I have a '66 Wildcat, under acceleration (even very light) it makes a very noticeable knocking sound, like the driveshaft is out of balance and knocking against the frame. Frequency is about twice per tire rotation. The noise stops if I put it in neutral. I jacked up the rear tires and ran the car in gear, no knocking. Even with a load from the breaks, no knocking sound with no weight on the rear wheels. Driveline looks okay, choices here seem to be driveline, rear differential, or rear axel...Am I missing any? Any suggestions on further troubleshooting steps before I start taking things apart? I'm a bit stumped on why I can't reproduce the problem with the wheels off the ground, what's getting pressure with the wheels on the ground that isn't with them in the air? Especially since coasting down a hill or in neutral makes the sound go away.
I am almost certain that shaft has a center support. Check to see if the rubber is broken on the support. Also check the rear tranny mount.
Is it possible it's the exhaust is hitting the frame somewhere? That would account for a noise under even slight load.
Yes, it is a two-piece shaft with a center support. The noise is coming from the rear end, near where it joins the rear axel. It's hard to pin down the location, of course, since the car has to be on the road and moving to hear it. The center support/joint looks ok, the shaft is pulled out a bit further than I would expect (about an inch), but it doesn't move in or out if I shove on it. Rubber looks ok, old and crusty, but intact. I'll take a closer look at the rear tranny mount. I'm looking for the wear marks where this would be hitting, but if it's a mechanical problem inside the rear differential I wouldn't be able to see it. Is this kind of knocking problem possible as an internal issue on that gearbox? I'll check exhaust tomorrow, that would be interesting if its the exhaust knocking - that would make sense with the doesn't-do-it-in-the-air problem, but does with weight on the wheels. Can I be so lucky?
Years ago I had a '68 Wildcat that had a knocking sound under the car. Turned out to be the center velocity joint on the driveshaft...............Mac
Yeah, I think it's got to be that middle driveline mount. I doesn't make sense that it would only do it when on the ground but not when on the lift, but it looks off to me. I'll pull it out and take a closer look. Here's a few photos of the driveshaft joints: http://gallery.me.com/noahpatton/100096/IMG_0094/web.jpg?ver=12817401120001 http://gallery.me.com/noahpatton/100096/IMG_0096/web.jpg?ver=12817401210001 http://gallery.me.com/noahpatton/100096/IMG_0101/web.jpg?ver=12817401330001 http://gallery.me.com/noahpatton/100096/IMG_0125/web.jpg?ver=12817402510001 http://gallery.me.com/noahpatton/100096/IMG_0126/web.jpg?ver=12817402580001 http://gallery.me.com/noahpatton/100096/IMG_0127/web.jpg?ver=12817402640001 http://gallery.me.com/noahpatton/100096/IMG_0128/web.jpg?ver=12817402700001 http://gallery.me.com/noahpatton/100096/IMG_0093/web.jpg?ver=12817401040001 http://gallery.me.com/noahpatton/100096/IMG_0092/web.jpg?ver=12817400990001 http://gallery.me.com/noahpatton/100096/IMG_0091/web.jpg?ver=12817400940001 http://gallery.me.com/noahpatton/100096/IMG_0089/web.jpg?ver=12817400860001 ...and a few glamor shots for fun: http://gallery.me.com/noahpatton/100096/IMG_0130/web.jpg?ver=12817402820001 http://gallery.me.com/noahpatton/100096/IMG_0133/web.jpg?ver=12817399900001
Pictures #5 and #6 show where the knocking sound was on my '68 Wildcat. Nice looking '66......................................Mac
Yup, I'm convinced that's where the sound is coming from as well. I took it apart, can't find any indication of anything rubbing/wear spots. It looks okay, feels solid, minimal play and smooth/balanced rotation when turning it by hand out of the car. Nevertheless, I'm convinced this is the problem, so I'm taking it in on monday to precision driveline in kirkland. I'll let you know how it goes.
