1973 Blue Bird

[Rudy]

Mark, I remember that you gave the spring can warning before. That sounds scary. I can assure you that I will never attempt to do that.

[Mark R. Obtinario]

It has been a while since I have looked at the wiring for the brake light circuit. Some buses came from the factory so that when the spring brake was applied the brake lights came on. Almost all Crowns came wired that way.

If you follow the air lines around you will find two switches that will energize the brake lights. One will energize when you add air as in when you apply the brake pedal. The other one will energize when you remove the air from the line as in when you apply the spring/parking brake.

With the kind of spring brake control that you have you really don't want to remove the wiring to the spring/parking brake circuit. Unlike the one button spring brake controls (the most common), the control you have is designed to work when your air system has been depleted. With the type of control you have you can move the vehicle with only the emergency air. The little handle then becomes your service brake. And every time you move the little handle it signals your intentions by turning on your brake lights.

Personally I don't understand the issue. If the engine isn't running with the key in the run position the low oil pressure buzzer is going to be sounding off. That would bug me more than a couple of lights energized.

[Rudy]

Mark, it's not really a big issue. I do have a buzzer that goes on when the pressure falls to around 50 or 60.

Now that I have LED brake lights, they will not burn out like the old ones did.

[Rudy]

WOW! Over 20,000 views on this thread. Must be all my questions.

[Dennis The Bus Dweller]

Mark, it's not really a big issue. I do have a buzzer that goes on when the pressure falls to around 50 or 60.

Does your system lose air? If so, you better get to the bottom of that before you roll out for sure

[Sharkey]

Now Dennis, don't stimulate Rudy's worry-wart genes.

All systems lose air. The only problem is when they lose enough air that the leaks and normal brake application losses exceede the capacity of the compressor to keep up the pressure.

Left sitting, you can expect your bus to gradually lose pressure. It might take an hour or two, or it might take weeks. When I first got my Corwn, it could sit for a month and lose only a pound or two. Now it goes down pretty much completely after 24 hours.

You bus should not be making lots of hissing noises after you shut it down, those type of leaks should be investigated and repaired.

My coach has an air fitting on the compressor so that I can use my 6HP shop compressor to pump up the system before I start the engine. That way, I don't have to listen to the buzzer squawk while the system builds pressure from the engine idling.

[Rudy]

Mark, it's not really a big issue. I do have a buzzer that goes on when the pressure falls to around 50 or 60.

Does your system lose air? If so, you better get to the bottom of that before you roll out for sure

Dennis, when the motor is running, it does not lose air pressure.

I did a test the other day. It took about 50 good pumps on the brake pedal in a row before the gauge went low enough to trigger the buzzer.

[Rudy]

Sharkey, there are no hissing noises when I shut the engine off. The next day, the pressure will be a bit over 30 lbs. It holds the 30 lbs for quite a few days.

[Dennis The Bus Dweller]

Hmm, I got one of those fittings to and I got 2 valves in the drivers side wheel to bleed off any water that builds up in the lines

[Rudy]

Ha Ha. Now I am gonna look for fittings on my bus.

The beauty thing is with everybody's help in my quandaries, I am learning more about my bus and am feeling secure with that knowledge.

You are right, Sharkey. How else could I know about my bus without the kind help of the "bus family"?

I am honored.

[Rudy]

It sure is great to have some mechanical wizards on this site. Thanks for the brake info, Sharkey.

I just read Ezra's thread and had a question for Mark.

You say that diesel engines don't have vacuum.

I thought that vacuum was created in a gas engine by the cylinders going down in their revolution. When they go up, they cause compression.

Pistons on a diesel go up and down as well.

I am wondering what may be the difference.

I am guessing that it has something to do with the valve system.

Would you please give a brief explanation. Thanks.

[Mark R. Obtinario]

Every air tank should have a drain valve on the bottom. Most of the newer vintage vehicles have automatic drains--every time the compressor cycles it will spritz a little and exhaust any moisture.

You should have a minimum of two tanks. The first in the line will be the wet tank. If you don't have an air dryer that tank will have a lot of fluid built up, particularly if you are operating in a humid climate. That tank should be drained every day. Best practice is to open the drain at the end of the day and let it drain over night.

The next in line is known as the dry tank. It should have little or no moisutre in it. This tank should be drained at every regular service interval. If any appreciable amount of moisture is found in the dry tank you will need to drain it more often.

The last thing you want is moisture getting out into your brake lines, valves, or brake cans. Not only will the moisture compromise things but when it gets cold they can freeze up on you. This is definitely not a good thing.

If you have more than two tanks (most of the Crowns and Gilligs I have seen had four) you will need to drain those on a regular basis as well.

Getting under and draining the tanks on a regular basis needs to be done even if you have spitter valves. Spitter valves do fail and they also do not drain everything out.

If your drain valves are attached to pull cords it just becomes a matter of holding the cord for ten or fifteen seconds every day.

[Mark R. Obtinario]

If you ever drove a car or truck with vacuum wipers you would understand.

At wide open throttle there is no manifold vacuum. So going up hill with the throttle wide open the wipers would quit. Going downhill with throttle closed or partially open the wipers would just about beat the windshield to death.

Since diesel engines have no throttle plates there is no way to create vacuum.

Which is also why so many of the accessories that used to be operated by vacuum in cars and trucks are no longer operated by vacuum. With the advent of EFI there isn't a throttle plate in the same sense a carb had a throttle plate. As a consequence, most modern vehicles do not have as much manifold vacuum as vehicles made back in the day.

[Mark R. Obtinario]

Just don't ask how a Jacobs engine brake works.

I have had it explained to me several times and I still don't understand how they work.

All I really understand is it shuts fuel off to the cylinders that are doing the pumping and instead of exploding fuel to create power it turns the cylinders into air compressors that slow things down.

Blue Ox and other exhaust brakes do the same sort of thing by blocking off the exhaust. By not allowing anything or allowing only a portion of the exhaust to exhaust it slows the engine down.

[Rudy]

I drove a 1961 Galaxie with vacuum wipers. I remember how they worked (or didn't work). So that vacuum came from the intake manifold? The vacuum was caused by the pistons?