Vibrations

[Ronw435]

Well took the truck on a 200 mile trip. I am still getting a pulsing vibration that is most pronounced at about 60. You can feel it in your seat as well as the steering wheel. It is not constant but is about a 2 second pulse then 2 second off then 2 second on.....etc.
Any ideas?

[cg285]

. alignment never causes a vibration
. worn suspension components don't cause vibration
. vibration from a transmission is not likely (converter/clutch issues are engine related and go away when in neutral at speed)
. verify if it is truly a rotating vibration vs something like a bad mount where there is no isolation from the frame/crossmembers

makeup a fixed pointer and position it by each wheel, rotate the wheel and check for run out at the bead (not the edge of the wheel). shouldn't have more than about .060 +-. if you do take the wheel off and check the axle the same way and verify axle or wheel.

if it were i, i would support it on 4 jack stands and mimic the action while feeling for the vibration but do not try that at home. that method would be only for trained professionals on a closed course.

[Ronw435]

I was wondering if my exhaust pipes could be transferring the vibrations from the engine. The engine seems to be running fine, but the rubber in the mounts for the exhaust system seem pretty hard. Its a 2" stainless system with two glass packs. Was thinking of removing the mounts and get some that hang with the heavy strap. The ones I have not are welded to the exhaust with a rod going through the rubber that is bolted to the frame.

[Keith Seymore]

Originally Posted by Ronw435

Well took the truck on a 200 mile trip. I am still getting a pulsing vibration that is most pronounced at about 60. You can feel it in your seat as well as the steering wheel. It is not constant but is about a 2 second pulse then 2 second off then 2 second on.....etc.
Any ideas?

Go back to the chart and start over.

Also (discussion regarding "oscillating" disturbances):

Originally Posted by Keith Seymore

In the biz, a "pulsating vibe" is called a "boom/beat".

It results from two disturbances, very close in frequency but slightly out of phase, such that the amplitudes gradually add and subtract over time. That's what results in the pulsating effect. The closer the two frequencies are the slower the boom/beat.

At any rate - it means you have two disturbances going on, like 4th order engine firing being very close to second order driveline, for example.

Fix either one of the disturbances (or dramatically change the frequency of one) and the pulsating effect will go away.

Originally Posted by Keith Seymore

Driveline imbalance is a "first order" of propshaft rotation disturbance (one "kick" per rev). U joints are a "second order" of shaft rotation (two "kicks" per rev).

Imbalance by itself usually results in a cabin "boom" (low frequency sound; almost more like a pressure that you sense) or a vibration that you feel, and normally is pretty steady. Large cabin volumes, like a crew or a Suburban, definitely are more sensitive to this. The boom/beat, or the phasing in-and-out, is a result of the driveline finding some other disturbance that is close to it in frequency.