Bad Vibration after rear end exploding and lift added

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thetacotown

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Okay, so about 2 months ago I suffered the loss of my rear axle. The G80 locker in my 97 suburban failed while I was going about 60KPH and the entire rear end locked up, ujoints broke off the yoke and driveshaft hit the ground. I changed both ujoints, put in a new rear end, and while it was apart I put in 2" lift blocks. I havent cranked the torsion keys to match the new height of the rear yet because I was waiting to sort out this vibration before I ruin my alignment. Now the entire truck shakes like a ****, up until 60kph(35mph) its not bad, 70(45) is bad, 80(50) is loud, 90(55) isnt that bad, 100kph(60) has a horrible whopping noise, and everything past that is horrifying. The vibration has just sort of gone away once or twice, and the truck runs amazingly smooth all the way up to 110, but then I go over a bad bump and its back to ****. Does anyone have an idea what could be causing this before I go out and pay a guy a buncha money to balance my driveshaft or something


Its a 1997 Suburban with 4x4. Its a 56" long steel driveshaft, that doesn't look to have any bad dings, nor does it have a lot of rust
 

michael hurd

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Could literally be anything from flat spotted tires to a bad mount for the transmission, transfer case crossmember isolators, worn output bushing in the transfer case, or simply the change in driveline angles due to the blocks.

Check the tires for out of round / belt issues on a wheel balancer, where you can manually spin the tire by hand looking for issues.

If they are good, turn the machine on and check the balance on the tire assemblies.

Climb under, grab the rear shaft near the transfer case output and try to force it up and down. May need a new bushing in the output, and a seal replacement.

http://www.drivetrain.com/images/stories/product_imgs_large/np231d_large.jpg
http://www.drivetrain.com/images/stories/product_imgs_large/np231d_large.jpg
If this was a used shaft ( I assume the original was destroyed ) are the U-joints any good? Did you pull the caps and check for brinelling on the cross? Move smoothly? Any rust on the slip that goes into the transfer case?
 

thetacotown

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I've checked for flat spots, and put a bit of antifreeze in the tires for balancing a while ago. The ujoints are all brand new, and the yoke looks brand new. It is still the same driveshaft that the truck came with. The output seal is ripped, but the bearing still feels fine and there isnt any play.
 

deadbeat

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How much runout you got on that driveshaft that hit the ground at 60kph? Get a dial indicator to check this or just take the driveshaft to a shop and have it checked. If you have a good garage floor and a good set of jack stands you can do a few checks to eliminate the tires and drums. You jack it up and turn it on and run it up to speed, take off the tires and do it again, make sure to put lug nuts on drums with wheels off. Then take drums off. After running it up to speed just turn it off in gear, do not hit the brakes. You can watch the driveshaft turn like this but if you see runout there is probably a lot and this could be the problem. My bet is driveshaft bent, possibly out of phase.
 

90halfton

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If it's the same shaft that smacked the pavement, I would think it could be tweaked. A machine shop can turn it on basically a couple bearings on a bench thingy with a dial caliper and check it out for ya.
 

aaronb

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Are the lift blocks you used tapered or non tapered? It sounds your pinion angle isn't right. You may have to use a pinion angle shim to rotate the pinion.
Get a magnetic protractor so you can check your angles on the driveshaft where it goes into the t case and at the rear diff.
heres a link on how to check the angles.
http://www.google.com/url?sa=t&rct=...0J9QEaMZfHO3GdwlA&sig2=AZxatk2I0dv3FELJiu4D2Q
You must be registered for see images attach
 
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michael hurd

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I missed that it is the same driveshaft that suffered the trauma. I'd put money on it being bent.
 

thetacotown

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My lift blocks are tapered, and the small end is to the front. Could I just use a magnetic bubble as one of those protractors and eyeball it?
 

aaronb

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A magnetic bubble isn't going to give you an accurate meassurment. If you aren't running a double carden joint on the driveshaft at the t-case. You don't want both angles the same. You want a one degree difference between the pinion and angle of the driveshaft.
When you are accelerating, the pinion will tilt up. If i remember right, im pretty sure a 2" tapered lift block will have around 3-4* of angle built in.
Take a pic of of the rear shaft at the diff.
 
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