So 2 weeks ago I replaced the rear control arm bushings with Polyurethane on my 74tii ( still need to do the subframe inserts). At that time I also rotated the tires and installed new steel braided brake lines. 2 days later on the way to work the car started to shake around 60 mph. The shaking/vibration can be felt throughout the whole car (in the seat and the steering wheel, etc...). The frequency of the vibration reminds me of a warped rotor, but it's happening all the time at a constant 55-65 mph (it's still there above 65-70, but not nearly as noticeable).
Thinking I had thrown a weight on a rear wheel, I got the wheels balanced.... minimal improvement.
I also visually checked for a tire out of round, but nothing that i could notice.
Trying to identify if I had a bad wheel, I tried rotating the tires back to original position. Again, maybe minimal improvement.
I've checked the guibo, but it looks in reasonable shape. It was replaced about 20 k miles ago.
Center bearing seems OK.
half shafts seem ok too.
So my question(s):
Could it be the guibo? I've read/heard that when these are going, the shakes come on around 30-40 mph. Also I would assume the frequency of the vibration would be much faster. Are there typical visible signs of one about to fail?
Could it be due to the new bushings and a change to the alignment in the rear? Not sure I understand the physics of how alignment could cause shaking, but.... And if it is, what options do I have since there is no adjustment to the rear alignment?
Could it still be a bad wheel? I may need to borrow a friends set of wheels to test this...
What else could it be?