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FMX or C6
Hi guys- 

so I just yanked the motor and trans on my 71 as both need rebuilding.  To my initial dismay i found that I have an FMX trans (came factory with a C6).  I've done some reading but want to ask here...

would you rebulid and keep the FMX or replace it with the correct c6??

From what I've read the main drags on the FMX are that it is very heavy and does not have much in terms of aftermarket performance support.  However, it seems the c6 drains a lot more HP.  The car has a 351C which I'd like to build to 400-450 HP.

Thanks for your advice/opinions

(also if anyone can help me ID the trans I'd appreciate it..... its cast D2AP700SAA and the tag appears to read PHB-E4 / D27FA M)
If you're looking for originality plus strength then the C6 is the way to go
If you're not bothered by keeping it original either look at doing the FMX but due to difficulty getting parts and extra cost why not go for a C4?
They can be built strong, less drag and plenty of parts available
PHB-E4 is a 72 Mustang & Cougar 351-2V transmission.

The C-4 was not really an option the 351 they made one fastback in 71 and 2 verts in 73 according to Marti. My 73 vert was changed to C-4 from FMX by PO and I just left it.

When a man is in the woods and talks and no women are there is he still wrong??
Hmmm.  My 2v is a factory FMX tranny that ran good when I had the car together.  At times it would want to stick in the lower gear if I were manually shifting and really getting into it.

The bigger engines and 4V clevelands all got the C6 as it was supposed to be a stronger unit, but it is a HP hog from what I have heard.  So my thoughts are, go with the C6 if you are going original, or go with an AOD if you want a nice cruiser with overdrive., 

I think the 302 and 6 cylinder 71's got a C4, but am unsure.  Considering the base engine for the Mach 1 was a Cleveland 2V a correct Mach 1 should not have a C4.

+1 on kcmash AOD choice

We're in the 21th century, OD is really nice and good for the engine & wallet on highways.
I know the AOD from my daily 5.0 T-bird will replace the FMX of my 73 once my 24 yo T-bird dies (not planning restore another car yet)
Tho, I must say that aside the missing OD, the FMX is an excellent and very strong trans. I would keep it otherwise.
It moves the much more heavy than Mustang t-bird with no problem for decades. I think it would handle your 351 engine out of the box.

I wish I could do the same to my 429CJ. I'd love to add the gearvendors bolt on OD its c6, but the price is just too much. 4.5k at least to get it here. Sad
As you are in the states, may be you could try to find a C6 with gearvendors OD for your 351...

73 modified Grandé 351C. Almost done. 
71 429CJ. In progress
(03-31-2019, 04:17 PM)kcmash Wrote: I think the 302 and 6 cylinder 71's got a C4, but am unsure.  Considering the base engine for the Mach 1 was a Cleveland 2V a correct Mach 1 should not have a C4.


Base engine in the 71-73 Mach 1 was the 302-2V w/3spd manual, C-4 optional.

[Image: MVC-852F.jpg]

351-2V std was FMX w/C-6 optional. 

351-4v & 429 were C-6

I would head in the AOD direction.

- Mike
I think base engine on 71 Convertibles was 6 Banger !

71-73 Mustangs never die, they just go faster!
The only aftermarket part you can't get is an aluminum pan. My builder had no problems finding performance parts, or a shift kit for my FMX. My FMX is very strong and is holding up to 475 hp just fine after I had my builder go through it. And he only charged me $800 for the rebuild with parts!!! And it drains less power than the C6.
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