Diagnosis? '71 F100 not shifting to 3rd

[RWVNRAL]

It's a '71 F100 Sport Custom with 302 and automatic C4 tranny, 2WD. Power nothing. Column shifter reads PRND21.

Just completed a total rebuild of rear axle. Everything is straight with that. I had a loose column shifter that made it impossible to shift the tranny into low (1). Pulled the column and replaced a cracked shifter bowl. Now I got first gear. Had to do this before I could determine if the transmission was hitting all three gears. I've always suspected that I'm only using first and second.

With the column shift working now, I am able to shift to 1st. If I start out in 1st, I can manually shift to 2nd okay. But then, after getting to cruising speed and shifting to D, nothing changes. If I start out in 2nd, the truck will get to a certain speed (usually 35 mph) and shift to neutral. If I start out in Drive (D), she will shift once at about 25 mph from whatever it is I'm staring in to whatever it is I'm staying in. It seems to me that I only have two gears. 1st and 2nd. No D/3rd at all. To back this theory further, I'm getting 8 mpg maximum.

I've got good vacuum. Modulator appears to be working okay. But, then again, I've not replaced it. Is there anything else I could do to determine what the issue is? Governor problem? Suggestions?

[BobbyFord]

Check the vacuum source, vacuum lines and modulator valve.

[Donnie]

too, how about starting out in the drive position under light throttle ( like a cop was following you) real easy like.. note & report the speed of the 1/2 shift.....keep adding fuel until you get a shift

Then do a hard throttle 1/2 shift, note that speed & report back after this test note below


When you let off the throttle doing this test, does the truck free wheel, or does it hold back?

I am assuming that you followed Bobby's tests to qualify the vacuum modulator & related tubing.
Pulling the hose off at the modulator valve with the engine running should produce a rough idle..
Another item to test is engine vacuum, leaks in other places, worn timing chain, etc..
I am suspecting a stuck 2/3 shift valve or hung governor if you have covered all the vacuum tests.....report back, someone will help you...........Donnie

[RWVNRAL]

Thanks, guys.

Overall vacuum checks out good. But, that's premature since I've not had a chance to run through the whole vacuum system....just did a test at the distributor. I have a dual vacuum distributor.

Took the truck out tonight and did as you suggested.

1) Starting out slowly, I get one shift at 20 mph. Once it shifts, the truck sort of lurches into the next gear. If I let off the accelerator, I have coasting with some resistance due to engine compression.

2) Starting on a rip, I get what appears to be some kind of really fast shift at 10 mph...but it's so subtle that I'm not even cool calling it a shift. After that, while still gunning, I get to 40mph before there is a shift to neutral. Once I let off the accelerator, she engages into the next gear.

It does sound a helluva lot like vacuum issues, doesn't it?

But why, when I sneak off the line, am I starting out in second? ...If that's even the case

[michael69]

You say it shifts in to neutral then when you let off it shifts into drive. Sounds to me like the transmission is slipping when you get on it and then finally stops slipping and goes in gear. If so its time for a rebuild.

[Donnie]

YOU SAID:Overall vacuum checks out good. But, that's premature since I've not had a chance to run through the whole vacuum system....just did a test at the distributor. I have a dual vacuum distributor. NEED MORE TESTING

Your vacuum line to the trans must connect directly to the manifold & not share any lines to anything else. Check ALL vac lines first----check your vac at the mod, you will need an accurate reading before progressing ..Pull the hose off the mod. WHAT IS THE VACUUM AT IDLE? Make sure that a vac cap is not off somewhere.. Do all the testing that Bobby Ford suggested, this is easy & a must do before we can call a fault...BTW, how is the reverse apply? do you have to wait on it a second or 2, or does it thump right in?
Third & reverse share the same clutch pack. As Michael said, you could have a 3rd clutch failure? You may also have a sticking gov..something you said led me there, like starting off the line in 2nd, that could be mod or GOV...You really need to make sure your vac is ALL OK...so as we don't mislead you. When you get it into 3rd going say 55MPH & kick it down into 2nd, does it go?? How does the shift feel when you let off a bit & it goes back to 3rd?
Does it go right in or not? Make sure that your vac system is OK-----then we can go on & check the Gov. or clutches...Diagnosis is difficult on here, but with the correct data, we can help you. If you do not understand anything that I say or ask you to do,, just ask for a better description....Donnie
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[ANGELO1]

I GOT A TRANS REBUILT CUS IT WOULDN'T SHIFT. LATER I TALKED TO A FRIEND AND HE TOLD ME THAT IT WASN'T THE TRANS, JUST A DIRTY FILTER. HE THEN INFORMED ME THAT THE FILTER IS DESIGNED TO FILTER AT THE MICRON LEVEL AND A DIRTY FILTER WILL KEEP IT FROM SHIFTING PROPERLY.

[cdeal28078]

The screen on our transmissions do not filter on the mircon level or anywhere near it. I think the holes in the screen are about 3/32" or so.
Are you SURE the shift linkage is set up right? How about a simple test?
Un-hook the shift rod from the arm on the tranny. Place the tranny arm in 3rd gear after blocking the tires and doing all of the safety crap you need to do to be safe. Take it for an easy ride and see if it changes gears twice.
Clint

[Donnie]

I GOT A TRANS REBUILT CUS IT WOULDN'T SHIFT. LATER I TALKED TO A FRIEND AND HE TOLD ME THAT IT WASN'T THE TRANS, JUST A DIRTY FILTER. HE THEN INFORMED ME THAT THE FILTER IS DESIGNED TO FILTER AT THE MICRON LEVEL AND A DIRTY FILTER WILL KEEP IT FROM SHIFTING PROPERLY.

Your friend is just trying to make you feel bad..As Deal said Ford only uses a screen, they can be washed out and reused.
A micron is 39 millionth of an inch........
I filter my soybean oel to 5 micron to run in my diesels......Donnie

[RWVNRAL]

Thanks for your time and effort here, friends. I'm having a hard time getting back to the project because of some family health issues. However, I think I'm going to pull the engine and tranny. The engine leaks terribly and is in need of new pan gaskets and seals. I figure I might as well pull the tranny out at the same time and give it a look see. I'll keep you up to date.

[Donnie]

Sorry to hear about your health issues, Hope all goes OK....When you get back on the truck there is one thing to remember:
A transmission is easier to diagnose while it is in the vehicle using faults & complaints & a pressure gauge than it is to have a bench full of parts & a head full of wonder.........Donnie

BTW, there are a lot of us on here to help you when you are ready..........good luck

[RWVNRAL]

Thanks Donnie! Finally got back around to this project. Engine and tranny are out. Tranny has been fully rebuilt. Now, having some issues with the Engine because it actually isn't the 302 I though it was. Turns out that the engine is a 351 Windsor that came from some unknown vehicle Ford built in 1978. I have posted for help resolving this. I would like to know exactly WHAT vehicle it came from so that I can source the proper replacement parts. If you have any tips or advice, I'm all ears.

BTW, I want to do away with all the EGR stuff. I want to do away with a dual-vac'd dsitributor too. I just want simple ported vaccuum to the Dizzy and tranny. Any ideas?

William