Which is better transmission -- C-4 or FMX?

[Jim LeMay]

My '69 Mustang originally had an FMX transmission in it, but found that it
now has a C-4. Apparently from what I remember, a transmission shop did a
switch on the transmission. Should I try to get an FMX back to replace it if
it is better?

Thanks,
.. Jim ..

[Jeff Cook]

Tough question, Jim.

Of course, if originality is important to you, go back to the FMX.
If strength is really important, it's hard to beat a small-block C6.
But these are kinda scarce.

In stock trim, an FMX is definitely a stronger box.
It's basically a truck transmission.
It's also heavier, with it's cast-iron main case.
The biggest problem with an FMX is it's lack of aftermarket support.
You can buy parts to beef up a C4 to make it capable of 9-second drag
strip duty, but for the FMX there's little or nuthin available.

So, it boils down to what you're looking for.

Are you having problems with your C4?

[Steve C]

Steve :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-)

	Minneapolis, Minnesota

[Jared Rude]

Personally Jim, I would keep the C4, but as Jeff Cook stated, originality
requires a FMX.

With the FMX, you may have to get a different driveshaft, or have the length
of your current driveshaft changed. You probably know this though.

--
Jared Rude
Mechanical Engineer
Motorola Paging Products Group
nospam...@bellsouth.net

Jim LeMay wrote in message <6gj1f6$a...@bgtnsc03.worldnet.att.net>...

[Robert Howell]

If you want a more stock apperance to the car get the FMX. They are
heavier unit in physical weight due to the cast iron main housing compared
to the C4 but they don't stand up to much punishment. Rebuilding them is a
nightmare unless you like alot of plumbing. For weight sake and
availability, stick to the C4.

Jim LeMay <JLe...@worldnet.att.net> wrote in article

[Schtoo]

On Thu, 9 Apr 1998 12:45:13 -0500, "Jim LeMay"
<JLe...@worldnet.att.net> wrote:

>My '69 Mustang originally had an FMX transmission in it, but found that it
>now has a C-4. Apparently from what I remember, a transmission shop did a
>switch on the transmission. Should I try to get an FMX back to replace it if
>it is better?
>
>Thanks,
>.. Jim ..

I wanna know too, but for different reasons. I have a strongish 351W
in front of an FMX, and I wish to know how long it will last
especially after the W gets a bit more curry. I have heard the FMX is
strong, but very hard on gears and such. The ultimate is of course the
C6, but as mentioned is hard to find. What are the possibilities, and
perhaps a basic comparison of the stock and modified C4,C6,C10 and FMX
might help me in my quest, aswell as Jim's.

[DarkWolfff]

i've got a fmx in my 67 galaxie behind a mild 390 with a little over 130k and
no problems. it can't be that weak of a trans to stand up to that kind of
torque in that heavy of a car. but like everybody said parts are a pain in the
ass to find. just replacing the gasket and filter took me a couple trips to
the parts store even with the filter with me they couldn't match it to
anything. they made so many differnet models of the fmx and everyone is a
little different.

[David Cole]

Use what you have till it goes bad, then take the plunge for a C-6.

I have a 69 Mustang Fastback with a 383-W stroker, solid roller, Dart srs.
I have a C-6 in it that I wouldn't trade for anything short of a Lenco.
This transmission has taken all the abuse I can give it. The car is 90%
strip and will run low 11's in the 1/4 on the motor only. It was installed
over 4 1/2 years ago and still works fine. The fluid looked fine from the
junk yard, but I had it built with a TCI kit. The kit included good
clutches, band, valve body kit, seals, etc. To install it I had a
driveshaft made up from a 80's Ford van core and had to buy a C-6
crossmember. The only problem I had was header clearance on the cable
bracket for my Qtr Stick shifter. It would not have been a problem with the
stock shifter and metal rod to the trans.
The small block C-6 is not that hard to find if you know where to look.
Mine came from an 87 F-150 with a 300-I6. I think that most of the 81-87
F-Series trucks with this engine and an auto trans got the C-6. The V-8
F-series also had the C-6, but it has a much longer tail shaft. The total
length on my C-6 is only 2.5 inched longer than a C-4.
As for power/weight: I haven't weighed them myself, but have been told that
a C-6 is 80 lbs heavier than a C-4. On the dragstrip this trans slows my
car down by .17-.18. Going by this, the extra weight should account for
.08, so the trans itself slows my times by about .10. I am more than
willing to give this time up for the trans to be almost bulletproof.
Cost to install (in Alabama 4.5 yrs ago)
junkyard C-6 $150 ( was supposed to be good, but rebuilt anyway)
TCI rebuild kit $160
bench rebuild by local ford guru $150
83 ford van driveshaft $75
shorten driveshaft by local 4X4 shop $35
C-6 crossmember from Mustang only junkyard $45

Total $615 and worth every penny

thanks
David Cole

[Bryan J. Lee]

Fmx's are very strong and heavy tranny. My friend has one behind a Shelby
289(shelby rods,steel crank with chrome journal, etc........). They have 2
problems. 1. They are know to slip out of park into reverse when at idle.
The rod inside the tranny that locks the in park wear out. 2. To save
weight they used a detacable alum. belhousing that crack with when tranny is
built to shift fast(hard). My friend cracked 3 bell housing in a year.
But the tranny is fine.
Schtoo wrote in message <352e1c6d...@news.webrider.net.au>...

>On Thu, 9 Apr 1998 12:45:13 -0500, "Jim LeMay"
><JLe...@worldnet.att.net> wrote:
>
>>My '69 Mustang originally had an FMX transmission in it, but found that it
>>now has a C-4. Apparently from what I remember, a transmission shop did a
>>switch on the transmission. Should I try to get an FMX back to replace it
if
>>it is better?
>>
>>Thanks,

>>.. Jim ..

[Schtoo]

No need for you to say thanks, I was asking! Sounds like the FMX will
stay until it does go pop. I have absolutely no idea what condition it
is in, other than it should be brand new like the rest of the stuff in
the car. The car it is in is a falcon sprint, for want of a better
comparison, an early model Mustang. But eventually t may have to deal
with a blown and 'enlarged' Windsor of 427 ci (The engine guy wants to
built one as much as I want one!). What are the estimates of the FMX
dealing with that sort of puishment, without having to do costly
modifications? Considering I am in Australia where parts from half a
dozen models are restricted to maybe 2. I have no problems handing out
the $$$, I just don't want to keep dishing them out.

[tonys...@gmail.com]

How to tell which is an FMXfrom the C4

[rimam...@gmail.com]

nope c4 are cookies ive got a worked 351 cleveland i did one good minute burnout and the tyres and gear box were toast i got an FMX installed instead the mechanic who installed it said i can garuntee this one,c4 i could kill in 30 min i said what's the good thing about the transmission he said its very strong, im from new zealand quite lucky to have an FMX apparently

[xb500f...@gmail.com]

Hey, im in New Zealand also, apparently the fmx is relatively rare over here. I had a fmx bolted up to a heavily worked 302c in my xb. Ran it for years before going to a manual box. The car was always driven as of it was competing in a targa stage and never had a issue with the fmx. From memory i think it pulled about 80 or 90kph in first stage, lit the rear tyres up when changing into 2nd and just kept pulling. I am actually considering putting it back in cause it was so nice. Have been offered $1500 upwards to sell it but i wont let it go

[jamieni...@gmail.com]

On Thursday, April 9, 1998 at 2:00:00 AM UTC-5, Jeff Cook wrote:
> Tough question, Jim.
>
> Of course, if originality is important to you, go back to the FMX.
> If strength is really important, it's hard to beat a small-block C6.
> But these are kinda scarce.
>
> In stock trim, an FMX is definitely a stronger box.
> It's basically a truck transmission.
> It's also heavier, with it's cast-iron main case.
> The biggest problem with an FMX is it's lack of aftermarket support.
> You can buy parts to beef up a C4 to make it capable of 9-second drag
> strip duty, but for the FMX there's little or nuthin available.
>
> So, it boils down to what you're looking for.
>
> Are you having problems with your C4?
>

> Jim LeMay wrote:
> >
> > My '69 Mustang originally had an FMX transmission in it, but found that it
> > now has a C-4. Apparently from what I remember, a transmission shop did a
> > switch on the transmission. Should I try to get an FMX back to replace it if
> > it is better?
> >
> > Thanks,
> > .. Jim ..

If your looking for better overall use of street-ability look into https://www.cjponyparts.com/mustang-aod-conversion-kits/c/60190010/ and dump the FMX and the C4

[jamieni...@gmail.com]

[lance....@yahoo.com]

On Thursday, April 9, 1998 at 12:00:00 AM UTC-7, Jim LeMay wrote:
> My '69 Mustang originally had an FMX transmission in it, but found that it
> now has a C-4. Apparently from what I remember, a transmission shop did a
> switch on the transmission. Should I try to get an FMX back to replace it if
> it is better?
>
> Thanks,
> .. Jim ..

I'm not a huge fan of the C4. It was only a few months after doing an engine swap on my '67 cougar that my C4 transmission needed to be rebuilt. It isn't that strong in its original form. I am told you can get rebuilds done to make it stronger. My preference would be to go with a C6. It's stronger. Like some people havew replied, it's tough to get support for an FMX.