High Pitch Whistle - help please

[Rob H.]

Hey there -

I had body work and a re-paint done on my '69 L36. Ever since then it has developed a high pitch whistle noise. It comes and goes, but when it comes it is relentless and drives me nuts. It seems to get worse as the rpms get higher and persists through the gears (M22) and will sometimes remain at idle. The pitch of the noise will change as the rps get higher. At idle it will sometimes go away when I tap the gas pedal.

I took it into my mechanic, but it of course didn't do it when he drove it. I read through the archives and there was mention of a clutch plate and a possible vacuum leak. FYI - I replaced the clutch recently at the beginning of the year before the repaint.

Has anyone experienced this problem before? I would GREATLY appreciate any help or advice. It makes for an unhappy driving experience, but more importantly is obviously a symptom that something is not functioning correctly.

Thanks in advance and happy holidays to everyone!

Best,
Rob

[Tom H.]

Re: High Pitch Whistle - help please

Can you at least pinpoint the area which the noise is coming from ?? Is it a mechanical "whine" or a true "whistle" . Under the hood, or is it from inside the cabin.

I'm trying to figure out what might cause this sudden condition after paintwork ?? Masking tape or paper in ductwork or in a door jamb ?? Just grabbing at straws here without some more info.

Stupid question, but it's not ignition noise from the radio, is it ??

[Gene M.]

Re: High Pitch Whistle - help please

If the only change you did was a new clutch them I suggest check the obvious. Take a look at the inspection cover. It may be contacting the flange of the crank.

[Rob H.]

Re: High Pitch Whistle - help please

The noise is difficult to pinpoint due to the fact that I can't seem to keep it going long enough at idle to get the hood open and inspect it. It is similar to a dentist instrument - a high pitched whine. The radio is not even hooked-up so that rules that out.

I will check out the inspection cover of the clutch. That seems to make the most sense...

Thanks for your input guys!!!

Rob

[Joe R.]

Re: High Pitch Whistle - help please

Check these things.

1. Take your alternator to a rebuild shop and get them to replace the bearings.

2. Make sure that your clutch throw out bearing is releasing completely from the face of the pressure plate. Proper adjustment in repair manual. If you don't have a repair manual it can be ordered from the NCRS in Cincy!

Don't forget it may be a good looking girl trying to flag you down in that newly painted Corvette. Yeah, fat chance!

JR

[Tom H.]

Re: High Pitch Whistle - help please

Possibly an alternator ?? Still grabbing at straws. I wish I could hear it ! Keep us posted.

[Rob H.]

Re: High Pitch Whistle - help please

...just had my alternator replaced, and it still makes the noise - so that is out.

I will check the clutch bearings - that makes most sense to me.

As for the girl theory - I am keeping hope alive!

Thanks again -

Rob

[Peter J.]

Re: High Pitch Whistle - help please

Rob,
I have 66 L-79 that had whistle so loud you could hear over the side pipes.
I looked everywhere for the source. I used a propane torch (unlit) looking for a vacuum leak around the carb and intake manifold but found nothing. It would quit and not whistle for a couple of days and the start up every time I turned the key. Greg Woodruff said it sounded like the base of the carb and the body of the carb had a warped surface and needed to be planed.
Mr. Woodruff was right - planed both surfaces and no whistle

[Rob H.]

Re: High Pitch Whistle - help please

Peter -

That sounds exactly like what I am dealing with - like yours, it will go away for a couple days then come back! I will definitely look into that.

Thank you and Mr. Woodruff!

Rob

[Steven B.]

Re: High Pitch Whistle - help please

Peter -

That sounds exactly like what I am dealing with - like yours, it will go away for a couple days then come back! I will definitely look into that.

Thank you and Mr. Woodruff!

Rob

'Know a guy with a 1965 L-79 that had the same problem and carb-intake sealing was his problem!

Steve

[Rob H.]

Re: High Pitch Whistle - help please

Steven - If that is indeed the solution I will have an early Christmas present!

Thanks everyone for your feedback.

Rob

[Steven B.]

Re: High Pitch Whistle - help please

Rob, hopefully you find it! Should be between the manigfold and air cleaner with any luck. Let us know.

Steve

[Rob H.]

Re: High Pitch Whistle - help please

OK, so I planed down the surface of the plate that rests upon the carb which was indeed warped, but I still heard the noise - although it diminished in tone and frequency. I am going to check again to make sure it is completely flush.

One problem I realized was that there was no carb air horn gasket. I have ordered one and think that this might have also contributed to the problem. Once I get that on and fine tune it I will check back.

Thanks again for all of the feedback and suggestions.

Happy New Year -

Rob

[Peter J.]

Re: High Pitch Whistle - help please

Rob,
Bob Khuns (spelling) the carb rebuilder once told me that I could put two gaskets instead of one between the body and base plate to take up the space between the two surfaces. Just something to try if the gasket isn't the answer.

[Kevin W.]

Re: High Pitch Whistle - help please

Not trying to speak on something that I am not an expert on. I have had several camaros with the rallye sport option which was all vacum oprated switches for headlight doors. I have experienced what sounds like the same noise and I all-ways found a vacum leak. You mentioned you started hearing noise after car was painted.40 year old hoses just simply moved have a tendancy to crack or the worst on split right at the nipple end. very hard to find when you pull the hose and the split is back together. Secondly you state the car will not stay running long enough to get the hood openand look. stumbling idle, bouncing timing marks when vacum advance is disconected sound coming and going with engine speed all very defining of a vacum leak. set idle screw up to approx. 2000rpms take a can of wd40 with the red tip on it. spray on head/intake gasket one side at a timesee if you get a drop or a spike in rpms. spray tip the other side. do this cold start and them when engine is at operating temp. continue to the carb base plate and manifold vacum fittings. If you get response there try doubling base gasket with a little bit of silicon between. If it quits sound or flucuates nidle this is a cheap TEST ONLY FOR CARB BASE GASKET LEAKS. When you have eliminated the manifold cold/hot and carb base cold and hot. start checking vacum lines from source to end when you disconect hose at either end make sure the engine stumbles. if it doesnt this could be your source check hose by putting thumb over one end and sucking on the other. You will then see if hose good or bad. When you reattach these hoses put a drop of dish soap on both ends. Push on with a turning motion, remember these hoses are old and brittle. If by chance you still do not find your source take a spray bottle and start spraying ends to see if any bubbles. IF YOU DONT UE THE RED END ON THE WD40 CAN it will suck it up into air filter down the carb with a false reading. Lastly did you make sure you had free play on the clutch fork and throw out bearing. The face on the bearing and the ends of the pressure plate make a hideous sqeeling when no freeplay. I would be willing to bet there is a vacum leak in the headlight system when you had it painted. Try turning on lights and see if pitch changes at a steady speed and rpm so that vacum is constant.Slam on the gas no vacum. at steady speed at low end of rpm (2000) vacum at it"s strongest. It is a simple process of elimination part by part money will not fix it. Just a little one on one with your car. 1 hr Max.Hope this might help.Remember when checking throw out bearing just pull rod out of fork pocket and and let itthe fork go forward to the front of car. then start car. I believe that your source is vacum specific because of the idling statement. Air horn gasket to air cleaner has no affect on anything other than dirty air into your motor. The carb does the gas to air ratio.