air break losing break

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caesar1967

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to start my engine on my 2007 National Trop-Cal motor home (340 diesel pusher class A motor home) the the AIR BREAK PRESSURE has to be be above  60. now the air pressure dropped to below 40 and I ca not start may engine. Is ther a way to start the engine? Also doe any body know where I can fined the leak or what the problem might be . I can not even fined the components for the Air break system > unfortunately the owners manual does not show me where they are neither doe the FREIGHTLINER MANUAL show me where to look. Help please. I appreciate a response if possible to  trinity [email protected]    THANK YOU
 
You might find something if you look under BRAKES and not BREAKS.

I have never heard of a motor home requiring air brake pressure to start. That makes no sense. All the air will normally leak off in a motor home after sitting for just a few days.

Whatever your problem is, it is not the lack of air brake pressure.
 
Have to agree with A Traveler. Low air pressure will prevent the brakes coming off, but shouldn't prevent the engine from starting. Failure to start, whatever the cause, will prevent the air compressor from running and building up air pressure.
 
Something is messed up, because the air pressure (or lack of) should have nothing to do with starting the engine. It's quite normal for the reserve air pressure to drop to zero when parked - that's how the parking brake gets set.

The air brake system is no different than most any truck or other RV chassis.  The air compressor is in the rear just ahead of the engine/tranny, the reserve air tanks up front roughly behind the front axle, and an air treadle valve on the front firewall to send air to each wheel cylinder when the pedal is pushed.

The rear axle brakes have big springs that apply them whenever the air pressure drops much below about 50-60 psi, so I'm guessing that the action of those brakes is somehow interrupting something needed to start the engine. Maybe moves a wire or something?  In any case, it is not something they are supposed to do, so look for a mechanical cause back by the rear brake cylinders.
 
  Surely they never made a motorhome with an air starter. That would get everyone?s attention in the campground when it cranked up. I guess some kind of interlock between spring brakes being set and starter is possible and it?s failed. I?ve seen such devices on large loaders, and they?re a simple device. Easy to imagine one on Motorhome and could be rigged up for under $20 by someone handy.(previous owner?)
  Guess you could hook air compressor to generator and air it up. Please post if it starts.
 
    First make sure your tranny is in park and the parking brake button is out....There should be NO reason that starting is dependent on there being air pressure in the tanks....at least not in an RV. Look for other safeties that may not be set. especially a neutral safety switch.
 
I agree I have never heard of an air starter on a RV. Some trucks have them which I always thought was stupid. When you started it before it didn't sound like a air impact did it? If it turned over like any other vehicle the air pressure is not your issue.
 
Uh, Air starters (I have been entierly too close to one when it started.. (Perhaps 4 feet) sound NOTHING like an Air Impact (Which I own 3 of) Nothing at all.

But they are effective.
 
This post is why no one should be allowed to drive a vehicle with air brakes unless they have a basic knowledge of how it works. In Canada you need an air brake endorsement.
 
It's not an air starter - you can trust me on that! The '07 TropiCal is built on a Freightliner Custom Chassis XCS (straight rail) with a 12v Denso electric starter. And a typical full air brake system with ABS, with the rear brakes spring-applied and air-released. [This info direct from FCCC website].

I do not see this as a possible interlock problem because it won't start until the park brake is released (air pressure built up). Clearly not a park brake interlock in that case. And it apparently will start when the air is up, so not a tranny gear interlock either. Of course, the rear  brake mechanism could be improperly opening or closing some interlock circuit as it applies.

ceeasar1967 hasn't been very specific as to what air pressure (front or rear) has to be up, nor the details of "won't start".  I'm guessing he means it won't crank when the key is turned, but hope he will verify that.

If he is waiting for someone to email an answer to him, I suspect it will be a long wait...
 
John From Detroit said:
Uh, Air starters (I have been entierly too close to one when it started.. (Perhaps 4 feet) sound NOTHING like an Air Impact (Which I own 3 of) Nothing at all.

But they are effective.
Click to expand...

I was trying to explain it to what he would understand. Scares the hell out of you if your not ready. Lol
 
moisheh said:
This post is why no one should be allowed to drive a vehicle with air brakes unless they have a basic knowledge of how it works. In Canada you need an air brake endorsement.
Click to expand...

I am suprised that an airbrake endorsement is not required. I agree. I do have a class A and agree there are to many people driving them that should not be.
 
HEY! I drive a Honda Accord...how much different can it be?  :p

I've been around a lot of construction equipment, mostly haul trucks, that had air start, usually very large Detroit Diesel engines...those would definitely wake up the entire campground if that kind of system was used on RVs...WHIIIIIIIIIIZZZZZZZZZZZZZZZ!
 
I doubt if many people could explain how the hydraulic brakes in their car work either. Or fix them if the engine didn't start when the brakes were on. Or know what to do when the brakes begin to fade or fail entirely.

I think an argument could be made for some required "driver ed" training in large vehicle operation, but IMO air brakes aren't the reason.  The challenges of handling a large and heavy vehicle would the same whether the brakes were hydraulic or air.
 
So Gary : I would ask why all10 Canadian provinces require asingle vehicle air brake endorsement to drive a MH with air brake?. Almost every state requires that truck drivers have studied air brake systems Air brakes do not operate like hydraulics and basic knowledge is important. I am surprised at your answer. It shows a complete ignorance of asafety item. Rvforums get wierd questions about airbrakes all the time because the driver knows nothing about the system. I have seen questions such as: Where is the park brake? How do I add brake fluid? Why do I hear air hissing? Where is the emergency brake. Why do I hear abuzzer every day and the mh will not move. Every carhas hydralicbrakes and drivers usually have some familiarity with that system. Ido agree that drivers should also have some knowledge of how to drive a large vehicle. What would a novicedo if he was driving 65 mph and the spring brakes applied? Would he know that something is amiss??
 
I am surprised at your answer. It shows a complete ignorance of asafety item.
Click to expand...
Well, mosiheh, I guess I'll remain blissful in my ignorance.  It's my opinion, and I'll stick to it.  8)


I already said there are things a driver should learn and certainly the location of the parking and emergency brake is one of them. You don't need an air brake endorsement for that.  I'm strongly in favor of a sort of a big rig familiarization training course, but that's much different than the air brake endorsement testing for a commercial driving license.  I even tried to lobby the RVIA to produce driver familiarization videos for both motorhomes and trailer towing, but they scoffed at the whole idea. Driver training is "not my job" was their basic reply.


What would a novicedo if he was driving 65 mph and the spring brakes applied? Would he know that something is amiss??
Click to expand...
The same thing he would do if the parking brake suddenly activated in his car: wonder what in hell happened to make it slow down so suddenly!  :eek:
 
I would ask why all10 Canadian provinces require a single vehicle air brake endorsement to drive a MH with air brake?.
Click to expand...

They don't, at least in QC that requirement did not exist several years ago when I inquired. I received a written answer by email to that effect.

The only requirement here at that time was a standard class 5 (car) driver's license, even for a class 7/8 tractor provided it was converted/registered as an RV. I have not checked more recently however.
 
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