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Old 10-05-2012, 03:04 PM   #1
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Air System

I installed an air pressure gauge on the dash so I see where my pressures were running. When running down the road it runs 110 -120 psi. When I park and put jacks down it drops to 80-90 psi. Within 48 hours the psi will go to 0 psi. Is this normal or do I need to look for a leak?
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Old 10-05-2012, 03:09 PM   #2
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On our DSDP it may take more than a month for the air to go below 60 psi and never down to 0.
You have a leak.
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Old 10-05-2012, 03:48 PM   #3
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On the Freightliner chassis there are leakdown specs. I'd imagine other chassis also have similar specifications. I've seen the leak check procedure for a Freightliner, and it is quite complex and lengthy. Mr D's Dutch Star is a VERY unusual coach to hold air that well. I doubt many could equal or exceed his performance. My experience is that almost all coaches leak down slowly. Yours might be dropping faster than many, but I'm not sure I'd be willing to invest the maintenance hours necessary to tighten it up.
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Old 10-05-2012, 04:45 PM   #4
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Mine goes to zero (I'm assuming you tapped the 3/8" o.d. plastic air line that goes to the lower dash idiot light panel).
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Old 10-05-2012, 06:51 PM   #5
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Not sure what pressure you are checking. If you are checking the front and rear suspension pressures you need 2 gauges. These pressures should be around 70psi. 120psi is the pressure the compressor on the engine should be set to. The real question is does your suspension deflate when you park on a level surface? Do not use the jacks as this will activate the height control valves and the results will be meaningless. If the coach stays level for 24 hrs you are good.
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Old 10-05-2012, 07:44 PM   #6
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Alpines don't have air brakes, we have air (in association with the HWH Jacks) leveling and the parking brake is actuated and operates by air pressure (well actually it’s not, but that is another story). If you park the coach, set the air brake, drop the air bags and level the coach, you will have almost no air left in the system. That is almost normal.

I believe if you turn off the engine after the system has charged up to full, holding your foot on the brake pedal, and cycle the parking brake, you will find it may operate three times before the coach has used all the air available to it.

Alpines don’t have an air (tank) reservoir on our rigs, and we don't need a lot of air pressure to do stuff when we are parked.

You have a most likely normal coach. If however, you are going down the road, and the coach leans to the right or left, you might have an air leak or an air bag which has failed, not real normal, but not unheard of either.

If you decide to go under the coach looking for leaks, make sure you put 12 ton jack stands at each corner, so the coach does not crush you when you disconnect an air line and it starts to come down. If you think you have an air leak, take it to Freightliner since they can work on air systems. Cummins wants to just work on the engines I think.

Before our accident, I had a right front air bag which loses air over a week’s time. I just drop the air bags around when storing it, so it does not sit lopsided when parked.
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Old 10-05-2012, 08:10 PM   #7
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When did they remove the compressed air tank? Mine has one.
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Old 10-05-2012, 08:55 PM   #8
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Hmm my 05 has one.
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Old 10-05-2012, 10:58 PM   #9
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Hey Mike! An air system schematic would be a nice thing to have. Did I miss it in the library; or is this one of those we'll have to draw up ourself?
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Old 10-06-2012, 12:01 AM   #10
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If I have an air reservoir (tank), I have never seen it, maybe it's a tiny thing. I have also not gone looking for it, since we don't have a lot of things which use it. Since I don't have the coach here, cannot look until I do.
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Old 10-06-2012, 01:53 AM   #11
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1) the air tank is above and ahead of the rear axle iirc, and everybody has one; its both a DOT req'mt & a practical one (you wouldn't be abe to release the parking brake w/out it till the air compressor filled the system). I believe on the Avalanche there are two tanks, front & rear for the air brakes, same on any Ltd that was ordered w/air brakes.
2) see post#12 by some crackpot here for a preliminary schematic, best we have to date, so if anybody wants to update it w/more info that'd be great. Not sure where the tap is that goes to the dash warning lights, and the sketch doesn't account for ride height valves for example.
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Old 10-06-2012, 02:27 AM   #12
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I tried to work on the ride height valves one time, and they are very sensitive, a little bit will do a lot. I never could get the leak to stop, so I recommended he take it someplace more familiar that I was on the system.

The older I get the more scared I get being under one of these things, under the car is fine, under the MH scares me bad, and I don't understand the reason, either one can hurt you. I have no recommendations on who does good air system work. And I for one don’t have a very good understanding on it at all, hence my ignorance about an air tank. Now I have been under the rear end to lube it, etc, and even ran a new temp sensor for the Xantrex inverter, which goes through that area, and I never saw it then, don't mean it was not there.
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Old 10-06-2012, 02:29 PM   #13
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The tank is up high and in the shadows from your flashlight.

I have two 5 ton acme screw jack stands to support the front end or either rear corner I might be working under while on the road. Here at the shop I have 12T jack stands. If you're going to be under the rig for other than a quickie looksee, break out the stands. My main bottle jack is a 12 ton unit by American Forge and the second (I carry both traveling) is a Craftsman brand; both cost a wad of sweaty money but I've heard tell of chinese sand casting bottle jacks blowing up under weight.
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Old 10-06-2012, 04:19 PM   #14
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I have a question about the crackpot schematic.
On the early coaches like mine the parking brake was released by hydraulic pressure and thus if the engine stalled the parking brake would immediately set as there would be no hydraulic pressure to hold it off. I understood this was a DOT requirement.
In the later coaches with air release it would seem that the parking brake would be held off until the air in the tank dropped below a certain pressure and this could take some time if the engine stalled. It would seem to me that either the air for the parking brake should come directly from the engine compressor or that a device has to be fitted to the brake release so that air is dumped immediately the engine shuts down.
Just wondering!
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