Curious about this feature.
What are the benefits?
When would it be used?
45 foot coaches drag the tail all over the placewith angles in and out of driveways.
Raise the rear to minimize dragging, when the angles of approach or departure are not in your favour.
Happy coaching!
Buswarrior
Pretty simple...
Can someone explain what is happening mechanically when the rear is raised and lowered?
Quote from: epretot on October 08, 2022, 05:14:27 AM
Pretty simple...
Can someone explain what is happening mechanically when the rear is raised and lowered?
U-joins change angle and shaft to transmission might slide in or out a bit. It would something anticipated in the design.
Quote from: epretot on October 08, 2022, 05:14:27 AM
Pretty simple...
Can someone explain what is happening mechanically when the rear is raised and lowered?
I'm going to guess here and make another educated guess.... An assumption if you will, and you know how I've messed that up recently. It's a pretty simple matter to have a Skinner valve get actuated and admit high pressure system air into the air bags at the rear, certainly through an inline pressure regulator, to literally override, go around, the leveling valves' air pressure settings.
This will temporarily increase the air pressure in the bags to raise the rear to whatever extra height the regulator pressure will produce. This function is also electrically interlocked with vehicle road speed so it will automatically return to proper leveling valve operation above about 15mph or so. I've driven many DL's and J's with this feature and it's very needed on many occasions when entering and leaving driveways. I usually turn it on as a matter of course when negotiating any driveway or suspect terrain feature..... just to be on the safe side. They drag on just about everything, so being able to lift the tail is a real blessing.
And, Yes, I learned that lesson the hard way Once. Once was all it took. They LIKE to get hung up on the tail. Ever notice those massive steel features on the bottom of the engine bay, those are the sacrificial scrapper "bumpers" instead of hitting something more easily damaged and costly. Plus they are used for towing when needed, thus the large through hole in them... They usually cut a decent groove in whatever pavement attempts to hang your bus up, Take That. I know MCI would say that they are strictly designed for towing, but I know I'd rather scrape those stout appendages on a nasty spot than impact the bumper or engine cradle assemblies, which like I said cost more $$$$.
There was, and still may be today, another variation of this type of Skinner air valve override for a normal bus air-ride function that comes to mind. It's usually been an extra cost option where you can dump the air pressure on the tag axle and put most of the weight on the driving axle for more traction in snow and ice situations. Sometimes this allows the breaking through of the ice down to the road surface below. I know they had this feature way back on the GM 4501 Scenicruiser's as standard equipment. Through the years, of course, lots of these little goodies got disabled or improperly repaired and then neglected, but they were built in originally and were very effective. All 'Cruisers had the air toggle valve for Traction (I do forget the actual wording) on the side panel under the window. I know mine did, even though it no longer worked. Plus being in SoCal I really didn't need it.
MCI has the same feature available as an option, as well as an option to actually RAISE the tag axle off the ground enough to secure it in place with a mechanical steel loop resembling a large chain link. There are actual steel hooks welded into the wheel wells for the tags, and may be on all MCI's weather they have the tag lift or not. I can't remember for sure, but that's my sense, and I've wondered through the years what they were for, until I found one that had the tag lift feature, then the hooks made sense. Otherwise you had to jack the tags up and secure them with the chain link on the hooks. Serious Snow country stuff I really never get into living here, thanks but tire chains are usually the extent of it here.
The MC7's had lots of cool valves everywhere for nice little extra air system features. Unfortunately they did all tend to create maintenance headaches. Anybody remember all the belt tensioning air cylinders used in the 5's and 7's?? Nice features to facilitate belt replacements, but boy did they leak and cause other problems so they were eventually eliminated and simplified to what was in place later. Simple turnbuckle adjustments that worked just as well. Early MCI's couldn't hold air after engine shutdown for more than a couple hours at best, due to all the auxiliary air system goodies designed in. Boy did they leak down fast.
I hope this is what you were asking about, but if not.... Nevermind. It was a good explanation anyway for general knowledge for anybody who might care, and I got kinda carried away.
I'm glad you did. Now here is my question. When the rear raise is enabled, what keeps the leveling valves from bleeding off air?
The reason I ask is that I'm seeking a way to bleed down all of the rear suspension to the bump stops when parked before using mechanical leveling jacks. It means the jacks don't have to travel as far and the first step up front is lower. I'm already using the Kneel function to lower the front.
I'd just as soon isolate the air bags from the tanks to keep the rest of the system pressurized if it isn't hard to do, but also I don't think venting the tanks will drop the air bags.
No point in me adding solenoid valves if there is already something in the system that will do the job.
Jim
I had manual overide valves (3 solenoid air valves per corner). Normally would run down the road on the automatic leveling valve. Then especially when parking at a campsite I used the manual setting to level the bus that took less than a minute. And in the event of a automatic leveling valve failure, could still go down the road on the manual setting. Good Luck, TomC