Thoughts on Transmission

[po51 21]

So  I'm about to get my 351W back as a stroker 408 going to put out around 425-450 hp. I still have my stock FMX trans, keeping my 3.25 posi. The stang is not a daily driver, weekends around town, few trips all under 50 miles. I'm not sure the FMX will handle the increase HP, so should I go with a built C-4 or C-6, Will a AOD handle the increased HP? I understand it can get rather pricey having a AOD built.Would like to hear from guys that are running a 408 and what trans they are using?

                                                                                                                    Steve

[det0326 198]

I guess you can build any automatic tranny to handle any horsepower for a while anyway. My vote is for the AOD but that is just me and how I would use my car.  

 

Dave

[Wycked69 20]

My $0.02....................The FMX is a pretty stout transmission. You can rebuild it to be as stout as any C4.

The FMX gets a bad rap for no real reason other than the fact its heavy due to the cast center section but its actually a pretty tuff tranny.

 

As Dave indicated., you can build any transmission to handle the horsepower you intend to attach it to.

[po51 21]

Wycked,

  I just seems hard to find parts for the FMX to strengthen it who makes the best shift kit?

[barnett468 418]

So  I'm about to get my 351W back as a stroker 408 going to put out around 425-450 hp. I still have my stock FMX trans, keeping my 3.25 posi. The stang is not a daily driver, weekends around town, few trips all under 50 miles. I'm not sure the FMX will handle the increase HP, so should I go with a built C-4 or C-6, Will a AOD handle the increased HP? I understand it can get rather pricey having a AOD built.Would like to hear from guys that are running a 408 and what trans they are using?

                                                                                                                    Steve

 

i would not run a tru 425 - 450 hp 408 stroker with 3.25 gears unless you run around a 3000 rpm stall converter or simply don't care how slow it will be off the line . . i would run 3.50 and if i had overdrive i would run 3.70.

[1969_Mach1 335]

My $0.02....................The FMX is a pretty stout transmission. You can rebuild it to be as stout as any C4.

The FMX gets a bad rap for no real reason other than the fact its heavy due to the cast center section but its actually a pretty tuff tranny.

 

As Dave indicated., you can build any transmission to handle the horsepower you intend to attach it to.

 

I don't know if the FMX is best for you.  But, I agree 100% with Wycked69 about the FMX transmission.  If you think about it, there must be some reasons Ford used the FMX instead of the C4 with 351W motors.  They also used a big block version of the FMX behind 390 motors as well.  As far as AOD or C4 trans, I'm certain one can be built for your HP requirements.  In stock form, Ford used a larger E4OD trans behind the 351W.  But the E4OD is much too large to fit in a 69 or 70 Mustang.  The AOD and later 4R70W was behind the 302 and smaller motors. 

 

I myself, prefer C6 for larger HP requirements then the FMX for lower HP requirements.  But, I've noticed other people wanting to squeeze out every last HP don't like the C6 because of the overall added weight and inertia of the larger internal parts.

 

As for rear axle gears, the ratios barnett468 suggests sound good.  The 3.70 ratio would make the car more fun to drive around town than the 3.50 ratio.

[Rsmach1 71]

I also agree with Wycked69, the FMX is a good trany. It weighs more than a C6,but eats up less Hp. Hughes has a couple good converters for it available at summit, and as far as shift kits definitely go with a transgo.

[panteramatt 1]

I have a great 4R70W and full swap kit for sale. 

[ashleesmach1 28]

Wycked,

  I just seems hard to find parts for the FMX to strengthen it who makes the best shift kit?

trans go makes the shift kit here is a link  

http://www.summitracing.com/parts/trg-fmx-3

[barnett468 418]

Wycked,

  I just seems hard to find parts for the FMX to strengthen...

 

buy red alto clutches and get the wide red alto band and the good metal discs.

[1969_Mach1 335]

I'm in line with others here, if you can parts for your FMX, go with that trans.  A long time ago in high school my older brother street raced his 69 Mach 1 a lot.  Never had a any issues with the FMX trans.

[RPM 1,268]

I also agree with Wycked69, the FMX is a good trany. It weighs more than a C6,but eats up less Hp. Hughes has a couple good converters for it available at summit, and as far as shift kits definitely go with a transgo.

Ditto. The fmx is a beast, even has torrington bearings. You should have plenty of torque to get your car moving even with 3.25:1 gears. With a 408w your only problem with street tires will be traction. You won't even notice the extra pounds of the fmx's iron center section with the added hp and torque of the 408.

[LSG 15]

  Steve, the FMX is a fine tranny, as are the C4 & 6, but they are museum pieces. Put it on the shelf and build an AOD with 4R70W gears. The AOD, with its Ravinaeux  setup is the FMX's decendant, AND you can have overdrive 4th. You can drive farther on less fuel, and have more fun in your car. I would not use a 3 speed auto in anything other than a drag race only effort.  LSG

[prayers1 153]

I have 351C 4V and once had a 4 speed Toploader w/ 3:55 gears.  I couldn't drive very far because the engine would rev so high at 55 mph (I forgot what rpms it was).

 

I found guy called Silverfox who builds AOD & AODE transmissions (silverfoxtrans.com) He set me up with a nice AOD and 2600 stall converter. Now I can cruise to the shows at 1800 rpms doing 55 mph. He installed a constant pressure valvebody that does away with all of the TV cable adjusments and a nice shift kit. I'm one very happy customer.  He's a very nice guy to talk to and will help you with your decision.  Thus far, it's the best mod I've done to my car.  Next, I'm gonna install 3:89 gears.

 

Check him out and Google him, he stands behind his work and ships all over the US. Hope this helps!

[RPM 1,268]

What's up with 55mph prayers1??? How is it possible to keep it that slow with a four barrel Cleveland? Just kidding ya :) I'm nursing a sore back and feeling chippy on these good pills.

[MikeStang 247]

Ditch the FMX and get a 4R70W and do a Jbody mod and baumans controller and bolt that shit in and call it a day.

Dont worry about the 3.25 gear in the rear, its what Im running behind my 408 with 4R70W and its a monster out of the hole if you can keep the tires planted

[1969_Mach1 335]

C'mon MikeStang!  There's nothing wrong with old technology.  I like the FMX.  I've seen them take a beating in stock form without any issues.  Also, maybe with a lower rear axle gear (higher numerical ratio) the tires wouldn't spin as much?

[MikeStang 247]

Oh don't get me wrong I'm not saying that the FMX wont take a hell of a beating by any means.

 I was just saying you can do a simple J-Body mod to a 4R70W and have a transmission capable of taking upwards of 450hp easily as long as it was a good unit to begin with.

Plus you have the added benefit of the OD gear which makes cruising AWESOME.

I filled my car up before I left for Houston and then stopped along the way and put 7 gal in it then filled up a mile from my destination and put in 4 gallons to bring it up to full.....Total fuel consumed 11 gallons ...total distance traveled 289 Miles = 26.2 Mpg.....and to be honest I know I drove more than 289 Miles because I took a detour of about 15 miles to pick up a Rifle LOL.

So just say 20mpg to make it easier and you will quickly see the benefit of a 4R70W and highway gears LOL.

I will likely swap to a 3.55 in the future tho for a bit more get up and go.

Altho doesn't that make tire spin WORSE LOL

[1969_Mach1 335]

An overdrive trans in older cars like these doesn't interest me because I don't have any intentions of cruising down the freeway in mine.  In northern CA the roads are so congested an accident seems inevitable, and there goes my 69 Mach 1.  Plus the car is not comfortable enough to drive long distances for me.  My left knee has to wedge between the steering wheel and door panel, and try to not hit the turn signal lever every time I use the clutch.

[fvike 173]

The FMX also saw duty behind the 427 SOHC "Cammer" in the1964 Ford Thunderbolt. It will take anything you can throw at it. But it is not a performance transmission, so there is very few parts for it in the aftermarket. Hardly even a shift kit.

[barnett468 418]

.

i would run a powerglide.

[Alan_Mac 48]

If you want to keep your Mustang stock the obvious choice is to put the stock transmission back in.  The FMX was the work horse trans for many years at ford.  It found its way in many demanding applications as fvike mentioned one above. Cost / performance drives auto parts obsolescence.  There are many very good parts that are obsolete and I put the FMX in that category.             

[Rsmach1 71]

This place has some decent stuff http://www.oregonperformancetransmission.com/mm5/merchant.mvc?Store_Code=OPTI&Screen=CTGY&Category_Code=FMX kevlar bands, rebuild kits, shift kits.

[sportsroof69 13]

I run a PA Supercomp C4 behind my 408, and smack it with some nitrous. Great Trans with great results that holds up to a pretty decent amount of power.

[Ridge Runner 1,202]

I vote FMX as well .I loved the one in my old 69 Mach with a 351 .I wanted a crisper shift into second and the mechanic said it was  simple as shims in the springs .It would light up  second  if i really got into it ,got me in trouble once in the rain when it spun me around .