[Archived]

petarm1 Look under articles, than go to Prevost Leveling System Diagnosis. This should help. Rick

[Bob]

Assuing you have “level low” what you describe is normal because once aux. system pressure drops below a certain value (30 to 35 PSI) the air in the tag axle dumps because the 3 port valve between the tag and drive axles requires that pressure to keep the valve from exhausting tag axle air bags.

There are a couple of options available. The first and best is to correct the aux system leaks causing the air pressure to drop. That is easier said than done. A second option is to revise the air circuitry a retrofit offered by Prevost. That revision has a fairly expensive cost but does eliminate the need to maintain aux system pressure. Any Prevost service center can probably give you a quote.

[Bob]

The buzz word if you call Prevost is “reverse tag logic.”

[Aleksander & Lucia]

thanks guys. i just did replace the auxillary tank. previous owner repaired a leak with silicone and a selftaping screw. i still have a leak to repair at my secondary air gauge. as soon as i figure out how it comes apart to repair the break in the line in the gauge. i also need to replace the left side take lift pot. it leaks around the band when the axle is up. so far that is all i have found

again thanks for the help

[steve]

i went to the diagnostic site in the articles section but it talks about some dial that controls the leveling system.

my bus does not have this dial.

petar

[Archived]

Your air leaks are hard to find. It is very unlikely you have the level low they speak of. Your coach was from a seated coach correct? The most common leaks are from leveling valves- air bags- brake pancakes- air tanks-air tank drains. Soapy water in a spray bottle is a busnuts friend.. Brittle air lines from age are another culprit along with norgen valve orings. Parking brake control valve is another. Air wipers are very common when aged.They can be valved out by installing a seperate shut off valve. It is possible to slow air leaks down is a 25 year old coach. Bob

[Ron]

One important thing for all bus owners to understand is that the air bags are part of the auxiliary air system. That means if the suspension system has air “locked in” via the current system logic of coaches with level low, brake and aux system pressures can go to zero and the air bags should retain their pressure and the bus should not drop.

I don’t know how the suspension system is set up on a seated coach so that might not apply.

[AL]

each leveling valve has a check valve to keep air from returning to the main system from the bags. These fail quiet often.The new ones I recieved from Prevost as replacement for the 98 last week had schrader valve type that installed in the supply line side on the valve. 3 lbs to open inlet side and held back 150lb (I bench tested). The only way I can see air returning/excaping from air bags now is leaks ,exhaust or norgren valves. To check your leveling valves remove put shop air to supply side and put in bucket of water. no bubbles= good note: valves must be in neutral position. Bob

[Larry & Diane]

Petar, It appears I have disabled the rear drop at 30 PSI function by simply changing the parking brake valve. That was not my plan when I replaced the leaking valve, but I noticed the new valve did not have the Bendix tape around it indicating “30 PSI” I found on the old one. Prevost Parts reps verified the part I ordered was correct for my seated coach, but I was surprised when the drop at 30 PSI went away. Now I’m wondering if I should simply be happy with the change since the new valve will allow me to dry camp longer before I must air up the coach. It may not be an issue if I’m successful in my current effort to stop leaks, but I’d be more comfortable if I knew for sure why the tag axle air is being dumped at that point instead of slowly going to zero with the rest of the system. Perhaps it’s a positive braking issue while parked? My coach doesn’t have the Level-Low system, but has the rear Low-Buoy.