Vibration help

[paintfumes]

So the new van has a vibration between 62-70ish. Doesn't do it at all above or below those speeds. Only vibrates on throttle and completely goes away if I throw it in neutral. So that rules out wheels/tires. I feel it more through my feet then the steering wheel, but I can feel it in the wheel some.

Got under the van and tried to feel for play in the driveshafts and cv's, nothing seemed sloppy there. Only place I have any movement is the lower transfer case mount seems to allow the transfer case to move a little. Is that normal?

Where should I start in diagnosing and fixing this?

Van runs and drives great other then this.


Thanks

[photo_van]

the new one with the lift eh? If it has lift shackles in the rear, I'm going with incorrect pinion angle.

[paintfumes]

That's the one unfortunately. Where can I find good instructions on measuring the pinion angle? From what the p.o. told me it's an overland 4" lift.

[photo_van]

I think the overland kit uses new springs and lift shackles.

I'm not sure how to measure it, maybe there are others on here that can help. I know that you want to keep the pinion in the same plane as stock. So if the rear of the leaf spring is lowered 1 inch then the front should be too. OR you can use pinion correction shims between the axle and the leaf. To use the shims you need to know the degree of correction needed.

I know many use the shackles w/o an issue, but I have read where some have vibration.

The easiest way to isolate the problem may be to temporarily move the leaf back into a stock shackle hight and see if the vibration goes away. Check and see what hole they are currently mounted in and if you can, shorten them.

[Stroverlander]

Discussed this on another forum when chasing vibration in that mph range and came across this TSB in the factory service manual that I thought was interesting.

It's related to vibration at 60-65 mph resulting from an engine firing harmonic at torque converter lockup. It is sort of a moot point though since the leaf spring and rear diff damper kits are NLA but good to know that it may not be as serious as a driveline related vibe.

Can read more about it here: http://www.brakeandfrontend.com/Article ... parts.aspx

Rolling Boom Noise Inside Vehicle (Install Pinion Nose Damper and/or New Rear Leaf Spring Dampers) #00-03-09-001B - (Oct 19, 2004)

Rolling Boom Noise Inside Vehicle (Install Pinion Nose Damper and/or New Rear Leaf Spring Dampers)
1995-2005 Chevrolet Astro Van Models

1995-2005 GMC Safari Van Models

This bulletin is being revised to add the 2005 model year, change a nut part number within the spring damper kit and change a quantity in the Parts Information. Please discard Corporate Bulletin Number 00-03-09-001A (Section 03 - Suspension).

Condition

Some owners may comment about a "boom" noise inside the vehicle while driving at speeds ranging between 97-105 km/h (60-65 mph). This condition is most noticeable from behind the driver's seat.

Cause

The condition may result from an engine-firing harmonic, which becomes noticeable at torque converter clutch (TCC) lock-up.

Correction

A new rear leaf spring damper kit (containing two dampers , one per spring) has been developed, to be used in conjunction with a pinion nose damper tuned to 86 Hertz (Hz), to reduce the resultant noise level.

AFFECTED VEHICLES MAY REQUIRE THE INSTALLATION OF THE PINION NOSE DAMPER, THE SPRING DAMPERS, OR BOTH. THE INSTALLATION OF EITHER OF THESE DAMPERS IS AT THE DISCRETION OF THE TECHNICIAN FOR BEST RESULTS. Use the following procedures and the appropriate part number listed below.

Important: Installation of these dampers will not totally eliminate the boom noise. The boom noise may only be reduced to a more acceptable level. There may be other boom noises, such as body or exhaust, associated with the vehicle and this fix may either diminish or enhance the noise. These other noises should be addressed prior to the correction for the TCC boom dampener being installed.

[doyoulikeithere]

I think the exhaust pipes can be a pretty good source of vibrations.

[paintfumes]

Thanks guys. Going to start with measuring the pinion angle this weekend and go from there.

[Stroverlander]

Generally, if you're running the Airbagit/OLV shackles in 1" lift position, 2° pinion shims and if in 2" lift position 4° pinion shims should work.

I had a rumble at 30-35 mph with 2" shackle lift an no shims which 4° shims cured and still have vibration at/around 60 mph.

[LiftedAWDAstro]

I chased the same vibration at around 60-65 mph for a while in the 98 when it was lifted 4-5". Ended up replacing the transfer case tail housing bushing and seal. My pinion angles were within 1/2 degree.

The transfer case will move a fair amount at the rubber mount.