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Driveline vibration

green 66

green 66

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Hi guys,picked up a 66 belvedere 440 ,727,391s-having a bad vibration in driveline.It starts at about 2000rpm and gets worse the faster you go.Drive shaft was 52.25 in long had cut retubed and balanced with new u-joints.Helped alot,but is still there.Even putting in neutral going down the road around 55-60 its still there,u can feel it on the floor with ur hand but not so on dash or seat.Would like some ideas on where to go next!
 
One place to look is the tail shaft bushing.
 
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Would the tail shaft have a lot of play or very little?

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I have heard a lot about internal and external balance.The motor has a 1 in harmonic balancer-no weights on t/c.Its a 1973 motor.
 
you can check the motor by holding rpms in park and checking for vibration.have ruled out tire and wheel balance as a problem?
 
no -would tire balance wear tires or wheels out of balance also show wear?But have not driven enough to find out Thanks ,i will check it out.
 
normally out of balance tires cause vibration at certain speeds,so i recomend checking anytime a vibration only happens at speed.cheep insurance to check em out.wear will not happen to out of balance tires unless they are driven that way for a long time.older tires can seperate and cause similar problems as well.just take em to a good tire shop and have them spin balanced.they can check for out of round issues at the same time.
 
I had a problem with stock rubber motor mounts that were weak and soft caused a weird vibration
 
If the vibration is indeed from the driveshaft, and you had that redone and balanced (assuming it's done right with correct length vs. tube diameter ratio) then you may have a U joint angle problem. On a MoPar the weld yokes are zero phase (in line) and that will not tolerate any side to side deviation. Your problem may be solved simply by replacing the tranny mount to get the angle correct or add a shim. Or roll the rear axle up with caster wedges. Looking from the top of the car the output shaft, driveshaft and pinion must be in a straight line. Looking from the side the output shaft and yoke must be directly in line but at different elevations to provide some U joint angle.
 
Thanks guys for all the help!Just checked trans mount and looks like it is tore-could that cause it?
 
I just went through this myself. A few things I learned.

1. Make sure the U-Joints are firmly in place. My yoke on the pinion was surprisingly worn out and created movement and binding. It was off by fractions but caused issues. There shouldn't be any play at all.

2. Check the pinion angle. Mine was way out and required shims. Did a ton of research on this. The tailshaft of the transmission and the yoke of the transmission should sit parallel to each other (on different planes) when the car is sitting with the weight on all 4 wheels. At the end of the day - this took care of it. My vibration went away the faster I went and got bad the slower I went. What was happening was as the axle rapped back under acceleration the pinion angle got better and when I slowed down it got real bad. Felt like I was driving on a washboard.

I ended up having to do a new yoke at which time I learned the rear gears and suregrip were shot so everything ending up getting replaced and rebuilt. Runs great now with no driveline vibration - gotta get the exhaust fixed now to take care of the rest of my vibration issues. Check some of my other threads out - some of the experts out here gave me some great advice!
 
I'm just gonna throw this out there 'just 'cause' I read you have an auto tranny: If after you replace your trans mount you still have a problems, check to make sure your torque converter isn't the later model externally balanced version. Probably isn't but I thought I'd just mention it. You can test it by advice 67 Coronet posted earlier: run the RPMS up w/o being in gear.

PS: I also saw you posted an earlier post about a cast or forged crank shaft: You may want want to make sure you have like for like regarding your engine setup. If you have a later cast crank engine, you need the correct balancer and torque converter. If your setup is an older forged engine, then you need the neutral balancer and converter.
 
just switched out trans mount-75 of vibration is gone!Driveshaft made biggest differance.Pulling rear axle next week,replacing axle bearings,seals,swapping out 3.91s for 3.23s.What is the best oil for this 741?
 
Cheapest thing to do is have the drive-shaft checked for balance. Recently bought a 70 RR and it had a drive-line vibration. Asked around and found out it is a common problem. Took it in for a check and sure enough it was out of balanced......they corrected the problem and all is fine......
 
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