No clutch left

well it is a manual transmission GEN 10 F150
M50D; M5R2; (both used)
4wd?
gee check gear lube levels first or drain and fill it with correct lub.
this is top of box shifter directly to shift rails , good that.
how many speeds is he box? 3,4,5? seems is 4 speed.
the clutch actuation parts (pedal to MC to slave is top failure
so first gear and reverse can not be selected
25 years of shifting can be $1 part on tip of shift lever making the H pattern dead or random and a huge pain.
i have repaired cars with manual boxes , all clutch parts and rebuilt the box every ,all bearings new and synchro, and bad forks..
wish I could watch you but
key off can you get all gears in the H pattern parked?
or is shifter acting crazy loose.?
can you start the engine in 1st gear now or put in to first gear ,key off then in first gear for sure key off start the engine.? and not have car lurch forward. (yes clutch held down)
sorry all I have are questions transmissions have lots of fail paths.
even M/T boxes do but last way longer. I went 300k miles on mine
and only 1 slave cylinder failure and 250kh on 2more cars.
is the MC (clutch only) full of fluid in its Reservoir. if low drops fast
the MC or Slave is bad and leaking fluid.
fix this first if is true MC fluid loss week by weak ,day by day loss
no complaints starting the engine in 1s gear or any gear.
non, and is A#1 TOP IMPORTANT FACT
OR CAN NOT SHIFT TO 1ST PARKED KEY OFF.
THE STARTER IS DEAD CLUTCH NOT DEPRESSES SO TESTS AR LIMITED.
BUT GEE , KEY OFF AND PICK 1ST GEAR , BRAKES OFF
AND HAND PUSH CAR TO SEE GEE 1ST IS WORKING,
BUT SURE WE WILL NOT BE SURE 1ST IS PICKED, IF THE LEVER TIP IS BAD.

NOW THE HORROR, ALL 3 ENGINES USE AN M/T BOX
THE SLAVE CYLINDER CAN NOT BE SEEN
IT IS A COAX SLAVE DEEP INSIDE, (i HATE THEM)
LAST ONE I DID 4WD WAS 10 HARD HOURS LABOR TO REPLACE.
IF THE SLAVE IS ON THE BELL HOUSING SIDE BE HAPPY.
IF You run the box dry of LUBE the shift fork (1 of many) welds and fuses to the gear and cannot ever be shifted again,and yes I have cured those too.
the shift lever bushing is due.
true name
Trans. code M50D; M5R1/M5R2 Manual Transmission, Plastic shifter bushing
this $2 part does not last long, 100k miles or so
and gets beat to deathh in city traffic.
Part D seen here. at the tip of the shifter stick bottom end
it just dies. and shifter H pattern is loose and RANDOM>

see the video fix this cheap bad part., see blue part
https://youtu.be/c82sTBMzito?t=769

if scared of grease use silicon grease as we use on O-rings.
100% safe that is. grease.
now the shifter works like it did in 1997 ,tight
if still scan no get 1st gear for sure idling Neutro
try reverse too. if reverse grinds or balks the slave is leaking
making the clutch dead and engaged full time.

the clutch manual is dead. clutch pedal manual transmission
the clutch MC is dry under hood I bet, clutch fluid reservoir.
car, getting in to neutral is easy for a tow.
using 2 person, one pushes car, other shifts.
all brakes off
no tires(tyres) to a curb or large rocks etc.
flat ground, if not call for tow.
as person 1 gently pushes shift lever towards N.
as person 2, jogs the car body, forward and back. easy. we are only moving car an inch (25mm) or so, and like magic N is attained
now can be towed.

this post assume cars shift is direct shift lever not those pesky cable shifter that cable snaps.
no such car in USA so can not see it or find books. related.

Shift the clutch into first and second gear several times before attempting to shift into reverse if you have a manual transmission. Sometimes the clutch jams between the torque converter. Some minimal shifting between gears usually loosens the clutch, which enables you to put the car in reverse again.

Don, Possible internal damage to transmission, take into a good shop for diagnoses and estimate on repair.
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when you put it in reverse,first thing you feel a spring.after tthat you lift,
a security plate,this plate prevent you from going reverse into 1 gear.
cause the axel turn a little further when you allreddy has stop the car.
this takes two sec.thats why when putting it in reverse after you feel the spring you wait two seconds,then puch al the way in reverse.

4l60e or 4l80e transmission?

air in the hydraulic control system of the clutch release is the most likely cause here, have the clutch bled of air, that should cure the problem.

The problem sounds like the clutch. If you put it in 1st., then start it up, does it try to move with you foot on the clutch? Does the clutch pedal feel different than normal.

You probably burnt the clutch up.
A good indicator is hard to get into 1st with out grinding as well as reverse, and over all poor ability to shift in any gear.

air in the slave cylinder is more then likely not your problem.
Its pretty hard to do.

not sure on the set up of whether its rods or cables on this model for your gear linkages but sounds like one has either detached or broken which should be a relatively easy fix and not too expensive.Get a friend to move through gears while you look under to see whats moving and whats not.