Yeah, they found that out the hard way at the local Chevy store a few years back, the tech ended up with two broken legs and a week in the hospital.

 

Also do this in both forward and reverse gear. That way you can see the excess movement from the torque in both directions.

 

Totally agree with your diagnosis Mike. I was just throwing out a Plan B if the mounts don't show up bad.

 

Agreed George, if the mounts check out, the control arm bushings should be on the list of suspect parts until proved to be either good or bad.

 

Update: This morning it was 55 degrees, and the clunk (and rattle) was almost imperceptible. I drove hard, as usual, to work, with the radio off to listen for driveline or suspension noises; only tire noise, unchanged from normal times, and no clunks even hitting potholes. The 60mph shimmy was there, but only had the braking shudder a couple of times (much much less than yesterday morning, at cooler temps). However, this evening, at 70+ degrees and stop and go traffic, all the symptoms reappeared in strength. I left the radio off, and again listened for errant suspicious noises...I only heard a very slight clicking (which I think is just my stock wheelcovers, because it varied on washboard surfaces and smooth), but when I would try to stress the CV's by making hard, sharp manuevers, there was no apparent increase in noise. I also checked for brake pulsation by taking off one (heavy steel toed) boot to feel the pedal under the "shudder" conditions. None detected, unlike 12000 miles ago when I had to re-do the pads/rotors. A new wrinkle> I just noticed the speedometer needle vibration during the shudder. I guess I'll have to wait for Saturday to perform your suggested checks, at my friend's shop. This is making me crazy...I almost wish for something to "snap", before I do, so I can pinpoint it. Thanks for your help!

 

I finally did the undercar inspection on Sunday, similar to my nut and bolt checks on my drag car prior to a new season. I found absolutely no looseness nor play in any component, nor loose fasteners, nor leaks or tears anywhere, even using a pry bar. I checked camber and toe-in, and looked for hub wiggle or even aberrant sounds from any wheel, when spun. The only play in the steering was when I would turn it one way, then the other, quickly, and then the steering wheel would vibrate and the underdash linkage would "rattle" slightly. This was done with wheels in the air, key off. Finding nothing else, we then went off on a parts run/test drive, with my friend driving, trying to duplicate my observed symptoms at the aforementioned speeds. Only once did the steering shudder occur, but very very slight. We gave up looking. Today is the third day since then, and every day the shudder has gotten worse on my 60 mile drive home from work. I don't feel it much in the a.m., and stop very seldom, but in the stop-and-go hell of the p.m. drive, it's very bad. I raised my tire pressure (cold) today to 33psi, and the wheel will move 2 inches side to side during a 35-20mph rapid stop. But not if I'm turning either direction. and still no pedal vibrations, but only steerring wheel and seat of the pants vibrations. I see that others have some similar probs, but not in the same combinations as I.

 

I don't know if anyone has been following this thread, but here are more observations of my Panel, "Rattler" (new nickname), and the problems with ride quality. 1)DFW area superhighways are washboards for the most part, and inconsistent surfaces are bad for diagnosing problems. 2)My tires will fluctuate up to 4 psi every commute, also bad for diagnostics. 3)To my consternation, the ride quality varies from good to apalling and back on the same test tracks driven the same every day... no consistency! 4) If I drive like a Grandma, the problems grow worse...conversely, if I brake insanely hard, and double the speed limit, the problems with "rattles clunks and shudders" seem to fade away. 5) My right dash area now has a harmonic at 45mph, very pronounced and new. 6) I'm almost to the point of driving my Chevelle to work, it rattles less, if I could get a tanker to follow me for enroute fillups (just kidding). New plan of action:try to find an "on car wheel balance" establishment, to see if that'll help, and if all else fails, take it to the Chevy dealership(s) I use, 4 different ones, sparingly, since none seem to want to follow my requests when I use them, thus I end up doing my own repairs (since '85).

 

I recently decided that the "warped rotor" and associated rattle/rumble while braking is probably the steering "horseshoe link" universal joint/intermediate shaft. Mine acts like a warped rotor, but no pulsation in the pedal, just vibration. New rotors, pads, hubs, CVs and calipers, ALL new rear brakes, including hubs, from the backing plate out. ALL new suspension, except for rear wheel control arm bushings. Still shudders on semi-hard braking. Only things remaining is steering column joint and rack & pinion, and it does not bother me that much!

 

Did your shudder/rattle/rumble come adn go as mine? Did your steering wheel move up to 2" or not at all? Why is mine so inconsistent? I would like to replace everything, but money and time are issues. I'm really leaning toward a combination cause for my troubles: 70k miles old, out of round Firestones and the intermediate shaft is worn (it's always the Chevy intermediate shaft; I know, I'm a veteran of the Silverado Shaft Wars).

 

Yes, come & go. I'm leaning towards rack and pinion or intermediate shaft. How do you suppose they could figure a way to mess up an U-joint that has relatively small torque? I do currently have a bad replacement rear hub, that could be my prob. The car goes straight when braking, no pedal pulsation, just the annoying shudder, sometimes even seeming to porpoise.