Having some highway vibrations
 

Hey everybody, having some vibration issues. New to blazers, love the truck, hate the vibrations. they start around 55 mph, and i get them in nuetral, so i consider them to be a rolling defect. I may be barkin up the wrong tree, but ive almost rebuilt my front end already and no luck. Little confused about my drive shafts. May be a dumb question, again Im new, is my front drive shaft supposed to spin freely in neutral, when in 2wd? Or ever for that matter?

Check front end for titeness, sounds like you have.
check tires for uneven wear...check all tires in several spots and compare.
check wheel alignment.

don't worry about the drive shaft spinning, just make sure it's balanced

look at the shafts make sure that all the weights are still on it. look for spots where rocks may have damaged it, look for spots that are rectangular about 1 inch in size and a different colour from the rest of the shaft...a weight probably fell of here.

check u-joints for play, they should be tight on the truck but not seized solid, like mine were. I thought they checked out ok because they were tight when I grabbed the shaft on the truck. but when I removed it to change the rear output seal they were seized solid.

Jpimp, thanks for the quick reply, I finally have a second and I'm gonna check all this out. One more question. It seems to be a "rolling defect" , because when I throw it in neutral , the vibration is still there . Is that normal for a drive shaft that is out of balance , or even bad u joints?

U-joints failure becomes very obvious at higher speeds. If the vibration becomes more pronounced at higher speeds and under load - in gear - then I would check the U-joints. By the sounds of it, if it was your U-joints, you should feel some play in the drive line while it's parked. Here's something to think about, if you are showing wear to the metal on your tires that could cause vibration in either end of the car.

Thanks for the reply, tires are about 5000 miles old, one thong I also noticed, and again I am sorta a rock with all this, but I'm learning , is that they sold me tires that are 235/70 when on my door panel it calls for 235/75, don't know exactly what that 75 stands for but they are not. Like I said though, I do believe its my universals but again, even in neutral I get the vibration, ........when rolling at high speeds. It's worst at around 65-70. That's when my rear view mirror is blurred

The 70 and 75 refer to the sidewall height of the tire. 235/70's are a little shorter than 235/75's. Your speedometer is probably a couple miles an hour off @ 60 mph but other than that won't cause an issue. Is the vibration coming through the steering wheel? Have you tried rotating tires to see if the vibration went from one end of the truck to the other?

I might be wrong but doesn't the rear driveline still turn while the truck is in neutral and moving. I just replaced the U-joints on my blazer a couple of days ago, total investment was 22 buck for both front and back U-joint on the rear driveline. I am not going to say it was easy to replace the U-joints, took me a couple of hours and a crap load of swearing. If you decide to replace them yourself make sure you get the grease fittings pointing the right way. Also mark the front yoke to the driveline so you can it get back in the same location, for balance.

Yes its vibrating through the steering wheel, and I have rotated them , vibration seemed the same

it very well might still turn while in motion , I'm not going to attempt changing the u joints myself, at this point, I just want the vibration gone,

U-joints are very easy to change out, especially if they are aftermarket. Four bolts that disconnect the drive shaft from the differential and 4 bolts for the rear axle, and four clips per u-joint. If they are originals, then you will have to get a torch or use map gas to heat it up in order to get the nylon out of the yoke.