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Old 08-16-2015, 11:33 PM   #1
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Air pressure ferrying home new 2005 XC RV

I got 1000 miles on the trip home with my new Airstream Skydeck. Blew the top radiator hose in the middle of no where. While I wait to go back and get the repaired RV I thought I would ask about my experience driving it so far.

First non-Sprinter diesel I have driven, first time with air brakes.

When I start the RV it runs fine, but it takes a long time sometimes to build up enough air pressure to go, and the driving so far has been highway, but I stopped at a friends and at the light the brakes popped on and indicator lights on the dash showed low air pressure. Soon the light turned green and honking started. Just before the light turned yellow the brakes finally allowed me to disengage and continue driving.

1) is this normal?

2) is there a way to drive it better? So was I bouncing my foot on the brakes and lost all the air, do I have a leak? Should I put it in neutral so it won't need as much braking? Or even pop the brakes at the light so I don't have to rest my foot on the pedals?

I am trying to digest the Freightliner manual but I haven't really found the how to deal with air brakes section of this or the RV manual.

-Randy
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Old 08-16-2015, 11:43 PM   #2
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Doesn't seem normal to me. On every DP I've owned (3 so far) the air pressure is up in less than 1 min. Have never had the parking brake switch pop out when the engine is running unless preforming the brake check.
"Bouncing" your foot on the brakes could reduce the air enough to cause the parking brake to pop on. This is a safety feature.
Just holding the parking brake for a light shouldn't cause a problem.
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Old 08-16-2015, 11:51 PM   #3
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Check your Haldex filter and also the air pressure line from the compressor to the Haldex drier filter for the air brakes. That flex airline has a steel mesh on it. The filter/drier should be located just behind the rear axel .
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Old 08-17-2015, 10:43 PM   #4
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Quote:
Originally Posted by israndy View Post
I got 1000 miles on the trip home with my new Airstream Skydeck. Blew the top radiator hose in the middle of no where. While I wait to go back and get the repaired RV I thought I would ask about my experience driving it so far.

First non-Sprinter diesel I have driven, first time with air brakes.

When I start the RV it runs fine, but it takes a long time sometimes to build up enough air pressure to go, and the driving so far has been highway, but I stopped at a friends and at the light the brakes popped on and indicator lights on the dash showed low air pressure. Soon the light turned green and honking started. Just before the light turned yellow the brakes finally allowed me to disengage and continue driving.

1) is this normal?

2) is there a way to drive it better? So was I bouncing my foot on the brakes and lost all the air, do I have a leak? Should I put it in neutral so it won't need as much braking? Or even pop the brakes at the light so I don't have to rest my foot on the pedals?

I am trying to digest the Freightliner manual but I haven't really found the how to deal with air brakes section of this or the RV manual.

-Randy
Randy,
Well Sir, no, your air system is not functioning correctly. Basically, it works like this:
On a completely drained and correctly working air system on a diesel coach/truck/coach etc., once the engine is started, the compressor should build air pressure immediately and, all the way up to what's known as the "cut out" pressure which, is governed by the air pressure governor. And that cut-out pressure is normally around 125-130 psi, plus or minus a few lbs.

And, if the engine is set on "high idle" it would do this complete build up of air, in about 1-2 minutes. You'll hear the air dryer spit out, once the build up is complete. Now, each time you apply the air brakes, you use air pressure that's stored in the tanks. When the tanks fall below around 80-90 psi., that's the "cut in" pressure that the governor is regulated to, to start the compressor to build up the supply again. And, if your air pressure falls to around 60-65 psi, plus or minus a pound or two, that's when you'll hear the mandated "Low air buzzer" come on. Above that psi, the buzzer cuts out.


And by the way, don't "Bounce" your foot on the brake pedal, there's no reason for that and, all it does is, deplete air pressure through the brake pedal "treadle" valve. In other words, you're WASTING AIR!

Now, that's how the system basically works. Your parking brake, is part of the air brake system. It's basic operation works like this:

The parking brakes are the same brakes as the rear brakes. Air pressure, in part of the rear brake cans, keeps the PARKING brake system from applying them. There are some seriously strong springs inside those rear brake cans that are what's used to apply those parking brakes. When you pull the parking brake button on the dash, you're simply releasing that air pressure in those cans, and therefore, those seriously strong springs, now apply those rear brakes. Simple huh?

But, by law, if you loose air pressure, or, are loosing it enough that your air compressor is un able to keep up the supply, as soon as your air pressure system is depleted down to around 30 psi, that is the point at which the springs in the rear brake cans AUTOMATICALLY apply the parking brakes.

As soon as you can build air pressure above 30-45 psi, (a basic figure, some are higher and some, around the 30 psi mark) you will then be able have enough pressure to fill the rear brake cans and, therefore release the brakes.

So, sorry for the long dissertation on how the air system works but, I thought it appropriate for this issue you're having.

Now, as to what's causing your loss of air, enough for your parking brakes to come on while at an intersection, that's a serious loss of air. There are a number of potential components that could cause this problem.
1. The air governor, rare but, it can happen
2. The Air DRYER, and various components within it.
3. Burnt, broke, or damage air brake lines in any part of the system, not necessarily near the actual brakes. In many coaches, such as our Freightliner equipped coach, there are plastic air lines that feed many systems and portions of systems. It's rare but, they can get damaged too.
Most of the brake lines that enter the brake cans are of stainless steel braided configuration due to DOT rules and regs.

Your drain valves on your air tanks, could be the culprit too. It's possible that one or more of those drain valves can be damaged or, are slightly open.

Well, you've got some things to think about. If I were you, I'd set aside a day and, get that coach up in the air a bit and, get a spray bottle of dish soap and water, (it don't take much soap, around a few drops in one of those spray bottles) and, try to build up the system to the point of cut-out and, make sure the coach is safely parked and, with the engine stopped, get under there and, start spraying fittings, air lines, drain valves and any other potential air fittings and valves to check for BUBBLES!

On a leak that intense, you basically should be able to hear it once your even close to it. Good luck and do report back if and when you find the cause.
Scott
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