Tranny vaccum

[ozarktrails]

My son has a 92 Ranger Automatic and it has started shifting poorly or not at times. There is a vaccum hose that runs from the back of the motor down the passenger side of the tranny and I hear hissing around there. So, I take the flexible hose from the side of the tranny and the hissing stops but starts again when I hold my finger over the rubber hose. I replace the hose and it still stopes when taken off and starts when plugged. I can't believe the metal tubing has a leak...any ideas? Also, what is it plugging into on the side of the tranny? It has a plastic wheel that looks like a small gear. My son also overfilled the tranny, will this contribute?

 

[MAKG]

The transmission has a vacuum modulator that tells it when the engine is heavily loaded and needs a downshift. High load = low vacuum.

It's possible for a metal tube to leak, but I'd look first at its joints.

It's VERY common for the vacuum modulator to blow, causing a vacuum leak, late shifting, and so on. It will also burn ATF in the engine. But I think you've ruled that out (I'm having a bit of trouble deciphering it).

Perhaps you can isolate the hiss further with a piece of (clean!) vacuum tube. Stick one end in your ear and use the other to probe for the sound.