GM Leveling Valve Question

richard5933 · September 27, 2018, 04:22:29 AM

Quote from: Lin on September 26, 2018, 10:12:52 PM
I have seen it recommended to adjust the ride height valve linkage by measuring the bus chassis to the ground. I find it easier to balance everything by measuring the extension of the air bags when on level ground. I think that my 5a is about right at 7 inches of bag extension. I may be off since I have not checked it in a while. I wonder if all of your bags would have the same extension on level ground. If not, you could adjust the linkage accordingly.

Our original ride height linkage had too much play because the grommets on both sides had rotted out.

We thought of that. When we finally got the bus at the right height the air bags did measure the same left and right. There is a specific measurement distance and measurement point listed in the manual for this bus. It is between the rubber bumper on the body and the flat spot it hits on the top of the axle housing. That's what we were working with. When that measurement was correct, the body was also correct so no suspicion of a twisted body or anything.

The left valve was replaced shortly after I drove the bus home. Prior to that it had sat for a while, so perhaps not all the debris worked itself through the system, causing the newly installed valve to get buggered up with particles of some type.

I'll have the shop install the new valve on the left before attempting to reset things.

buswarrior · September 27, 2018, 05:42:21 AM

Hang on...

These are not really "levelling valves"....

Some of the story describes exactly what the coach should be doing. The valves maintain the distance from body to axle under changing load conditions, necessary evil with an air suspension that in stock service was exposed to a weight change of almost 50% ...

So if the axle is on an angle, so will the coach body...

Airing up quickly in an old coach makes me suspicious that the original air volume is missing, either bypassed, replaced with smaller, or full of solid crud or liquid crud.

Faulty Busnuts are famous for just bypassing a leaking tank, and since the coach still "works" down the road they go... replacing blown lines and parts with the wrong sizes.... suspension not going to react well without proper air supply. The trouble could be several steps back from the problem.

Remove fitting to levelling valve, and let the wind blow through, observing for strong, sustained wind and the passage of crud. Anything comes thru, best to start working all the way back thru the system, find and eliminate the source.

Always wear eye protection....

happy coaching!
buswarrior

chessie4905 · September 28, 2018, 04:22:23 AM

Very little chance you are getting "crud" from air to leveling valve. You don't have air beams and air comes from air tank under driver's,, which comes from main dry tank, then main wet tank. Couple things you could do. One is to put level onside of coach to make sure it is plumb when valves are adjusted. Tweak setting as necessary. You could tilt the plumb setting slightly for crown on road, maybe one or two degrees, just enough that no lean is noticeable on level road. Then you could raise rear clearance setting maybe an inch or so, which would stiffen rear bags some to help counteract rocking, at least till you add rear sway bar. I wouldn't go much over an inch or you might experience some drive line vibration issues. Not sure how much raise would cause any issue, if any.. You need to figure how to mess with the settings yourself with proper blocking, till they suit or the guy doing it has the time to do it.

richard5933 · September 28, 2018, 05:50:20 PM

Quote from: buswarrior on September 27, 2018, 05:42:21 AM
Hang on...

These are not really "levelling valves"....

So if the axle is on an angle, so will the coach body...

Airing up quickly in an old coach makes me suspicious that the original air volume is missing, either bypassed, replaced with smaller, or full of solid crud or liquid crud.

Faulty Busnuts are famous for just bypassing a leaking tank, and since the coach still "works" down the road they go...

happy coaching!
buswarrior

I would be happy if the body of bus stayed parallel to the axle. That would be great and what we're aiming for.

Air tanks and lines are, as far as can be assessed, are OEM and in good condition. Bill pulled the lines from the valves to confirm flow.

Right now, the working theory is either a faulty left rear valve, or shocks. Actually, my hunch is that the shocks are allowing far too much bouncing and side to side rolling, which in turn is causing the valves to have a caniption fit.

When backing into a site today which was rough and had some bumps at the front, my co-pilot (who was behind the bus guiding me in) commented on how bouncy the bus was. For my co-pilot to notice means things are really really bouncy. Now that I think about the past few trips, things have gotten worse.

New shocks were shipped yesterday and will be installed before height valves are touched.

buswarrior · September 29, 2018, 06:22:08 AM

Systems, if one darned piece... and then the layered failure, fix one, more to go...

When an old bus is worn out...

It's ALL worn out...

Not unlike a busnut?

The busnut ends up all worn out by the end of it...

Happy coaching!
Buswarrior

dtcerrato · September 29, 2018, 09:04:48 AM

As long as the busnut is not all worn out, the bus will run forevever... :-)

luvrbus · September 29, 2018, 09:40:10 AM

Since GM uses double action shocks I would have bought Monroe double action gas adjustable shocks and move into the 21th century oil filled shocks are a thing of the past and IMO a waste of time and money

gg04 · September 29, 2018, 09:53:59 AM

Had about the same problem when we first built this bus. Threw out all the ride height valves, added four air seat valves, gauges and new airline to each corner. No more problem. If on the super slab actually drop the ride height to put my front air dam 3" off the surface. Plus you can adjust for crown. Don't have load
of freight or passengers coming on or off at every stop so why ride height valves???
Works for me..

dtcerrato · September 29, 2018, 11:06:19 AM

Adjustable gas shocks were not an option with Gabriel nor Monroe when cross referencing from replacement part numbers from da book.

luvrbus · September 29, 2018, 11:28:55 AM

Hum I better check my records back a few years because I installed a set on a 4106 or a 4905 can't remember which,they weren't that expensive under 50 bucks each

buswarrior · September 29, 2018, 12:20:23 PM

The parts book cross reference typically offers up the same old current replacement, not other options that will fit.

Upgrades require a knowledgeable person working the reference books.

Luvrbus, please find your part numbers for these, I'm sure lots of GM owners would love to upgrade!!

Happy coaching!
Buswarrior

richard5933 · September 29, 2018, 04:50:19 PM

Quote from: chessie4905 on September 26, 2018, 07:17:15 PM
Underneath, the rear of 4905 and 4108 are identical. It even states it was optional in service manual under rear suspension.

Found the entry in the service manual. Went out and checked the rear suspension of our 4108, and it seems that adding a stabilizing bar wouldn't be that easy. From what I see in the book, the stabilizing bar mounts to the radius rod brackets through a flange with holes for bolts. Looks like we'd have to change out the radius rod brackets before being able to mount a stabilizing bar, so that we had compatible brackets. This is starting to sound like more of a job than I want to do right now. Unless I'm totally missing something here, which wouldn't be the first time.

Regarding shocks, the price was about $66/ea for OEM style shocks. That's what we're going with for now. If necessary we can change later on.

chessie4905 · September 30, 2018, 10:11:32 AM

I went down to the pit and rechecked my rear bar. Changing the rod mounts that has thru bolts that connect the struts, not that big of a deal. The piece that the upper end of the links attach to is welded to rear air bag risers. Check if yours has this mounting hole. It would be crosswise hole on a mounting bracket welded to the upright piller that attaches to bottom of rear rear airbags. If yours didnt come with that bracket, then the whole lower beam under airbags would need exchanged also. Either way not a job for you. Check if Luke has a donor coach he can rob these parts off of and what'll cost with or without the upper brackets on yours. Check yours first. Definitely worth the expense on getting the bar.
On a side note, the manual lists a radius rod lateral bar for the rear as optional equipment. Don't know anything about this option and what benefit it would be.

TomC · October 01, 2018, 07:24:10 AM

Add manual leveling valves controlled from the driver's seat. I have three, and leveling the bus takes all of about one minute. Especially when parked at the curb of a high crown road-can be steep enough where you can't open the door. Leveling the bus solves this. Good Luck, TomC

richard5933 · October 02, 2018, 11:28:31 AM

Quote from: TomC on October 01, 2018, 07:24:10 AM
Add manual leveling valves controlled from the driver's seat. I have three, and leveling the bus takes all of about one minute. Especially when parked at the curb of a high crown road-can be steep enough where you can't open the door. Leveling the bus solves this. Good Luck, TomC

What did you use for manual leveling valves? How difficult was it to run the air lines to the driver's seat? Any photos you could post of how you made this work? This might be a project for next year, as I don't see us changing the weight distribution more than a hundred pounds here or there.

Quote from: chessie4905 on September 30, 2018, 10:11:32 AM
The piece that the upper end of the links attach to is welded to rear air bag risers. Check if yours has this mounting hole. ...

Checked ours, and it's definitely NOT set up for the stabilizer bar right now. I'm going to wait and see how the new shocks change things. Hopefully they will take out enough of the problem that we can continue on as is for now. I'd like to add a stabilizer bar at some point, but right now there is not money to pull out a rear suspension which is in relatively great shape. If it needed major work anyway I'd pursue it now, but the way things are it'll have to wait.