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2-3 shift issue after vacuum modulator replacement

SamD

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Feb 25, 2014
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214
I replaced the yellow vacuum modulator with green adjustable modulator to try and solve a hard shift, but now I'm experiencing what feels like a slipping shift between 2-3. Is this something that can be resolved with adjustment or do I have a new problem?

At idle my pressure gauge moves slightly between 18-19 lbs.

Sam




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SamD

SamD

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Tiko433

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It should be adjustable. Small screw in the hole where vac line connects. They are preset from the factory. From what I remember you can should not turn it past 3 turns either way. So you could try 1 1/2 turn in and see if it helps. Put some tape on it and note what turns. If you still have the yellow one you could turn it out 1 1/2 and see how it does. When you changed it did you make sure the pin was behind it? Some change the length of the pin to adjust shift. That's all you are doing by adjusting the modulator is making the pin shorter or longer.
 
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SamD

SamD

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It should be adjustable. Small screw in the hole where vac line connects. They are preset from the factory. From what I remember you can should not turn it past 3 turns either way. So you could try 1 1/2 turn in and see if it helps. Put some tape on it and note what turns. If you still have the yellow one you could turn it out 1 1/2 and see how it does. When you changed it did you make sure the pin was behind it? Some change the length of the pin to adjust shift. That's all you are doing by adjusting the modulator is making the pin shorter or longer.



Could the new vacuum modulator be causing the 2-3 flare shift? I haven't changed anything else. I've adjusted it in 1 1/2 turns so far with no change.

Sam




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Tiko433

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Did you verify you still had the pin behind the modulator? A few ways to go here . Another 1 1/2 turns in and see if it helps . You could go back to the yellow stripe and see if your original problem came back, the hard shift. Then adjust it out to see if you can soften it.
 
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SamD

SamD

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Did you verify you still had the pin behind the modulator? A few ways to go here . Another 1 1/2 turns in and see if it helps . You could go back to the yellow stripe and see if your original problem came back, the hard shift. Then adjust it out to see if you can soften it.



Yes, the pin came out with the old modulator, and I put it back in with the new. The old modulator isn't adjustable.

I will go another 1 1/2 turns in and if that doesn't work, I will put the old one back in.


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broncokak

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Jun 13, 2006
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3,968
I had that problem years ago with my 76. I couldn't adjust the screw enough to correct the shit and wound up making a new pin (can't remember if I made it longer or shorter though) out of a nail. Once I got it dialed in it worked fine.
 
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SamD

SamD

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I've adjusted the new VM a total of 3 turns in and it hasn't stopped the flair shift from 2-3. The flair shift wasn't happening until I replaced the VM, but after testing again last night, the flair happens even when I manually shift. Does this still sound like the VM is the cause? What are the recommended next steps?

Back to old non adjustable VM?

Band adjustment?

Sam


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DJs74

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Apr 1, 2014
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I've adjusted the new VM a total of 3 turns in and it hasn't stopped the flair shift from 2-3. The flair shift wasn't happening until I replaced the VM, but after testing again last night, the flair happens even when I manually shift. Does this still sound like the VM is the cause? What are the recommended next steps?

Back to old non adjustable VM?

Band adjustment?

Sam


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Since the shifting issue started with the new modulator and you are not able to make any difference adjusting it, I would suspect the modulator is bad or possibly the vacuum source - broken hose, unhooked by mistake, ??
Typically the vacuum line is primarily steel with short rubber ends to make the bends and connect. I would check the line thoroughly for cracks, breaks, etc.
In my experience with modulator valves, 1/4 turns at a time make noticeable differences so if your up to 3 full turns and nothing is happening, something is wrong IMO
You could try the old one again as a test to see if anything changes - if yes, I'd say the new one is faulty. If still no changes with the old one, something else is going on.
You can adjust the bands pretty easily but I probably would not until you've ruled out the modulator as being faulty - too many changes at once can makes things harder to diagnose and confusing for yourself.
If you decide to make band adjustments, there is a procedure on how far you back the screw out on Low-R (passenger side rear) & 2-3 (driver side front) depending on what's inside. Stock or factory configurations are 'X' and C4s with shift kits installed or other performance work is 'Y"


Shift kit configurations I've installed are normally as follows:

Low-Reverse:
► tighten screw down to approx. 120 in lbs. then back off 3 turns, tighten nut while holding screw in position

2 - 3:
► tighten screw to approx. 120 in. in lbs. then back off 1 1/2 turns, tighten nut while holding screw in position

stock C4 probably something different.

if you haven't changed the bands though, I wouldn't think they need to be adjusted just due to replacing the modulator. I think something is up with the modulator itself or the vacuum source.


DJs74
 
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SamD

SamD

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Since the shifting issue started with the new modulator and you are not able to make any difference adjusting it, I would suspect the modulator is bad or possibly the vacuum source - broken hose, unhooked by mistake, ??
Typically the vacuum line is primarily steel with short rubber ends to make the bends and connect. I would check the line thoroughly for cracks, breaks, etc.
In my experience with modulator valves, 1/4 turns at a time make noticeable differences so if your up to 3 full turns and nothing is happening, something is wrong IMO
You could try the old one again as a test to see if anything changes - if yes, I'd say the new one is faulty. If still no changes with the old one, something else is going on.
You can adjust the bands pretty easily but I probably would not until you've ruled out the modulator as being faulty - too many changes at once can makes things harder to diagnose and confusing for yourself.
If you decide to make band adjustments, there is a procedure on how far you back the screw out on Low-R (passenger side rear) & 2-3 (driver side front) depending on what's inside. Stock or factory configurations are 'X' and C4s with shift kits installed or other performance work is 'Y"


Shift kit configurations I've installed are normally as follows:

Low-Reverse:
► tighten screw down to approx. 120 in lbs. then back off 3 turns, tighten nut while holding screw in position

2 - 3:
► tighten screw to approx. 120 in. in lbs. then back off 1 1/2 turns, tighten nut while holding screw in position

stock C4 probably something different.

if you haven't changed the bands though, I wouldn't think they need to be adjusted just due to replacing the modulator. I think something is up with the modulator itself or the vacuum source.


DJs74



Does the Modulator have any influence when you shift manually?




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DJs74

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Does the Modulator have any influence when you shift manually?




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The modulator valve works off vacuum and controls shifts based on what vacuum is being applied through the steel line to the valve. There is a pin inside the valve and a spring/valve-plug a little further in, the vacuum or lack of vacuum works diaphragm inside the modulator which activates the pin and spring, which works with the valve body to create the shift points.
So by shifting manually, you are sort of bypassing the automatic feature and controlling the shift points yourself but if the modulator is faulty and not working correctly with the valve body, even if you shift manually... it'll still feel like a totally messed up shift.
So for example: if you put the gear selector in "D" and let it do its thing automatically and the shifts are delayed or just in general screwed up due to the modulator and/or vacuum signal not getting to the valve body correctly... if you put it in "1" and shift yourself, it'll go to 2nd immediately because 2nd is 2nd no matter what else is going on but when its time to go to "3", the problems will show up again if the modulator and vacuum signal are messed up - no matter if you shift to 3rd yourself or let it do it on its own.
By choosing to shift manually when it still is an automatic by design, you can't really override the automatic functions and all the components that make it an automatic are still trying to function - the manual shifting does let you control the shifting from 1 to 2 and theoretically lets you control the shift from 2 to 3 but once you reach 3rd, if things are not correct that work the automatic shifting... it'll probably show up and act goofy.

From what you are experiencing and the problem showing up as soon as you installed the new modulator, I think the modulator itself or the spring or the pin or the vacuum source is where the issue might be.

When you changed the modulator, do you remember the pin coming out and/or going back in? Any chance the spring and little plug looking valve got out also?

The pin coming out with the modulator is pretty common but you almost have to pull the spring and plug out - they are a little ways up inside the port.


DJs74
 
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SamD

SamD

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The modulator valve works off vacuum and controls shifts based on what vacuum is being applied through the steel line to the valve. There is a pin inside the valve and a spring/valve-plug a little further in, the vacuum or lack of vacuum works diaphragm inside the modulator which activates the pin and spring, which works with the valve body to create the shift points.

So by shifting manually, you are sort of bypassing the automatic feature and controlling the shift points yourself but if the modulator is faulty and not working correctly with the valve body, even if you shift manually... it'll still feel like a totally messed up shift.

So for example: if you put the gear selector in "D" and let it do its thing automatically and the shifts are delayed or just in general screwed up due to the modulator and/or vacuum signal not getting to the valve body correctly... if you put it in "1" and shift yourself, it'll go to 2nd immediately because 2nd is 2nd no matter what else is going on but when its time to go to "3", the problems will show up again if the modulator and vacuum signal are messed up - no matter if you shift to 3rd yourself or let it do it on its own.

By choosing to shift manually when it still is an automatic by design, you can't really override the automatic functions and all the components that make it an automatic are still trying to function - the manual shifting does let you control the shifting from 1 to 2 and theoretically lets you control the shift from 2 to 3 but once you reach 3rd, if things are not correct that work the automatic shifting... it'll probably show up and act goofy.



From what you are experiencing and the problem showing up as soon as you installed the new modulator, I think the modulator itself or the spring or the pin or the vacuum source is where the issue might be.



When you changed the modulator, do you remember the pin coming out and/or going back in? Any chance the spring and little plug looking valve got out also?



The pin coming out with the modulator is pretty common but you almost have to pull the spring and plug out - they are a little ways up inside the port.





DJs74



When I changed the modulator, the pin came out, and I pulled the throttle valve out with a magnet. Both were placed back into the transmission and then the modulator after them.

Sam


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DJs74

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Try another modulator or the one you took out and see if anything changes. If nothing else was changed or adjusted, nothing should've changed or need adjustment

DJs74
 
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SamD

SamD

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Try another modulator or the one you took out and see if anything changes. If nothing else was changed or adjusted, nothing should've changed or need adjustment

DJs74



You mention a spring coming out in a above post. I don't recall seeing a spring. The only things I've seen is the Modulator, pin, and the throttle valve. What spring are you referencing?

Sam


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DJs74

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Messages
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You mention a spring coming out in a above post. I don't recall seeing a spring. The only things I've seen is the Modulator, pin, and the throttle valve. What spring are you referencing?

Sam


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I misspoke, I don't think there is a spring on the pin and valve side. Sorry. I think I was thinking about the spring feel when you push the modulator in which is due to the spring inside the modulator.
Just the stepped valve and round pin after the modulator.

Did you try switching anything or get any different results?


DJs74
 
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SamD

SamD

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I misspoke, I don't think there is a spring on the pin and valve side. Sorry. I think I was thinking about the spring feel when you push the modulator in which is due to the spring inside the modulator.

Just the stepped valve and round pin after the modulator.



Did you try switching anything or get any different results?





DJs74



I just picked up a new green stripe VM today and more transmission fluid. If i have time before I fly out tomorrow I will try the new VM and if that doesn't improve things I will give up and put the old one back in.

Thanks for your help!

Sam


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DJs74

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I just picked up a new green stripe VM today and more transmission fluid. If i have time before I fly out tomorrow I will try the new VM and if that doesn't improve things I will give up and put the old one back in.

Thanks for your help!

Sam


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Sounds like a plan, good luck and safe travels


DJs74
 
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SamD

SamD

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Feb 25, 2014
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214
Any luck solving your problem?



I installed a second new Green Stripe modulator and tried a couple of adjustments without much (if any) change. I reinstalled the original modulator and the 2-3 flair shift is gone but my "clunk" is back.

At the very last second during about half my stops, I get a "clunk" that I think is the transmission down shifting back to first gear. At first I thought it was axle wrap, but it even happens on easy stops.

Sam


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