Air Governor Increase

[truk4u]

Last night in Hectors presentation, Joe C. mentioned that he turns up his customers air governors to 135 psi to help raise the rear of the bus when the tag axle is lifted.

Anyone have any technical info or Prevost recommendations on whether this increase in pressure will have any adverse effect on the bus pneumatics? This would then change the compressor cycle cut-in/cut-out from around 95/120 to about 110/135.

[dreamchasers]

Tom,

To add to the question, during one of our suspension sessions, I had one POG member mention that his tag axle did not lift. He stated that when he moved the tag axle switch, to the left of the drivers seat, he could hear the tag air bags release, but never witnessed the tag axle actually lifting. He stated that he thought in XLII's, that the tag did not lift, only the air would release from the air bags.

Do an XLII owners have any comment on this? On my XL, the tag axle will lift after a few minutes.

Hector

[truk4u]

Hector,

The 40'S will lift off the ground, but 45's generally just unload the tag.

[jack14r]

The tag on my coach does not lift off the ground,I think that the switch only exhaust the bag.

[Jon Wehrenberg]

The Prevost Maintenanced manual is very clear. The maximum pressure is to be 125 PSI.

Our coaches have a lot of pressure limited components including brake chambers and air bags. If the increase in pressure is to correct a problem then that can be compared to taking aspirin to treat a brain tumor.

I have heard all sorts of reasons why air pressure should be increased and so far every one has been to fix something that isn't working as designed for a reason other than air pressure. Some coaches that are just too heavy on the front axle have had pressures increased in an attempt to get the front up to driving height or above. Part of the problem could be the front air bags are the wrong ones (a problem identified and corrected at OKC) or the owner has too much weight on the front axle.

If the rear will not rise when the tag is lifted that can be caused by too much weight in the rear or an issue caused by the lack of the hydraulic system designed to prevent the rear from dropping, or unreasonable expectations. When the tag is lifted the 4 air bags on the drive axle are to carry the load. On my bus they will have to carry 8000 pounds. They will lift the rear to the driving height but I need to be patient.

If the tag is not intended to be raised then you will not have what looks like a #30 brake chamber just above and to the rear of the tag axle. Depending on the mechanical advantage provided by the lifting arm that pivots the brake chambers can lift 3000 pounds at 100 PSI each. If your tag will not lift you have an axle and wheels that weigh more than 6000 pounds or there is something wrong.

As far as limits any time system pressure is increased it masks the real problem. I realize some converters have ignored axle weight limits and some owners cannot resist carrying everything they can cram in the bays, but be aware at 135 to 140 PSI the coaches are right at the air system limits for over pressure devices which were installed to protect you, the bus and components from being over pressurized. Good luck those of you that have become test pilots.

[Joe Camper]

HMMMMMM very interesting. Catching up on old stuff

Bluevost mentioned Prevo Mira-loma fixed his enimic front axle preformance with, U guest it, turning up the air pressure.

I know from experiance if Prevo sends U a "260"bag for the stear axle on a early 90s chassis the air dryer will sneeze stoping the compressor before the bus gets to ride height in the front, at 120psi. U gotta pump the brakes down to get the compressor going again and after about 3 times of doing that it will finally get there to ride height I mean. 130psi and all that rigamarole goes away. Push the button UP IT GOES, as does the ride height valve also respond giucker.

130 is not a crazy or dangerous psi to set your govoner. Quite the contrary. If U have a heavy front axle or a slide coach it sometimes needs to be there.

Adjusting the regulator on an 8-V in an XL is no easy task. My sugestion is get bag "259" and it WILL respond at the lower 120 psi most coaches and the different bag to fix the problem is way easier than going up with air PSI on an 8-V in an XL. The "259" is also for sure the best bag for the front for these buses and they work very well in the tag axle position too. Because of the additional 4 inches of travel for the lift it travels almost 12 inches. The drive bags only have 8 inches of travel yet many of the buses call for all same on the back 6. The 259 at the tag does not apperar to be slightly overextended like the 104s or 105s that are called for all the way around.

More pontification, IMO, this is what I concluded, draw your own conclusions did I cover everything ;)

The real early 90s and late 80s XLs need the hole enlarged in the top plate on the bus for the bigger fitting on the inlet of the air bag in order to to accept either of these 2 upgrades but the tool is an easy one to make to get it there.

Jack 14R where where was the psi on the brake tanks set to on your XLIIDS new?

Im going to start a thread to repeat the condition I mentioned on Hectors seminar that was incorectly put in the first post.

Its some good info for the early 90s vintage guys many are unaware for sure and It will also correct the record.