tag pressure

[busshawg]

Sorry about all the tag axle questions. Any hoo here we go again. I have been through the achives but am not completely happy with the info. I want to increase the air pressure in the air bags on my tag. How EXACTLY does one do this. There was mention in the achives that I would have to decrease the ride heighth on my drives and therefore I'd have to do the same with my steering to keep the ride heigth even. There was also mentioned to control it by how far one would turn the valves in the passenger side engine access door.  My ride heighth is even and exceptable now, the valves in the door are turned all the way.  I just really need to get a little more pressure in my tag axle air bags. Pls help. I know there is a reg. on the bulk head but not sure if this is where to adjust it nor do I know how. There's got to be a way. Thanks in advance.

Grant

[JackConrad]

     Follow the supply air line back from the 2 tag axle control valves located just inside the passenger side engine compartment door.  The line goes to a pressure regulator located on a bulkhead above the alternator and more centered side to side.  Factory setting is 35 PSI, but I have heard several peiople say they increased it to 40 PSI.
    I once connected a pressure regulator directly to a tag axle air bag air line to try to help free a stiff tag axle.  Since Mohawk told me to limit the air pressure to 85 PSI when manualy leveling my bus, I felt I could safelay put 85 PSI in the tag axle air bag. When I cranked the regulator up to 80 PSI, a safety relief valve on the tag axle air bag released. Scared the bejeebers out a me!  Jack

[busshawg]

Thanks alot Jack, you have been a life saver with all yor experience!!  Do you know how to maually increase the pressure at the pressure regulator to 40 lbs, or is it pre-set with no adjustment. I guess we now know not to put more that 80 lbs in the bag, haha

[Hartley]

Up on the ceiling of the engine compartment forward of the alternator
should be a pressure regulator attached to the floor-step area where the
rear seat was located. About dead center.

On my MC-9 that is where it is. The Tag pressure should be around 35 psi.

There should be an a/c type fitting or air chuck fitting over next to the valves.
where you may be able to attach a gauge or a/c hose & gauge set.

Typical downforce should be around 6,000 lbs for the tags. Or about 2 to 3 inches of unloading lift on the ride height as viewed when the tags are turned on.

Note: Porposing and Excessive drift/lane changes and other wierd stuff can happen of the tags are not loaded or empty. Heavy brake application will
skid the tags if you don't have enough downforce. ( been there done that!! ).

What happens in the back end directly affects the handling on the front end 30+ feet away. Tags generally should be left on unless you need more traction on the drive axle ( soft ground or such. ) Or if you are trying to make tight low speed turns that scrub the tires. ( leaving black skid marks on your buddy's concrete driveway for instance. )

I use the tag valves when hooking up to a trailer. Let the tags down, back under
the hitch and apply air to lift the ball into the hitch...

I wouldn't tamper with the ride height on the drives until you are sure that the tags are loading correctly. If they were factory set and have been fine, Don't mess around with them. ( takes a PIT to do it right! ) or it's a PITA ....

[buswarrior]

The regulator is adjustable. bolt on the top screws in and out. You need to have a good way to measure the pressure so as to set it the way you want.

If you have the side instrument panel mounted tag unload switch, there will be two regulators and associated solenoids. The tag unload regulator is set to 15 lbs, the regular regulator is set, as noted to 35 lbs.

I replaced mine some 8 years ago, due to corrosion leaks. I think brand new from MCI, the regulators were $44 each, the rebuild kits were $22, so the choice was clear, I got new ones. I set them on the bench before installing them, and the scale weights didn't change, so they were set the same before I changed them.

The ride height is a separate issue all together. Ride height needs to be set correctly for suspension geometry voodoo reasons. Just boost the pressure in the tag regulator a little to get the weight carrying transferred the way you want and the ride height will take care of itself.

Beware, on the older MC7-8-9 the tag axle rating is only 6000 lbs. With the propensity for tag axle bellow structures to crack or otherwise collapse, I would be cautious to put only enough weight on the tag wheels so as they may provide heavy braking without sliding the tires. This seems to require somewhere above 3500 lbs bearing down on the road. If you weigh north of 32 000 lbs, you might need a little more weight on the tags, and you'll definitely need the braking!

happy coaching!
buswarrior

[JackConrad]

I would be cautious to put only enough weight on the tag wheels so as they may provide heavy braking without sliding the tires.
happy coaching!
buswarrior

      Per my MC-8 part manual, beginning shortly after my early MC-8, MCI added a pressure regulator each tag axle brake line. The regulator was to be set at 25-30 PSI. Limiting the pressure was to prevent sliding the tires. I do not know if this applies to MC-7's or 9s.
      On our bus a typical brake application is 10-20 PSI. We had problems sliding our tires on hard application such as that idiot pulling out in front of us or that traffic light chaqnging at the last second 35-50 PSI application pressure). Installing the regulators ended that problem.  I had considered increasing the tsag axle air pressure to 40, but decided to leave it where the factory set it. We castty about 2500# on our tag axle, about 18,000 on the drive axle and about 11,000 on the front axle

[busshawg]

There we go, all the info I was looking for, I am making progress , slow as it is but progress none the less, Thanks a bunch guys!

Grant