I have been working on this problem for years (7). Between 60 and 75 I have and annoying vibration. Not terrible just cannot get rid of it. 1. Engine: 455, just had new rebuild, balanced motor. Vibration continues when coasting in neutral. Do not think it is the engine. 2. Transmision: 200-4r. Again no vibration coasting in neutral. 3. Driveshaft: Thougt this was going to be the probem. Replaced with a Dynotech driveshaft (no one makes a better driveshaft.) 4. Rear end: 66 chevy 12 bolt. New posi, Edelbrock upper control arm, Currie lower control arms. 5. Tires: same on 3 different sets. Have a brand new set on right now. The vibration is cyclical, the intensity goes up and down. I can feel it in the steering wheel, see it in the fenders, and through the seat. Any ideas? I am thinking pinion angle. Or am I looking in the wrong area and should go to the front end? About the only things not replaced there are the idler arm and the drag link.
Sounds like a tough one after all you've already checked. Does it do it in corners as well as straights? Does it do it with brakes applied lightly? You are sure the axles are straight and the wheels are true? I'll give it a shot. If you think it is pinion angle, throw about 300 pounds in the trunk. That should cause it to squat enough to alter the pinion angle. I know my car only ever tried to wheel hop when I had it jacked up in the early 80s with 10" rims and wide tires. You could also jack up the rear of the trans and put a few washers between it and the mount to shift the angle slightly. While you are under there, make sure the trans tail shaft bushing isn't sloppy, letting the drive shaft move around. We used to put a bit more toe (in or out) on the front end alignment just to see if it would make a difference. Loosen up one side tie rod adjuster and put 1/2 a turn on it to see what happens. Worst case scenario, it does nothing and you put it back. None of this is meant to be a permanent fix, just troubleshooting tools. To eliminate the front end, put it on jack stands under the rear axle (or take it to a dyno :laugh: ) so that the front tires are no longer rolling. That will narrow it down to either the drive train or not. You can also watch or have someone else examine things like the trans mount, drive shaft, rear end and u joints this way. All of them are $0 and only time to do it.
Could also be an exhaust resonance. My car has a bit of a vibration that got better when I put in an X pipe. Before that, it sounded as if the engine was surging, but it wasn't. The tachometer was rock steady. If you have headers, are they close to the frame, steering shaft, or suspension part? I don't think our 40 year old technology cars will ever ride as smooth as a newer car. My 98 Riviera spoils me for the 70.
I am wondering the same as "Knuclebusted" . Even though you have had three different set of tires, were the wheels the same? If so. try a different set of front wheels. I would find a shop the will balance the wheels while they are still on the car (it will make a difference). With the vibration in the steering wheel, it is in the front end some where. One more thing. Have you had the front end aligned lately?
I have a similar set up in my car with the same vibration you are describing. Pinion angle was off so I installed adjustable upper arm to correct, vibration still there but not as bad. Checked everything in the rear end and did not find any problems, even had a friend balance the brake drums with no change. Different tires and wheels didn't change anything either. Still looking for the problem, but I'm starting to think it may be a resonance issue as Larry mentioned. What type of exhaust system are you using? I would check the pinion angle regardless and correct if needed. Worn steering parts generally don't cause vibrations. Keep us posted on your findings.
Try flipping the driveshaft 180 degrees. That made a diffrence on mine. The vibration used to start at 55mph, now it doesn't start until 85mph, which is fine, I don't usually go that fast on he street.
Lots of good ideas, thanks everyone. I already have and x-pipe. I like the exhaust resonance idea but wouldn't that be a constant vibration instead of the throbbing vibration I get? My tranny guy was just working on the car and he said the output shaft was fine. Will check runouts next week if I can. I wish I could find someone with the old balance tools that they did on a car. Had a guy that used to do that but he is retired now. Those things were so cool. They could run the tire over 100mph. That would help isolte things too. Unfortunatly that skill is dying off (literally.)
What kind of tires are you running on and how old are they? I had a set of General tires that were crap from day one and caused the cyclical vibrations you describe.
Just put on a new set of tires and made no change. Wheels are American Racing saltflats. So I have seen the problem on two different sets of wheels and 3 tire sets.
Have not had the time yet. Seems my daughter wants a deck built. Guess who gets to do that! Been doing a little work getting rid of oil leaks. Had an o-ring rupture on the hydro boost and every time I hit the throttle it would look like a burnout as the fluid hit the headers! Also trying to seal up the Poston oil pan. That thing is designed to leak. So the main projects right now are to run down the vibration, get the oil leaks reasonable, make sure the electrical system will handle the fans and fuel pump. Thanks for keeping track.
Pretty well every guy that's done a 200r4 swap has that vibration. Mine has it too. I believe it is pinion angle related. The tailshaft C/L to transmount surface on the 200r4 is 1" smaller than my old ST-300. Not sure about the TH-350 or TH-400, but I'd bet it is the same issue. So basically the 200r4 sits 1" lower in the rear then the original trans. I'm experimenting with shimming up the trans mount and have 3/4" shims in there now, but still have the vibration. I'm gonna try to squeeze the last 1/4" in there, but it's tight. So next option is the adjustable upper C/A's? Brian
I've had my 70 with a 200-4R on quite a few miles and I don't detect any vibration in any range. I have a pretty thick trans mount though so that could account for it. I have no adjustable control arms either.
I do have adjustable control arms. Also have polyurethane trans mount. Seems to me that I have set the angle at 1.5 down. Going to take the car over to a friend that sets up circle track cars and get a good accurate measurement. Will let you know.
