We're a week into a two week trip and have been having issues with the ride height valves (leveling valves) on our 4108. It was my understanding that the purpose of the leveling valves on the GM was to maintain a constant body-to-axle distance. When one side was loaded or unloaded, the valves would adjust to keep both sides of the body the same height. The manual shows a measurement taken between the top of the axle and the rubber bumpers.
1) Whenever the road is crowned or we park on a lot which slopes side to side, the bus seems to have a lower ride height on the side of the bus on the downhill side.
2) The ride height seems to want to randomly change and drop on one side, usually the curb side.
We were at US Coach this week for some routine service. While there Bill tried to get things adjusted for us but for some reason things did not cooperate. Even though both rear valves were replaced with new less than a year ago, he replaced one again since it looked like it might be the problem. After much trial and error, he got both sides to stay even after dumping the air and refilling.
Of course, things couldn't be that simple. We pulled into a campground yesterday evening. The lot had a good slope to it, and on the downhill side (curb side) the top of the tires was even with the bottom of the fenders, and on the uphill side (driver side) there was about 2" above the tires. The bus was clearly slanted way more than the pavement under it. Normal is about 3/4" of space above tires/below fenders on each side.)
We pulled into our site which slopes the other way, and for whatever reason the side that had the low ride height in the parking lot was still low. I pulled into the site with the side with the lower ride height on the uphill side of the site, so for now we're sitting level. Good for camping here a few days, but worrisome as we hit the road.
When driving on a road with a decent crown I can feel that the bus is exaggerating the slope. Oftentimes if there is a reverse crown it will exaggerate it the other direction.
Any collective wisdom out there about this? Any one able to explain what's going on and why the leveling valves seem to have a mind of their own? Any secret tips to getting things adjusted properly.
A few facts: Compressor easily brings up the bus to 120psi. Recovery is quick, so compressor appears to be working. The leveling valves both exhaust and raise the sides when the arm is moved manually. I stood in the pit with Bill and watched them work. The adjusting blocks move freely and the mounting points are solid and don't have any wiggle or slop to them.
Some play or slop in the leveling valve links? Maybe different brands of valves have more or less sensitivity to movement.
Replace the leveling valve on that side. They have a delay valve built in and they can give trouble. Check the mounting bolts first though, if they are loose it can cause the same issue.
Richard I recently replaced the right side leveler valve on my AM General transit I unhooked the linkage on the new valve with the bus level and used a hook to operate the leveler arm on the valve, when I had the bus level I reconnected the linkage, it turned out to be very little adjustment from the old valve. mine was about 6" from the top of the tires to the wheel well, seems to adjust itself to the road crown. >>>>> John.
Both leveling valves were less than a year old when this started. The rear right was just replaced again since we couldn't tell if it was acting stupid. I've got the left rear on the way just in case. I've got an appointment next week at the Interstate shop in Milwaukee for their bus guy to try to get things leveled out.
The problem with the road crown is that the leveling valves seem to accentuate the crown - if the crown slopes down to the right, the right side of the bus goes lower than the left, making the bus tilt even more than the crown would on its own. Same (but opposite) if the crown slopes to the left.
Not sure what else could be involved here, but the bus sure seems to want to roll around a lot going down the road.
Not a GM guy on other buses no free play (3/16) adjustment in the overtravel causes that on 1 or both
You want to stop the roll around? Install a rear stabilizer bar on the rear. Were standard on 4905's and optional on 4108's. Luke should have a take off from one of his parts coaches.
Quote from: luvrbus on September 26, 2018, 01:24:35 PM
Not a GM guy on other buses no free play (3/8) adjustment in the overtravel causes that on 1 or both
I think I understand what you're talking about - there should be a 3/8" dead spot/free play in the center of the adjustment?
Can you explain a bit more about this so I can explain to the guy at the shop who will be climbing under?
Thanks.
They should be adjusted where you have 3/16 of inch of free play up or down when the set height is achieved they work that way on other buses.I posted 3/8 th it should be 3/16 sorry I will correct that
The GM RTS has a built in lower left side to compensate for road crown. Don't know about other GM coaches. If you're squirrelly on the road it could be from weak sidewalls on your tires.
4108's were known for more side rocking than other models. Also, have you considered new shocks? 35 years old.
Quote from: Geoff on September 26, 2018, 03:04:13 PM
The GM RTS has a built in lower left side to compensate for road crown. Don't know about other GM coaches. If you're squirrelly on the road it could be from weak sidewalls on your tires.
We're running Firestone FS400 with an 'L' load rating. They are aired up to about 10% over the chart amount for the actual weight. Unless there is some hidden damage to the otherwise great-looking fairly-new tires I don't think that's it.
Quote from: chessie4905 on September 26, 2018, 01:30:32 PM
You want to stop the roll around? Install a rear stabilizer bar on the rear. Were standard on 4905's and optional on 4108's. Luke should have a take off from one of his parts coaches.
I have the parts book for the P8M4108A & 4905A in front of me, but I don't see a rear stabilizer bar on any of the charts. There is one shown for the front, but not the rear. Was that something the earlier models had which was discontinued? If so, would it fit the setup on a 4108A? Any more information about this?
Quote from: chessie4905 on September 26, 2018, 03:45:32 PM
4108's were known for more side rocking than other models. Also, have you considered new shocks? 35 years old.
Actually was thinking of that while starring at the undercarriage yesterday. They appear to function well, at least based on my understanding of how things should be. That said, are the shocks something that can be sourced by the shop at home in Milwaukee? Do you have a modern part number for these? Or, is this something that should be gotten through Luke?
Underneath, the rear of 4905 and 4108 are identical. It even states it was optional in service manual under rear suspension.
The fact that you were in the pit with Bill running through some test cylcles confounds me why they didn't show up then. Let's throw a couple more variables into possible leveling valve issues. From past experience on our GM 4104 (retrofitted with 4106 leveling valves) the following items can make a leveling valve work weird or for a better choice of words inconsistent. 1 - dirty or partially blocked filters. On our air input line to the leveling valves are cintered brass strainers (filters) inside a small enclosure that resembles a pregnant coupling. On some set ups there is also a filter on both sides of the leveling valve to also filter the air which returns through the leveling valve from the air beams to be exhausted. In our case we don't have the 2nd filter mentioned, instead there is a copper tube approx 2-3" soldered into the bushing threaded into the bottom of the air beams for the plumbing to attach to. This little vertcal copper tube prevents oil, debris, & in some cases water that lay in the bottom of the air beams from entering into the plumbing during air discharge of that beam. Wonder which set up you have? As Jon stated water will haunt a leveling valve but so will oil or debris. 2 - the GM "check valve" officially called the leveling "adapter" can be malfunctioning, partially. or intermittently fully clogged or constantly open. Even running fairly new or recently changed out leveling valves - unless the system environment was totally checked out prior to installing the new leveling valve - presto same problem can prop up. Hope that all makes sense.
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.
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.
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
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.
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.
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
As long as the busnut is not all worn out, the bus will run forevever... :-)
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
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..
Adjustable gas shocks were not an option with Gabriel nor Monroe when cross referencing from replacement part numbers from da book.
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
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
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.
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.
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
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.
Quote from: richard5933 on October 02, 2018, 11:28:31 AM
What did you use for manual leveling valves?
many use air seat height adjust valves
how I did mine
1 air line from each corner to the drivers seat area to a control unit
4 in from air bags and 1 out to fill the bags . so 5 air gauges
push to add air pull to let air out .
no power needed no switch no wire just air . as Tom I could adjust height at any time from the driver's seat
I wish the featherlite had this kind of system way way simpler then the H and H system
dave
Quote from: sledhead on October 02, 2018, 02:52:27 PM
how I did mine
1 air line from each corner to the drivers seat area to a control unit
4 in from air bags and 1 out to fill the bags . so 5 air gauges
push to add air pull to let air out .
no power needed no switch no wire just air . as Tom I could adjust height at any time from the driver's seat
I wish the featherlite had this kind of system way way simpler then the H and H system
dave
Interesting.
The GM uses one leveling valve in front and two in the rear. Does that mean I'd use three controls in my setup? Something about not wanting to twist the body by using four-corner lifting on the GM.
If I understand this correctly, all three of the current valves would be eliminated. The air to fill the air bags originates in the aux tank. I'd re-route that feed from the aux tank to this new control panel, and then three lines would be run - one to the front and one to each side in the rear, and these new lines would be what fills the air bags as controlled by the driver.
Where does the exhaust port run on your setup?
the exhaust is right at the valves . no stink just a slight rubber smell at times
I liked the 4 corner system as when on uneven ground it worked great .
it was easy to install other then the 1 piece air lines from each corner to the unit ( no connections ) I installed a 10 gal. air tank with a one way valve from the auxiliary air tank . the system would hold air for months
dave
The one I have has a line from front tank under driver to selector valve and line going back to origonal line that goes to leveling valve supply. The selector valve either gives highway position and operates leveling valves in normal operation or in parking or camping position, it routes air to individual air bags through 4 push-pull valves with 4 attached pressure gauges. Between each line going to each air bag there is a Bendix double check valve. The center port connects to air bag. Of the two remaining ports, one connects to output of leveling valve. The other port connects to one of the push-pull valves. There is a shuttle piston in the double check valve. If air is supplied from leveling valve, the air pushes piston and it blocks port from push-pull air supply. If air is supplied from push-pull valve, piston moves to block air supply from leveling valve. Two double check valves are used at front bags and lines are separated from left and right bags. They all four work together normally in highway position, and the left and right pairs work individually in parked or camping position.
As far as twisting body, if you are on unlevel ground, you aren't twisting body, you are making it plumb and level. The axles are doing the twisting, although twisting isn't the correct term in this case. To twist body, you need a plumb and level coach and then add significant pressure to one or opposing airbags. Why would someone do that? Due to the way our coach bodies are constructed, I think it would be hard to get any significant twist.
For under $50 dollars & two days work (with a pit) we put 12 vdc solenoids at all three valves enabling us to manual level when camping or parking. We carry blocks if its extreme but only use them a fraction of the time. Four toggle switches in the drivers cockpit for the three solenoids at the levelers & one at the aux. air tank to exhaust down to 65 psi so the levelers wont try and re-level. Other than that the entire air suspension system is as designed. We like it.
You can exhaust the air down each time as explained above, or install an additional 12v normally open solenoid between the auto leveling valve and the air bag. This cuts off the auto leveling valve. Then between the normally open solenoid and the air bags install a T to have the other two normally closed solenoids-one for adding and one for exhausting. I have that system (3) and works well. Takes all of about a minute to level the bus at campsite. Good Luck, TomC
UPDATE:
Picked up the bus today from Interstate. They've got a senior tech there with decades of experience on GM and MCI buses. He worked a day and a half on my bus. I didn't think it would take that long, after all it was just changing shocks and leveling things out. However, he knows how OCD I am about these things, and he got it right.
First, the shocks made a HUGE difference. I had no idea how worn out the old one were, but apparently they were really worn out. The bus handle dips, bumps, and curves in the road with much more stability and nearly no bouncing now. And these were just original equipment style shocks from Luke, and they were only $66/ea. Very impressed with the improvement a set of shocks can make.
The leveling issue was apparently a combination of the failed shocks and a very finicky set of valves. The extra up & down motion from the failed shocks was not allowing the leveling valves adequate time to do their job as they were constantly trying to adjust. Once the new shocks were in the tech was able to get things set correctly.
Very happy bus nut today.
Glad you resolved your issue. Congrats.
Glad to hear your shocks remedied at least a couple woes. We're really looking forward to seeing the ride difference in our bus since we're putting new shocks on.especially after reading how impressed you were with the shocks change out & your ride
Quote from: dtcerrato on 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.
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Bought ours from a truck parts store based on open-collapsed length, and load..were Monroe's .