FMX to C4 swap help needed.

[Erik72]

I recently lost second gear in my FMX and was told by the transmission shop that it would better if I swapped out my FMX to a c4.

I have 2 questions.

will it be a straight swap from FMX to c4 in a 72 mustang with a 351c or will I need to change things to make it fit?

Or is it better to rebuild the FMX with a shift kit? If so any suggestions on a shift kit.

Thanks for any input

 

[TommyK]

No personal experience with this swap but here are my thoughts.

The FMX shifter and linkages will need to be changed out to a C4 parts or adapted to work with the C4. I believe the flex plate will need to be changed as well. The driveshaft will need to be changed or reworked for length and the yoke changed. I think the neutral safety switch wiring will need to be modified as well.

A C6 is an easier swap.

 

[will e]

Greetings from Phoenix! What are your long term plans for the car? Are you going to keep it a long time and what kind of budget do you have to work with?

As mentioned above, a C6 swap is probably eaiser. If you plan on holding on to the car a while it might be worth it to convert it to a more modern 4 speed auto with an overdrive.

 

[Erik72]

will e

I plan on keeping it in the family as it was a wedding gift from the wife.

I have had it since 1999. Had the motor and trans built in 2002.

I lost the bands in second gear running it hard one day.

Pulled the trans out and sent it off to a trans shop to rebuild the FMX and put a shift kit in it.

The mechanic said that it would be better to replace it with a c4 and that it would be a straight swap. After doing so reserch it appears that there is more to it than that.

I would prefer to put the FMX back in as it did well for the first 44 years. I had it freshened up in 2002. but over all good Trans.

Here are the motor specs

I have a 351c 2v that has been ported with comp cam, scorpion roller rockers, holly 770 carb, holly street dominator intake port matched, full MSD ignition, hooker headers, 9 inch with 411 gears.

 

[boilermaster]

Erik72,

You will also perhaps need a motor plate for a c4, as the starters are in a slightly different location.

This (may) depend on which c4 you get or have.

you are going to find that there are 2 different styles of front pumps and case filler or pan filled, motor plates will be different depending on which transmission you select.

You are also going to need a c4 transmission crossmember.

as far as the neutral switch you should be ok (fmx) in in the shifter housing and c 4 resides on the transmission.

This now brings up the shift lever on the transmission, floor shifted cars are going to be different from column shifted cars, you have a choice of buying the correct OEM piece for big bucks or an aftermarket piece for about 35 bucks.

transmission kickdown lever is going to be different as well and I am unaware of any correct piece to use.

My current plan is to make one up out of several used pieces.

my driveshaft was very tight, but that may have been solved by using a shorter pinion yoke (I have Daytona pinion) you probably do not.

Cooling lines are going to be slightly different as well.

Speedometer gears will be different.

Will add more if anything else pops into my head.

Boilermaster

 

[will e]

The FMX is not a bad transmission. There is less aftermarket support for them than the c4 or c6 but if your goal is a nice driving car and you want to keep the budget lower I would just rebuild the FMX. You can slap it back in the car and be back on the road quickly!

 

[Carolina_Mountain_Mustangs]

The PO of my 73 did the swap from FMX to C-4 and did not put the rod going from steering column to shifter back on. Does anyone have one of those? I would be interested in purchase. I think I saw someone post a picture and part numbers for the three different rods.

Sounds like it is a pretty big job to change over. I have a FMX parts car but no C-4.

David

 

[turtle5353]

The FMX is not a bad transmission. There is less aftermarket support for them than the c4 or c6 but if your goal is a nice driving car and you want to keep the budget lower I would just rebuild the FMX. You can slap it back in the car and be back on the road quickly!

+1 what he said! ::thumb::

 

[kcmash]

My vote is the FMX rebuild or an AOD conversion.

 

[Erik72]

Thanks for the info. Looks like Im sticking with the FMX.

 

[Omie01]

The only thing I have not been able to get for my FMX is an aluminum tranny pan. I had it rebuilt last year by a local shop telling them that my goal is to put it behind a 475 hp Cleveland, They did a "reprogram or shift kit" $800, I installed a 3000 stall converter, $300, and now my tranny guy says it should be good to go!! I also swapped out the kickdown bar for a Lokar cable, this makes the kickdown point more adjustable. Good luck with whatever you decide!!

 

[OMS]

The PO of my 73 did the swap from FMX to C-4 and did not put the rod going from steering column to shifter back on. Does anyone have one of those? I would be interested in purchase. I think I saw someone post a picture and part numbers for the three different rods.

Sounds like it is a pretty big job to change over. I have a FMX parts car but no C-4.

David

You still need the c-4 lock out rod

 

[will e]

This is always an option...

http://www.tciauto.com/tc/6x-six-speed-transmission-package-small-block-ford-bellhousinghtml

6 speed automatic and small block ford bell housing. The price is difficult to deal with. It comes with a pretty low first gear and OD so you could get away with 3.00 or 3.25 gears and have a heck of a combination. I found this searching the web for something else, this is why I shouldn't surf the web.

 

[Don C]

This is always an option...

http://www.tciauto.com/tc/6x-six-speed-transmission-package-small-block-ford-bellhousinghtml

6 speed automatic and small block ford bell housing. The price is difficult to deal with. It comes with a pretty low first gear and OD so you could get away with 3.00 or 3.25 gears and have a heck of a combination. I found this searching the web for something else, this is why I shouldn't surf the web.

Those have been around for a while and are based on a GM 4L80E transmission that the controller activates OD with 1st and 2nd gears to produce 6 speeds. They cut the Chevy bellhousing off and bolt the conversion bellhousing to the front pump bolts.

And, that price doesn't include a torque converter