Loud Clunk from chassis when dumping air bags

[Bill Lampkin]

I was just wondering if there is a rubber bump stop(s) to prevent the clunk.

[Bill Lampkin]

Well, Lots of stops to choose from, now, where to put them?

https://www.suspension.com/universal-bump-stops.asp

[Joel Ashley]

I don’t get under the rig that often and can’t remember that specific arrangement, but I’m sure there are substantive guards in place to prevent “bottoming out” too hard between body frame and chassis, just as with any vehicle.  The “thunk” I don’t believe involves the bumpers... it’s too much like something catching and releasing against another component.  Others here with more chassis systems experience might have ideas.  If I were in the proximity of Henderson’s in Grants Pass I’d have them advise.  In my mind Bob Henderson and his team are the best regarding Motorcoach chassis’.

Joel

[Bill Lampkin]

I get a loud clunk sound when I dump the air bags prior to leveling. Happens at the end of travel, as there is no more suspension movement after the clunk. Are there some bump stops on the chassis somewhere to prevent the air bags from bottoming out?

I hijacked another thread to ask this question (apologies) and reposted here.

[Bob Stone]

Sometimes it's the simple things that are overlooked. Is it possible it's just the rock guard/mud flap getting out of the way as the coach settles? Just a thought...

[Bill Lampkin]

Coach doesn't drop far enough to have the Beaver Tail hit the ground, on level ground anyway. So that's not it. Keep thinking!

[Eric Maclean]

 Bill
You probably won't find any bump stops on the chassis you can look up the air bag specs most air bags have a rubber bump stop built inside them.
As for the cluck it's hard to find that type of noise as you have to be under the coach to locate the noise and of coarse you don't want be under there when the air is released unless your on a wheel off or Inna service pit.

A couple of things to check would be first look for interference between suspension axles and frame part this sometimes happens if the vehicle is settled on uneven ground this is usually evidenced by scratch marks or wear .
 Second check the torque rods for rusted or seized ends as they will torque up and cluck when they release as the vehicle settles.
Also shocks can create that type of noise with tight bushings.
Sometimes the air bags can clunk as they flex but that's usually on reinflation.
The only way to know for sure is to actually be under the coach and witness the noise .
Hope some of this helps
Eric

[Mike Shumack]

I get a loud clunk sound when I dump the air bags prior to leveling. Happens at the end of travel, as there is no more suspension movement after the clunk. Are there some bump stops on the chassis somewhere to prevent the air bags from bottoming out?

The air bags have a "bump stop" built in. 

I also heard that creaking and banging as my Coach airs down. I sprayed all the suspension bushings and greased the drive shaft slip yoke and that seemed to quite it down a lot.
I think most of the noise is just due to the "tens of thousands of pounds" of house moving "down" on the suspension as the air bags deflate.

[Eric Maclean]

Mike makes a good point it is very important that the sliding plunge joint on the drive shaft has to be free to travel if for some reason it seized up and can't slide the result is damage to the transmission tail shaft and or differential pinion bearings.
Eric

[Bill Lampkin]

Why would the clunk sound have anything to do with the drive train? Isn't the entire drive train supported by the chassis? Not trying to be argumentative, just scratchin' my head.
If we can get out on the road this summer, I may have Source Engineering in Eugene Or take a look at it. Thanks guys!

[Eric Maclean]

Bill
the drive shaft extends from the transmission which is mounted in the frame as you suggested but the other end of the drive shaft is connected to the rear differential which moves independently from the frame with the suspension .
Each time the vehicle rides up or down over a bump the suspension absorbed the bumps and the slip or plunge joint has to allow the drive shaft to length or shorten as the distance between the transmission and differential changes.if the drive shaft slip joint were to seize and not slide in and out as the vehicle trave!ed over bumps the rear suspension frame would try to move forward and backwards as the drive shaft traveled up and down through an ark this would result in stress on the suspension torque arms as well as the transmission tail shaft , differential pinion bearings motor and transmission mounts any of which could create the clunk you hear.
When the air is released from the air bags the suspension settles farther than its usual travel and the sliding plunge joint in the drive shaft is worked beyond it usual travel .
This is only one possibility
I believe the most likely cause for your clunk is one of more of the rear torque rods has dried out and its bushing(s) are torqueing up and releasing as the vehicle settles .The first thing I would do is access the rear torque rod bushings and spray then with a penetration oil then work the suspension up and down to see if your noise changes it may take several applications to free them up,
Hope this help
Eric

[Eric Maclean]

Bill
I just thought of a couple of other things to check.
There is a torque rod which runs from the differential over to the frame known as a track bar which keeps the rear axle from moving sideway out from under the frame .
This track rod  has on some of  Magnum chassis either broken it's attaching bracket pulled free of the differential or cracked and broken the frame rails where it attaches.
A crack in the frame on the passenger side frame above the rear axle can be witnessed if this is the case the crack could also cause a noise when it is flexed.
Not all that common but its worth checking.
Eric

[Carl Boger]

Hopefully you don't have a cracked frame at the strut rod, but if you do here is what it looks like, both before and after the fix.  It is hard to see with the tires on.  Mine was only found when I was changing tires, even then it wasn't obvious at a casual glance.

[Bill Lampkin]

Carl, Don't scare me like that!!

Happy New Year!

[Carl Boger]

Didn't mean to scare you just wanted you to know where to look.  Actually it isn't that bad to fix, just hard to find. Happy New Year!