What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Driveshaft "binding" heavy vibration under hard acceleration

76k5blazerr

76k5blazerr

Git-er-dun
 Premium
Joined
Nov 13, 2013
Posts
1,587
Reaction score
744
Location
North Carolina
Guys on my 76 blazer when I hit the gas semi hard, not even close to flooring just kinda hard like when you go to make a left turn and there's someone coming in the other lane so you get on it kinda hard. My truck vibrates vigorously almost like the driveshaft is binding up or something, only when I accelerate really hard. What could this be, U joints are brand new, as well as tranny mounts. It Also does this occasionally in reverse when backing up a hill, it'll almost feel like the axle is hopping.

And one more thing. What are you guys opinions on welding the front diff? It's the cheapest "locker" out there and would not affect street driving because I'm in 2hi on the street. Good or bad idea?
 
just cause a u-joint is new doesn't mean they shouldn't be checked to rule them out
 
grabe the shaft next to the joint and see if there is play in it it shouldn't move very much if at all.move it up down side to side
 
Being stock height, it'll probably be easy to find. This stuff doesn't usually happen as often in stock rigs. Like everyone else, I'd say u-joints, u-bolts, or bushings. The fact that it does it going forward and backing up makes me think (if not u-joints) that your axle is moving around.

Any banging or popping, or just the binding feeling?
 
Mostly just the vigorous shaking and the driveshaft feeling like its twisting up under the truck or something, kinda hard to describe. Yall think its the bushings? I don't think its the U bolts or u joints.
 
With the u bolts if theyve been on there for a long time basically the top spring plate is either going to be tight or not. Dont try to tighten them up anymore, if theyre original or very old you'll wind up snapping them. If theyre loose you'll need to replace them and you should disassemble to inspect for a bent leaf center pin.


Bushings just take a pry bar and check for movement. A very bad bushing will also produce a clunk and is visibly obvious.
 
OK, how to describe this.......
Look at all your axle mounting points for signs of past movement.....
If your axle is moving on the springs, it will leave marks. If nothing else, the dirt will be disturbed.
Look where the U-Bolts are around the axle tube, where the spring perch contacts the spring pack, right at the joints.
If there is any movement, there will be shiny, or rusty marks. Or the dust and dirt will be scraped back.

Also, put the tranny in neutral, CHOCK THE WHEELS, and then grab the driveshaft and try to bend it.
Pull it up, down, sideways, there should not be any movement other than rotation. Watch for axle movement or transfer case movement.

Don't worry about hurting anything. Unless you have green skin, you will not put anywhere near the load on any of the parts that normal driving does with your bare hands.

Also, look carefully at the end caps of your U-Joints. They should be nice and evenly dirty.
Any movement or rotation of the caps is wrong.
Also, who replaced the U-Joints? Its real easy for one of the needle bearings to fall out.
I always make sure there is plenty of grease in there to hold them in place, and its usually more likely for one to turn sideways in the bottom than actually fall out, but it has happened.
 
Thats a thought. If so, he should smell it on the auto tranny dipstick. Don't take a lot of slippage to cause that lovely burned smell in the oil.
 
Check the motor mounts. If they are bad enough the engine could move around enough to cause issues, maybe the fan it hitting the shroud from bad mounts under certain circumstances even.
 
Wow, thanks for all the responses yall. Ok so to answer fordums question, I replaced the U joints a week ago, I'm pretty sure their fine but I will check them. Diesel4me, my transmission was rebuilt less than 3000 miles ago and the fluid is nice and red and smells fine, so I don't think that's a problem. 4x4HIGH I know this is not anything I should trust.... BUT, the PO said that the motor mounts were new when I bought the truck a year and a half ago, and when I dropped the motor in they looked good to me. And back to you Fordum I'm going to look tomorrow at all of the things you said to look at and I will post back with what I find out. Thanks a lot guys
 
This may seem like a stupid question, but any chance you have a locker in the rear end? What you are describing sounds like either fairly normal locker action, or a possibly malfunctioning limited slip unit.
 
You must log in or register to reply here.

Latest Posts

Top Bottom