How much does a A4LD vacuum modulator move the pin?

[Devo55]

My 1993 Explorer doesn't shift on it's own anymore. I have to let the rpms go to 2000 then ease off the gas so it drops to 1500 then it shifts. My question for today is...how much movement is happening with the pin inside the vacuum modulator. Does it push it into the transmission or pull it away. I did a vacuum test with my modulator that I suspected being bad and the pin sank deeper into the modulator. I've been trying to find an explanation or some animation on how a modulator works but so far no luck.

 

[92exp4x4]

I couldn't find any info on the distance the pin moves, but i have attached pics of the pages of the service manual for checking the modulator. Hopefully this helps. There are plenty of other things that can affect line pressure which is probably out of spec on your machine. Has your trans been serviced recently?

I just had the valve out of one of mine. It had no TC lockup or 3-4 shift. I cleaned dirt out of the valve and freed a sticking valve. Now it has lockup but no 3-4. I'll be tearing it down in the spring.

 

[CDW6212R]

FYI, with the A4LD you can install a longer modulator pin(1/8" longer), and it will improve the shifts slightly. That's an old trick and it helped both my 91 and 93 Explorers to shift more firm. Some aftermarket modulators are adjustable, with an adjustment screw in the outer center hole of it. Those might do the same thing as a 1/8" longer pin.

 

[BrooklynBay]

The pin sticks out of the modulator but gradually goes in with more vacuum being applied to it. Full vacuum will pull it in deeper into the modulator. No vacuum with the engine off will cause it to go back into the direction of the transmission.

 

[Devo55]

The pin sticks out of the modulator but gradually goes in with more vacuum being applied to it. Full vacuum will pull it in deeper into the modulator. No vacuum with the engine off will cause it to go back into the direction of the transmission.

Thanks. That helps uncovering the mystery of the modulator.

 

[Devo55]

FYI, with the A4LD you can install a longer modulator pin(1/8" longer), and it will improve the shifts slightly. That's an old trick and it helped both my 91 and 93 Explorers to shift more firm. Some aftermarket modulators are adjustable, with an adjustment screw in the outer center hole of it. Those might do the same thing as a 1/8" longer pin.

Great info! I didn't know that.

 

[Devo55]

I couldn't find any info on the distance the pin moves, but i have attached pics of the pages of the service manual for checking the modulator. Hopefully this helps. There are plenty of other things that can affect line pressure which is probably out of spec on your machine. Has your trans been serviced recently?

I just had the valve out of one of mine. It had no TC lockup or 3-4 shift. I cleaned dirt out of the valve and freed a sticking valve. Now it has lockup but no 3-4. I'll be tearing it down in the spring.

View attachment 424814 View attachment 424816 View attachment 424817

Awesome! Which service manual is this? Haynes? As far as service goes I did replace the 2 o rings on the low rise reverse servo (because of slow, weak reverse) and the rear output shaft seal. Thanks it. Thanks.

 

[BrooklynBay]

It's in the ATSG rebuild manual. I'm adding some PDFs for you to look at.

 

[92exp4x4]

Awesome! Which service manual is this? Haynes? As far as service goes I did replace the 2 o rings on the low rise reverse servo (because of slow, weak reverse) and the rear output shaft seal. Thanks it. Thanks.

That's actually from the 94 Ford service manual. Its what the dealer would have had when these were new.

 

[92exp4x4]

It's in the ATSG rebuild manual. I'm adding some PDFs for you to look at.

This will probably be handy for me as well. Ill be rebuilding one of these in the spring. I've not been into one yet. Thanks!

 

[Devo55]

It's in the ATSG rebuild manual. I'm adding some PDFs for you to look at.

Holy ****! This manual is great! Thanks for the upload.