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goochieman83

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Alright everyone, after a little bit of time and money I finally got some major issues fixed on Ol' Blue. I have a rebuilt trans, rebuilt transfer case, new 1350 rear cv shaft, removed t-case drop, and rotated and welded rear spring perches (for cv angle). Yet somehow I am still getting some vibration from the rear during very light throttle and immediately upon decelerating, it isn't anything major, just enough to make me mad. Cruising and driving with moderate to heavy throttle it is smooth as can be. The only thing I can thing of is the rear end. There is a little excess backlash but supposedly within specs for a locked 14 bolt. Any ideas?
 
I can't help directly but am curious on suggestions. I'm approaching the same boat. 2" lift with slight vibration with a t-case drop. I have a slip yoke kit in garage to install and then CV driveshaft. Can't believe I have vibration with such a mild lift but I do. Much worse with Tcase in factory location so I'm keeping my fingers crossed!

If I still have it after my work....I'll be right where you are now. Good luck!
 
Whenever you get to a point where you put the cv shaft in you can take out the t-case drop, just make sure you do it before you weld the perches to make sure the pinion angle is correct. I was glad to get rid of the rigged drop in mine.
 
goochieman83 said:
Alright everyone, after a little bit of time and money I finally got some major issues fixed on Ol' Blue. I have a rebuilt trans, rebuilt transfer case, new 1350 rear cv shaft, removed t-case drop, and rotated and welded rear spring perches (for cv angle). Yet somehow I am still getting some vibration from the rear during very light throttle and immediately upon decelerating, it isn't anything major, just enough to make me mad. Cruising and driving with moderate to heavy throttle it is smooth as can be. The only thing I can thing of is the rear end. There is a little excess backlash but supposedly within specs for a locked 14 bolt. Any ideas?
Click to expand...

Your angle could be a little off due to axle wrap. For instance, when you load the drivetrain during cruising, the axle rotates slightly, which effectively changes the pinion angle. Most people set the pinion angle a degree or two different to compensate. If it's moving excessively, you may have a suspension issue.
 
The pinion angle is slightly lower already to accommodate for the pinion rotating up during acceleration. That's why I am so stumped. Also the spring perches are 7" long to help with the axle wrap.
 
Ok so I just crawled underneath and took a look at stuff, I noticed that the t-case and pinion are not in line with each other. Just in case that doesn't make sense the pinion is offset from the t-case. There is nothing I can do about that obviously but is that normal?
 
Take a close look at your transmission cross-member mount and motor mounts, anything with a rubber/poly bushing, along with all related bolts/nuts. Actually stick a big ass pry bar somewhere in there and move the entire drivetrain around while you look at it. A rubber/poly mount, even new ones, can be totally blown out, but almost invisible to the naked eye when the truck is static. A bit of torque is all it takes to expose those. Or, have someone in the seat, cycling through the gears while you watch the mounts.

Tighten all (at least put a wrench on them) crossmember, motor mount, trans mount, leaf spring and shackle bolts, u-bolts, transmission/t-case adapter bolts, bell-housing bolts, hell, even have a look at your flexplate to converter bolts, if automatic. If it's all been apart recently, that's an even better idea. Anything you've rebuilt, changed out or repaired.

Actually drop your driveshafts to inspect your u-joints and actually pull the caps off the joints to look at the bearings and cross. Even if they are new.

The easiest answer to the pinion and tcase output not looking at each other, is a blown motor mount and/or trans mount and possibly leaf spring bushings. Or if you messed up a measurement while re-welding your perches. Worst case scenario is somthing bent.

If you've done all that stuff already, disregard of course. At that point, it's probably time to start lookin at internal parts.
 
Awesome. I checked the trans crossmember bolts (just replaced), u-joints, u bolts, shackles, and t-case to tranny bolts. Need to change the trans mount and engine mounts probably. Do the output shaft and pinion output not face each other from the factory, because I did a little browsing on the ol Internet and saw a lot of them are offset side to side slightly. Which is why I was curious if anyone else's truck was like this. Also the rear axle isn't shifted at all from rewelding the perches, so that's not it either.
 
I'm not sure the difficulty of 6.2 motor mounts. Im sure one of the 6.2 guys will chime in.

No matter what anyone says, no matter how many pictures you look at, for these trucks, there should be as straight and centered a line as possible from the crank pulley, through the t-case output, all the way back to the rear pinion. No left/right deviation, centered true and square between the frame rails. If you have that crosseyed look, then one or multiple of the following needs attention- motor mounts, tcase mounts, spring hangars, spring bushings, shackles, shackle hangars, ALL crossmembers, frame,...anything where the axles or drive train connect to the frame. Just those things can cuase vibrations....and cause you to chase false positives around till you wanna blow up your truck with 50lbs of tannerite. :haha: Pay special attention to frame rivits around crossmembers. Look at them and see if you can see that they are shifting around. It is easy to tell...just like a loose bolt.

Get those things sorted, and if you still have vibrations...you'll probably know almost instantly what it is.
 
Then I will check out the engine and trans mounts first and see how that changes things. I know the trans mount is an easy change. The transfer case had a drop and I replaced the bolts to bring it up to factory when I rotated the rear axle. It does have a 14 bolt rear and I don't know if the differential is off center from the the 10 bolt. It is just hard to believe that a rubber mount can throw it off like that, even though I believe it.
 
On my truck, I'm more or less working my way down the frame from the motor mounts back, fixing everything. I had to replace the front frame shackle hanger bushings yesterday, cause yet again I got bad parts from diy4x..not the first time with them. I built totally new engine mounts using bushed dom sleeves and 9/16's bolts. Next up is the trans cross-member, then the drive shaft carrier bearing cross-member. (crew cab dually with 2 piece rear shaft), then rear spring and shackle bushing check, and last but not least, my long rear shackles, 6" I think, do not have a crossbar between them, they lean slightly, allowing the axle to shift back and forth with weight transfer while driving. That's hard on everything...bushings, bolts, mounts, shocks, ujoints...everything. Crossbar thingy will help that, by keeping the shackles parallel to each other.

So most of this stuff is fresh in my mind. It may or may not fix your vibration, but it will make it waaay easier to diagnose stuff afterwards. Clean slate= good. :)
 
Just went out and snapped these pictures. Taken with camera directly under the d70 pinion snout. These are repairs in progress pictures. There is no trans cross-member, it is being held up by a ratchet strap and that floor jack as a fail safe. The motor mount bolts are not tightened, the carrier bearing cross-member is janky as fock and the carrier bearing itself is shot. The rear shackles/bushings/bolts need attention too, as you can tell. That all contributes to the crooked everything under there. :eek1: It'll be straight as an arrow when I'm done with it.

Either way, this is a good example of what it shouldn't look like. lol

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Mine looks near identical in offset. And I also have 6" shackles with no center brace and the diy4x flip. I will definitely check the mounts and see if I can get a positive result from that.
 
I am still slightly confused. If the axle was offset from the t-case output shaft wouldn't it make the vibrations occur at different or all speeds? Which is why I was wondering about the backlash issue. I just don't see how it only vibrates under very light throttle and when I first let off the throttle. All this stuff is very irritating.
 
Are the spring perches not wide enough? that shackle angle looks like its binding up. I recently reset my perches and ended up moving them outboard about 1.5" but my axle was under a jeep before I got it. I had to roll the pinion wayyyy down to line it up with t-case. i got it set within 0.5 of a degree but I still have a brutal vibration starting around 45 and ending around 58 mph. Seems to be a never ending chase for me but my driveshaft was home lengthened before I got it so thinking maybe its out of whack.
 
Any new progress on this? I'm chasing next to you as well. I did install a new tranny rubber mount. Is it possible to align the t-case/tranny to the rear axle slightly? Meaning, can adjustments be made at that mount to shift the engine/tranny/tcase a little left or right to align better with rear axle pinion?
 
Not that I am aware of, as far as I know with new motor and trans mounts it should be in line. Mine has decreased since the new mount, but is still slightly there upon immediate deceleration. I have checked all t-case and trans mounting bolts as well as the rear end and everything is fine. Yet it is still there. All I can think of is excess play from the Detroit in the rear or axle wrap.
 
Sounds like the pinion needs to go up a 1-1.5 degrees. Vibes on decal or light throttle would indicate the pinion needs to come up.
 
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