HELP: Violent Vibration off the line on lifted rig

[minelson17]

Hello All,

I get a bad vibration from the rear end when I'm first getting off the line and I'm not sure what the cause is or how to go about curing it. Till now I've just been babying the rig out of first gear to let it get rolling before giving it much gas. The vibration is especially bad on a steep grade. I don't have any issues shifting up or down from any other gear, or vibrations at high speeds..etc.

Relevant Rig Configuration:

- Rear Suspension Lift is aftermarket 4" lift Rear leaf-springs + a SOA conversion creating a little more than 9" of lift in the rear.
- Extended Rear Drive Shaft to account for extra lift
- 4.88 Yukon Gears
- Dana Spicer Trac-lok LSD
- M5OD-R1 Manual Transmission
- 35" BFG KM2s

Like I said, if I baby it off the line, it's not as bad, but it's still there. I've also found that if I hammer on the gas and dump the clutch (like if I were trying to drag race) it's not as noticable...or maybe just shorter because I get up to speed quicker. The drive shaft is balanced, the u joints are good and have been recently replaced. Ring and Pinion were also recently replaced (due to an issue most likely caused by this vibration).

Is it possible that my angle is too extreme? It seems to me I've seen plenty of rigs with much more extreme angles with 0 issues.

Could I perhaps be experiencing axle wrap? Wouldn't think I had enough torque for that to be happening.

Or maybe the rig is underpowered for the size of tires I'm running? Got the ol' 4.0 OHV that is getting up there in miles...

Any help or guidance would be appreciated!

 

[Rick]

Are the Ujoints new?

Do you have enough slip yoke engagement?

 

[minelson17]

The U-Joints aren't brand new, but certainly not that old. I just had the rear end worked on (Pinion was slipping/slipped out of the Ring when coasting which chewed up the teeth) and they told me they (u joints and drive shaft) were good. The shop told me the reason it slipped out was caused by a seal going bad and possibly not having gear oil with an anti-friction agent put in when I last changed out the diff oil. This (the vibration) is something I've been living with since we installed the lift over a year ago, so it wasn't anything the shop did or didn't do.

To be honest, not sure how to check if I have enough slip yoke engagement....:scratch:

 

[Flip4ford]

Could be clutch shudder? Since it is only @ take off. Pinion angle ect is a vibration at different speeds.

 

[minelson17]

That was kind of what I was thinking....if it was an issue with the angle, that I'd experience it elsewhere other than from a dead stop.

From what I've read, the clutch shudder issue is caused from some sort of problem with the flywheel and/or pressure plate. This perhaps could be my problem. The clutch has been due an overhaul for some time....and shifting into 1st and 2nd aren't as smooth as they used to be.

I just wanted to make sure this didn't sound like something else other than the clutch.

 

[adamsbro2]

Just a thought cause I just found it bad on mine doing similar things, but look over your trans mount really good. Mine looks fine at a quick glance but get under the truck and try to push the transfer up toward the floor with your feet. If it moves the rubber is probably gone like on mine!

 

[minelson17]

Thanks will do. I'm going to get under there this weekend and give everything a good hard look...see if there is anything out of the ordinary.