noise/ vibrations at 70Mph
 

Hi

I am experiencing now strange noise/vibrations mainly at 70Mph. It starts at 50Mph and ends at 75Mph but maximum is at 70. Frequency is about 48Hz at 70Mph so it is somethings between noise and vibrations. I feel it in whole car without specific location. It takes place during acceleration, deceleration, running on neutral (N) with 2Hi either 4Hi engaged.
I have replaced both universal joints for rear shaft - no change, shaft has been balanced, wheels were balanced, motor and AT mounts replaced, all suspension checked - still the same and no change.
Last idea was to replace transfer case bearings. What do you think about? Any other idea?

Regards, Marcin

Sounds to me like one of the rear wheels is out of balance. I'd take it to a tire shop and explain what all you've done and ask to get all four re-checked.

Or maybe if you haven't rotated the tires lately, do so. If it's a wheel balance you'll feel it in the steering once it's moved up front and then you'll know that's the problem.

All tires balanced and checked with special tool including road force tires balance. Also frequency should be lower for tires about 8Hz and for shat considering rear diff ratio about 26Hz. 48Hz is really high.

Oh. Sorry, I didn't apply enough brain power about what Hz means in this situation, and I agree tire balance noises would probably be much lower than 48.

If it's doing it in neutral and 2Hi I wouldn't think it would be the transfer case bearings. I would be more suspicious of the rear differential or wheel bearings. This is getting beyond my knowledge and diagnostic abilities though so I can't give the best advice and hopefully someone else can be more helpful.

Also: a Blazer in Poland!? Cool! :)

Now Blazers are getting old but still from time to time you can see it here in Poland. There were also European version popular here but mine is US with head and tail lights replaced for EU.