fmx transmission needs warm up before driving

rbancy

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May 12, 2020
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1969 mustang, rebuilt 302 with 200 miles, FMX transmission

Hi just wandering if anyone else has these problems with a fmx transmission. Have a 2200 - 2500 rebuilt stall converter. it was a sunny 9 cel / 48 fah outside. Let the car warm up for 4 minutes before driving it. Always happens , car revs up to almost 4000 rpm but barely moves. After 10 minutes of driving it on side streets or when thermostat hits 150, i can then take it out on the busy roads and it drives with no issues thereafter. Seems like the first 10 minutes rpm will spin 3500 - 4000 and car will go about 10 - 15 miles...... after that 45 minutes of driving is no problem.

anyone else have these issues with the fmx transmission ?
 
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08GT500

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Jul 12, 2018
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1969 mustang, rebuilt 302 with 200 miles, FMX transmission

Hi just wandering if anyone else has these problems with a fmx transmission. Have a 2200 - 2500 rebuilt stall converter. it was a sunny 9 cel / 48 fah outside. Let the car warm up for 4 minutes before driving it. Always happens , car revs up to almost 4000 rpm but barely moves. After 10 minutes of driving it on side streets or when thermostat hits 150, i can then take it out on the busy roads and it drives with no issues thereafter. Seems like the first 10 minutes rpm will spin 3500 - 4000 and car will go about 10 - 15 miles...... after that 45 minutes of driving is no problem.

anyone else have these issues with the fmx transmission ?
Hi,
Quite familiar with the FMX. Very easy to rebuild with few specialty tools required.
Was this FMX one you had previously run..TC rebuild only & external seals, etc..basics?
Sounds very typical of one with high mileage, internal seals harden up & leak, takes a little thermal expansion before it functions as it should. Are ways to improve it with additives, rebuild is the right answer.
I’d imagine you had confidence in it if coupling it to a fresh 302, If it was gone through it’s likely a simpler matter. Few questions..
Trusted spot rebuild the TC.. tested?
Any other changes made e.g., a shift kit, external oil cooler vs Radiator, Kickdown, etc?
What fluid are you running.?
Have you checked line pressure a/o yet?
Any other hard shifting prior to it being warm, shuddering, etc?
Apologies for response w/ more questions, trying to narrow it vs a vague response.
Best!
John
 
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rbancy

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Thanks John for your reply;

I do not know the history of the transmission. 69 mach 1 fmx . Im not very familiar with transmissions.
The car hasn't been on the road for over 10 years, and I know the transmission hasn't been built. After warming up, it makes
a chirp sound when it does shift though.

The torque converter I bought from ebay which was a rebuilt fmx 2200-2500 stall. Its actually listed right now from the same
seller i bought from. Item number 233763310672 on ebay. Just checked it.

I do have the kick down connected, no external cooler besides the acp alluminum 3 core rad. Im running the standard atf trans fluid.
The trans fluid is topped off , even past the line.

No hard shifting , just doesn't seem to want to move until the thermostat his about 150 or 10 minutes of driving. Really noticing this now.
Then again the engine was just rebuilt 2 months ago.

Next sunny day I will try using an additive. What i read was to try Trans-X additive. See if that will help it a bit. I will keep you all posted after tring
this to see if it helps.

I believe it does need a rebuild .. . I know the fmx are strong and can continue driving like this , but I thinking of changing to a C4. Any suggestions on this ?

Will have to change the torque converter, trans cross member, netural safety switch, driveshaft yolk, few other things that i just dont want to get into
at the moment.


thanks
 

08GT500

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Hi,
So, sound like a rebuild candidate.
Before you settle there 100%, there’s a few ways to better hone in on it’s inner health as well as some other reasons it may be doing what it is. Wouldn’t feel right if these bases weren’t covered first.
FMX’s are good Transmissions for what they are & function well, sometimes the kickdown adjustment being off will make it shift harder than stock, as if a shift kit installed for that purpose, as well as make it a bit lazy. I’d double check that.
Torque Converter RPM is mildly high, obviously a lumpy Cam, how much vacuum is that 302 pulling at an idle?
Keep the (Hot) fluid level between the high and low lines on the stick, never above...
I don’t subscribe much to additives, but some have proven their merit.
A few basics to glance at here:
https://itstillruns.com/diagnose-ford-fmx-transmission-problem-4810525.html
We’ll start basic & move on. See what you find..
As for a C-4 swap, it’s a stout Trans that can deliver a broad range of performance in a small, light package.
Looking further out, if you’re driving your Pony distances you can save your motor from extra RPM’s long term, and pull the trailer hitch for the fuel tanker off, opt for an OD gear addition.
No sacrificing snap by running taller rear end gears to “hit the middline”. Run 4.10’s & enjoy!
Seems you’re trying to stay period consistent (!!applause!!)- the parts for the C4 swap are readily available as is an OD tail shaft kit, or even more fun (perhaps even a tad crazy-so lines up these days)a 6 speed C4 conversion..Super street seat pegged fun & yet only wind 1,500RPM’s @75...:lol:
https://www.gearvendors.com/f2wd3s.html
Best!
John
 

08GT500

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“After warming up, it makes
a chirp sound when it does shift though.”
From the tires, or the Transmission..?
-John
 

rbancy

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May 12, 2020
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Victoria, BC, Canada
“After warming up, it makes
a chirp sound when it does shift though.”
From the tires, or the Transmission..?
-John
it makes it from the transmission while shifting a different gear. Someone said it can have a shift kit, also the same thing you advised - to check the kick down; which also may need adjusting. I do not know the history of the transmission and what it has.
 

rbancy

Member
May 12, 2020
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43
Victoria, BC, Canada
Hi,
So, sound like a rebuild candidate.
Before you settle there 100%, there’s a few ways to better hone in on it’s inner health as well as some other reasons it may be doing what it is. Wouldn’t feel right if these bases weren’t covered first.
FMX’s are good Transmissions for what they are & function well, sometimes the kickdown adjustment being off will make it shift harder than stock, as if a shift kit installed for that purpose, as well as make it a bit lazy. I’d double check that.
Torque Converter RPM is mildly high, obviously a lumpy Cam, how much vacuum is that 302 pulling at an idle?
Keep the (Hot) fluid level between the high and low lines on the stick, never above...
I don’t subscribe much to additives, but some have proven their merit.
A few basics to glance at here:
https://itstillruns.com/diagnose-ford-fmx-transmission-problem-4810525.html
We’ll start basic & move on. See what you find..
As for a C-4 swap, it’s a stout Trans that can deliver a broad range of performance in a small, light package.
Looking further out, if you’re driving your Pony distances you can save your motor from extra RPM’s long term, and pull the trailer hitch for the fuel tanker off, opt for an OD gear addition.
No sacrificing snap by running taller rear end gears to “hit the middline”. Run 4.10’s & enjoy!
Seems you’re trying to stay period consistent (!!applause!!)- the parts for the C4 swap are readily available as is an OD tail shaft kit, or even more fun (perhaps even a tad crazy-so lines up these days)a 6 speed C4 conversion..Super street seat pegged fun & yet only wind 1,500RPM’s @75...:lol:
https://www.gearvendors.com/f2wd3s.html
Best!
John


HI john ,


yes the cam is lumpy. Its a comp cam part # 35-424-8 / a rollerised one i went for this time around as my build 15 years ago
was a flat tapped voodoo for my 68 fastback i had.
lift for intake and exhaust: .513
.006 tappet lift 276 intake / 282 exhaust
Duration @ .5 224 intake / 230 exhaust
lobe separation 110


really like the cam / engine builder said the stall matches the cam.
Gears are 3.25 's . Later on will change to 3.5. Liked the mid range.

as years ago when i had the stock 279 and switched over to the 3.40s i really liked. Just want a good streetable car.

thanks for the website - will definately check it out.

as for the OD - yes very tempting with gas. Im still waiting to hit 500 km so i can do my first oil change after rebuild. I was just looking at one today guy had a conversion kit for 3500 at his shop. Standard T5 would be fun to drive. Everything for the conversion and t5 transmission. Very tempting ...

I try my best to keep things original or at the era. After reading these T5 conversions it is quite tempting though.

Firstly i will try the Trans X - i know its just a bandage fix if it does help a bit, but will try and keep you all posted of the result. Just waiting for the next sunny weekend.
 
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08GT500

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Was Hi,
Well, there’s many options no doubt, I’ll get through this & give you my thoughts- just for an outside opinion.
What fluid are you running? Type F is your best bet in the FMX.
Color of oil and odor right off the stock are both helpful. When AT’s sit a while check balls stick, seals dryrot & ma
Detergents in type F are be helpful, and O-rings will swell up, maybe enough to help your finicky FMX as well.
Once unrebuilt, nostalgic era AT’s with miles gets new fluid, sometimes it affects how everything in the unit functions. Usually not for the better..
f I pulled the pan to swap a filter I’d catch & reuse at least some if not all of my original fluid (note this is for non rebuilt Tranny’s of the mid 60’s-70’s.
Seal design, materials, integrity have improved greatly since 69’, Dextron would work just fine in thaRealize you have no history on this FMX..did you pull the pan & swap the filter, or not leave it as it was & drain fluid fully, or replace fluid entirely?
T-5 conversion?! Welcome to my undivided attention, lol! Certainly would’ve mentioned that, your interests seemed AT specific (the FMX to C4 swap comment).
So, let’s see what the oil looks like, check your vacuum lines for cracks to the Trans, adjust your Kickdown & go from there..
I’ll post the rest down below.
Good luck!
-John
 
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rbancy

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May 12, 2020
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Victoria, BC, Canada
Hi John , yes i am running the type F fluid. There is also no odor coming from it. I was told to smell it and if it smells sweet like or has bubbles can
have a mixture of anti-freeze. I will definately try dextron first.

All the trans lines vacuum lines and vaccuum lines are new when I got the engine built.


also will try adjusting the kick down as well.. try the basics first before thinking of a new or built trans.

I even looked at your previous thread about gear vendors which is really neat. I never heard of that . I personally wouldn't get it , just my personal opinion, but it is a brilliant idea for someone who wants overdrive or for distance driving.

thanks john for your suggestions.
 

08GT500

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Jul 12, 2018
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Hi,
Last post edit, was exhausted & editing was lacking, my apologies..no worries, btw, I’ll help if I can.
To add some clarity..
Suggest sticking with type F fluid. Dextron in a non-rebuilt FMX Trans. with mileage will likely potentiate issues.
If coolant is leaking into the fluid, it’s milky appearing. Can also look at coolant as it Trans fluid may end up there, too.
In earlier, tired AT’s I’ve setup for screening out large debris, hot looping in 70% old, 30% new, motors running & monitoring line pressure, etc. Check Diaphragms with a MityVac. Filter, I’d swap.
Tranny fluid in an older AT is it’s custom tailored blood type, if not burnt or otherwise contaminated, a 100% fluid swap may cause a perfectly functional trans to slip, shudder, fall on its face,etc.
Obviously, Trans is worn internally, but the Achilles heel is a fluid swap.
So, in absence of other external issues, your FMX still may improve over time. FMX’s are rare in that capacity as they generally fail over extended periods, allotting time to plan ahead.
Cross contamination with coolant was one reason for the external Tranny cooler question I’d asked, more in the 1st link I sent you, glad you liked the 2nd- as mentioned.. a 6 speed FMX/C4/C6 is not for everyone, but certainly is pretty cool.
They source other useful components, including typical OD tails.
Based on your XR276 bumpstick, I’m guessing a 390-425 HP build, 400Ft/lbs(?)
Great retro-roller Cam, btw..
Potential T-5 swap in the future:
if
you decide on a MTrans. the T-5 is light (75-130lbs), many variations (40) exist, Titles misleading, e.g,. A stock ‘world Class T-5’ sounds strong, yet 300Ft/Lbs & a hard launch..hard 3rd gear shift, pray you paid the annual AAA bill.
Cost & time saving route is locating a low mileage late model T-5 at leisure.
Then, a rebuild by a reputable shop, after a dry fit, driveshaft length, buy the parts commensurate with your build.
Good spot to read of the T-5’s potential..

https://www.astroperformance.com/product/new-485-torque-a-5-gear-kit-package-1985-93/
Good research reads on T-5, TKO(Z), T-45, T-56, Tremecs, 3550, 3650’s..

http://www.mustangandfords.com/news/mump-0208-five-speed-mustang-transmission
Good luck!
-John
P.S. I have (9) Cars & (2) are Auto’s.
Any Pic’s of your 69’?
My 71’, 351C w/ built FMX. Last pic’s taken before the motor came out & I stuck it on the lift. It’s miffed... 408 In process..

E90F96FE-00D4-43E3-ABDA-D1205039DB5B.jpeg

1F3AE67B-DAF7-4AC4-922D-628C1C4A6AA1.jpeg EC12DB37-B7C1-4659-A527-7C9B812F8730.jpeg
 

rbancy

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May 12, 2020
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Victoria, BC, Canada
I don't have the aluminum heads and have only the 600 cfm carb. Heads are studded as well. At 5600 rpm it ran 350 for torque and 325 horses. Engine builder thought it would run around 285 to 300 so they were suprised with the numbers. I also have the dyno video as well. I just want a street machine, not planning on going on the strip. I like the lumpy cam in it. The anti-freeze is a bit rusty coloration, but i hear thats quite normal with a new build. I was running water to flush it out, but had to flush it out as temperatures were dipping to freezing on clear nights.

I appreciate the links you sent, i am checking them out right now. The trans fluid does look good though .

wow 9 cars you have ? all classics ?
 

rbancy

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May 12, 2020
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Victoria, BC, Canada
Just read the article on the T5 transmission. Your right, looks like the 3rd gear when reving high is not as strong. Its uaually the 2nd or 3rd gear you like to get the rpms high. I think i'll try dextron and pray it helps. If it does, just going to stick with the fmx. They are heavy, but I hear can take a beating and will always keep going.