Lost an Airline in Vallejo, CA

[Ryker]

I was driving down Hwy 37 today with the windshield wipers on. I noticed the wipers slowing down, then noticed that I was losing power. I checked the air gauge and it was at 30 lbs but the low air alarm was not going off. I immediately pulled over and coasted to a stop on the side of the freeway. I checked the engine bay and a high-pressure, steel bradded, 3/4" line came apart at the compressor.

A couple strange things happened:

During my ownership, on occasion, I press the parking brake button and the brakes are not on. The normal procedure is to pump the brakes and then they release. I noticed today that the brakes were off before I touched the pedal. I am wondering why my brakes did not engage all the way down to 30 lbs. I feel I may have avoided a disaster by losing my air on a flat freeway.

I started it when the tow truck got here to make sure the transmission was in neutral because I am having problems with my transmission toggle switch. When I tried to turn the engine off, it kept running. I used the emergency shut-off for the first time. Does this have something to do no air?

I am a bit nervous to drive anywhere if there is a chance of losing air with no warning. I am pretty good at watching my gauges but this air loss was very quick.

[richard5933]

I can't answer all your questions, but a couple I can...

The engine shut-down cylinder is air operated. You need to have some air in the system or you cannot shut down the system using the switch on the dash. Important to remember this, as once your air bleeds down you cannot shut down the engine for a few minutes from the dash.

If there is reason for concern about having to shut down before air builds, or if you know that air won't build, then it's probably best to start the engine from the rear of the bus. The only way to shut down (other than the emergency stop) is to manually work the lever that the shut-down cylinder normally operates.

Your e-brakes should have popped at 60 psi. When is the last time you tested that system? Sounds like at the least you need a low-air sensor and/or a new parking brake valve. Others know more about the air brakes and hopefully someone will provide more definite answers on this one.

Transmission toggle? Have you checked for loose wires/connectors behind the toggle?

[Ryker]

I understand the engine shut down now. That makes sense to me, and is what I suspected. I did not think of working the lever but I am familiar with the lever, so that is great advice.

Good to know that when it is working correctly, I will still have control over the brakes in the event of air loss. I feel I still had some brake power left but I mostly coasted to a stop. I was trying to make an offramp but I was also concerned that the brakes would simply engage at any moment, which is about as bad as no brakes at all. The brake button did pop but the brakes still are not engaged. My low air light always works, so I wonder why it failed this time. When working properly, what is supposed to happen? I would think alarm at 80 lbs, brakes on at 65 lbs. It all worked out but I feel I got very lucky. Had trouble sleeping last night thinking of different possible scenarios both losing brakes or suddenly engaging brakes without warning.

[chessie4905]

You can jumper the low pressure switch to check it. Could be the low pressure switch or the buzzer in panel to left of driver. Have you ever had your brakes inspected and adjusted. You shouldn't pump brakes to get them to release. A full air pressure brake application should release them after previously setting by pulling up on brake button. This is if the system is in good and properly adjusted condition.

[buswarrior]

Glad you are here to ask questions.

First, this is a 1974 coach? FMVSS 121 did not take effect until 1975, so everyone's "airbrake knowledge" doesn't apply to this coach.

Yes, it might be configured to just keep on rolling with no air pressure, by the manufacturer, or by someone doing "repairs" over the last 45 years...

Transmission toggle? Do you have an air shifter?

Brakes not "on"? With the button in the "parked" position? When we're the brakes adjusted last, and by who? Tightened up, or loosened off?

Low air warning. Where in the system is it plumbed, how many are there, and have they all been tested individually by emptying that particular part of the system? (HUGE failing for this for those with dual system, which low air sensor was tested when you fan the brakes down, which wasn't?)

Which kind of brake system is, or was, in in this 1974 GM coach? DD3, spring brake, hand brake?

This compressor pipe failure may have uncovered something more important.

You want this whole system gone through, to be sure it is "safe" according to its design, and working properly.

And you want to know how to do the periodic tests to be sure.

Happy coaching!
Buswarrior

[richard5933]

I'm not sure that your braking system is working the way it's supposed to based on your description. Here's a bit of text from the Operator's Manual:

EMERGENCY OPERATION - If normal application fails to stop the vehicle, emergency brake application should be made by pulling the control valve knob all the way up. This system is designed for emergency use only, producing a severe, sudden stop, and should be used ONLY under emergency conditions.

LOSS OF AIR PRESSURE - A warning tell-tale, "LOW AIR" will light and a buzzer will sound when the air pressure in the system drops below 60 pounds. The vehicle should be stopped and the cause of pressure loss determined and corrected before proceeding. However, if warning devices are ignored and parking brake pressure drops below 40 pounds, making operation of the vehicle unsafe, the emergency brake will apply automatically.

If your pressure dropped to 30 pounds and the e-brake did not engage then something in your system is not functioning properly. Since you said that your buzzer did not sound either, then my suspicion is that your low-air sensor is not working or not connected. If your button did pop but the brakes did not engage, then perhaps the pressure dropped so suddenly that there was inadequate reserve left in the parking brake tank.

There is a thread on one of the bus forums about what happens when the e-brake applies while the bus is in motion. If I remember correctly, it applies the brakes forcefully, but not enough so to lock the wheels or make the bus uncontrollable. Regardless, in most situations I'd assume that stopping suddenly is better than not being able to stop at all. I've had that experience and it sucks (we survived due to a well-placed berm next to a driveway which caught under the nose of the bus.)

My advice? Get the entire air system checked out by someone knowledgeable/qualified to diagnosis things properly once you get the air compressor line repaired.

[buswarrior]

Richard, that bit of operator's manual quote only applies to one brake system type.

Until we know what brake system is involved, all we're doing is driving Gary's Google points up without helping.

GM built 'em whichever way the customer ordered 'em.

Ryker?

Happy coaching!
Buswarrior

[richard5933]

Richard, that bit of operator's manual quote only applies to one brake system type.

Until we know what brake system is involved, all we're doing is driving Gary's Google points up without helping.

GM built 'em whichever way the customer ordered 'em.

Ryker?

Happy coaching!
Buswarrior

I thought that DD3 brakes were standard on these - did GM offer other options in 1974 in a 4905?

[buswarrior]

45 years is a long time for foolishness to happen.

Ryker, what parts are really under your coach?

On the rear brake chambers, is there one, two or three airlines attached?

Happy coaching!
Buswarrior

[chessie4905]

They are dd3's. No room for anything else, btw.Only change with later models was short lived antilock and then dual brake system

[Dave5Cs]

Same with MCI 5's and 7's
I saw it in change orders that came with my manual years ago. I thought interesting in 1979 and older that they would have anti-lock. a mechanic told me at greyhound that they took them out because they didn't work well on wet and icy road.

[Ryker]

Man, this has gone from bad to worse. Got the air hose made and back on yesterday morning and drove about 20 miles with no issues, air at 120 lbs. Stopped for a couple hours then drove just 3 miles and started losing air again. Dropped to 60 lbs and would not come up so I pulled over and air went back up to 120 lbs while parked and idling. Shut it down for a couple hours, started it up and drove 80 miles with no issues. This morning was driving home and made it 25 miles and white smoke started billowing out the back, started losing power and engine died. A couple people honked at me because smoke was so bad. I coasted to the side of the road, and I still had air and brakes. Jumped out to make sure there was not a fire in the engine compartment.

One point to make is that about a month ago I heard a very loud whistle coming from around the rear axle. Air was leaking out of something. I haven't heard the whistle since but my 15 year old niece and 30 year old daughter heard it a couple times this week. They said it was very loud but my 52 year old ears could not hear it. It was not the pressure release valve high up in the engine compartment because I checked that when I was hearing it, and I also replaced the valve because it used to bleed out all of the air.

Not sure these issues are related but maybe the air line popping off pointed to bigger issues.

Now getting it towed home.

[Dave5Cs]

Where is Home? About city or area?
did the engine even turn over after that? You might want to just try Baring it over to see if it turns but make sure your rack is turned to no fuel, fuel shut off is turn to off if you have one before the fuel filters or just pull your fuel filters or it could start. If you just hit the key trying to start it and it does start and you have a mechanical issue. It will only make it worse.

Those clear white air lines if there were any still there go bad over time and crack or snap off. It needs to be DOT vinyl hose or flexible copper on any lines.

[Ryker]

I'm in Sacramento, CA.

I got it to my shop and before I saw your response, I tried to start it. The starter just makes a big clunk but will not turn the engine at all. Am I jumping to conclusions that the engine is seized? Tomorrow I will pull the muffler and put a socket on the accessory drive nut to see if I can turn it.

[richard5933]

Just a wild thought, but could the compressor have failed and caused the engine to seize?

Possibly the governor failed first, resulting in a high-pressure situation - possibly explaining how that 3/4" line blew.

When it fully failed, the failure went further into the engine, which explains the white smoke seen from the rear of the bus?