Ferrari

Air Brakes Warning System - Pressure Guage Erratic Reading

53 posts in this topic

I have an Allegro Bus, year 2000, 38 foot diesel pusher. My air pressure gauge will drop down to zero and then fluctuate between zero and 130 psi. While the gauge is going through this gyration, the air brake warning buzzer is on. Then, after a minute or so, the gauge will settle at the appropriate air pressure of 130 psi or even with the second gauge (which works perfect). I don't loose any of my air brakes, but it's a nuisances having this gauge perform in this manner (it doesn't do it all the time, just occasionally. Does anyone know the cause of this problem?

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Ferrari, Welcome to the Forum.

It could be as simple as a loose wire on the guage or at the sending unit.

Herman

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Check with your chassis maker, particularly true if a Freightliner chassis (a fairly common issue).

Brett

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Read the thread,

Possible Coach Air System Problem: http://community.fmca.com/topic/3407-possible-coach-air-system-problem/

Started by Trabuco, 22 Nov 2011

This sounds like the same issue, Like Brett said if you have a Freightliner Chassis, this is a very common problem caused by a cold solder connection in the module sending information to your air pressure Gauges.

Rich.

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I am going through this now and have to get it back to the place to work on it. It wouldn't do it for them, but it drives me crazy because it will do it for 15=20 min sometimes!!!!

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Does anyone know how to fix the "cold solder" issue on the air brake gauge fluctuation issue? I have a 2000 Fleetwood Discovery. Thanks

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Dryclnman, I will send you a personal message. It will be in the envelope in the upper right corner of the forums page so you can reply.

Rich.

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Thank everyone for your suggestions. I had it checked out and it turned out to be a faulty "Control Module" which controls all those gauages and lights on the dashboard. Replaced the old with a new one and everything works just GREAT!

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I have a 2003 Fleetwood Discovery on a Freightliner chassis and when I tried to lift the unit to move, only the rear bags inflated. The front pressure gauge never moved off of zero. This is the first time I have had this problem. Could this be a control valve or a compressor problem? I did not hear any air leak from under the coach while trying to lift the unit. Any ideas??

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Welcome to FMCA !!

Have you cycled the dump valves, to rise and lower the coach?

The fact that both front air bags do not inflate narrows down the problem. The rear would not inflate if the air pump had issues.

Could be a valve or a manifold problem.

Do your air gauges read normal ? 120 psi on both gauges?

I'm a little confused in regards to you mentioning front Air Gauge. Most coaches have a primary gauge and a secondary gauge. The primary reads the pressure in the braking system and the secondary reads the pressure in the air ride system.

Rich.

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I am having the same problem with my 99 Fleetwood Discovery, can you tell me what control module and where it is located.

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The Secondary Air supply feeds the Air ride system. Air flows from the tank to a manifold with one line in and three lines out. One air line from the manifold goes to rear air ride bladders with one ride height valve.The plumbing is different for different models, year and manufacture. The front air ride has two bladders, but each one is controlled by its own ride height valve. These bladders are supplied air from the same manifold. The air path is controlled by the air dump valves. When open the air is released from the bladders and vented out via the valve(s) lowering the coach.

A defective ride height control valve or missing control rod or adjustment problem can dump air from the system as fast as it comes in. These system are supplied air through a 1/4 in. line, remember this is a closed system so the size of the line can be small relative to the weight of the coach. Its pressure not volume doing the work. Therefore, any small leak or restriction in the system can have a profound effect on the system.

The main issues are dump valve(s) working properly, Ride height adjusted properly, Ride height linkages adjusted properly, Air system is free of water and contamination in the system and the air driers and the air tank vent lanyards have been pulled on a regular schedule to keep a build up of water in the tanks from happening.

There is no magic answer to a problem with an air ride system all the items work in concert.

Rich.

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I would also appreciate any information on a the "cold solder" correction. Thanks

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had same problem,after many hours spent in my shop, and @ least 1 on the phone, found cracked solder @TCM. Cause: the screws had come out of panel holding the module, allowing it to lean out and rest on the connections, made better mounts.

Repair, TCM is mounted on the left rear of coach in a compartment, when under coach, forget the wiring, there are miles, look for 1/4" air lines yellow & blue?, feeding the module.

Was advised solder repair could be iffy, depending on amount of damage and age, so bought new module, around a $100.00.

Results, works like new, 1800 mi since repair, did my own solder repair, and carry for backup, have since traded twice to RV'rs, when areas of no parts.

Northern Nevada Prospectors, Pres F230071

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Well, after much fanfare and searching, my TCM box was on the engine firewall, assessable under the bed/engine compartment and sure enough, two mounting screws had fallen out and the unit was dangling and loose, allowing it to wiggle pretty good. I removed it, opened it up and it looks just fine and is dry and clean. My question is, in regards to the "Cold Solder" issue, What inside might be loose? And, Does anyone with experience with this issue think that just mounting the unit back firmly to the wall, not allowing it to shake and wiggle, that this will cure the erratic air gauge issue to stop. I did notice that the problem occurred more often on bumpy roads and kind of went away on the interstate. Any input or opinions would be greatly appreciated. Thanks for all the help...!!

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There is another post in this thread that indicated his problem was much the same as ours. He opened the unit up and touched up the soldered connections where the connectors are attached to the board. If my prob returns, that is what I intend to do. My mounting bolts were a little loose and after removing the unit found only 2 of the mounting studs had shock mounts (rubber inserts around the studs). While monitoring the system found that just tweeking the unit a little bit the gauge returned to normal. The shock mounts were both on the rearward two studs. Move them so they were crossways and tightened all four down (not too tight) and the problem went away. That probably is a short term fix. We shall see.

Hope this is of some help.

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Rich,

Thanks for the response. Since posting my question, I built a new RV garage for the beast. Now all I have to do is get it moving so that I can use it.

Yes I have tried many times to cycle the dump valve to raise and lower the coach. There are two gauges on the coach and the front air gauge reads zero while the second gauge will fluctuate between 90 and 120 psi.

I now understand that only the front gauge is used to inflate the air bags and the rear gauge is for the brakes. Now neither the front or rear bags will inflate. I'm not sure where the air pump/dump valves are located. I would like to try and fix this myself if possible. It could be the air pump itself, not sure. Could also be the the air pump filter causing the problem? If yes, any recommendations!

Don

Welcome to FMCA !!

Have you cycled the dump valves, to rise and lower the coach?

The fact that both front air bags do not inflate narrows down the problem. The rear would not inflate if the air pump had issues.

Could be a valve or a manifold problem.

Do your air gauges read normal ? 120 psi on both gauges?

I'm a little confused in regards to you mentioning front Air Gauge. Most coaches have a primary gauge and a secondary gauge. The primary reads the pressure in the braking system and the secondary reads the pressure in the air ride system.

Rich.

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I had this problem on a '99 Discovery and had to replace the air pump filter. Was still working a few years later when I traded the coach.

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Don,

The year and make of your coach could have a Cummins ISB 300 to 330 hp engine, Cat came in around the same year, 2003.

The air supply for the compressor often is from the intake manifold, boost side of the turbo. I get a heads up on the air intake filter condition by watching the time it takes to air up the air brakes and air ride. The filter air restriction monitor does read a little higher, but the air up time is by far a better indicator that I need to change the air filter.

There is a rubber hose between the air intake manifold and the air compressor that runs along side the manifold and can be a little hard to see. This hose can fail over time, causing low engine power and slow air up issues.

The system air pressure regulator (Governor) should be set at 120psi. The blow off valve is located under and is part of the air drier assembly in most cases.

There are manual air bleeders on the primary and secondary air tanks, with lanyards coming through the front right frame rail, just behind the tire.

Always a good idea to pull them for a few seconds twice a year. If you get a mist or water spray, hold the valve(s) open longer, release; re-air the system and pull them again. Then plan on replacing the air dryer filters ASAP. Water build up in the air systems is not good !!!

When checking the system for leaks, get some kiddy soup bubbles and a spray bottle and squirt some around all the connections and valves. You get different sized bubbles depending on the size of the leak. Little bubbles = little leak -- Bigger bubbles = bigger leak.

After that check back in and post your findings. Some one has most likely been through the issue at some time.

Rich.

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To all who have responded regarding my airbag problem and air pressure gauge reading zero:

I finally found the problem, a broken line (red) that was pinched in the channel where ALL the wiring and pressure tubing are feed thru. It was a bugger getting to it but I finally was able to correct the problem. Went to ACE hardware store and bought new 1/4" tigon tubing rated at 150psi working and spliced in a new section. Everything is back to normal and I moved the beast into the new RV garage - YEAH.

Thanks again for all your concerns and support.

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Hi Don,

Thanks for posting the problem and repair information for the group.

You might send a note to FCC and let them know the Vin number of your coach and the problem, they then would have a record of the air line failure. Pictures and mentioning where the location of the line that was damaged.

They might be able to determine if it was a passable production line issue or the coach manufacturer moving things to get clearance for there portion of the assembly process.

Can not say that I have run into this issue, being mentioned before. So thanks again for posting the information.

Oh! did the bubble test help in finding the problem area in the bundle?

Rich.

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<p>I would be very leary of a "tigon splice" in an air line. Better to get DOT-approved air connections and line (or that may be what you did and I mis-read).</p>

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Hi All !

I'm not sure what is going on with my coach. It is an 02 Phaeton on a FCC XC chassis. I have had it in storage since last Sept. Started it today and all seemed OK, but the front air gauge was reading 125psi and the rear air gauge was reading 0psi.

Any suggestions would be greatly appreciated.

Thanks,

Txphantom

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