Vibration resonance sound.

Hello, i have a resonance/vibration in the cabin on my 308,, in about 3000 rpm, it is not pleasant, it sounds like the exhaust touching the frame, i have checked everything an it is ok, now i'm starting to think that the hoses from the aircon is touching somewhere it should not, anyone recognise this?

 

It makes that kind of noise in my 328 at about 4000 rpm, and I've yet to figure out what it is. I look forward to replies to this thread . . .

 

it was the hoses, i have rereote the hoses and but a foam between chassis and hoses, but it is not 100% perfect,need to find out a good solution, the hoses is very stiff, old technology, steel braided hoses, you could probably change them to more flexible hoses, but gonna try to fix it with the original hoses.

 

Really common issue. A/C hoses going over the fuel tank bearing against the body work. The angle of the fittings at the compressor need to be readjusted. In a few cases I stuffed foam rubber between hoses and body work above fuel tank. Sometimes the correct angles prevent connection to the A/C service ports so they get adjusted wrong. I just change the angles after the A/C is charged.

328 and 308 both do it but at different RPM. Flat crank V8s have rpm ranges of vibration and because of the different stroke they are in slightly different RPM ranges.

Steel braided A/C hoses? Those are not original.

 

Very interesting - thanks for this detailed response! I will have a look at those hoses today and hopefully get this sorted out.

 

When I replaced my AC hoses there was some soft foam rubber around the AC hoses where they went above the gas tank and then into the forward area.



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i assumed it was steel braided, with that i don't mean steel on the outside, steel in rubber, high pressure, so it seams impossible they are plain rubber.

 

Many, in fact most high pressure hoses do not use steel. No need. Steel braid on the outside is not for high pressure. It is for abrasion resistance.

 

yes nowadays, but interesting that they used other material then steel in high pressure hoses in 1980, can you tell me what they used instead?, because im talking about hoses in the god old days, and in this case the compressor hoses on our old 308, not high tech nylon or kevlar hoses in 2023.
that's why i said that they were stiff and it should be possible to change them to modern hoses with nylon or kevlar core.

 

Modern nylon?

Its been in use reinforcing rubber since the 40's.

Stiffness is one of the hallmarks of nylon. The difference between truck tires and RV tires is truck tires use nylon cord. RV tires use polyester usually because nylon is too stiff and makes RVs ride bad.

We have been using it in tires for over 70 years because it is so strong.

 

Yes Sirs, I have the same Problem driving me nuts. I was going to add a 1/2 lb to the A/C anyway, so gotta take apart the Tubs.

 

i have trye some diffrent ideas, first don't add any foam or other isolation stuff between hoses and body panel, it will transfer some amount off sound/vibration, relocate hoses so you get about 10mm from body, on the tank you have a welded
flat iron on the backside/side of the tank, the hoses i believe should be between this 2 welded peaces on the tank, put some isolation foam inside and leth the hoses lay on the tank, the tank is heavy and filled with gasoline so it acts like a vibration damper, the body don't.

 

Yeah, I get what yer saying. Suddenly it has to wait while I fix the Sahara TJ. Oy Vay, always something.