Vacuum whistle
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Joined: Sep 2008
Posts: 59
Likes: 12
From: London Ontario, Canada
Vacuum whistle
My 1981 Vette works great, but once it's warmed and in gear( automatic 350 turbo) I get a vacuum whistle , but only in gear. It shifts and drives fine. Any ideas on where to look , I can hear it but I can't seem to find it, it's just a little annoying.
thanks in advance
thanks in advance
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
First thing to do is purchase a mity vac hand pump tool.
Engine off, disconnect the main Vac line off the back of carb or Intake port.
Take your tool and apply vacuum to the hose. You can apply a lot of vacuum without making any noise.
Listen for any leaks. Note the tools gauge. Dropping rapidly? Or slow decline?
Next.
You have either four bolts or four nuts holding down the carb. Snug those down in a crisscross pattern. The base gasket under the carb is a highly likely source of vacuum leaks. They get fried, crumble from all the gas & heat exposure.
Next-next.
Some carb models can & will have vac leaks at the primary throttle bushings. Those can become quite loud on the road but may not make a sound in the garage.
Good Luck
Engine off, disconnect the main Vac line off the back of carb or Intake port.
Take your tool and apply vacuum to the hose. You can apply a lot of vacuum without making any noise.
Listen for any leaks. Note the tools gauge. Dropping rapidly? Or slow decline?
Next.
You have either four bolts or four nuts holding down the carb. Snug those down in a crisscross pattern. The base gasket under the carb is a highly likely source of vacuum leaks. They get fried, crumble from all the gas & heat exposure.
Next-next.
Some carb models can & will have vac leaks at the primary throttle bushings. Those can become quite loud on the road but may not make a sound in the garage.
Good Luck
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,150
Likes: 4,264
From: US-PNW
I believe there is just one vacuum line directly tied to the transmission operation: the vacuum modulator on the passenger side of the trans. It has a steel line that runs from the trans, up the firewall, to the back of the engine intake manifold. Should have short joining rubber lines at each end - maybe swap out those little rubber sections for new and ensure both ends of the metal tube are fully seated in their fittings (if applicable).
