Air Ride Suspension and Air Brakes--Explanation

[zmotorsports]

Originally Posted by barmcd

So, from reading the replies, I have a leak on the brake side since the air pressure bleeds off the air tank, but the suspension is good because the coach stays level when parked. It hasn't sagged a bit over a 30 day period of just sitting.

Yes, that would be my assumption and where I would start looking, or at the tank connections themselves.

Mike.

[96 Wideglide]

Could be anywhere!

Mine will actually purge air out of the bottom of the air-dryer, hours after the engine has been shut off !
Air-dryer manufacturer says thats perfectly fine!

[windsorbill]

A common area where your brakes will bleed down is the parking brake plunger on your dash (or in my case, on the left side panel)

[garlind]

Does anyone have a good part number for the pop off valve on the air tank in a 2004 neptune

[barmcd]

I just wanted to update this thread with the reason my coach maintained ride height even though the air tanks went empty and the part numbers used on my coach.

First, at least on older Monaco coaches like my 2000 Dynasty, the accessories that use air like the PAC brake, front and rear levelers, and step cover are connected to the tank with a pressure protection valve. The part number specified, N15759DC, opens at 65 PSI and closes at 56 PSI. The valve will remained closed until tank pressure reaches 65 PSI, then it opens and will supply operating pressure to the accessory. When the tank pressure drops below 56 PSI the valve closes and air is no longer supplied to the accessory. This is what ensures that the brakes will have between 56 and 65 lbs of aire pressure before supplying air to any accessory. This is a completely mechanical system.

My coach is equipped with hydraulic jacks, not air levelers, so I don't have the air manifold like coaches with air leveling. That would add an extra level of complication to the system. Each end of the coach is separate from the other and is a very simple system with only one part which is common to both sides and four parts which are duplicated on both sides. That's a total of nine parts in the system. Here's what my rear suspension looks like:

1. Pressure protection valve (common)
2. DS ride height valve
3. DS front air bag
4. DS rear air bag
5. DS dump valve
6. PS ride height valve
7. PS front air bag
8. PS rear air bag
9. PS dump valve.

My coach uses a Hadley H00450CE ride height valve. The valve requires 90 PSI to operate normally and has three positions, the first allows air to flow to the air bags, the second dumps air from the bags and the third doesn't let air flow either way.

Both my pressure protection valves installed on the rear tank had leaks which caused the tank to bleed down to 0 PSI over 5-7 days. The ride height valve kept air pressure to the air bags even though the tank bled down.

Since I started this thread, my coach has started to sag on the rear left side. I'm in the process of replacing the pressure protection valves and my left ride height valve.