73 f100 auto tranny question.

[Victor Estrella]

Hi folks. I've only had the truck two weeks and I spent most of that time just getting it ready to use as a daily driver. (new heater core, welding floor boards, etc) Yesterday I took it on a long drive and it performed excellently- better then expected. But there was one thing that concerned me. I noticed that 2nd gear was drawn out before shifting. I hope it's a characteristic of that transmission and not a looming problem. PLease advise.

 

[m78]

Sounds like the vacuum modulator valve, or the lack of vacuum to it.
They're inexpensive and simple to replace.

 

[Victor Estrella]

Sounds like the vacuum modulator valve, or the lack of vacuum to it.
They're inexpensive and simple to replace.

Thanks for the heads up. could you tell me how I can change it? Is there a diagram and or instructions here on the site? I'd love to do it myself if it's not too hard. After the heater core I feel I can do anything on this truck.

 

[Fellro]

A vacuum modulator is pretty simple to change, take the bolt out of the retainer and slip it out, oil the o-ring, slide the new one in, put the bolt and clamp back on.

 

[LEB Ben]

Yeah...they're not the toughest task in the world to accomplish...it'll be on the passenger side. I believe there are also 3 different styles you can get, there's a black band, purple band and red band...all with different shift characteristics (not that noticeable IMO)...or you could also opt for an adjustable modulator and tune to preference.

 

[m78]

Look for the vacuum hose attached to the passenger side near the rear of the transmission.

 

[Victor Estrella]

Yeah...they're not the toughest task in the world to accomplish...it'll be on the passenger side. I believe there are also 3 different styles you can get, there's a black band, purple band and red band...all with different shift characteristics (not that noticeable IMO)...or you could also opt for an adjustable modulator and tune to preference.

No hot rod here. Just which ever shifts calmly and smoothly. OR which ever one the store has when I get there.

 

[Victor Estrella]

OK I found the modular vacuum valve. Very accessible. I checked the vacuum hose and it was full of liquid. So valve appears shot. The hose was old and weak also,so I'll change that too.

There is a type of round ledge around the valve that has another hose coming from it. It runs parallel to the vacuum hose from the modulator they both run up and around the tranny. What is that hose and do I need to do anything with that?

The modulator is old and there is no color band on it OR if there was, it has worn out over time. My local auto parts has all three colors in stock. I'm curious, what are the characteristics of the different bands supposed to be? I want a smooth car like drive (if possible-hah!).
Hey, I want to thank you folks again for the help so far. It sure makes it easier to wrench on stuff!

 

[Victor Estrella]

I believe it's called a dual diaphragm modulator. What now? Perhaps the tranny is not original.

 

[DNFXDLI]

A dual diaphragm is listed in my 79 book, so I would guess they might have used on in 73 as well.

 

[Victor Estrella]

Oh boy. Then perhaps I'll pull the modulator and take it in and try to match it up. I think different ford vehicles' transmissions had them in 73. I could also try to find out what tran I have on my hands.

 

[Fellro]

I think those were generally for use when changing altitude a lot, like mountain driving. Might be such it can be switched to a single line regular modulator, would have to see where the second line goes.

 

[Victor Estrella]

I found the valve I need on Mac's auto website. Dual diaphragm shift moderator valve for 73-76. F100. Let's hope it fits!