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Discussion Starter · #1 ·
I need some help on this problem before I go CRAZY or broke. Started as a vibration on my way back from Big Bend. I have 98 extended cab, 33 inch tires with 4 inch springs in back, standard 3 inch Downey lift in front. 4.88 and ARB in rear. Lift is 20k miles old and tires are 10k old. Vibration sounds like what I have heard in an airplane where the 2 jet engines are not in phase with each other. The vibration gets loader and softer ever second and a half or so. I would say it is like a harmonic inbalance noise. I hear it from 55mph and up to 70 or so when my tire noise drowns it out, but I can still feel it in the truck.
I have check the rear bearings, stealership says some play is normal and as long as bearing is quiet, all is OK. Took the drive shaft out and replaced carrier bearing, new slip yoke, 2 inches added on to rear shaft, new rear U- joint, and balanced.
Still vibrates.
Lowered carrier bearing a little more than 3/8 inch and still have vibration.
MY questions are does this sound like the drive shaft or does it cause a constant vibration when out of wack? With 4 inches of lift in the back should I drop my carrier bearing down more? How much drop would be too much?
Thanks for taking the time to read all this. :eek:
 

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Jack up the rear of the truck and chock the front wheels to keep them from rolling. put the truck in drive and look at the rear drive shaft. If it is out of balance, you will see it vibrating .
 

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Welcome to the club.. :)
I have a 99 extra cab with Downey 3" coil over and 3" body lift runing 33" tires and have bad vibes at the same speed you do.
I've tried and checked pretty much everything related to and found nothing wrong. The only thing I have not change are the tires.
The tires is a big cause of many vibrations.

Sorry no much help here.

Good luck.

FS
 

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dropping the carrier will only get it closer to grabbing rocks...ask Dean ;)

the proper fix (getting your pinon angle back to 0 degrees) is to add wedge shims to the leafspring pks. A 3 degree shim will take care of a 3" lift, 4* for 4", etc.
get them here:
http://www.4crawler.com/4x4/ForSale/Shims.shtml

other than that have your drive line checked.
 

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Discussion Starter · #5 ·
Thanks for the replies. I will try spinning the rear tires in the air first and order the shims. The shims sound like a move in the right direction, if nothing else. Does the sound I described (harmonic)sound like a drive shaft or does a drive shaft vibrating make a constant roar?
 

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texascoma said:
Thanks for the replies. I will try spinning the rear tires in the air first and order the shims. The shims sound like a move in the right direction, if nothing else. Does the sound I described (harmonic)sound like a drive shaft or does a drive shaft vibrating make a constant roar?
it sounds like a rear driveline problem but it can be the shaft out of round or just from having too steep a pinion angle. If you don't take care of it soon your U-joints will fail and possibly the pinion bearing. (check those for any play as well, that might also be the problem).

http://www.4crawler.com/4x4/CheapTricks/Driveline-101.shtml
read this for some good info, especially the tech article links at the bottom of the page.
 

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Definitely check the driveline angle, and for vibs. Also by any chance are yours brakes rubbing or out of round? From my experience most tire shops never properly balance large tires. They can be a joke. I had a similar problem and after banging my head against a wall till it bled, I found that after many rebalances they never did it properly. I had to buy my own garage model to fix the problem. The reason I suggest this is that the vibration is slow and probably in rotation with the tires. As your driveshaft will spin 4.88 times as fast. This may not be the problem though. Check for worn U joints also. If you never clipped a rock, don't have bad joints, and there is no play it may not be your problem. You could also remove the shaft and take it around the block in Front wheel drive (4WD). I don't know what affects this will have on your gears though as this would have a coasting affect on them.
 

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At those speeds, and the out of phase sound coming and going, it's probably the tires.
 

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Discussion Starter · #9 ·
I'm thinking it is a drive shaft problem because when I coast with the clutch in, the noise is not as bad as when the clutch is engaged. I know that the tires can be a pain but what else can you do to get them balanced. I had them balanced a few days ago and it didn't fix it. It pisses me off to no end when I have to have someone else balance tires or do the alignment. You can only do so much yourself. Thanks for the suggestions. I'm going to try the pinion angle shims next and I will hopefully relay my success story in a week or so.
 

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texascoma said:
I'm thinking it is a drive shaft problem because when I coast with the clutch in, the noise is not as bad as when the clutch is engaged. I know that the tires can be a pain but what else can you do to get them balanced. I had them balanced a few days ago and it didn't fix it. It pisses me off to no end when I have to have someone else balance tires or do the alignment. You can only do so much yourself. Thanks for the suggestions. I'm going to try the pinion angle shims next and I will hopefully relay my success story in a week or so.
with a tire-balance problem the vibrations will come and go with different speeds. With a DL problem they just get worse with speed.
 

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I'm thinking it is a drive shaft problem because when I coast with the clutch in, the noise is not as bad as when the clutch is engaged. I know that the tires can be a pain but what else can you do to get them balanced. I had them balanced a few days ago and it didn't fix it. It pisses me off to no end when I have to have someone else balance tires or do the alignment. You can only do so much yourself. Thanks for the suggestions. I'm going to try the pinion angle shims next and I will hopefully relay my success story in a week or so.
Dude I feel your pain... I've been trying to work out a vibe and having no luck. (1) I had a new driveline with a CV made, (2) cut the spring perches to change the pinion angle to zero, (3) thinking I went to far with the angle added a shim, (4) today I noticed a woble in the output flange and the dust cover. I'm begining to think the output shaft is bent.
 
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