Kenmorth T600 straight truck, tandem axle, air ride rear, spring fronts. Air system has two leveling valves for rear system. When loaded truck rocks side to side when traveling. Is it possible these valves are ‘fighting against each other’? While its rocking, it is not like it gradually leans over than gradually comes back, it like it leans, then hits a point than quickly snaps back to level, then gradually leans the other way, then hit a point then snaps back again, rinse repeat.
Generally dual levelling valves are much more stable than the single valve setups. I have come across this issue before on another truck. Dual leveling valves but one was replaced with the wrong valve. One was more sensitive than the other, so the sensitive side dumped/filled the bags on that side much more rapidly. Swapped it out so they both matched and it was all good.
A levelling valve for each side is actually a legitimate factory option from most manufacturers. Typically found on trucks that run off pavement often. Very rare to see on a highway spec truck.
Kenworth used them on trucks early to mid 2000s and i am sure others. They were most common on the 8 bag suspensions. I removed one valve on the ones that i could not get to work right for long and ran the valve on LFD. It may have been intended to stabilize cornering but i have no idea.
Yes, this is a 2006. Actually and thankfully 90% of the fleet is pre-def, pre-regen. 100% manual transmissions. This particular truck has a 4300 gal, single compartment tank on it. So with natural rock, and surges with hauling liquids having leveling valve not working proper adds to the excitement.
Stability mostly I think. Rather than all 4 corners being equal pressures, the bags on each side are equalized. With a single valve, the truck will lean if its loaded heavy on one side. With dual valves, the heavy side will get more pressure in order to keep the frame level.
