77 308 - High-speed "thrum" noise over 90MPH?

i doubt it is a/c hoses. the same noise in the same circumstances was cured on my '79 gts and '78 400 by making sure my wheel bolts/lugs were often retightened/torqued to spec. with the magnesium wheels the lugs often loosen slightly. you have to do it more often than you would think.

brett

 

I experience that A/C hose problem on my car. In my case it appears as a vibration/buzzing noise in the same spot you describe. I get it at lower speeds/RPM than in your case - mine makes the sound as I drive up through the lower gears and it happens in the 2500 -4000 rpm area.

I have proven the A/C hose is the culprit by stuffing foam insulation between it and the body. This area is only seen by taking the passenger side rear wheel off, removing the fender liner, and removing the fiberglass scoop that connects the air intake duct on the side body to the rubber hose on the air cleaner. Once this is done you can peer into the spot where the hose runs through and possibly see where it is rubbing.

Its possible that by loosening the A/C hose at the compressor it might be repositioned in such a way that it doesn't rub or doesn't rub as much. The downside is that you might need to re-charge the A/C after doing this - which has discouraged me from trying this out.

I would try stuffing some insulation in there just to see if the noise goes away. In my case this fixed it for a few miles until the insulation moved. But it gave me the piece of mind that the problem wasn't major -another reason why I haven't focused on it so much.

Good luck and I hope this is your problem.

 

Greg
I read regular 3/4" or 1" pipe insulation with the slit down the side you can get at Lowes will stop that vibrating hose. The insulation cost around a buck and is much cheaper than moving the hose by loosing it from the compressor.

Good luck.

 

Keep it below 90---Bam--no more problems