transmission issue??
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Junior User
Joined: Aug 2010
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transmission issue??
I have a 97 7.3 ltr F-350. It has approx 180,000 miles on it. In the 35 mph range the is a hissing or sound like a vacuum problem that occurs. I haven't noticed this at higher speeds. Is there a vacuum or some kind of shift assist for this gear range? The transmission was gone thru by a transmission shop about 1500 miles back. thanks
Lead Driver
Joined: Mar 2006
Posts: 5,111
Likes: 1,549
From: western SD
I'd be more inclined to say the hissing you hear is from a bad hose or connection to the climate controls. They run off the vacuum pump. The manual trannys have No vacuum connections, and I don't think the autos do either, as they are shifted electronically.
Lead Driver
Joined: Oct 2003
Posts: 8,476
Likes: 37
From: Madison, WI
Keep in mind that there is no engine vacuum. What you're probably hearing is the exhaust back pressure valve closing. Do you notice a loss in power when this happens? Do you happen to notice that the noise subsides when you mash the go-pedal to the floor? Does it stop happening after the engine is warmed up?
Postmaster
Joined: Mar 2004
Posts: 3,897
Likes: 9
There is a valve on the turbo that closes to help warm up in cold conditions. You should be able to hear the hiss while parked as well. The purpose if it is to create back pressure to make the motor work a little harder. Even at idle you should be able to hear it a bit.
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