Bad Vibrations

[Baumi]

My 56 Chevy is giving me some headaches right at the moment....

Here´s the story:

During the last winter I installed airbags and a 62 Chevy rear suspension. Everthing worked out fine and it was a real smooth ride at any speed until I noticed a little crack( about 1" long) in the frame rail besides the panhard bar bracket .
Ok, not a big deal. So I´ve cut the bracket out, welded the crack, fabricated an L-profile out of 4mm steel plates to reinforce the frame rail and welded the bracket onto the L-profile.

Now, that the bracket had a 4mm "spacer" plate I had to shorten the panhard bar (4mm)and reweld it to make sure the axle rests where it was before. Now the clearence between the outside of the frame rail and the rim is exactly 4" on both sides.

During the test ride I ´ve noticed some bad vibrations between 3400 and 3800 rpm maybe from 65 to 75 mph. I ´ve found a ripped tranny mount but changing the rubber mount didn´t cure the vibrations. They are still there....

I wonder if I could have changed the driveshaft angle but I´m pretty sure the axle is in the same place as it was before.
The universal joints look ok to me too, the rear one has a bit( about 1mm) up and down play. But I´ve no clue how much is too much...

My other thought was a damaged rearend bearing...

Maybe I broke something when I ripped through the gears during the test ride http://www.jalopyjournal.com/ubbthreads/images/graemlins/confused.gif

Please let me know your ideas,I´m through with mine.

Thanks a million for your help!

Christoph

http://www.image-hosting.net/images/messageboard/SmokinMike/firstrollout1.JPG

I also hate the rims http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

[porknbeaner]

Christoph,
It is probably totaly unrelated to the other problems but I might want to check on the play in the U-joint. I try not to have any play in mine. But you also might check if the play is in the U-joint or the pinion shaft.
Also of I had found a crack in my panhard mounting area I might be checking to see if any of my suspension link mounts had the same problem.
I don't think that a crack in any of the mounts would cause a vibration, but it would be a good idea anyway.
I'm thinking probably the u-joint or perhaps a bad pinion shaft bearing.

[Baumi]

Thanks for the hint!The last thing I want is to lose my rearend. http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif
I´ve already about 2000 miles on the car since I changed the rear suspension and I can´t count how often I´ve been inspecting all the welds. The crack next to the panhard bar bracket was about to happen because the top end of the bracket was right in the middle of the frame rail which I think is the weakest point. To be double sure I´ve corrected my mistake and reinforced the rail. All the other welds are strong and welded to the frame from three sides.

I´m sure you are right about the u-joint. I´ve just checked them again and I noticed that not the u-joint bearing itself has play but the joint slips in and out the bearing cup...about 1mm.
http://www.jalopyjournal.com/ubbthreads/images/graemlins/confused.gif

How can I check the pinion shaft bearing? Rockin´it up and down?

[yorgatron]

any play in the U-joint is too much.

[Chili Phil]

Make sure the driveshaft's in phaze. That's when the u-joints are lined up.