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Long standing pulsating vibration issue that I need help solving

Took the driveshaft off. U joints look good and I get about 4in of engagement


The bearing doesn't look or feel bad but there's a ton of rtv around it

20250208_110732.jpg

20250208_112621.jpg
 
dang that's a lot of spline for that short of yoke. Is it possible the rtv was keeping the bearing or cover from seating completely ?
 
dang that's a lot of spline for that short of yoke. Is it possible the rtv was keeping the bearing or cover from seating completely ?
it gets better than that. the bearing sits loose in the output cover. I have a spare cover and its nice and snug. One on the truck. loose. Cnat see it but you can feel it


also isnt there supposed to be a snap ring on the output shaft? I didnt have any. just spacers
 
welp put it back together and a good chunk of the play is gone but the vibration at 70+ is still there
 
I am sure you did,but have to ask. Did you check the yoak on the rear differential,to make sure there is nothing loose while you had driveshaft out. There is a crush sleeve on the pinion under the yoak that preloads the pinion bearing. If it is not crushed all the way then the pinion can have some play in the bearing.
 
How severe is this vibration at 70+ ?
Am not sure any lifted Blazer is completely vibration free.
If a heavy pedal is needed to maintain 70+ you might be enough axle wrap to change the angle
 
do you have a go pro ? point it at the pinion and go for a drive. Lets see if twist any. If the pinion rotates above 0, 1°-2° or worse you should consider adding anti wrap system.
 
Are you sure it's not from the tires?
Also did you have your driveshaft balanced?
Sorry if you already mentioned it.
im not 100% sure its not the tires but ive been through 4 sets and 2 rims already. current set has been balanced twice with notoing noted from the shop( there is a TON of weights on the tires though)

and yes the driveshaft is balanced
 
do you have a go pro ? point it at the pinion and go for a drive. Lets see if twist any. If the pinion rotates above 0, 1°-2° or worse you should consider adding anti wrap system.
ill see if i cant get the go pro on there here this weekend. I do have anti wrap bars on already.
 
Have you tried putting it in another gear at the same vehicle speed or the same engine RPM at a different vehicle speed to see if the vibration follows vehicle speed only or engine speed?

This won't solve the problem but it will certainly confirm you are working on the right parts, I think the guys are likely correct and getting you on the right track.

If it follows vehicle speed you can also swap tires front/back and see if the vibration goes from your butt to the steering wheel. But if all of your tires are not round or require a lot of weight to balance they may never be smooth at high speeds on the road.
 
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This is the problem.

This doesn't usually equate to a smooth running tire. Did you check them for roundness?
I was going to say if a tire too too much to balance it's not a good tire and it will shake at higher speed
 
Those splines are worn unevenly too. A lot heavier wear on the left side of the picture than the right.


IMG_2249.png
 
Are the joints in phase? If the yoke is removed it has to be reinstalled in phase.

Uneven wear on the splines is not good.
 
It's a strange driveshaft. Almost like the slip spline and yoke aren't a matched set. I mean, what's the point of some of the spline always sticking out? It kind of looks blue-coated, but kind of not. Plus, you don't need much slip travel in the rear of a leaf-spring truck. If you can get any movement (besides linear, of course) in the spline it's going to put it out of balance.
 

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