Hi all,

I have a 1998 Chevrolet Blazer LS 4x4, 170K miles. I only use the two wheel drive setting ( 2 HI). Whenever I take my vehicle on the highway around 65-70mph and let off the gas pedal get a violent tight vibration for about 2-3 seconds. Pushing the gas pedal around that speed only makes a very brief vibration (1s). It sounds and feels like you are driving on a rumble strip very fast. I thought I felt it beneath the drivers seat, but my nephew says it sounds like its from the rear.

I took it to a local mechanic shop and he told me to replace a whole bunch of suspension parts : sway bar links, front upper control arms, pitman arm, front CV axles, front driveshaft CV joint, both rear driveshaft U-joints ( up and bottom), both front wheel bearings, passenger caliper and rotor. I even replaced the rear differential cover and fluid. I got new tires, rotated, balanced, and an alignment.

My transmission threw a P1870 code last time I drove it on the highway for an hour going 70mph. Not sure if its related. It only threw it towards the end of my trip after everything was heated up. Hasn't thrown the code since ( now I drive 60-65 desperately trying to not cause the vibration).

Any ideas where to go next? I was thinking a possible out of balance rear driveshaft, but I'm taking any ideas about now I'm worried it's wearing down something.

Best,
Peter R

 

Sounds like either u-joint(s) or wheel bearings in my opinion.


Also check your lug nuts. Sounds stupid, but last time I had a vibration that occurred when letting off the gas only, my left rear wheel and tire got further to work that morning than the rest of the truck did, if you know what I mean...


NOT on the Blazer...

 

I do have a bad rear wheel bearing, but I swear the vibration feels right underneath me ( engine/transmission area).

U-joints have absolutely no play in them. Lug nuts are good as well since I have recently taken off the rear and front wheels to inspect their brakes/bearings.

I have noticed that the vibration seems to be always with me, just no where as violent as engaging or disengaging the gas pedal. The vibration is not always short. Sometimes when going down hill on the highway and keeping a steady gas pedal, the intense vibration will come back and continue to vibrate until I either let off completely and let it slow down or if I give it more gas.

Maybe I'll record some video. One of these days this car is going to vibrate itself to death.

 

Motor mount?

 

I'm going to need a spare hand for that one

For checking motor mounts-> Have someone shift between the gears and see if the engine starts to pop out of the bay? Hahaha. Anything else I should try to troubleshoot?

Thanks!

 

not the motor mounts, i`m going with wheel bearings

 

Motor mounts had some play. Not horrible like Chris fix's YT video... Not sure what normal is suppose to be like.

Looks like I'll investigate visually the rubber motor mounts, and I'll replace that rear wheel bearing that has been irritating me.

I'll get back to ya'll in a week once parts come in and repairs are done.

***Edit: Just looked into the work the replace the rear "wheel" bearing... It is nothing easy like the front. Correct me if I'm wrong but the sequence to replace a rear wheel bearing on a 98 Chevy Blazer ( rear disk brakes) is to:
~from another fourm~
"To remove
1. Pull Diff. cover
2. Remove brakes, rotor & Brake Caliper & Bracket
3. remove the bolt that holds the spider gear's in place?
4. Push the axle shaft in
5. Remove the "C" clips on the end of the axle shaft Diff. side
6. Pull Axle shaft out
7. To make it EZ use a slide hammer bearing puller
8. Drive in new bearing
and put it back together the way it came apart
New Diff. gasket and rearend grease"
No need for limited-sllip additive since I do not believe it is needed for mine.

So I'm replacing the bearing... anything else I should replace while the rear end completely apart? Seals? Tips for the job?