C4 2nd to 3rd Flare shift

[Bronco Sully]

I searched a couple of threads and have an idea as to some of the problem childs for this type of problem. Just wanted to post a pic or two too see if anything on the face seems amiss.

The hoses seem to be hooked up fine. On a fairly high level scan, none seemed to be cracked. I have not checked the vacuum pressure yet but should get to that this afternoon. As you can see, there is a bit of a leak but it is very slow. I cleaned this area off the other day and this is what accumulated after a couple days of driving. No pooling on the floor.

fluid level is perfect and the color seems normal.

The rig is a 1973 pretty much stocker. I have owned it for a couple of weeks. Other than the shifting, it seems very much mechanically sound.

If I replaced the VM, can I expect a bunch of T-mission fluid to come out? Fairly easy to do? If I did this...any other "while your at it" things to do?

I know about as much about transmissions as I do brain surgery...which is nothing!

Thanks in advance!

 

[Blue Bastard]

yes fluid will be coming out. expect it to accumulate in your armpit as you change it. also there will be a pin that may or may not come out with it that need to be swaped out put in the new one.

 

[Quick & Dirty]

Adjust the bands as well. Excess travel in the intermediate apply/release piston uses fluid volume and reduces pressure on the high clutch, allowing it to slip until the release travel is complete.

The intermediate band adjuster is forward of the shift linkage. Loosen the lock nut and tighten the screw to 10 ft-lb. Back off exactly 1-3/4 turns. Hold the screw from turning and tighten the locknut.

The low/reverse band adjuster is near the vacuum modulator. Loosen the locknut, torque screw to 10 ft-lb and back off exactly 3 turns. Hold the screw from turning and tighten the locknut.

This is what the adjusters look like:

 

[Viperwolf1]

Not much to add. I doubt the modulator is causing the problem. It is leaking though and you can probably get by with an o-ring replacement. If the band adjustment doesn't help you might have a worn direct/reverse clutch.

 

[Bronco Sully]

Thanks gents. Have not checked the vacum pressure yet but located (i believe) under 40years of north texas red clay/mud and grease, the low reverse band just above the VM. The intermediate was a bit more recognizable and a bit less caked with history. Once I get them clean, I will give the adjustments a go. Prob not till next weekend. Fingers crossed.

And if that does not work...I will be back to pick your brains again.

 

[Rustytruck]

When you get a new modulator get a green stripe one. Pull off your vacuum lines and see if there is tranny fluid inside of them indicating a ruptured diaphram inside the modulator.

 

[Lmfp]

I had the same problem. Did a mild rebuild with new clutches and a shift kit (screwed up the shift kit so im buying a new valve body) any ways. The flair up is gone but it wont shift out of first if i dont let off the gas, guess my 351w is a lil more than my c4 wants. But like i said we'll see after the new valve body.

 

[BwoncoHowie]

I searched a couple of threads and have an idea as to some of the problem childs for this type of problem. Just wanted to post a pic or two too see if anything on the face seems amiss.

The hoses seem to be hooked up fine. On a fairly high level scan, none seemed to be cracked. I have not checked the vacuum pressure yet but should get to that this afternoon. As you can see, there is a bit of a leak but it is very slow. I cleaned this area off the other day and this is what accumulated after a couple days of driving. No pooling on the floor.

fluid level is perfect and the color seems normal.

The rig is a 1973 pretty much stocker. I have owned it for a couple of weeks. Other than the shifting, it seems very much mechanically sound.

If I replaced the VM, can I expect a bunch of T-mission fluid to come out? Fairly easy to do? If I did this...any other "while your at it" things to do?

I know about as much about transmissions as I do brain surgery...which is nothing!

Thanks in advance!

What you described was solved on my '73 by by putting a BB in the small vacuum line to plug it, while leaving the rear larger hose normally connected and unobstructed. You have a dual diaphram VM that was used on the first EGR equipped Fords in 1973-74. Later vehicles found it no longer necessary to use the Dual AKA Red-stripe modulator. If you were to update yours, let's say with a single-port Green-stripe unit, you would need also the single-port specific retainer, because the dual modulator uses a different retainer that if used with the single diaphram modulator, you wouldn't be able to connect the hose.

What is your Vacuum reading @idle In-Hg.

The drip could be the O-ring, or the diaphram. The diaphram could be checked for leaks with a hand vacuum pump or disconnecting the hoses to check for ATF inside the vacuum lines. BH

 

[jckkys]

The single diaphragm is the one you want. The modulator should, if original, be the push in type that has an O ring. Many were screw in. These establish part throttle shift points and are adjustable. Can't remember what size tool to use or what direction turns raise or lower the shift points but tranny shops do. Don't put a shift kit in a Bronco C4!

 

[ugly74]

. Don't put a shift kit in a Bronco C4!

Why not? Mine has had one forever, and shifts awesome. Nice and crisp, no delays.

 

[Blue Bastard]

it is a very small standard srew driver needed. Adjust a little ata time as it doent take much to change the setting. 3 full turns is the max if remeber correct.

 

[Justafordguy]

I had the same problem. Did a mild rebuild with new clutches and a shift kit (screwed up the shift kit so im buying a new valve body) any ways. The flair up is gone but it wont shift out of first if i dont let off the gas, guess my 351w is a lil more than my c4 wants. But like i said we'll see after the new valve body.

A 351w is not to much for a C4 to handle if it's built correctly. I bet it's your valve body/shift kit.

 

[Bronco Sully]

Quick update. I did a vacuum test this evening. The lower hose to the VM pulled 19 in-hg at idle (I am roughly 50 ft above sea level). I did not have a good male/female adapter but got a decent connection. Easily felt when I covered the hose opening. The smaller hose nearer the top of the VM leaked ATF when pulled, probably like a shot glass worth. There is no detectable vacuum on that line at idle speeds. I am unsure what it is for. Nothing came out of the VM when the hose was pulled at idle.
t
I am guessing the VM is compromised. Should I go ahead and replace it (I understand they are not that expensive)? If I convert to the single/green stripe Howie, is it fairly easy to make the modifications you suggest?

If that fails, then I thought I would try the band adjustments.

Thoughts?

 

[Bronco Sully]

Update: I replaced the modulator with another red stripe VM. It did not fix the problem with the flare shift between 2/3 gear. Just went for the red one just because it was easy to do without finding a new bracket for the green one. I will try to play with the screw adjustment I have a feeling that is not going to do the trick.

Changing the VM was fairly easy except for access to the bolt that holds down the VM bracket. Once I figured out how to loosen it ( due to its awkward location) it took 10 minutes. Lost a little ATF, but not much. I did not need to add any afterwards. I had the replacement handy to plug in after grabbing the push rod and plugging it into the new one.

Next weekend I will try the band adjustments to see if that helps. Fingers and toes crossed.

 

[BwoncoHowie]

Hi Sully,
Did you try plugging the small line on the new modulator yet? or even disconnect it at the top and plug the line going to the engine.
Then take it for another road test and come back and tell us what it does.

You have a strong vacuum signal that would probably work well with a yellow band modulator.

Quick update. I did a vacuum test this evening. The lower hose to the VM pulled 19 in-hg at idle (I am roughly 50 ft above sea level). I did not have a good male/female adapter but got a decent connection. Easily felt when I covered the hose opening. The smaller hose nearer the top of the VM leaked ATF when pulled, probably like a shot glass worth. There is no detectable vacuum on that line at idle speeds. I am unsure what it is for. Nothing came out of the VM when the hose was pulled at idle.
t
I am guessing the VM is compromised. Should I go ahead and replace it (I understand they are not that expensive)? If I convert to the single/green stripe Howie, is it fairly easy to make the modifications you suggest?

If that fails, then I thought I would try the band adjustments.

Thoughts?

 

[Lmfp]

A 351w is not to much for a C4 to handle if it's built correctly. I bet it's your valve body/shift kit.

Thats what im betting (hoping for) i have 2 weeks of school left then ill be jumping back on it to get it finished before next semester.

 

[Bronco Sully]

Hi Sully,
Did you try plugging the small line on the new modulator yet? or even disconnect it at the top and plug the line going to the engine.
Then take it for another road test and come back and tell us what it does.

You have a strong vacuum signal that would probably work well with a yellow band modulator.

Well I'll be as Son of a B... Howie! If I just learned how to read I would not had to have gone thru this mini-ordeal or plunked down some cash for a new VM. How i just blew by "What you described was solved on my '73 by by putting a BB in the small vacuum line to plug it, while leaving the rear larger hose normally connected and unobstructed." in your first post is beyond me.

Pulled the second line, plugged it (with a used fuse from my MG), took it for a spin. Went from 2nd to 3rd so smooth I thought for a second it never changed gears. Drove it around a bit in the neighborhood and on the freeway and it continued to shift very smooth. Well if anything I know a shed load more about the C4 automatic transmission than I did before which I guess is worth the price of the VM and the ATF/Grime that fell on my face.

Thanks to all for tips and suggestions. This is why I am a contributor.

 

[ugly74]

and there goes another happy customer!

 

[BwoncoHowie]

Well I'll be as Son of a B... Howie! If I just learned how to read I would not had to have gone thru this mini-ordeal or plunked down some cash for a new VM. How i just blew by "What you described was solved on my '73 by by putting a BB in the small vacuum line to plug it, while leaving the rear larger hose normally connected and unobstructed." in your first post is beyond me.

Pulled the second line, plugged it (with a used fuse from my MG), took it for a spin. Went from 2nd to 3rd so smooth I thought for a second it never changed gears. Drove it around a bit in the neighborhood and on the freeway and it continued to shift very smooth. Well if anything I know a shed load more about the C4 automatic transmission than I did before which I guess is worth the price of the VM and the ATF/Grime that fell on my face.

Thanks to all for tips and suggestions. This is why I am a contributor.

Dont worry about replacing the modulator, What U described with words and pics indicated that your trans needed a new one anyway.

If you didnt want grime to fall on your face, you shouldnt have bought a Bronco %) ;D Hee hee!