Hey guys, bi#^#in forum going here. I have a classic 79, street ported with a weber carb, just got it fired up again and now I'm dealing with the problem it got parked for. I have the worst vibration between 35 and 60, worst around 55. It feels like a horribly imbalanced tire, naturally I had that checked, all good. I put it up on a lift and the driveline looks good, replaced the u-joints as well. Still no fix, this car has been driven like a true race car that it is including down shiting,.....hard etc. Is my last option to pull the rear end out or just the axle? If so can/should I try and put a limited slip or posi in? Any input would be greatly appreciated.

 

Did you run the car in the air and look at the wheels rolling. That should give you an idea whether you have a bent axle or not. Also check to make sure the bolts that hold the driveshaft on to the diff flange are tight. Is there any evidence of something that might have hit the driveshaft?

 

Yes I did run it in the air and there was no obvious sign of problems, like you would think as bad as the vibration is. The wheels looked to be straight and smooth, and no apparent damage to the driveshaft. I'll check those bolts tonight, but I'm pretty sure they're tight. Thanx for the response

 

Forgot to mention. Have you inspected all of the front end steering and suspension components and the front wheel bearings?

 

I've inspected as far as looked closely but not really more than that. What else could I do to inspect the bearings better, like put it in the air and shake the tire back an forth with the steering locked?

 

You can't just look at the parts. You have to check them for play. The inpsection process is in the FSM. Recommend that you inspect the whole frontend. More than likely you are going to find problems.

 

Thanx Doc! I'm a painter not a gear head so....... thanx for the advice!!

 

in addition to what doc said, i'd also check for play in the u-joints. very commonly overlooked. also, when's the last time you had your tires balanced?

 

Try moving the front wheels to the back, and see if it changes anything. Maybe one of the tires is out of round due to sitting?

How long was the car out of commision for? Did it have this problem before you parked it for storage?

 

Tire runout does sound like the most likely problem.

This is less likely, but worth looking at: Check the fit of the driveshaft into the back of the transmission. A bad front U-joint in the past could have ruined the brass bushing in the tailshaft housing of the transmission, letting the front driveshaft yoke wiggle around in the back of the tranny. This usually shows up at higher speeds.