1999 peterbilt 379 ext hood bounce wobble

Yeah me too on mine. thought about buying new rims. mine are steel so maybe not that expensive, though never priced them.

 

I would not replace gas shocks with oil ones... the stiffer the shocks the better. I am considering getting Road King shocks for my truck. I had a chance to talk with a guy who installed all 6 of Road King shocks and he was really happy with a ride quality.

 

Now we are getting some where, if you feel it in the seat and floor sitting still it is an engine vibration. The first thing to do is pull all the belts, see if you can duplicate this vibration. If its a CAT or detroit the water pumps are gear driven so it can run a long time without the belts just sitting still. A cummins ie belt drive pump but will still run a few minutes just watch the heat gauge. This will eliminate fan and hub, Alternator, tensioners etc. I have seen A/C foam in side and cause the compressor to vibrate. Keep in mind it runs when the defrost is on even in winter. Also fan the air down with belts off this will eliminate the Air Compressor, it usually vibrates worse when building air if it has trouble. If it still does it with all accessories un hooked then its definitely engine related. I have seen clutch dust build up on one side of the flywheel or not be cleaned out properly after a clutch install. From there look at balancer, see if rubber is coming out. Also are you sure it isn't a miss or flutter. The fuel preheater on CATS and Cummins behind the ECM stops up and the system will maintain pressure but not flow. Installing a vacuum gauge as close to the suction side of lift pump as possible will tell the tale, 0 is sucking air, 6 is ideal, 10 or more is a restriction.

 

You need to check your Air Ride Height it sounds like it might be set to high

 

Also check your rear rims when they were put on might not have been centered right

 

I just realized when you mention Straight Pipes, when I installed my 7" straights, I would get a drone sound inside the cab at a certain rpm. It would make the cab some what vibrate. Just a thought.

 

CWARREN379..... just wondering if you’re still around and if you ever figured out your issue?? 4 years after your last post we have the same truck, same issue, and have been through all the same parts as you. Just hoping maybe you could shed some light....

 

Did you ever figure out your issue im battling same exact issue now