Which Auto Transmission is this?

Hi All, just pulled out the engine and trans. The code on the side of the transmission is  D4AP-7008-AA. It's from a 1973 Mach 1 behind a 351C-2V. It's the original gearbox as the car has only done 26,000 miles.

From what I can find online, it seems to be an FMX (rather than a 'C' series) - which apparently comes in 2 variants Small or Medium case Cruis-O-Matic. Can anyone point me in the direction of confirming exactly which one it is and its specs/ratios please?

How good is the box in terms of reliability?

Also to confirm matching numbers - where is the one on the trans?

Thanks for your help as always.

That is likely not the original trans. That trans with a casting number starting out “D4” would have been made sometime from 1974 up to I think 1978 when they quit making the FMX. Since your car is a 1973 it is not the original trans.

Easy way to ID early Ford transmisssions

3 piece unit (bellhousing, maincase, tailhousing) - iron maincase - FMX (use a magnet to check)

3 piece unit (bellhousing, maincase, tailhousing) - aluminum maincase - C-4

2 piece unit (maincase, tailhousing) - C-6

GeoBW, the FMX was a pretty hardy transmission for it's day and has been around in various forms for several decades. The last year Ford production installed them was 1981. As posted by Jason that is a 1974 transmission. The D4AP-AA indicates it is from a 74 full size Ford with a 351C.  While not as tough as a C6, it was capable of holding it's own. I had one behind a 70 M code Torino GT (that I tried to beat to death) and a Cougar XR-7 and never had any problems.

There was a ID tag that was usually attached to a pan bolt or a tail shaft to main housing bolt that would further identify the transmission. You noticed I said WAS, most of them were tossed just like carburetor and distributor tags that the grease monkey at the local garage felt were in the way.

Not all the FMX's received a VIN stamping. Most of my friends I checked with that had a FMX transmission did not see a stamping. One that has a 70 Mach1 said his was stamped on the upper flange of the main housing where it bolts to the bell housing.    

The small case size is 9 7/8", the medium case is 10 7/32", the large case is 10 7/8"-11.6" but was not used after 1965. Ratios are 1st: 2.40:1, 2nd: 1.47:1 3rd: 1.00:1 R: 2.20:1

I have posted some illustrations showing trans ID by pan shape and the location where you might find a partial VIN stamp on your FMX plus one of the locations for the ID tag. If found it will more than likely start with a 4 for the model year, a letter indicating the assembly plant (several plants built the full size Ford) and six numbers indicating the numerical sequence number of the donor vehicle. 

The small case size is 9 7/8", the medium case is 10 7/32", the large case is 10 7/8"-11.6" but was not used after 1965. Ratios are 1st: 2.40:1, 2nd: 1.47:1 3rd: 1.00:1 R: 2.20:1

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Thanks everyone that's very informative. Looks like she's not as original as I thought - will see if I can speak to previous owner to find out. 

One question, maybe for Secluff, what's the difference between the small case and the medium case in specs or otherwise?

Also, can anyone recommend what I should do in the way of servicing this tranny now that we have it out of the car? Any particular parts we should replace, for example?

[what's the difference between the small case and the medium case in specs or otherwise?]     GeoBW, each transmission be it a FX, MX, or the final FMX was continually being improved over the years. The 68-81 FMX was a combination of the best of the previous generation FX and MX. The improved transmission had the MX's stronger rotating parts and used the FX smaller case  which cut down on transmission weight. It also help reduced the complexity of having three similar transmissions both at the transmission plant and for the parts department. The large and medium case transmissions came into use on large heavy cars such as T-Birds, Lincoln's and Full size Ford's. Until the C6 was released in 1966 it was the only automatic transmission up to to task of standing up to truck use.

They are pretty tough transmissions. As I posted earlier I had one in a 70 M code Torino GT where the M was slightly "Enhanced" and the  FMX was stock. It would bark the tires when it shifted which was good for a couple of tickets by cops that didn't appreciate the squealing tires as much as I did!  

At this point the only thing bad about them is there is not the parts support for them that the C4, C6, and Fords modern automatic's enjoy. You can get rebuild and normal maintenance parts for them, but "Hot Rod" stuff is rare and hard to find.

If the transmission was operating properly before you pulled the engine and transmission, I wouldn't do much to it. I would check the vacuum hose to modulator valve to see if there are any signs of the valve leaking such as a spongy hose and smoking exhaust from the fluid being sucked back into the engine. Check the manual shift arm seal for leakage and defiantly replace the front and rear seals. Replace the trans filter (Good time to replace the manual shift arm seal if needed). Check the fill tube to make sure the O ring is not leaking.      

FMX transmissions used type F fluid (ESW M2C33-F)

Easy way to ID early Ford transmisssions

3 piece unit (bellhousing, maincase, tailhousing) - iron maincase - FMX (use a magnet to check)

3 piece unit (bellhousing, maincase, tailhousing)  - aluminum maincase - C-4

2 piece unit (maincase, tailhousing) - C-6

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Hey Killer, this was the simplest of all diagnostic systems - and yes - iron maincase = FMX  :goodpost:

I have an FMX in my '71 Mach 1 "H" code 2v. I had the FMX trans rebuilt with a TransGo shift kit for firm, crisp shifts. This was done 15 years ago. I drive the car everyday, and also tow with it. The FMX performs perfectly to this day. I added an auxillary trans cooler ( In series, after the radiator trans cooler )when it was re-done and I also run a stock converter. While not as serviced with aftermarket parts as the C6 and C4, there are shift kits and torque converters ( I think TCI makes a series of converters ) so I wouldn't shy away from doing one up if that's what your car has. I'll bet if you really called around, there's some performance transmission shops that are into it and have some tricks that can be done as well, but most street transmissions don't need all the "magic" stuff done to them aside from kits and converters.

I have an FMX in my '71 Mach 1 "H" code 2v. I had the FMX trans rebuilt with a TransGo shift kit for firm, crisp shifts. ... I also run a stock converter ...

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That's very helpful advice Spike - will go down that path.

I think I will need to mod the converter to 2000+ to allow for the Thumpr cam I will be using.