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Author Topic: Tag axle low air warning  (Read 1581 times)
captain ron
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« on: December 03, 2006, 06:07:28 AM »

I pulled out of Indy this morning around 7am after stopping for a couple hour nap. a few miles down the road my tag axle warning light started flickering getting brighter then slowly getting dimmer and eventualy going off and staying off. It was extremly cold. my water froze. Is this possibly due to the cold or something I need to look in to?
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larryh
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« Reply #1 on: December 03, 2006, 07:04:13 AM »

This sounds like typical air line freezing make sure you drain your air tanks daily and check into adding alcohol to tanks.

LarryH
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« Reply #2 on: December 03, 2006, 07:54:35 AM »

Yeah, you proabably got moisture in your air system. I'd suggest draining all the tanks after running for awhile so it's all warm. Especially, drain the valve in the engine compartment, under the tag axle unloading valves. You should also service your air dryer soon, if you haven't done it recently. Replace the dessicant cartridge and rebuild the purge valve. Make sure the electric heater element is working properly, too.



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Craig Shepard
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« Reply #3 on: December 03, 2006, 08:40:40 AM »

quote "my water froze. Is this possibly due to the cold " unquote  Npt sure,  but possible.
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buswarrior
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« Reply #4 on: December 03, 2006, 10:56:17 AM »

Hello CR.

If it has been awhile since you've done air system maintenance, I'll echo the advice already given.

The tag axle system, with its shut off valves, pressure regulators, in-line filters and the pressure switches themselves, has lots of places a lick of moisture could fool with you.

Get under there and open all the drains, 4 tanks and the valve in the engine room curb side door, and watch what comes out. You should only get the smallest amount of mist from the wet tank and a bit of oily wet from the engine comp drain. The rest should just blow clear air. Any mist at all from the others, or a lot of water in the wet, you want to get that thing dosed with alchohol as a defensive move, and get the air dryer freshened up as the cure.

You count on the bus for paying gigs, don't want it to let you down!

happy coaching!
buswarrior
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Kristinsgrandpa
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« Reply #5 on: December 03, 2006, 06:05:50 PM »

When you get under there and open all the valves, it helps to have air pressure on the tanks.

Since no one mentioned that, I thought I'd bring it up.

Ed
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Dallas
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« Reply #6 on: December 03, 2006, 06:17:12 PM »

I just helped a new owner of a P8M4905A get it on the road the other day.

He decided he wanted a airhose quick connect on the air tank above the batteries.

when he took the connection apart where he was going to install the Tee lots and lots of goo came shlurping out.

It took a couple of hours to get most of it out, and when we finished, we had almost 3 gallons in a tub and another half gallon in a jug.

We didn't even get to the wet tank since it was raining by that time.

This post really has no point, except to say, Keep your air tanks emptied! If you don't, it will destroy seals and make stuff not work at all, (like the wipers).

Dallas
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Kristinsgrandpa
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« Reply #7 on: December 03, 2006, 06:44:50 PM »

WOW.....Dallas that was your 1000th post.

Ed
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captain ron
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« Reply #8 on: December 03, 2006, 07:54:16 PM »

I don't know where all the tanks and valves are on this bus. only the one under the drivers area. enlighten me, no manual.
78 mci crusader
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henrymc7
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« Reply #9 on: December 04, 2006, 07:32:28 PM »

In addition to your accessory tank under the driver's compartment, your 78 MCI should have 3 more tanks. The one everyone calls the "wet" tank is the first after the compressor and air dryer. It is also called the supply tank and is meant to catch any moisture and contaminents the air dryer misses. It is located in between your rear duals. It also gives the hot, compressed air a chance to cool down. Cooler air may still have some moisture in it so it should be drained every time you use the bus. The other two tanks are near the front axle. One is your primary reservoir, which is monitored by your air gauge in the dash. The other one is your emergency brake air, part of the DD3 system.

Draining the wet tank right down first usually takes away any residual moisture but as an extra precaution, draining the remaining tanks (doesn't matter which order, just empty each one before moving on to the next) is good preventative maintenance.

The first time I drained my MC-7's tanks, the wet tank had quite a bit of rust-colored water and the others small amounts. Now, when I drain them, the wet tank has next to nothing and the others nothing at all. BTW, if you do this consistently, you will see when your air dryer cartridge needs replacing (excess water) and if the compressor is having problems (any oil).

Henry
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tekebird
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« Reply #10 on: December 04, 2006, 07:55:07 PM »

Ron, you need to get yourself a parts and maint manual if you are going to be out trekking

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buswarrior
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« Reply #11 on: December 05, 2006, 02:31:26 AM »

Hello.

Henry, they switched 'em on you!!!

The wet tank on post 1975 MCI's is up front at the front axle, the dry tank is back at the rear axle, the parking tank is the other one up at the front axle, and the auxiliary is under the driver.

Ron, if you lie on the ground, just behind the front wheels, you'll see the bottoms of the front two tanks mounted in the middle of the bus against the bulkhead, just back of the front axle. Drains are on the side of the tanks at the bottom.

If memory serves.... the wet tank is on the driver's side..... I think..... Hard to remember when you do all this fooling around lying on your back and crawling in from this side and that side....and mine doesn't show me any water to help me remember.....

The air dryer will be mounted up there just ahead of the front axle on the opposite bulkhead from the tanks.... if you have one. Some fleets didn't option them.

The rear tank is hard up against the bulkhead that is the back wall of the last baggage compartment. That bulge in the compartment bulkhead fits the tank.

You already know where the aux tank is under the driver.

You may need a pair of pliers to open the valves, and put some lumber under there to prevent the bus from falling on you.

happy coaching!
buswarrior
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ChuckMC9
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« Reply #12 on: December 05, 2006, 07:16:23 AM »

Now, when I drain them, the wet tank has next to nothing and the others nothing at all.
Same here. But I've been wondering if one is supposed to bleed them enough to insure the obvious moisture is gone, (which is hardly any) or completely evacuate all the air inside each one after every run?
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buswarrior
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« Reply #13 on: December 05, 2006, 09:41:46 AM »

Hello.

Draining the tanks is a contentious issue as to the "proper" methods.

Regardless of what you were told, or what you believe, or what you have faithfully done for many decades, or days, as the case may be....

The goal is empty tanks, and how you get them doesn't matter. Daily, weekly, monthly, annually....

So, for a bus with no air dryer, drain far more often than a bus with one. A worn out air dryer will need to be drained more frequently than a fresh one. Operate in a humid place, more water, operate in a dry place, less water. Warm is more humidity, cold is less. And how long has the compressor run in the last period of time? Some busnuts compressors run as much in a year as a commercial truck's might in a week.

The long and the short of it, we drain the tanks so that there is no build up of moisture or contaminants.

The moisture is condensed water from the humidity of the air the compressor sucked in and pumped into the system.

The contaminants is engine oil that lubes the compressor that got past the rings of the compressor pistons, or dirt, if the air filter has failed to catch it. That oil is laced with engine combustion byproducts, so it is acidic and corrosive in nature.

A properly serviced air dryer does a great job of catching most, if not all, of the stuff from a normally functioning air compressor.

If you are pumping oil with your compressor, the dryer desicant is ruined. Replace the compressor and the desicant.

The contaminants/moisture take up space meant to store air, water in the air lines will seriously harm brake timing, and the crud will damage the internals of the valving, rust the return springs, harm the rubber seals, pit the seats for the seals, cause things to stick, lead to freezing of valves in the cold places...

If left for long periods of time, the contaminants and moisture seperate and a sludge forms in the bottom of the tank. A thick milk shake consistancy that gloops out if you leave the tank drains open for an extended period is a sign of neglect.

The goop will not neccesarily come out if you give the drains a quick blast. The air pressure races out the drain, over the top of the sludge and prevents it from moving. The sludge will drip out slowly after the air is gone.

Picture the dirt in the bottom of the bathtub. It leaves at the end, when there is some flow at the bottom.

Cable drains are great for ease of a quick drain, but a real contributor to problems, since they cannot be easily left open overnight, and often have fairly small openings.

Want to see how yours is?

Drain all the air, and leave the drains open. Remove them, if it is easier than tying the cable back. Opens a bigger hole anyway. Position a piece of paper towel under each drain and see what you get overnight.

Hopefully nothing but a drip or two from the wet tank.

If you get goop, you might want to consider flushing the tank, as part of trouble shooting the whole thing, compressor and dryer. Loosen off another fitting to let air out and introduce some suitable solvent up through the drain, let sit to loosen and drain it out.

I have heard a story of an old truck having so much goop in it, the goop had stiffened up to the consistancy of flood plain mud, and when cut open with the sawzall, the sludge was contoured with the lowest point at the drain, and built up away from it, like the tornado effect when you drain the bathtub.
Spare truck, kept in the back of the yard, infrequently used as a loaner or to a new driver.

It was found when a grizzled veteran driver complained to the shop that the air compressor was cycling too often and the pressure drop on the gauge was quite large for any brake application. The mud had stolen close to half the volume of the tank, yet when you pulled the drain, a little blast of air/moisture and that was that. They cut it open because they were surprised at the weight of it when they replaced the tank.

happy coaching!
buswarrior
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ChuckMC9
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« Reply #14 on: December 05, 2006, 10:12:40 AM »

The goop will not neccesarily come out if you give the drains a quick blast. The air pressure races out the drain, over the top of the sludge and prevents it from moving. The sludge will drip out slowly after the air is gone.

Picture the dirt in the bottom of the bathtub. It leaves at the end, when there is some flow at the bottom.

Cable drains are great for ease of a quick drain, but a real contributor to problems, since they cannot be easily left open overnight, and often have fairly small openings.


Want to see how yours is?

Drain all the air, and leave the drains open. Remove them, if it is easier than tying the cable back. Opens a bigger hole anyway. Position a piece of paper towel under each drain and see what you get overnight.

Hopefully nothing but a drip or two from the wet tank.


MAN, BW, you're getting better all the time! What a PERFECT answer that 'splains everything! Boy am I GLAD I've started reading the boards again!

Many thanks - Chuck
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