I have a 2002 2dr rear wheel drive Blazer that has had a vibration since purchase. I have replaced all tires, all rotors, all break pads, both front end shock absorbers, both front end lower ball joints, both front end upper control arms that included ball joints, both front end wheel bearings, both front end sway bar links, both rear sway bar links, both driveline u-joints, water pump, fuel filter and have done countless front end alignments and tire balancing. It still has a vibration after all of this work and I'm feeling at a loss for what's left I could possibly do or check. Please if anyone can help me I would really appreciate it. I love my Blazer and I don't want to have to give her up. The vibration noticeably starts around 65 and just gets worse as my speed increases. I have taken it to multiple mechanics and they can not isolate the issue as well.

 

My vibration diagnosis of unknown, unclear sources.

Preliminaries:
Get a clear idea of what you are looking for.

• Can it be heard? Do other persons which do not know about the problem notice?
• Can it be felt? Where can it be felt? In any seat or just on the steering wheel?
• What frequency range are we talking about? You may use a site such as this for reference Online Tone Generator - generate pure tones of any frequency

Actions before starting do diagnose.
You can do this also step by step if you can consistently reproduce the issue and drive there on a daily basis, this will facilitate your work. Or just go all-out and clean up, before starting do diagnose.

• Remove everything from your truck that is loose and does not belong into the truck. Trash, sports bag, the bowling ball, that baseball bat, the chain in the trunk, everything that does not belong to the vehicle.
• Do the same for the outside. Do you have a roof box? Take it down. Do you have an aftermarket roof rack? If possible remove it as well. The same goes for wind deflectors and spoilers if aftermarket. Why? Simple, there is something like aerodynamic buffeting.
• Have an outside tire carrier? Remove the spare tire for the test rides. Do the same for tires under the trunk. Check that the jack is correctly fixed, or remove it as well.
• Check all doors for locking/alignment. Any door loose? Rear door? External tire carrier? Hood?
• Fill a possibly clear and smooth surface, transparent bottle, half full with water. Makes a nice vibration indicator. Bumps disturb the whole surface, while vibration tends to make symmetric ripples.
• Before going for a ride, check all reservoirs for looseness, fill them up, do the same for all the radiators, are they loose? Just rattling them is enough.
• Fill it completely up at the gas station.
• Go ride it

Have somebody with you - Either he/she drives and you listen and observe, or the other way round. One has his eyes on the road, the other diagnoses.

1st checking location and dependence.

• Switch everything which could create vibration "off". (HVAC to OFF / A/C to OFF / FAN to OFF / RADIO to OFF / any other multimedia stuff to OFF)
• RPM dependent? (Look for a road without traffic, large parking lot, industrial road on week-ends. Drive it while accelerating slowly in 1st, 2nd gear. You may not make 3rd or 4th gear as the speeds would be too high. Try highway, do the same.)
• SPEED dependent? (Start in 2nd gear as this will not shift, observe and figure out if it is speed dependent. Try in 3rd gear, accelerate on road which allows the speed to be reached. You will nearly for sure need a highway.
• Is it still present? (After having cleared out all the stuff it may already be gone) If yes, try moving about in the vehicle and locate where it can be heard/felt strongest.

Make videos and write down the exact parameters when it happens. Road, rpm, speed.

Can it be reproduced consistently and every time even on a different stretch of highway?

You should know a lot more about that vibration now then you knew before and it cost you nearly nothing except some time and fuel.

Have I forgotten something or does anybody have better diagnostics?