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Author Topic: Parking valve doesn't pop up  (Read 3802 times)
it_mike
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« on: June 16, 2010, 05:28:05 PM »

Failed inspection in part due to the air brake system. Apparently, my parking brake valve is supposed to pop up when the pressure falls below a certain threshold. Any ideas where to start? I'd presume the valve needs serviced or replaced. Additionally there is no 'low air' warning.

Thanks,
Mike
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1980 TMC Crusader II
robertglines1
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« Reply #1 on: June 16, 2010, 05:35:22 PM »

valve is pre set to pop up at set pressure..replace is easiest about 45$..low air pressure switch is a elect activated switch in air system..ck bulb first..make sure wire is attached to alarm or light...if memory serves me right the low pressure switch is in the spare tire compartment...Bob
« Last Edit: June 16, 2010, 05:41:14 PM by robertglines1 » Logged

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bevans6
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« Reply #2 on: June 16, 2010, 05:39:09 PM »

what kind of bus?  Spring brakes or DD3?

Brian
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« Reply #3 on: June 16, 2010, 05:41:58 PM »

Mci 9
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bevans6
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« Reply #4 on: June 16, 2010, 06:03:35 PM »

My understanding is that the push-pull valve only pops up on low air pressure with spring brake systems.  DD-3 is supposed to apply the parking brake automatically at about 40 psi but I don't think the valve pops up.  At least it never has on my bus, I guess I will check tomorrow!  The low air sensor is mounted on the front wall of the engine bay, on the drivers side beside the rear electrical panel, and reads pressure in the accessory tank.  The  buzzer in in the front electrical bay.  The same buzzer is shared amoung all the alarms through three isolating diodes, so a diode could have failed. 

I have to write the air brake exam again (license renewal) in a few weeks so I have to relearn all the spring brake tractor trailer air brake stuff all over again.  Which colour glad hand is which, and what a tractor protection valve does and why.  Oh well.

If you have a DD-3 system, your inspector needs to know that or it will fail.  It's not the same as a spring brake system.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
it_mike
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« Reply #5 on: June 17, 2010, 03:42:13 AM »

Thanks!  I'm sorry, I should have included the bus details.

It's a 1980 TMC Crusader II, which I believe is the same as the MC-9.  I can't / don't know how to find the details on the brakes.  How do I tell if they're DD or spring brakes?

They also failed me because the tie rod ends seemed too loose on one side and too tight on the other.  Is this another unique item that's 'as designed'?
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1980 TMC Crusader II
bevans6
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« Reply #6 on: June 17, 2010, 04:14:36 AM »

Nope, tie rod ends are simple maintenance items, along with the drag link from the steering box.  I  remember talking to MCI who said the original tie rod was superceded by a newer version, my bus simply had a whole new tie rod assembly to the new pattern installed when it was brought into Canada, along with a new drag link.  They weren't expensive in 2002.  If you look at your rear brake chambers and count the hoses, if there are three hoses then they are DD3.  Common wisdom has it that it's extremely hard to change the DD3 to spring brake, since the spring brakes are a fair bit larger.  It can be done, though, I am told.

I am going to check to see if my push/pull valve pops the same way a spring brake system does  this morning.  I really don't think it does, though.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
Tom Y
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« Reply #7 on: June 17, 2010, 04:32:08 AM »

Brian, Yes it should pop up. I think that is what does the work setting the brakes.  Tom Y
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« Reply #8 on: June 17, 2010, 04:35:22 AM »

Mike, The low air alarm senser should be in the spare tire area. The alarm next to the driver in electrical panel?  Tom Y
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« Reply #9 on: June 17, 2010, 05:29:08 AM »

Mike,
   You probably have DD3 brakes. To confirm this look at the brake cans on the drive axle. If they have 3 hoses they are DD3, 2 hoses if they are spring brakes. Our parking valve pops up when the air pressure reaches about 40-45 PSI, this sets the DD3 parking/emergency brakes on the drive axle.
   Do you have the manuals and wiring schematic? You can jump the wires on the low air sensor to confirm operaqtion of the low air light and buzzer (both are required).  Jack
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« Reply #10 on: June 17, 2010, 05:58:04 AM »

My valve does not pop up automatically, so I guess I have some troubleshooting to do.  It's unclear to me if the pressure being discussed is the pressure in the dry tank, or the emergency brake tank.  It seems to me that when the pressure difference between the two tanks exceeds 30 to 40 psi, the shuttle valve operates presenting emergency tank pressure to the system.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
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« Reply #11 on: June 17, 2010, 06:05:59 AM »

Hope you can read this

John
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John Riddle
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it_mike
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« Reply #12 on: June 17, 2010, 06:26:45 AM »

Thanks John.  I have to get one of these manuals  Embarrassed
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1980 TMC Crusader II
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« Reply #13 on: June 17, 2010, 06:51:53 AM »

No matter which system, spring or DD3, the parking control valve will pop up when the air pressure being supplied to it drops below the strength necessary to hold it open against its internal spring.

Typically that's down someplace 25-40 lbs.

In a spring system, the parking brakes already started coming on as the pressure dropped through 60 lbs or so, and you'll be stopped before the parking brake control pops out.

In a DD3, the trouble is, the parking control valve is supplied by the isolated parking tank, which doesn't have a gauge to show you what's going on.

You can't get the parking control to pop on a DD3 without the parking tank pressure dropping far enough.

So, for this "inspection", your inspector needs to do some homework, and get the dust covered DD3 checking procedures out of his library. He was applying the wrong tests to your bus.

happy coaching!
buswarrior
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bevans6
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« Reply #14 on: June 17, 2010, 07:11:10 AM »

I guess if I kept fanning the brakes, engine off, then eventually I would have lowered the pressure in the parking brake tank enough for the spring to activate the push/pull valve.  Another way to check would be to blow the wet tank, the dry tank, the auxiliary tank and then the parking brake tank.  At that point the P/P valve should be able to operate.  I will go try that out!

My manual copy is handily missing that page, it starts chapter 4 at page 4-3.  I always wondered what was on page one and two...

Edit: went and tried it, it all worked exactly as advertised so I thankfully don't have to start troubleshooting anything.  Which is handy as I am leaving for a long weekend at the vintage car races at Mosport in an hour! 

One more question, sorry to drag this very good conversation out, but I need to know...  Page 4-21 of my manual says that the generator control and low air pressure switch is on the front of the left side firewall of the engine compartment, and I know there is a switch there.  My manual doesn't have a schematic of the charging system.  There is a schematic page that shows the alarms, and that schematic calls out a "FR LOW AIR SW", connected to stud 13 in the front electrical bay.  Which is right?  My alarm and tell tale light go off absolutely simultaneously with the generator coming on, AND I hear a click of some sort in the front of the bus under the floor or behind the dash.   Does anyone know for sure how this bit of the bus is supposed to work?

Brian
« Last Edit: June 17, 2010, 07:37:21 AM by bevans6 » Logged

1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
it_mike
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« Reply #15 on: June 17, 2010, 07:31:24 AM »

My manual copy is handily missing that page, it starts chapter 4 at page 4-3.  I always wondered what was on page one and two...

I've been using the online manuals, I'll have to see if they're missing those pages.
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thomasinnv
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« Reply #16 on: June 17, 2010, 07:41:22 AM »

My manual copy is handily missing that page, it starts chapter 4 at page 4-3.  I always wondered what was on page one and two...

I've been using the online manuals, I'll have to see if they're missing those pages.

is that online manual only for the 9, or is there one for the 8?
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1977 MCI Crusader MC-8
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« Reply #17 on: June 17, 2010, 08:24:06 AM »

Sorry, only mc9
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1980 TMC Crusader II
it_mike
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« Reply #18 on: June 17, 2010, 08:31:43 AM »

Quote from: buswarrior
In a DD3, the trouble is, the parking control valve is supplied by the isolated parking tank, which doesn't have a gauge to show you what's going on.

You can't get the parking control to pop on a DD3 without the parking tank pressure dropping far enough

OK, now I'm confused again. If I use pumping action on the brake pedal to drop the main system pressure, will this cause my valve to pop-up?  Brian,  are yours DD3 or spring brakes?
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1980 TMC Crusader II
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« Reply #19 on: June 17, 2010, 09:03:42 AM »

I guess if I kept fanning the brakes, engine off, then eventually I would have lowered the pressure in the parking brake tank enough for the spring to activate the push/pull valve.

It doesn't matter -- he was using the wrong procedure, watching for the pop-up at a particular gauge reading.  Your gauge and tank system aren't set up to match the procedure, and most examiners really don't know anything that isn't in their manuals.  Some schools, truck and bus companies specifically ask for the good ones by name when setting up an inspection, and will even send their trucks from one end of the state to the other for inspections because it's cheaper for them to go all that way than to have trucks fail inspections that they should have passed.

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bevans6
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« Reply #20 on: June 17, 2010, 09:12:02 AM »

On your bus and my bus, both with DD3 systems of similar vintage, the P/P valve handle will ONLY pop up on it's own when the pressure in BOTH the dry service tank and the parking brake tank are below 40 psi simultaneously.  If EITHER is above 40 psi, it will not pop up automatically.

You probably could do it by fanning the brake pedal, but there is a lot going on there, what with the inversion valve switching things and the shuttle valve switching between the dry service tank and the parking brake tank.  I know that I fanned my brakes down to 10 psi on the gauge and it did not pop up, because I still had pressure in the parking brake tank at that point. 

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
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« Reply #21 on: June 19, 2010, 07:43:28 PM »

And remember, it is the Inspector's responsibility to have his/her proper procedures in order.

How did they inspect all the older coaches?

Get your tie rod fixed and back you politely go!

happy coaching!
buswarrior
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« Reply #22 on: June 20, 2010, 12:14:00 PM »

If you think you have problems with inspectors not using the correct procedures, you should try owning an MCI in Australia where DD3 brakes are just about unheard of. Every year I have to get out the manual and go through the system with the inspectors - otherwise I WILL get a defect because they only know about normal spring brakes
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