"thrumming" from the rear?

[megaladon6]

it starts about 80-90mph and i think it's coming from the rear. you can feel it through the car as well as hear it.
the tires are new and balanced and it doesn't feel like them. other than that i'm not sure what to look for.

[megaladon6]

anyone?

[Nessumsar]

I believe I have the same problem, and everyone said to check pinion angles, and to get the drive shaft balanced. Hope this helps!

[HILROD]

Check the driveshaft universal joints. It could also be a bad pinion, or side bearing in the diff. When the pinion bearing is just starting to go bad, it can cause this vibration before there is any side play in the pinion shaft.

[megaladon6]

u-joints are new. i'll see what i can do to check the bearings.
how far off does the pinion angle have to be to cause problems? i did lower the car and install tubular non-adjustable arms, so i don't know where it is.:pat:

[JEFFTATE]

Check the relationship angles between the Transmission , Driveshaft , and Rearend pinion centerline.
If the u-joint working angles are not right they will bind and/or cause the driveshaft to rotate in an out of balance way.
Do a search on pinion " angle" here on this board.

Here's a link:

http://www.prostreetcamaro.com/dshaft.shtml

or here:
https://www.pro-touring.com/forum/showthread.php?t=44835&highlight=pinion+angle

[PhillipM]

it starts about 80-90mph and i think it's coming from the rear. you can feel it through the car as well as hear it.
the tires are new and balanced and it doesn't feel like them. other than that i'm not sure what to look for.

We have this same "Thrumming/Vibration" in our 65 Olds. It has a 455/T56 and brand new driveshaft and rear end. We have quadruple checked the pinion angles and had the driveshaft balance checked.. all is okay. Now I am kind of stumped where to go from here. When you sit in the back of the car you can hear it comming from the front and when you're in the front it sounds like it is coming mostly from the dash area but could also be coming from the back. The "thrumming is that lougd". But the you can feel the vibrations in the floor just about everywhere and this is with dynamat down on the entire floor. We have also had all of the wheels/tires double checked. Anyone experienced something like this before?? Where to go from here?

Edit* I just thought of a few more pieces of information.
1. It will sometimes go away for a brief second if your coasting down a big hill in 6th gear
2. It is most noticable in 6th gear cruising under a load. It gets worse if you stand on it or slowly creap up the MPH range. (>70MPH)
3. It goes away if you pull it out of 6th and down shift to 5th but we don't have a tach so it is hard to nail it down so far.
~Not trying to jack this thread.. I just feel our problems sound similar.