Hi all,

I have a 1970 with the 350/350. It has a Holley 650 DP carb and an Edelbrock Torker intake and a non-stock cam (don't know what it is, previous owner did it). At ~2500 RPM, the engine makes a loud high-pitch "chirping" or squealing noise.

A while back, some had suggested it could be the alternator belt slipping. When I started looking at that I noticed the alternator belt was actually rubbing on the power steering pump. I thought that must be it...that at certain rpms, the rubbing belt resonates or something. In other threads, with many of your help, I have resolved this. I have replaced the alternator and power steering belts. There is no more rubbing and the belts are brand new. I know the tensioning of a belt is not "precise" but in my opinion, I think it's tight enough? I didn't use any tools to pull/pry on the alternator or the power steering pump...I just pulled with my hands and then tightened the holding nuts.

After replacing the belts, the sound is still there. If anything, now it happens slightly sooner? Before it would happen at 3000 and now it seems to start closer to 2500 or 2700. And, if I continue up the rpms, the noise gets worse and changes pitch a little?

Does anyone have any suggestions? I know I have a few small exhaust leaks (one or two where the headers mate to the engine, and one or two where the headers connect to the pipe that runs to the back of the car)...is it possible that the exhaust leak could make this sort of noise?

I agree it kinda sounds like a belt issue...but I'm just surprised that I replaced both and it didn't help. Do I just need to make them even tighter? Or is it possible I have the wrong belts (meaning they are not the correct width and/or pitch)? I used Gates 7520 for the alternator and Gates 7355 for the power steering.

I tried to take a short video with my phone...on the video, you can hear it a little from inside the car, and can hear it better from outside the car. Note that in person, you can hear it plenty good from inside the car as well.

 

I would recommend getting some spray-on belt-dressing and carefully apply it to suspected belt. Do only 1 belt at a time so you can isolate the location. If it is the belt slipping, then that should help you locate which one. I only buy brand-name belts after a guy at NAPA told me that it made a difference when I could not get rid of a squeal (but it seems that you did). If you identify the belt, then you may try to tighten it a little bit more and see what happens.

 

I have a bar of Irish Spring soap I use for this. Works just as good as anything. A guy even older than me showed me. It works great too.

 

those belt numbers do not match what Gates has for a 1970 350

http://navigates.gates.com/Parts.asp...Passenger+Cars

 

MPLS,

Is the noise present without the belts on?
Just thinking bearing failure somewhere.

Steve

 

I had the same issue on my car and solved it. But spent a lot of needless money on parts.

I took it to advanced auto parts and the guy said it sounded like metal on metal. He said it sounded like the fan clutch was going out. So I spent a lot of money on a fan clutch and blade because the previous owner put a generic fan/clutch. At least I got that part back to original.

So, thinking I fixed it, I started up the car and it was still there! It seemed to go on around the 3000 - 3500 rpm.

Wasn't fun when I would drive down the road with the squealing. At least everyone could hear me coming.

So, I was thinking that I might not have tightened the belt enough. I also tried adjust it myself without any tools. So, I got a crowbar and loosened the nut and pulled back. Had a lot better leverage. I tightened the bolt and started the engine. Worked!! no more sound.

I haven't had an issue since I did that.

So, after spending a lot of money on an original fan and clutch all I need to do was to tighten the belt with a crowbar.

 

sounds like a power steering pump is going bad could be the source of your belt noise. Ck the bearing for slop
Dealing with factory belts and that stuff drove me nuts not to mention embarrassing, went to serpentine never had a problem since.
The stock pulleys arent real light so soemthing that revs quick or high can make an issue where there wasnt one stock

If your belt sits too far down in the pulley it can make noise...too high up may throw it. Like the old Vbelt look but finding the right one can be a pain these days

 

I have a 1968 L-71 that I have owned for 26 plus years. When I bought the car it was mostly stock under the hood. The first time I tried to change the belts I ran into trouble.

The NAPA guys told me that my belt width was no longer available. I had a choice, too wide, too narrow or reproduction belts for show cars.

I ended up using Reproduction belts for my car and had to change them every 500 miles or so as they were not made for everyday use.

On my '68 you had to use a crow bar to get the "correct" power steering belt to stop slipping when ever you revved up the engine.

I have seen cars where they use short belts to go from crankshaft to water pump have slippage issues. My Brother had a Merkur XR4Ti which needed a "matched set" to stop the slippage of the belts. Even a fraction of an inch in length made a huge difference in slippage noise. They got a pretty penny for the pair of matched belts as they had to be precise.

It took me a while but after spending a lot of money on belts I ended up putting on a Marche Serpentine belt kit. The serpentine belt has not slipped or gotten too loose on my engine causing any noise.

It may not look stock on a older car but it works well. The only issue I ran into was putting a remote reservoir Power Steering pump on to use the Marche system.

Good Luck with your Corvette!

 

Good idea. I will take one belt off at a terrible and try it. At least that will tell me which belt/components to focus on. Seems like most of you think it is belt issues.

When I get it to that 2500-3000 range and it starts squealing, it will squeal the while time it is up to rpm. I have noticed that it starts squealing a little sooner (lower rpm) when cold, and as it warms up, it will start at a slightly higher rpm.

 

As for belts;

For what it's worth, I once installed a new narrower-than-standard alternator belt on a car, and it squealed like hell at every start. Woke up the damn neighborhood. Replaced it with a standard sized, and no more squeal.

Steve

 

Check your pulley grooves, a little sandpaper can help if they are slick

 

Have the same issue with my '75. Same rpm range too. Except mine only makes the squeal when you hit that range. It then goes away I replaced my belts with Goodyear gator back belts. Didn't help. Then I replaced the alternator. Didn't help. So I still haven't solved the issue

 

Could the noise be caused by a bad or failing fan clutch? It sounds like that would be another likely possibility.

I found this note on a web site:

"Sometimes the fan clutch in your car will start making squeaking and squealing noises."

There is more there if you care to read it all. It was located at:
http://www.doityourself.com/stry/tro...isy-fan-clutch

I hope that this might help you resolve the squealing you are dealing with.

Good Luck with your noises there Gentlemen....

 

Good info but it does not specify what causes the squeal sound to start only above 3K RPM.

I think my problem is the Fan clutch, though a bad pulley bearing or oil leak are possibilities.....Must test...

 

Best thing to do is take one belt off at a time and see if it goes away,it sounds to me like the alt bearing.If the noise does not stop after you have removed one belt at a time than take all the belts off the water pump and see it could be the water pump bearing.

 

Hi guys - thanks for the notes and suggestions. I'm finally back in town and working on it. I pulled the power steering belt off...noise is still there. I then pulled the alternator belt, and the noise goes away. So...how do I test to see if it's something with the alternator itself, or the fan clutch, or the water pump (short of buying all these components and replacing one by one)? All of these things are run by the same belt. I think I have eliminated any potential mis-match of belt and pulley groove, since I'm using the same belt width and such on the power steering and that seems fine.

ok - more news. I had always noticed that it would start squealing at a lower rpm when the engine was cold...and as it warmed up, the start of the squeal would be a slightly higher rpm. And to be clear, if the squeal starts at 2500 rpm, it will continue squealing at rpms higher than 2500...but then when it drops below 2500, the squeal stops, until you get up to 2500 again.

So - I put everything back together to drive it to the local auto parts store as they said they would look at it. I noticed that the start of the squeal is a higher rpm now. So, this morning it probably started around 2200, but now it doesn't start until ~3000. I would say that the alternator belt is probably a little tighter now than it was this morning. But, the people at the store thought the belt was now certainly tight enough. More people came over to look at it while it was there and one guy didn't think it was in the pulley system at all. Ugggg. Is there any possibility that it's something in the carb? But, it didn't make the sound when the alternator belt was removed...so still tells me it's either the alternator, water pump, fan clutch....

Sorry - one more crazy idea...could it be something with the thermostat? I don't notice any temperature problems...but what if when the water pump turns faster, it pushes more water through the thermostat and something is stuck and making it whistle? I know...crazy right?

 

Is your fan belt the correct width for the pully you are using? Is it tight enough? Higher performance engines like my L-82 used deeper pully grooves and wider belts ~1/2". Once you have the belt verified that it is correct and tensioned properly, there's a good chance your sound disappears. Mine did!

 

Well - good point. I thought...no, assumed it was because I matched what was on the car when I put these new belts on. But, I'm finding a few things that my former (key word) Vette mechanic messed up and I almost wonder if this noise started when he changed the belts and maybe that's the issue. How do I confirm what the belt width and such is supposed to be? I have the 350hp 350 motor in my car. No A/C.

 

I finally figured it out! The power steering belt was wrong. It was only going from the crank to the power steering pump. So, I had the alternator belt going around the crank, water pump and alternator...and the p/s belt just going from the crank to the P/S pump.

In trying to figure this out, I read in some forums that if you don't have enough belts on the car, that can cause belts to slip and make noise. I then found a diagram showing the proper belt routing, and it showed the P/S belt to go around the crank, water pump and P/S pump! So, when I got the correct belt, and ran it around all three pulleys...and got it tight...problem fixed!

So - thanks again to my previous Corvette mechanic that screwed that up for me....