bad Vibration from rear

[benzjed]

I have a new issue that has me baffled... I have replaced every bit of the front end of my truck with new, I have new Rancho 5000's all the way around, I have replaced everything including drums on the rear end for brakes. been running and driving great, this week, all the sudden, if you are driving above 55 mph and hit a large expansion joint or pothole with the rear of the truck, it immediately feels as though you have blown a rear tire due to the violent vibration. You can hit the brakes and drop the speed down to 45-50 mph and it smooths back out. This has happened 4 times this week. I can get it all the way up to 75-80 and it stays smooth as glass, but any moderate bump to the rear makes it shake so bad the Guys on the radio start to stutter... I can't find anything that looks out of the norm, it has new tires on it with maybe 1500 miles on them. The rear shocks are new, I have no play in the driveshaft, the leaf spring bushings are dried and have some fine cracks in them but don't look terrible, the u-bolts are tight...I'm at a loss and help would be greatly appreciated

 

it's a 89 4wd automatic short bed 4.0

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[cruiser54]

Sounds like it might be a rear tire with a tread separation.

[Abyx]

Sounds like it might be a rear tire with a tread separation.

 

This

 

Also, run your hands along the sides of the tirewalls, and feel for any abnormal bumps...there generally is at the most one bump, which is the belt joint in the side wall...if you feel more than that, I'd try another set of tires on the rear and see if it goes away.

 

I had the problem of belt separation in a set of Uniroyals I had gotten for free...they made all kinds of weird noises, vibrations and made my jeep jump all over the road. If I hit a bump good enough, my rear end would chatter sideways across the pavement. It was scary, but I got used to it.

[87Chief]

Take the tire off, or just lift the rear end and spin it and lay your hand on it to see/feel if anything is off (bumps, lower tread in a certain section).

[benzjed]

I have done this, I have rebalanced them and they were still dead on. I will go ahead and warranty the tires and see if it makes it go away. I bought them from our supplier so warranty is no biggie. It feels like tires but I can't see or feel anything wrong with them, and like i said it runs smooth till you hit a bump or something and soon as you slow down it goes back to smooth

 

Thanks for the suggestions :cheers:

[Pete M]

swap them front to rear and see if anything changes. :thumbsup:

[airspeed]

Could one of the new shocks gone bad?

[benzjed]

Rotated tires last night, same thing happened this morning...UGH...still coming from rear. as far as the shocks go, I have not removed them to check them, but they are still pretty and white and show no signs of leaking.

 

How bad would leaf spring bushings have to be for this to happen??? I can see they are still filling the holes up but can't really tell how tight they are. They are dried and cracked some, but not huge cracks or where chunks are missing. This is really getting frustrating, luckily it's not a Daily Driver but I do use it a lot.

 

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