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Modulator Valve - Missing something?

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Old 06-19-2017, 01:38 PM
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Modulator Valve - Missing something?

I put a C4 from a 73 in my 66 F100 (6-300). The transmission did not have a modulator valve so I ordered one based on the transmission ID stamp. It's the push-in with a green stripe. The tranny won't shift. I have good vacuum. Here's what I'm wondering: the modulator valve pin seems very loose when I put it into the hole in the tranny, almost like its free floating. Is it supposed to insert into a spring or something that might be missing in there?
 
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Old 06-19-2017, 02:16 PM
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Throttle valve

If the modulator valve was not installed there is a chance that the throttle valve may have fallen out and isn't in there anymore. No valve no shift. That's my guess.
 
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Old 06-19-2017, 02:22 PM
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Old 06-19-2017, 02:28 PM
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Thanks Duster. That's a great diagram. Looking at it I'm thinking if the throttle valve was missing, wouldn't the pin just go on in? It does stop up against something, which I guess has to be the valve. I wonder if the throttle valve could be stuck? It's supposed to slide back and forth, right?
 
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Old 06-19-2017, 03:34 PM
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Originally Posted by Old Coyote View Post
I put a C4 from a 73 in my 66 F100 (6-300).

The transmission did not have a modulator valve (diaphragm), so I ordered one based on the transmission ID stamp.

It's the push-in with a green stripe: D5AZ-7A377-B (Motorcraft TM-34) .. Single Area Diaphragm = 1975/79 200/250 I-6/C4 Passenger Cars; 1976/79 F100/250 & Econoline 300 I-6/C4).

The tranny won't shift. I have good vacuum. Here's what I'm wondering: the modulator valve pin seems very loose when I put it into the hole in the tranny, almost like its free floating.

Is it supposed to insert into a spring or something that might be missing in there?
Missing modulator valve, the modulator valve rod was also missing. Inserts into the valve, then the valve is installed in the tranny.

Some people are unaware of the rod, so when they remove the valve, the rod falls out.

Install a new modulator valve without the rod, the tranny won't shift as a result.

Originally, there were 5 different rod lengths, so if people bought only one and didn't like the way the trans shifted, had to go back and buy another, and maybe another and etc.

Ford solved this problem in 1973:

D3AZ-7A380-B .. C4 Modulator Valve Rod Kit-comes with 5 different length rods / Obsolete

GREEN SALES CO. in Cincinnati OH has 12 = 800-543-4959.
 
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Old 06-19-2017, 03:52 PM
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I appreciate you passing that along, ND, but I have the pin. I was told it is the one that goes with the setup when I ordered the modulator. As I said in the previous post I thought something might be missing inside the tranny where the pin inserts because I can't get it to shift. Now I'm wondering if the throttle valve is stuck.
 
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Old 06-19-2017, 04:19 PM
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Originally Posted by Old Coyote View Post
I appreciate you passing that along, ND, but I have the pin. I was told it is the one that goes with the setup when I ordered the modulator.
There cannot be one rod, because originally there were 5 different rod lengths.

But, the real problem is, if the tranny is from a 1973, you installed the wrong single area diaphragm (modulator) with the green stripe (part number/applications in post #5).

D3OZ-7A377-A .. C4 Dual Area Diaphragm - red stripe (Motorcraft TM-34) / Obsolete

1973/74 E100/300 & F100 240/300/302; 1975 E100 300; 1975/76 F100 300/302.

Misc: 1973/75 I-6 & V8 Passenger Cars; 1976 Pinto/Bobcat 2.3L & Torino/Montego 351W
 
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Old 06-19-2017, 06:57 PM
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Well I went and checked best I could lying under there and the stamp on the round cover on the passenger side of the tranny (I think it's called a servo cover?) starts with C8, which I guess means 1968. The only other number I can see is on the casing on the drivers side. It starts with D4 (1974). There is no tag on the servo cover. So, who knows. I'm thinking my best bet is 1974, and I I understand ND right that means I should try the dual outlet modulator.
 
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Old 06-19-2017, 07:07 PM
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Originally Posted by Old Coyote View Post
Well I went and checked best I could lying under there and the stamp on the round cover on the passenger side of the tranny (I think it's called a servo cover?) starts with C8, which means 1968.

The only other number I can see is on the casing on the drivers side. It starts with D4 (1974). There is no tag on the servo cover.

So, who knows. I'm thinking my best bet is 1974, and I I understand ND right that means I should try the dual outlet modulator.
The tranny ID tag is located under one of the bolts that retains the servo cover to the case. But if the number is on the servo cover itself, that's a different story.

No part numbers were marked on parts after 1956, just casting or ID engineering numbers (when applicable).

So, what you're seeing is the ID engineering number and FoMoCo is infamous for replacing/updating 10's of 1000's of part numbers EVERY YEAR!

So, while the ID number prefix may begin with C8, that doesn't mean that the part number prefix will begin with C8.
 
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Old 06-19-2017, 07:20 PM
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Yes I understand, in the absence of that tag the numbers are not much help. I think I'll try the dual modulator. For what it costs it's worth a try. Thanks ND.
 
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Old 06-20-2017, 04:08 AM
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C4

Originally Posted by Old Coyote View Post
I put a C4 from a 73 in my 66 F100 (6-300). The transmission did not have a modulator valve so I ordered one based on the transmission ID stamp. It's the push-in with a green stripe. The tranny won't shift. I have good vacuum. Here's what I'm wondering: the modulator valve pin seems very loose when I put it into the hole in the tranny, almost like its free floating. Is it supposed to insert into a spring or something that might be missing in there?
It's hard to trouble shoot long distance, so a couple of questions.
When you say it doesn't shift I assume you mean it will move in first but won't up-shift?
You did witness this transmission actually working when it was in the donor vehicle, right?
The pan was pulled and checked for loose part numbers and burned clutches? And a new filter installed.
If yes to those. Take a pair of needle nose pliers and pull the throttle valve out, the picture is a C6 but they are pretty much the same. Inspect it, make sure it moves easy.
Make sure the kick down linkage is correct for your truck and adjusted properly.
I'm going to stop right here for now because if those two things don't get it going your problem is deeper in the transmission. Good Luck keep us posted.
 
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Old 06-20-2017, 08:14 AM
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That's right, it does move in first but won't shift.
I did not witness it working.
Before I installed it I drained it, changed the filter and fluid.
As for the kickdown linkage, looking at it now I recall that it's set up so with the throttle wide open the linkage is fully engaged and there is a small space between the adjustment screw and the lever on the linkage. I forget the amount of space but I recall looking it up at the time. Does that set-up sound right? If so, I will check the movement of the throttle valve as you suggest. Thanks
 
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Old 06-20-2017, 09:36 AM
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Throttle linkage sounds like it should work. Might need tweaking after you get it shifting. Check that throttle valve. If that's ok then it's going to take some disassembly to find the problem. Or at least putting some gauges on it to check the line pressure.
 
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Old 07-04-2017, 08:58 AM
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After checking that the throttle valve was moving freely I tracked down and installed the dual port red stripe diaphragm and am happy to report she's now shifting. Just want to close the loop and say thanks to Number Dummy and Crop Duster.
 
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