ProComp 6” lift 35BFG’s vibration at 47mph HELP!

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Hutchinson

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1996 white Z71 4x4 totally restored from frame out, HT383e, 0411pcm swap, helical locker rear, FLT built trans, long tube headers, etc, etc, etc,.....problem I’m having - 6” ProComp lift with 35x12.50x15 BFG All Terrains K2 on ProComp rims - I have a medium vibration on floor, and in seat of pants, at dead on 47mph (passenger seat shakes too) that’s driving me slap *ss nuts. Been this way since I restored it little over a year ago.

Don’t have any vibrations before this speed,....and, as soon as I hit 50mph, it’s smooth as glass. Had tires balanced 3 times (even road force balanced em),..,even went and bought those Centramatic balancing rings (the ones the SemiTruckers use), and still it’s there. Been investigating pinion angle, but, don’t see anyone on net that has this problem on a ProComp 6” lift. Even tried cruising down a long hill, at 47mph and bumping it into neutral,...no change.

Rear axle was fully rebuilt, with all Yukon shafts, R&P, Detroit Helical locker, etc,....so don’t know if it’s within the axle rebuild, or what.

Bad thing is, when I restored it, I changed everything on the entire truck at same time (took me 6 months), so vibration could be coming from many things.

Just a shame, I spent all this money $26K/ time restoring everything, and now dealing with an annoying/ persistent vibration. Other than that, it’s a blast to drive. Runs like a ***** ape when I jump on it. I still ain’t put my foot to the floor in it yet,.....it’s plenty quick enough at 5/8 throttle.

Anyone had this issue before/ heard of it/ know where to start/ how to fix?.......
 

b454rat

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New u-joints? Could be the angle is off some. Try a small shim, or maybe even shimming the t-case down. Sounds like something simple.
 

Hutchinson

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I was kinda thinking those angled rear axle lift blocks ProComp provides in there kit is throwing my trans to pinion angle outside tolerance. I understand if they don’t match within 2 degrees, it could cause driveshaft vibration,......but, don’t know.

I looked at changing the tapered rear blocks with flat ones, then getting a double caradin driveshaft made,.... but, don’t want to spend all that coin, and it not fix the problem. Anyone know of any checks I can do to rule that one out?
 

Hipster

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Try flipping the orientation of the u-joint 180 in the rear end yoke. Sometimes this can create/eliminate a slight vibration.

If it's pinion angle problem you can buy 1-4 degree tapered shims for the perches.

Double check the trans mount make sure it hasn't separated and it just sitting there.

What yoke was used on the rear? oem? Some replacements have been known to has some runout.
 
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Hutchinson

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Thanks B454rat and Hipster. Will do both,....good idea, I’ll go ahead and flip the drive shaft 180, can’t hurt..... I might have missed re-installing it on the marks I made, from when I originally took it apart (several beers were annihilated, over 6 months, between those activities). I put a new Yukon ring and pinion in, along with a Detroit Helical locker, so don’t know if this could be an issue,.... is there a way to check it out/ some YouTube University vid I can check out? Thanks to whoever came up with YouTube,.....teaches dumb *sses like me a lot.

When I redid suspension, I put all new urethane bushings everywhere,...including urethane motor and trans mounts.

Might go ahead and get some flat blocks, instead of tapered (as supplied by ProComp) for the rear axle,....but, then my u-joints might bind/ driveshaft (at slip joint on Transmission) may end up being shorter than comfort,....yeah, I’ve had a couple beers tonight.

Nice lookin truck Hipster.
 

Hutchinson

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You only had vibrations at circa 47mph? I did put a new torque converter in when I installed the new FLT trans. How can I check if it’s the TC without dropping the trans?

I gotta wait till the weekend to do what you guys suggested above. I work construction, so I work 5-12’s,....don’t leave much time during the week to get *hit done.
 

Hobie

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Had the same issue and it ended up being the torque converter.
I could see it being the torque converter if it only done it while in gear. Since the OP said it still vibrates while in neutral it's got to be something in the driveline (axle to transfer case) or a suspension related component. Now my truck shakes like a pig at 71mph because my u-bolt brackets on my rear axle are bending. (Looking to replace them soon lol) but if I were the OP I would recheck every bolt that holds the suspension together, check, and then recheck all engine/trans mount bolts, and then measure the driveline angles. That will give you a good view to narrow down things that may be the issue
 

GreenZ98

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I could see it being the torque converter if it only done it while in gear. Since the OP said it still vibrates while in neutral it's got to be something in the driveline (axle to transfer case) or a suspension related component. Now my truck shakes like a pig at 71mph because my u-bolt brackets on my rear axle are bending. (Looking to replace them soon lol) but if I were the OP I would recheck every bolt that holds the suspension together, check, and then recheck all engine/trans mount bolts, and then measure the driveline angles. That will give you a good view to narrow down things that may be the issue
Yep bad reading on my part, didnt even see the putting it in neutral part of it.
 

Hutchinson

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Agree guys, good suggestions,....time to roll up the sleeves. I replaced all the rubber bushing with urethane (suspension, trans, and motor) - everything from frame out was taken off, painted and reinstalled with everything new. Reckon I need to go through and check it all again.
 
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