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Discussion Starter #1
07 colorado 2wd 72k miles. Installed rear leaf springs and shackles last night to net approx. 2" of lift. Long story short i had to do the leafs because some of the bushings were seized.


Today I have a faint but consistent vibration when going through the gears from 20-35 mph.

Also, when I got in on the highway it made a loud, higher frequency vibration around 80 mph when I was on the gas, and it would become faint when I let off the gas. It ould do it intermittently. When I got to work I took a brief look underneath and didnt see anything awry.

I didn't run into anything strange during the install, everything seemed to go together fine.

Anyone have any ideas?
 

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Did you ask this in another forum or thread? It sounds very similar to what I recall reading recently.
The only that comes to mind is the universal joints in the rear drive shaft. Maybe they are wearing out and the new drive shaft angle could be amplifying the worn out bearings.

Otherwise, perhaps something is slightly misaligned and causing a vibration. You could double check your work, loosen the hardware and retighten just to ensure all the parts are in proper alignment.
 

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Discussion Starter #3
This is my first post on the topic.

I didn't disassemble anything on the driveline. But I'm thinking the noise i was hearing/feeling had to be the u joints or carrier bearing.

I was mostly looking to see if someone would recommend pinion shims, but i wouldnt think a small 2" lift would require that.
 

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No pinion shims. I came in to respond about my last post. I was thinking your vibration could be just the feeling of the stiffer suspension, but didn't remember if there was a sound.

The hum sound that comes/goes with power applied and removed sounds like R&P, but what you have done is done every day and no differential work is necessary.

What work did you do to the front, if any?
 

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Discussion Starter #5
It's clearly a new, pronounced vibration that has to be coming from something in the driveline. I've had u joints go bad in other vehicles and it feels exactly like that to me (the vibration seems directly proportional to the rpm of the driveshaft).

A few months ago I added a front 2.5" lift, and had it aligned. At lunch I went out and looked at the pinion angle, and it clearly has some misalignment, like 3-5 degrees.

I'm thinking what I need to do is go home and inspect all my u joints, carrier brg, and pinion bearing and see if i find excessive play.
 

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If it is your diff, then you will be the fist with that concern. :(

If universals are pretty old (miles) then it's possibly because they are wearing and noticeable with the new angle of the universals.

Good luck, keep us posted.
 

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Discussion Starter #7
I just checked pinion bearing, all u joints, carrier bearing, etc. Everything seems tight with the exception of the carrier bearing, which is rubber mounted. It's always been a bit loose so I'm not sure what to expect to see there.

However, I'm now concerned with the slip yoke going into the transmission on my driveshaft. The slip yoke appears to have about 1.5 inches of exposed shaft after the dust seal. I'm not sure if that is normal. There also appears to be a fair bit of play between the transmission output shaft and the slip yoke, not too excessive that something is clearly wrong and I think it has always been like that.
 

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This is beyond me now. I don't know about those things you've mentioned, as far as what should be considered normal.

Just odd that you have these symptoms and nobody seems to. Hopefully it's really nothing of major concern.
 

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Actually, the pinion angle may be your problem. Believe it or not pinion angle should match the transmission output angle, and there are specifications for this. If the angle is off, it can result in driveshaft vibration and premature wear. The problem with shackle lifts is that by changing the position of one end of the leaf pack you rotate the axle a couple of degrees and change the pinion angle. The correction for this is measuring the pinion angle and using proper shims, or an extra leaf as opposed to a shackle for the rear lift.
 

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They do make simple pinion angle measuring tools. I'll take a look at the shop manual and see what is specified.
 

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The shop manual states that the difference in working angles between cancelling u-joints should not be more than 0.25-1.0 degrees.
 

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Discussion Starter #12
Update.


To review. ext cab z85 2wd with approx 2 inch rear lift. expereinced vibes after lift install. Checked all u joints, carrier bearing, and pinion bearing nothing is awry.

I just installed 2 degree shims on my axle and now my pinion angle is much better aligned, although i havent measure it. It looks like 1-2 degrees. Still vibrate just as before though.

could it be that my u-joint on the rear of my front driveshaft (next to the carrier bearing) is still at a 5 degree? angle and that is what is causing my vibration?

Please help.
 

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Discussion Starter #13
I now have a pronounced whirring noise at all speeds when off the throttle, with the 2 degree shims.

Is it possible I blew my pinion bearing?
 

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Which way did you shim your axle? Tipping the pinion up is not the problem - the pinion angle needs to be the same as the angle at the transmission output.
 

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Discussion Starter #16
Pittman,

I shimmed it to towards the center bearing. I now releazid that's a no no with u joints (apparently it's ok with a center CV joint). I'll pull those shims, change the center bearing, and all 3 u joints next week and see what happens.
 

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That's right. Initially it seems to make sense that shimming the pinion up and reducing the angle should be the right thing, but that actually makes the vibration worse. The angles need to be balanced, which is why you need to measure the angles.
 

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how many miles on your truck? sounds like worn out u joints.
 
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