Volvo air ride height leveling valve question

My truck is a ‘15 VNL 630 with the Meritor MT40 rear axles and Volvo air suspension. Front axle is spring ride. I’ve had the truck since brand new and it’s sitting on 421k miles now. My problem is this thing has started riding EXTREMELY rough down the road especially on anything that looks like Indiana’s abandoned highways! I don’t mean like spill a single drop of coffee if I sit my cup on the dash and hit a ditch line. No no.... I’m talking about “punching out a new sunroof with my head and then getting ejected back to the bunk” kind of rough! I just changed all 8 shocks including the little cab shocks, put 10 new Bridgestone tires all the way around, 3-axle alignment, and centramatic wheel balancers on all 6 axle ends. This did help the problem quite a bit but still nowhere near what it used to be. It bucks, bounces, and shakes so much it sounds like the dash is gonna fall in my lap. It has knocked my cabinet doors off before.

The truck used to hold 120 psi for 2 weeks easy. Now it’ll go down to about 60 psi in 30 minutes and all the air bags deflate too when the pressure drops. Does this sound like a bad ride height leveling valve? The actual ride height is pretty close by my calculations, so I will adjust that to spec, but it seems to me like there is a lot more air in the 2 bags on the rear drive axle than there is on the front drive axle. I’ve heard this “mismatched” or “uneven” air pressures on front/rear axles will cause the exact same symptoms I’ve having. Does anybody have any experience with this or maybe some other advice I could try? I gotta get this thing fixed. It bounces my hood & headlights so bad, I’m constantly getting hi-beamed all night long and can’t take it anymore! Thanks

 

The leveling valve actually looks like it is pointing up just a fuzz, in relation to the top of the frame rail. I don’t understand why all 4 air bags are deflating as the truck’s air pressure drops. Isn’t the suspension system supposed to have a check valve in-line somewhere to keep it from doing this if truck looses air? I’m pretty sure my main air leak is the range splitter air line “quick-connect” on top of transmission so I’ll get that taken care of today. I remeasured ride height and came up with 6.50 - 6.75” on the front drive and 7.25” on the rear.

 

Is this supposed to be the factory ride height setting? I have the bigger 300mm frame and I thought it was around 7 but I don’t really know for sure

 

Ding, ding, ding... I think I found the issue! I installed new Monroe shocks all the way around, as well as the Centramatics. Ran through the entire suspension piece-by-piece and thoroughly inspected everything. I did all this and never really thought about the 5th wheel position at all because when I originally weighed the loaded truck/trailer out & set it up, I slid it up almost all the way (2 notches from top towards the cab) because this put me in the “middle” range of both steer and drive axle weights. In other words, not too much up front & not too much out back (11,300 / 32,700) I’m always loaded to 80,000 lbs with the same type of trailer & liquid cargo so it always stays the same. Well just for kicks I slid 5th wheel all the way back as far as it would go and scaled out. Ended up with 10,040 lbs on the steer axle & 33,960 on the drives. Bingo! There was probably a 70% improvement in ride quality right there just with a simple 5th wheel position adjustment. Even if it’s a little on the heavy side out back, my kidneys say oh well!! It’s just amazing that such a relatively small adjustment can make so much difference in the ride & handling of the truck.

I did a little more investigating and found that the chassis manufacturer (Cheetah) uses el-cheapo tires on all their new trailers with no balancers of any kind. Dana, the company who leases these chassis trailers to our shipper, uses even more of an el-cheapo Chinese no-name replacement tire when the originals blow out or cup real bad. Again, God forbid Dana fork out $400 on a couple sets of balancers but that’s outta my hands. I’m willing to bet if I could get a good set of American tires and some Centramatics to go along with ‘em.... that 70% improvement would go up to 90-100%

Thanks everybody for all your help & suggestions, my truck & I both appreciate it!