I just changed the gears in my car as well as the leaf springs, as they fell apart upon removing the back axle.

I went from 2.56 gears to 4.11 and added a posi. The leaf springs are a 1.5 inch lowering. I had this nasty vibration going through the car. I had a drive shaft custom mae for it with all new parts. The vibration is still there. i checked the axles and tehy seem to be all right.

Could it be a bad transmission or motor mount? Can the angles be off on the drive shaft? i thought that is what universals were for?

Please help!!!!! my car feels like its going to shake and groan itself apart.

 

It is possible the angles are off. To check get yourself an angle gauge (they are rather inexpensive). The easy wat is to start at the crankshaft. Place the angle gauge on the vibration damper and read the angle. Now go to the rear, remove the driveshaft and rotate the yoke so the saddles are vertical. Place the gauge on the saddles and read angle. Your readings should be the same or within 1 degree. If not you can get shims to place between the leaf spring and the mount that will compensate. They are available from Summit and are sold by degree of tilt they put on the differential.

Also, make certain the driveshaft has room to slide into the trans when the car is sitting on the ground. If it is too long it can bind which will vibrate under power.

 

I'm also thinking that it might be the driveshaft binding between the rearend and trans. Your new springs in essence raised the rear axle closer to the frame, which would have driven the driveshaft forward slightly. But "slight" may have been all the clearance you had between the slip yoke and trans tail with the old springs.

 

We need a little more info, When does it vibrate? under load all the time? does it get worse with speed or does it smooth out. Most of the things talked about are under load vibration. Auto or stick?
With a spring replacement and new drive shaft you need to check to see if the rear is sitting straight check you angles ( I use a choke gage angle right on the U-joint faces) and lastly is the Drive shaft phasing. Make sure the U-joints are in line with each other. They should within a 1/2 a degree. You can use the choke gage for that also.

 

I had someone come and drive it with me, and they are telling me that it is most likely a bad drive shaft again. I had it built brand new and it seemed ok, but they could have screwed up.
The car is an automatic with a TH350 behind it. It really only seems to make the droaning and vibration noise between 2500 and 3500 rpms, when in 3rd gear. once you take your foot off of the gas it starts up again as it is slowing down. It also seems to go away some when i'm on the throttle a lot. That could just be because the car is moving so fast and hard that I'm not even noticing it.

 

Just wanted to update everyone on the problem i was having. Seems that whomever was responcible for installing my tranny to my motor (reluctantly it was me...) failed to tighten the bolts as tight as they should have been. very poor work on my part, of which i am embarresed. but just thought i'd fill you all in.