I have a 2004 with a 5 inch skyjacker lift on it. I get a really bad vibration when I take off, and when I stop it's seems to be ok when i am at cruising speed. I was trying to narrow it down so I took out the front drive shaft and it was no better. I know this question has been on here before but i couldn't find it. please help

thanks

 

With your 5" lift you most certainly have a larger than stock "arch" in your rear leaf springs.

This "larger arch" limits the ability of the rear leaf springs to control "axle wrap", which is most likely the major contributor to the vibration you are experiencing.

Axle Wrap defined (briefly - ha!)

At standstill in gear, when you apply throttle and thus torque to the rear pinion of the rear differential, the pinion gear tries to "climb" the ring gear (which is attached by axleshaft to the wheels - wheels are at standstill, thus ring gear is at standstill).

When the pinion tries to climb the ring gear, a torque is applied to the rear axle housing and the nose of the pinion wants to move skyward or earthward.

Keep in mind the job of the rear leaf springs is 3-fold: 1. to transfer load from truck chassis to axle housing, 2. to transfer forward and rearward force from the axle housing to the truck frame (under acceleration and deceleration respectively), and 3. limit the rotation of the rear axle housing when under acceleration/deceleration as it will try to rotate or twist under torque from the pinion.

Stock springs are close to flat (very slight arch as comapred to lifted springs) and do a much better job of #3 described above. The lifted springs have poor control of the axle under torsion and thus allow greater rotation of the pinion, and thus far more "axle wrap".

Your problem can be solved by adding traction bars (axle wrap limiters) or by removing the lift. Even stock trucks such as mine have noticeable axle wrap. With a 5" lift your "wrap" under acceleration must be enormous, especially with a CTD behind it.

Try this experiment:
1. get someone to drive your truck

2. while the truck is at a standstill position yourself a safe distance from the vehicle but close enough to see the rear driveshaft yoke (where the rear driveshaft meets the rear axle housing).

3. Have the person in the truck accelerate forward while you watch the pinion of the rear axle housing. The nose of the pinion will travel "wrap", i.e. travel up-down-up-down-up-down rapidly and in-tune with the vibrations you feel while accelerating.

This is easy to do and drives the point of this discussion home.

good luck

 

Is it a longbed?
What did you use to lift the rear?


I just looked at your picture, looks like a longbed.
You need to drop the carrier bearing on your two piece diveshaft.

 

ya it's a longbed, and add a leafs we're used.

 

how much shoould the carrier bearing be dropped??

 

Go to suspensionconnection.com, tuff country makes them. I don't have a longbed so I never really looked around to see who all makes them. When I helped my buddy lift his 2003 long bed, we made some spacers ourselves, but he had 6" in the back. I want to say that we dropped it 1.5", but that was a couple of years back, so I don't exactly remember. I'll ask him.

There is also a possibility that you may have to shim your axle to rotate it a bit. I would do the carrier drop first, you need to drop it regardless, those 2 piece driveshafts always seem to vibrate with any lift.