Whistling???

[jonnyc]

Over the years I've had an intermittent whistle from under the hood. It's usually very quick and has only ever occurred right after I shut the engine off. I've looked for any air leaks around the brake booster and found none. My vacuum is currently very steady at 20. Just this afternoon I had to go up a couple of relatively steep grades and I got the whistling under load in 4th. I eased on the gas and it disappeared. Everything seems to be running fine and there aren't any brake issues I can feel.
Thoughts?

[jonnyc]

Anything???

[mearstrae]

Whistling is usually cause by a vacuum leak, but can also be caused by an exhaust leak as well. And if the leak is at the carb itself it may not show up on the vauum gage.

'95 R.R. Classic LWB
'76 Series III Hybrid 109
'70 Rover 3500S

[jonnyc]

Recently rebuilt the carb and went nuts in the engine compartment to find and eradicate any vac leaks, so I'll start with a potential exhaust leak in the manifold/front pipe area.
Thanks.

[mearstrae]

Just a thought, does it do it with the air filter off? Could be that simple, or possibly the flame-trap from the valve cover to the intake [if you have one]. I've seen [heard...] alot of crazy things cause an engine whistle.

'95 R.R. Classic LWB
'76 Series III Hybrid 109
'70 Rover 3500S

[jonnyc]

Only heard it with the air filter (K&N) on.

[westcoastkevin]

Leaves or debris stuck on the filter element can make noises like that. They often fall off again when you shut it off. Just a thought.

[Tim Smith]

I'm betting it's the booster check valve or possibly the booster begining to leak.

My lightweight has done this for years and I've gotten it to the point that under full load (ussually on the highway or up hills) I can make my truck wistle the tune I have going in my head by adjusting the throttle ever so slightly within range of the whistle. If it's the check valve, eventually it will whistle at you after you shut it down too.

If there is a leak somewhere else in the system, you can easily find it with a spray bottle of water squirted liberally around the intake and vacume system while it's running. If the engine speeds up a momentarily while doing that, you may have found a leak in that area. If no change then it's likely the booster or check valve.

[jonnyc]

Up until 2 days ago, I had only heard it after shutting the engine off. Looks like the valve is a simple Pop out/Pop in affair.

[Tim Smith]

Up until 2 days ago, I had only heard it after shutting the engine off. Looks like the valve is a simple Pop out/Pop in affair.

Yes it is easy but sometimes the valve can be a right stuck piece. If you have trouble then spray down the rubber grommet holding the valve to the booster with silicone. Cheap fix but I'm keeping mine as is until I get atleast one song note for note perfect.

[cetesse]

Hi all,
What does the booster check valve do? Any pictures of what it looks like?

[Tim Smith]

Hi all,
What does the booster check valve do? Any pictures of what it looks like?

In this picture it's the thing with the little red dust cover on the end on the upper left. Yours probably won't have a red cover on it though as that is either for an extra vacuum port or just for shipping.

Basically it holds vacuum in the booster canister after the engine is shut down. This is done in case the engine stalls while moving. The theory is that it will give you a couple of uses of the brake peddle before all boost is lost.

Any car with vacuum boost brakes will have something similar, so you can see what I mean by shutting down the engine of your favorite car and fully pressing the brake pedal a couple of times. Eventually it will get really hard to move the pedal until you start the engine back up again. The booster on series brake systems aren't all that powerful so the effect isn't that obvious, but you can still notice it if you try.