Screech at 70mph.

-

Pawned

N.R.A. Lifetime Member - And damn proud of it
Joined
Jun 29, 2013
Messages
1,605
Reaction score
186
Location
Valle del Sol, AZ
This has been going on for a while now, but I am ready to deal with it now.
When I drive the 71 Duster 318+4 down the highway everything runs just fine.
If i am accelerating, even slightly, at 70 mph I hear a screeching sound. Not super loud but still I hear it.
If I let up on the gas, even the slightest, it goes away. If I add a little gas it comes back. I think once it starts cruising and not under torque the screech stops.

I thought it was the belts, and sounds like it could be, but I have replaced them since this started. I have also used some belt conditioner.
But it makes sense as the torque needs to be involved. But only happens at 70.
and does not happen as the car shifts up to speed and the engine hits the rpm level a couple times already.
I think it may sound like a wheel bearing, but why only at that speed and under torque. A wheel bearing should be sounding at all speeds. also the wheel bearings apparently are only a couple thousand miles old. My mechanic said he replaced them when he did the brakes. I do not always trust what he tells me.

Something else. I wish I could find the video of this. Before I replaced the belts. One of the belts would flip over while the car was running. I would put it in normally and after 30-45 seconds the belt would flip over tooth side up. Replacing the belts remedied that
 
Speedometer cable? Disconnect it and try it out. Just a thought.
 
It very well could be the carburetor.
(Air noises from a gasket edge or something along that line)

The thing to do is narrow it down via symptoms.
Tighter or looser belts will change the noise.
A bar of bath soap touched to the running belts will silence a belt squeal.
Note throttle openings and loads that it does it, and if only in one gear at one speed and no other.
I realize that is what you said, but are you absolutely sure as you can be that this is the case?

Only at one speed and one load sounds like a carb noise to me.

(Unless it's the speedometer) :D
 
Last edited:
It still sounds like it's related to the belts to me. Maybe your belt pulleys aren't lined up right, or you don't have the right pulley somewhere, or your water pump bearings are wearing out and are causing the belt to squeak or the alternator bearings are wearing out and causing the belt to squeal. Try replacing the alternator and triy lining everything up well and see how that works.
 
As I read this, I do know that the belts are not perfectly in line. Actually not aligned at all.
Never thought of the carb. This may have started when I put on the Edelbrock 1406 4 bbl
 
Try lining up the alternator and anything else that's out of line with the crankshaft pulley. If you shim some things or change some pulleys to make it line up, I bet you your squeal will go away.
 
Try lining up the alternator and anything else that's out of line with the crankshaft pulley. If you shim some things or change some pulleys to make it line up, I bet you your squeal will go away.

A squeal only at 70?
Don't think so.
Maybe a fan pulley under load, but it would do it at about the same rpm in any gear.
Same if it was the alternator doing it.
 
idk why but im thinking throw out or pilot bearings...alternator and water pump bearings,..p/s to if equipped,.....if you dont trust your mechanic you need to find a new one you do trust and pay him to check them wheel bearings again,could be your issue to....only other thing i could think of at 70 mph only might could be the air pressure pushing down on car body causing a tire rub issue but thats pretty far fetched....
 
idk why but im thinking throw out or pilot bearings...alternator and water pump bearings,..p/s to if equipped,.....if you dont trust your mechanic you need to find a new one you do trust and pay him to check them wheel bearings again,could be your issue to....only other thing i could think of at 70 mph only might could be the air pressure pushing down on car body causing a tire rub issue but thats pretty far fetched....

I only use this mechanic for things I won't do. I had them rebuild the engine, because it would have taken me a few months and it took him 1 week. I had him do the brakes because I am not comfortable working on them..... for saftey reasons.... Other than that, I have done everything else.

4 speed or automatic?
automatic
 
He said the belts are not lined at all. It's the cheapest most obvious fix to line up the pullies that the fan belt rides on. I'm just not positive as why it only does it under load. Maybe it has a fan with a clutch in it that's going bad?
Pawned, let us know what you find that fixes it, or doesn't fix it.
 
Could even just be the wind over the body whistling, and that would explain the only at 70 part.
 
I didn't know he could go 70!
Screech.jpg
 
He said the belts are not lined at all. It's the cheapest most obvious fix to line up the pullies that the fan belt rides on. I'm just not positive as why it only does it under load. Maybe it has a fan with a clutch in it that's going bad?
Pawned, let us know what you find that fixes it, or doesn't fix it.

OK I just now finished moving the alternator 1/2" forward on the engine. I personally do not think this did it, but IT HAD TO BE DONE anyways.

Could even just be the wind over the body whistling, and that would explain the only at 70 part.
No, but I did hear a rattle when the car go on the freeway, that turned out to be the wiring to the front marker light. I had not secured the wiring after painting.

I am still very suspicious of the carburetor. But then again, lining up the belts may have done it.
I will take it out in a few hours. Need to rest up for a while. this COPD is kicking my butt the last couple days
 
The carb is whistling.

Or the ole tried and true "when doubt, gas it, it may not fix the problem but it will end the suspense".
 
anxiously awaiting the results of your test ride
I turned onto the freeway and as I was coming up to speed I heard the screech for a split second, I glanced at the tach and it was at 3Krpm. Then the noise seems to be just as before. I kept my window open and I think I heard it differently than thru closed windows.
It was more like a whistle/screech as opposed to only a screech.
This leads me to believe that it is either a anomaly in the grill or some part of the front end of the car. Or it may be in the carb as suggested before.
But I am pretty certain it is not a wheel bearing, or the belts. Either of which can leave me stranded. Where as the other possibilities are a nuisance as oppose to a break down
 
As the car is finished, I took her out for her inaugural spin. Forget about the 2200 miles I have put on it so far, it was not finished.
I had her on the freeway for 70 some miles. Between 65 and 80 mph. At one time going 80mph, I kicked it down to the floor and she took off, not lacking any power. I am pleased.
About 5 minutes before I got home I noticed something. I had not heard the screech/whistle the entire trip.
I have done a bunch of little things. tied up wiring, played with this and that. The only major anything was moving the alternator forward 1/2". But I did hear the screech after I did that.
Interesting, looking at the fan belts before and after I moved things, what use to be 1/2" too far back is now about 1/4" forward of true. I am not touching it.
Before it was noticeable, now you have to look for it
 
-
Back
Top