C6 modulator valve not modulating?
Thread Starter
|
Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
C6 modulator valve not modulating?
I have a built C6 behind a 351w. Raybestos Blues, E4OD forward drum, billet R servo, transgo shift kit, 3000 stall, black stripe modulator valve. It is shifting way too early for my liking… But here’s the thing, I keep working my way in in the screw, adjusting it clockwise a quarter turn at a time, but nothing changes… until suddenly, suddenly it gets to where it won’t shift at all. No middle ground. No modulating. I am running vacuum from a manifold vac port on the front of a Quick Fuel 600 cfm. I also tried from the rear port, but no difference. Do I have a bad modulator valve? I’ve never had this happen before on any of my built transmissions. Thanks for any suggestions
Cargo Master
Joined: Oct 2020
Posts: 2,676
Likes: 785
I had a similar problem with my truck after I changed the engine from the stock 460 to one that had more torque and manifold vacuum. Transmission shifted too early with a slight flare into 2nd gear after previously working perfectly. C6 with a Transgo kit. I could not get the modulator adjusted correctly. I took out the modulator and made a new pin that was about 1/8th inch longer to replace the stock one using a piece of welding rod. After that I was able to adjust the modulator to work just right.
Thread Starter
|
Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
Thread Starter
|
Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
I just changed it out with a green stripe modulator, using the same pin... it's the same, no adjustability, and even earlier shifts than the black stripe...
Trending Topics
Cargo Master
Joined: Oct 2020
Posts: 2,676
Likes: 785
Before I made a longer modulator rod for my truck I experimented with temporarily giving it a slight vacuum leak right down by the modulator using a T fitting in the hose just to see if it would reduce some of the manifold vacuum from the engine that the modulator could "see". Sure enough that fixed the problem with the shifts.
The manifold vacuum pulls on the diaphragm of the modulator and compresses a spring that's inside. The more it pulls back the farther the modulator valve moves and the more it lowers the line pressure in the transmission. All making the rod longer does is keep the modulator valve a little farther in with a given amount of manifold vacuum so that it drops the line pressure less when running at less than wide open. It shouldn't make any difference as it approaches wide open and the manifold vacuum drops to basically nothing.
The manifold vacuum pulls on the diaphragm of the modulator and compresses a spring that's inside. The more it pulls back the farther the modulator valve moves and the more it lowers the line pressure in the transmission. All making the rod longer does is keep the modulator valve a little farther in with a given amount of manifold vacuum so that it drops the line pressure less when running at less than wide open. It shouldn't make any difference as it approaches wide open and the manifold vacuum drops to basically nothing.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
Thread Starter
|
Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
so, should I try to create a vacuum leak? I could use an old manual boost controller from one of my old turbo cars I guess… though I still can’t imagine what’s wrong with this set up
Before I made a longer modulator rod for my truck I experimented with temporarily giving it a slight vacuum leak right down by the modulator using a T fitting in the hose just to see if it would reduce some of the manifold vacuum from the engine that the modulator could "see". Sure enough that fixed the problem with the shifts.
The manifold vacuum pulls on the diaphragm of the modulator and compresses a spring that's inside. The more it pulls back the farther the modulator valve moves and the more it lowers the line pressure in the transmission. All making the rod longer does is keep the modulator valve a little farther in with a given amount of manifold vacuum so that it drops the line pressure less when running at less than wide open. It shouldn't make any difference as it approaches wide open and the manifold vacuum drops to basically nothing.
The manifold vacuum pulls on the diaphragm of the modulator and compresses a spring that's inside. The more it pulls back the farther the modulator valve moves and the more it lowers the line pressure in the transmission. All making the rod longer does is keep the modulator valve a little farther in with a given amount of manifold vacuum so that it drops the line pressure less when running at less than wide open. It shouldn't make any difference as it approaches wide open and the manifold vacuum drops to basically nothing.
Cargo Master
Joined: Oct 2020
Posts: 2,676
Likes: 785
I just did the leak thing to test it. The new fresh engine made so much more torque down very low that it didn't need much throttle to drive the truck. This made the manifold vacuum high and made the transmission not have enough line pressure under those conditions. Giving it a leak made the modulator "think" that the vacuum from the engine was lower than it really was and doing that made it shift just right again. I did that just to know for sure that it wasn't anything wrong with the transmission.
After that I got rid of the leak, took out the modulator and the rod and made one that was a little bit longer. I don't think that I had to play around with the length very much to get it close enough that I could then adjust the modulator a little bit and get it just right. I would just make a new rod and start out about .100 or so longer.
I know there are different modulators for specific engine combinations but I don't know if all of the rods are the same length or not, maybe not. That transmission always shifted perfectly after that modification until I took it out about 20 years later and installed an E4OD.
After that I got rid of the leak, took out the modulator and the rod and made one that was a little bit longer. I don't think that I had to play around with the length very much to get it close enough that I could then adjust the modulator a little bit and get it just right. I would just make a new rod and start out about .100 or so longer.
I know there are different modulators for specific engine combinations but I don't know if all of the rods are the same length or not, maybe not. That transmission always shifted perfectly after that modification until I took it out about 20 years later and installed an E4OD.
Thread Starter
|
Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
makes sense… but here’s something I don’t understand. When I am adjusting, there was no change as I’m turning the screw in, until all of a sudden it won’t shift at all anymore. And this is turning 1/8 to 1/ quarter at a time only… I would have thought with the amount of adjustment in the screw that I could’ve got to a point where there was some change in the shift timing, but there wasn’t.
I cut an 8 penny nail just a little bit longer to try and see if it makes a difference.
I cut an 8 penny nail just a little bit longer to try and see if it makes a difference.
I just did the leak thing to test it. The new fresh engine made so much more torque down very low that it didn't need much throttle to drive the truck. This made the manifold vacuum high and made the transmission not have enough line pressure under those conditions. Giving it a leak made the modulator "think" that the vacuum from the engine was lower than it really was and doing that made it shift just right again. I did that just to know for sure that it wasn't anything wrong with the transmission.
After that I got rid of the leak, took out the modulator and the rod and made one that was a little bit longer. I don't think that I had to play around with the length very much to get it close enough that I could then adjust the modulator a little bit and get it just right. I would just make a new rod and start out about .100 or so longer.
I know there are different modulators for specific engine combinations but I don't know if all of the rods are the same length or not, maybe not. That transmission always shifted perfectly after that modification until I took it out about 20 years later and installed an E4OD.
After that I got rid of the leak, took out the modulator and the rod and made one that was a little bit longer. I don't think that I had to play around with the length very much to get it close enough that I could then adjust the modulator a little bit and get it just right. I would just make a new rod and start out about .100 or so longer.
I know there are different modulators for specific engine combinations but I don't know if all of the rods are the same length or not, maybe not. That transmission always shifted perfectly after that modification until I took it out about 20 years later and installed an E4OD.
Thread Starter
|
Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
I tried a pin that was a 16th of an inch longer that I made, it didn’t want to shift at all, and had a slight preload clamping the modulator in place.
i’m beginning to wonder if my low-Ish vacuum of 11-12 inches from the B cam might have something to do with it…? 😞
i’m beginning to wonder if my low-Ish vacuum of 11-12 inches from the B cam might have something to do with it…? 😞
Cargo Master
Joined: Oct 2020
Posts: 2,676
Likes: 785
It seems to me that if the manifold vacuum was generally low then it wouldn't have had the soft early shift problem. It is weird how making the rod just a little bit longer caused it to go the other way to the late and very hard or no shift condition. I don't know why it would be so sensitive. It might be worthwhile to give Transgo a call and ask them if there's something in the valve body, a spring or valve that could be hanging up making the modulator unable to control the line pressure smoothly.
Thread Starter
|
Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
Thread Starter
|
Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
It seems to me that if the manifold vacuum was generally low then it wouldn't have had the soft early shift problem. It is weird how making the rod just a little bit longer caused it to go the other way to the late and very hard or no shift condition. I don't know why it would be so sensitive. It might be worthwhile to give Transgo a call and ask them if there's something in the valve body, a spring or valve that could be hanging up making the modulator unable to control the line pressure smoothly.