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Author Topic: Air leak at brake valve  (Read 5641 times)
Tenor
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« on: May 28, 2008, 05:35:40 PM »

My brake valve seems to be constantly letting air out the rear side of the valve body through the vent.  I assume this is not normal.  My brake lights are also remaining on.  I suspect I need to rebuild the valve, but I'd like advice.  The bus is my MCI 7.  Thanks!

Glenn
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Glenn Williams
Lansing, MI
www.threemenandatenor.com
1968 MCI 7 Ser. No. 7476 Unit No. 10056
8v71
4 speed Spicer
ol713
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« Reply #1 on: May 28, 2008, 06:40:26 PM »


Hi;
   Would like to know which valve we are talking about.  You have the
   brake application valve and also park brake valve.
                                         Merle
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Tenor
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« Reply #2 on: May 28, 2008, 06:45:21 PM »

Thanks for the clarification!  This is on the brake application valve.
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Glenn Williams
Lansing, MI
www.threemenandatenor.com
1968 MCI 7 Ser. No. 7476 Unit No. 10056
8v71
4 speed Spicer
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« Reply #3 on: May 28, 2008, 07:56:27 PM »

Glenn,

Since air pressure is triggering your brake lite switch, I have to assume air pressure is also being applied to your brakes, so its possible the brakes are dragging. If they are dragging, you can get the drums hot enough to start the tires on fire.

 In my experience the treadle valve is usually not the problem even though its passing air. First thing to try is to pull up on the pedal to be sure it returns all the way. Sometimes air glitches come and go so you should build air and pump the brakes down, (empty the tank) a few times to give a stuck valve a chance to free its self.

Air valves work fine for the most part without alcohol, but they still seem to like it and if I was having any problems that were not related to worn out parts, I would run some air brake alcohol thru the system. Bendix sells a good product.

How long have you had this unit? Has the treadle valve recently been replaced? Most valves have extra ports making it easy to leave out a plug or re plumb a line wrong.

The largest air line hooked to the treadle valve is likely supply. You normally need only one supply so you can loosen each of the other lines hooked to the valve and see if one is returning air. If one is returning air to the valve, see where it goes, and report back!

I think a coach has to balance the front and rear pressures, or they will leak off the high side, make sure that both sides are full of air and that the problem doesn't resolve its self or that you don't find a big air leak on one side. Did some one turn a wiper on?

Is the emergency air supply tank (stored air) full, and not leaking? Is the emergency air supply tank control button stuck down? or up? ( The green one).

Well, theres a few ideas! Have fun.
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Tenor
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« Reply #4 on: May 28, 2008, 08:17:42 PM »

Thanks for the leads!

I have only had the coach since Sept, and I have put very few miles on it - about 40 this weekend, and I noticed that the brake lights were on as I arrived at my destination and that they would occasionally return to off, so I expected it to be an electrical issue.  Today, I discovered the source of the air leak that I have been aware of while doing other maintenance and found it to be the brake application valve.  I have no way to know if it has ever been removed - the bus sat for 8 or 9 years after the PO lost interest.  I have made sure the pedal linkage is clear of the valve and it should be returning to it's closed position, unless there is some foreign matter in there.   I'll disconnect the air lines going out of the valve tomorrow and see if one has air passing out when the valve is closed.  I'll also run the alcohol through the system.  Been meaning to, just hadn't got there yet.  The emergency brake valve has been working fine, but tonight the warning light for it came on as well.    Where does this lead you?

Glenn
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Glenn Williams
Lansing, MI
www.threemenandatenor.com
1968 MCI 7 Ser. No. 7476 Unit No. 10056
8v71
4 speed Spicer
Fredward
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« Reply #5 on: May 28, 2008, 08:32:04 PM »

Is the parking brake applied when you notice your brake lights on? A lot of coaches turn on the brake lights when the parking brake is applied. (I know you are talking about a leak at the brake pedal)
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Fred Thomson
Tenor
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« Reply #6 on: May 28, 2008, 08:34:31 PM »

Fred,
The lights are on whether or not the parking brake is applied, however, they have occasionaly returned to off when the parking brake is not applied as they should.

Glenn

Should the parking brake (emergency brake) dash light come on during parking brake use, or does it only come on if there is a problem in the parking brake system?  I'm starting to wonder if I have a leak in the parking brake system, that is causing air to be evacuated from the application valve.  Thoughts?

Glenn
« Last Edit: May 28, 2008, 08:36:55 PM by Tenor » Logged

Glenn Williams
Lansing, MI
www.threemenandatenor.com
1968 MCI 7 Ser. No. 7476 Unit No. 10056
8v71
4 speed Spicer
Tenor
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« Reply #7 on: June 04, 2008, 01:34:43 PM »

After talking with Luke at US Coach, we agreed that the application valve was bad, so he sent me a new one and it went in today.  That took care of my brake lights sticking on.  However, the new one constantly allows air to pass through it and out the wire mesh vent with the parking brake on or off.  I have done several hard pumps, rolled the bus forward and back, and there is no change.  The emergency brake tell tale is still lit.  Da Book says that no air is to escape through this vent when the brakes are not applied or during application.  Only during relase.  Any ideas?  I'm stumped.

On a side note, I ripped the tendon for my left bicep from my forearm on Saturday night and I go under the knife Friday.  I'd really like to get this puzzle fixed before I get laid up for a week or two!  While injured, I've built bunk beds, fixed my engine shut-off wiring system, re-wired the speedo (don't know if it works yet) and removed and installed this air valve.  I'm makin' progress!

Glenn
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Glenn Williams
Lansing, MI
www.threemenandatenor.com
1968 MCI 7 Ser. No. 7476 Unit No. 10056
8v71
4 speed Spicer
Sojourner
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« Reply #8 on: June 04, 2008, 10:54:50 PM »

Tenor.....Assumed application valve is OK, all lines are properly installed and still air leaking could be one of these steps:
1)   Main rear relay valve leaking via piston's "O" ring through “signal” line to application valve to exhaust.
2)   “Push & Pull” valve’s exhaust port connected to front wheel brake chamber’s line

I would loosen one nut fitting (not the supply line) at time and hand over exhaust port tight while spray soapy fine mist on loosen nut for air bubbles. The one that bubbled is the one to determine where it connected to.
If it comes from main rear relay valve….need to be replace.
If it comes from front brake line….trace the line for tee other than the normal tee to brake chambers. Other words, if more than one tee…..trace the extra tee where it connected to….in my MCI manual show it connected to Push & Pull’s exhaust port. If air is leaking from PP valve’s port…..replace it. Or you could have more than 2 tees on that same line….keep tracing until you find it.

Let us know your finding.

FWIW

Sojourn for Christ, Jerry
PS...leaks detector liquid is teaspoon of dishwasher liquid to pint of soft water.
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Tenor
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« Reply #9 on: June 05, 2008, 05:32:51 AM »

Thanks Sojourner, that's a logical step by step method.  I'll do that today and post back.
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Glenn Williams
Lansing, MI
www.threemenandatenor.com
1968 MCI 7 Ser. No. 7476 Unit No. 10056
8v71
4 speed Spicer
buswarrior
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« Reply #10 on: June 05, 2008, 08:15:10 AM »

oh dear....

happy coaching!
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« Reply #11 on: October 01, 2008, 08:14:43 PM »

hey i'm openign this back up because i'm still having an issue with my brakes.  they seem to be working ok, but the brake lights stay on.
previous posts seem to indicate valves?  so what do you check, are replacements hard to find?  i don't want to dismantle something that is hard to replace, or hard to dismantle.  i've got limited skillset, time and tools for doing this in the driveway.

with engine running, brake off, seems to roll easy so i don't think theyr'e sticking, full 120 lbs, the light by the park brake is on, and so are the lights in back.  we made a 60 mile trip, and the lights went out, but on the way home, never went out, so looked like i was riding the brakes.  i kept close eye on everything and no problem other than lights on.

tenor, what did you do and did it work?  wehre did u get parts, how expensive, and were they in stock? 
thanks.
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Tom
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« Reply #12 on: October 01, 2008, 08:29:17 PM »

Tom,check your switch on the model 15 if it hasn't been moved it is in the bottom door under the drivers window disconnect 1 wire if the brake lites go off you need a new switch and NAPA has those   
good luck
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gus
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« Reply #13 on: October 02, 2008, 07:41:09 PM »

Some brake light systems use a relay. I have no idea if an Eagle uses this system but if it does it is possible the relay is sticking.
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PD4107-152
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Tenor
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« Reply #14 on: October 03, 2008, 05:55:27 AM »

To follow up, I ended up replacing the brake application valve and the parking brake application valve.  The light went out once I replaced the application valve and has not come on since.  I think the application valve was a couple hundred bucks.  Not cheap!  The parking brake valve I got locally for 35.  I still leak air out the application valve, but I have no operational issues.  Later this summer I had to replace an air line to my pass side brake can, but still I have the air leak. 

On a side note, the surgery went great and I was back to 100% way ahead of schedule.  While I was out of commission, I installed the genset, remote radiator,  and rebuilt the couch base. 
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Glenn Williams
Lansing, MI
www.threemenandatenor.com
1968 MCI 7 Ser. No. 7476 Unit No. 10056
8v71
4 speed Spicer
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