How to tell if a shock is bad?

natsys · Oct 12, 2019

So I've searched and read all forums with the word "shock" in them, and I can't find a definite answer. I've been trying to find the source of a vibration in my 2011 Hino 258 LP for months. It has 24,000 original miles and the original tires. I've had the front tires balanced and checked for run out, which was within spec and the tires were oriented with the biggest part at 12:00 when reinstalled. Basically it feels like the passenger is riding up and down when travelling about 15-20 mph on a smooth highway so I strongly suspect something on the front passenger side isn't right. There's a slight squeak that can be heard from that side when the window is down and I'm travelling next to a wall or fence that increases with final drive speed--may or not be related. I took the lower front shock off and it doesn't provide much resistance-some, but not much. When extended I can lift it with one hand. When compressed it has a bit more resistance, but that seems normal. I don't think they're gas charged shocks--if they were I'd know they weren't right, but my experience with shocks and struts is limited to cars and light trucks. I haven't jacked up the front end to check for play, but the inspection station I use is pretty thorough so I think they'd flag anything that wasn't right and there are no oil leaks from the shock or the bearings. The shocks aren't that expensive so I could just throw a new set on, but I hate to start shotgunning parts in hoping to find a problem. Since the truck basically sat unused for 5 years before I bought it that's why I suspect the shocks, but they could be fine.

I'd appreciate hearing suggestions on determining a bad shock or anything else that could be causing the problem.

Turtle · Oct 12, 2019

natsys said:
There's a slight squeak that can be heard from that side when the window is down and I'm travelling next to a wall or fence that increases with final drive speed--may or not be related.

That right there points to wheel bearings or CV (or ball) joints, rather than shocks and struts. A bad ball joint can cause a squeak, and can definitely cause a vibration. It could also be a driveshaft that's out of balance (or worse, bent).

Hino123 · Oct 14, 2019

There are no Cv shafts or ball joints on Hino's. They use a straight I-Beam front axle with kingpins. If it is a conventional then it's a Meritor front axle and if it is a COE then it is all Japanese. You could have a wheel that is out of round making a hop. Swap the fronts with the rears and see if your problem goes away. If the shock is not leaking and is tight I pass them inspection wise. You can measure the temp of the shock front to back and see if the rf is getting hotter than the others. I always recommend to replace in pairs. There are a lot of other tips and how to perform them if you perform a google search as well. Good luck let us know if you find the squeak.

natsys · Aug 11, 2021

Well, it took a while, but the problem "resolved" itself....at 65 mph on Route 90 eastbound. Sounded like a grenade going off and did just about as much damage. Not even 40,000 miles on the tire and it was wearing evenly but something definitely wasn't right. Fortunately I was in the right most lane with light traffic and was able to steer the truck to the breakdown lane. $600 and 2 hours later had a new tire and was on the way home. The truck ran a lot smoother, but could still be better.

I bought the same tire for the other side and changed it out myself (homemade slide hammer style bead breaker a must!). Then we removed all the wheel weights from both front tires and installed a set of Centramatic 600-627 wheel balancers (bolt pattern is perfect, had to file just a wee bit from the pilot hub nub locations). All I can say is, Wow! What a difference! This is the ride quality I've been chasing for years. When I change the rear tires I'll add Balance Masters or Centramatics back there too.

The whole hood needs to be replaced and the bumper is bent too along with the rear fender and splash guard. The appraiser said he looked at another blowout like this previous to mine, but it rolled 3 times so all in all, I consider myself fortunate.