I have a air horn kind of sound coming from what appears to be my dash.It sounds just like a hand held air horn.It comes when the motor is under load and building rpms.It lasts in a certain rpm band and goes away above it or below it.But is constant at about 1700 rpm.If I rev the motor in nuteral it does not happen. I cannot pin point the location and all that is air on the dash is the tag axel switch and park brake.I know the air compresor govoner is just outside the firewall on the passenger side,it could be from that,but I dont know.It is a 1980 Mack DM.Any Ideas would be great as I dont know where to look.Its loud as well.Thanks

 

I am gonna guess that you dont have a boost pressure gauge in the dash on that old DM? Its not likely unless someone added one. Does it have a filter minder in the dash? Highly unlikely as well?

All you can do is take the dash panels out and run it down the road and see if you can pinpoint where it is coming from. From what you described it sounds boost related. Is this noise coming from behind the center panel or the speedometer/tachometer panel?

 

Its loud and hard to pin point but my best guess is the center of the dash and maybe even passenger side.Thats why I was suspect of the govonor.

 

After you suspecting the turbo,I checked all the hose connections on the turbo and I found a broken clamp.I have not test drove it yet but that may be the problem.Thanks

 

I bet you found it! Keep us posted.