2000 Blazer ZR2 - Shakes at Highway Speed

[mavrim]

I have a 2000 Blazer ZR2. The truck would vibrate (shake) really bad at approx 70 miles per hour. As the truck gets up to speed there is a slight jitter or thump as the truck goes from 20-30 miles per hour. My BFG all terrain tires were worn (above lincoln head on penny). I wasn't sure if a rim was out of balance or something in the drivetrain was causing an out of balance issue? Last week I had the tires replaced and the problem was barely noticible, even at 70 mph on highway. Now after a week of driving, the problem has reverted to its original state. As a hunch, I removed my custom hypertech transmission shift firmness and alteration program and it is now stock. No difference! From 2000-2005 I had a meyers trimline snowplow on the truck. Not sure if the transmission would cause this vibration (shake)? Any ideas? I do recall having this problem start last year after having brake rotors replaced and new pads installed. Could that cause this type of problem?

Thanks for your help!

[Chris Stewart]

Where do you feel the vibration? Seat, steering wheel, floor?

[AJT1961]

When my 2000 Blazer had those same symptoms it turned out to be bad ball joints, a common Blazer problem. How many miles on the vehicle? Ever replaced the ball joints? Check them for play -- the lowers usually go first, but given the amount of work involved, it makes sense to replace all 4 if you are doing the job. If that is your problem, spend the extra money to get oem or Moog parts unless you want to risk replacing them again in a year. There are some really crappy aftermarket ball joints out there.

[MT-2500]

Always check for worn/lose parts and bent rims or slipped belts on tires.

But the major cause of viberation or shake at 60-70 MPH is tire balance.