Tranny vaccum

ozarktrails · 10-01-2007, 06:41 PM

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** · 10-01-2007, 07:09 PM

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.

10-01-2007, 06:41 PM	#1
ozarktrails New Member Join Date: Oct 2007 Year: 1992 Make: FORD Model: RANGER Posts: 4 Rep Power: 0 iTrader: (0)	Tranny vaccum 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?
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10-01-2007, 07:09 PM	#2
MAKG RBV Technical Advisor Join Date: Aug 2007 Location: California central coast Year: 1991 Make: Ford Model: Explorer Engine: 4.0L Class: 4x4 Posts: 4,643 Rep Power: 21 iTrader: (0)	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. __________________ 1990 VW Jetta GL, 1.8L 8V gasoline engine, manual transmission, painted in oxidized red paint and ponderosa pine sap, unknown mileage. 1991 Exploder, 4.0L, M5OD-R1 manual transmission, electronic BW1354 transfer case, 3.54 gears, 31 inch tires, icky two-tone blue paint with little clear coat, 230K miles. 1972 Chevy C-10, 250 I-6, SM465 (2WD) four-on-the-floor, 3.73 gears in a GM 12-bolt, puke green with a white cab. The "4 wheeled trash can," with x70K miles. x is probably 2.
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