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Fmx transmission2-3 shift

Whats wrong my fmx transmission, when i accelrate hard transmissin not shift 2-3. When i off pedal then shift to 3rd gear..
[Whats wrong my fmx transmission]
Its a 50 years old transmission. If it's never been revised or long ago, there are tons of stuffs that can lead to this.
Can be a tiny bit of dirt jamming one valve into the valve body or clutches loose way beyond clearance specs..

I'm not a trans specialist at all. Far from that, but I do have a FMX in running condition, serviced minimum stuffs like the pump and just rebuild my 71 C6.
So with that tiny trans guts knowledge, if of any help, that's what I'd do:

Start by making sure you have the right fluid ATF-F at the right level (trans needs be hot and level checked while running in park)
before fill, smell the oil at dipstick. If it smells like no oil should, burned or sometimes even like fish.
No need to search further, fill it to level and be gentle with it, till you get the parts or a shop, as the trans needs be revised.

As it operates and shifts,
When you are engine running and go from reverse to D and once engaged back to R. Does it shifts in less than a second while engine idles or does it takes more time?
I'd look first if the modulator is well connected ( if not connected at all, the trans could slip a bit even make weird noises)
You can also (carefully, not damaging the gaskets) inspect the servos and clean everything in there. The piston seals or entire units can become hard loosing their sealing properties.

If the trans is in its "juice" for decades, I'd bet it's a piston o-ring that is damaged, where it seals when pressure isn't too high but leaks under higher pressure.
probably also because friction plates lost their thickness forcing the piston to travel more.
On my c6, never serviced, which ran 25 years ago before the car was parked. I saw that because of the heat caused by friction, the plates were very thin and blue, and because of the heat, the inner o-ring of the forward clutch piston was damaged, burned/cut. It stayed in place because it can't go anywhere trapped in its groove. So trans would operate, but because of the leak, the piston would not set the clutch under the full right pressure, causing slipping, which causes heat and wear on the plates, making the situation a bit worse every time. It likely leaded to similar situation as you describe for yours. Which unfortunately also means the trans needs to be revised.

73 modified Grandé 351C. Almost done. 
71 429CJ. In progress
Check modulator.


1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

https://youtu.be/SoW1fhaFPzY  Burn Out Video. 

[Image: 044.jpg]
[+] 2 users Like turtle5353's post
+1 on the vacuum modulator, start there and kickdown adjustment.

“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
Might be absolutely nothing wrong with it.

WOT 2-3 shift point on an FMX car is going to be in the 70-80 mph range. These FMXes were only installed behind 351-2V and 302-2V cars, which all had 2.75/2.79, 3.00 & 3.25 gears. Take a look at the attached shift speed matrix for a C6. FMX will be very similar.

[Image: SHIFTPOINTS.jpg]

[+] 2 users Like Hemikiller's post
I'll add to make sure the shift linkage is adjusted correctly. If it's off a little, the shifter may say "Drive" but the lever on the transmission might be between 2 and 3. Cheap easy check, no parts to buy.
Had a similar problem with my car except would almost seem stuck between gears... Was a weird sensation turned out to be my kickdown rod.
Thanks to the answers.
Vacuum system and pressure cheked and modulator and governor. 
Yesterday i removed the  sump and ther are only 1.5 L oil  Big Grin 
My oil stick has something wrong. Now i waitin it i can test drive.
(11-27-2019, 02:34 AM)Terpatin Wrote: Thanks to the answers.
Vacuum system and pressure cheked and modulator and governor. 
Yesterday i removed the  sump and ther are only 1.5 L oil  Big Grin 
My oil stick has something wrong. Now i waitin it i can test drive.

Check also this check ball in upper body of the valve body for free movement. It has to sit in the slightly wider area below its current location. 

[Image: 20190202-141035.jpg]
[+] 1 user Likes Vicus's post
I changed new type-f oils and test drive. Not working. ? maybe i must rebuild it
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