 2 rebuilds has not been solved - it won't engage reverse only when hot, otherwise 'box works perfectly.

I'm considering a C4/C6 conversion with parts supplied by either Summit Racing or CJ Pony Parts, however neither can advise on all the components I need for the conversion and suggest I join a forum. So here I am.
[Image: IMG-2502.jpg]

Anybody on here done the conversion? Or able to advise on what I specifically need to order and what I can reuse - eg Starter Motor, Kickdown Cable, support cross member etc.

Your help and advise will be much appreciated
Parts that will be different

Shifter rod
Steering column lock out rod
drive shaft
cross member ... depends on what you go with

Your starter will work for any
Welcome from Oklahoma. this link may be of some help. https://www.7173mustangs.com/thread-fmx-...ansmission
Sorry to hear you are having FMX problems as I always they were a fairly reliable tranny.  Mine came with the Cleveland 2v and FMX from the factory.  When I bought from the original owners in 1982 the tranny was having problems engaging in drive or reverse, especially when cold.  I changed the filter( main filter in the pan area) and the problem went away.

From that point forward the only problem I ever had was it hanging in 1st or 2nd if I tried to manually shift under heavy acceleration.  That and the thing would start to leak if it sat for too long, the leaking subsided with use.

I suggest getting another shop to look at that tranny. Preferably someone with a good reputation with older tranny's. I think you will have a better future with the FMX as it is a more robust unit than the C4. ( I think the FMX was used in the 69 and 70 Shelby GT350 too)

Good luck.

I make no claim to know much about FMX transmissions. I do know that the reverse band works with another clutch to operate low gear (I know very strange). One potential test is get it to temperature, come to a stop, manually place it in 1st gear accelerate to perhaps 20 mph and release the gas pedal. If the reverse band is working the car should engine break and slow down pretty quickly. If it does not engine brake then it may point the reverse band being faulty or improper adjusted. Just a thought. Chuck

I can not vouch for the accuracy of the attachment. So verify before attempting to use it.

Attached Files
.pdf   2012-01-04_151824_1970_ford_mustang_5.pdf (Size: 69.68 KB / Downloads: 6)
+1 on kcmash
The FMX is a fine strong trans behind a 351, there is no real gain to go to C6.
If you really don't want to open it again for some reason and want perse another trans, I'd go for an AOD, at least after you're done, you have overdrive..

Oh and welcome from the Netherlands

73 modified Grandé 351C. Almost done. 
71 429CJ. In progress
+1 on the AOD, or an AODE (4R70W). The FMX is a decent transmission, strong, but heavy.

“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
Welcome from Omaha!

71-73 Mustangs never die, they just go faster!
Julien where in the UK are you based?

1971 Grandé
I had my FMX rebuilt with shift kit and upgraded parts and it works AWESOME!! My tranny guy said stick with it there is no benefit to C6 over FMX, and he has been rebuilding trannys since the 60's.
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