||08-14-2005 02:23 PM
More evidence the driveline ringing is "thermal"
I have suspected ths beofre, but last evening I got more evidence that the driveline ringing noise I, and some others, have, is related to a thermal expansion effect.
On my way through Alabama last evening, I encountered a very unuually "abrupt" rain storm. By "abrupt", I mean that I could literally see where the road up ahead suddenly turned wet, and sure enough, when I hit that point, the rain was instantly voluminous - no ramp up at all, just sudden downpour!
The same effect occurred on the way OUT of the storm - I could literally see bone dry pavement ahead, and sure enough, when I hit that dry pavement, the rain stopped RIGHT NOW.
What hs this got to do with the driveshaft ringing noise?
Well, at least in my SSR, that noise starts being audible when the vehicle hots about 35 mph and has NOT yet been on the highway at 60 or 70 mph speeds. It goes away after the vehicle has been at those highway speeds for 12 to 15 miles. I have theorized that the sound disappears, or at least becomes inaudible, when the driveline gets HOT.
When I drive through rain, I can't hear the noise even if it is there, because of the noises created by water on the road and rain hitting the top of the vehicle. And, when the rain stops, it normally does so SLOWLY and there is los of residual water on the roads.
The situation last evening was a rare case of the "exception to the rule". Before I hit the rain, I had been traveling more than 150 miles non-stop, so the driveline was hot and there was no audible noise. And yes, the rain and roadspray were loud enough that I could not have heard the nosie if it was there when traveling through the rain.
But, when I hit that abrupt "exit", onto DRY pavement, guess what happened: The nosie was THERE, but only lasted for a few minutes if that, then disappeared again.
My theory is that when I hit the rain, the water splashed up from the road COOLED the driveline. Water is an excellent coolant - that's why we use it in radiators! - and at 60 to 65 mph, there is a LOT of water hitting that driveline when in heavy rain, as I was.
But, when I nsuddenly hit the dry patch, the rain noise and road spray noise disappeared abruptly, but the driveshaft was still cool as a result of the dousing it got in the rainstorm. Therefore, it made noise again until it once again heated up to normal highway temperature.
So, again we have some evidence that supports a thermal effect: the noise disappears as some part (astll unidentified) heats up, because a metal part is slightly BIGGER when hot than when it is cold. The expansion of the part changes the interaction of that part with SOMETHING else, and eliminates the noise.
The question is: what part?
It could be the driveshaft, as that certainly gets a lot of direct exposure to the water in a rainstorm, as a result of road spray under the chassis. However, the entire rear differential housing also gets doused, and the parts inside it would get INDIRECT cooling as a result.
So, we still don't know WHAT is causing the noise. But, each piece of knowledge gets us closer . . . :)