Author Topic: Mc8 won’t air up past 60 psi  (Read 727 times)

Offline SeanM

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Mc8 won’t air up past 60 psi
« on: November 02, 2019, 02:56:30 PM »
HELP  :'(.  Started off not being able to get air to register on gauge. Replaces brake chamber and lines, then two air bellows. Finally got it to build pressure.  However would only go to 60 psi. Looked around for more leaks...found one. On one of the tanks in the front of buss (driver side tank). Was able to temporarily plug it. Have a new tank on the way from US Coach. Still it will not air past 60. Getting frustrated on this thing. Anyone in Tampa that knows the system and can help would be greatly appreciated. Tired of chancing my tail on this.

Offline Ed Hackenbruch

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Re: Mc8 won’t air up past 60 psi
« Reply #1 on: November 02, 2019, 03:00:00 PM »
If you have a ping tank on the back bulkhead wall, check to see if it is plugged up.
Used to own a 1968 MCI 5A with 8V71 and Allison MT644 transmission.

Offline SeanM

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Re: Mc8 won’t air up past 60 psi
« Reply #2 on: November 02, 2019, 03:24:37 PM »
I’m able to add air to bus from the pink tank attachment but still doesn’t want to go past 60. And the ping take way takes forever. Is that normal? I’ll usually stay from ping tank then at about 30 I’ll turn bus on and use motor to fill quicker

Offline richard5933

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Re: Mc8 won’t air up past 60 psi
« Reply #3 on: November 02, 2019, 03:56:08 PM »
Stuck check valve? Air dryer stuck open? With the pressure stuck at 60, I'm wondering if there is a safety valve somewhere which is stuck?

Just stabbing in the dark here a bit, since my time has been spent on GM buses. If your manual shows the air flow circuit I'd start following from back to front.

On my bus there is an airline connection in the engine bay - that one will allow me to fill the entire system to 120 psi. There is also a connection under the driver's seat, but it doesn't fill the entire system. Perhaps you have multiple air connections?
Richard
1974 GMC P8M4108a-125 (Custom Coach "Land Cruiser")
1964 GM PD4106-2412 (Former Bus)
Located in beautiful Wisconsin
KD9GRB

Offline robertglines1

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Re: Mc8 won’t air up past 60 psi
« Reply #4 on: November 02, 2019, 04:33:54 PM »
common problems and solutions . air beams (built into bus frame one each side of rear and one across front) leak---solution use block off plates between top of air bags and air beams. You can do without the storage area/volume. with little noticeable ride differance = longer term problem solver.  Check to see if tank your talking about is leaking around straps.  PPV pressure priority valve-- Makes sure any pressure in system is directed to brakes first. Usually 45lb min.   Mix you up some soapy water( I like dawn) in a old spray bottle.  Make sure check valve between wet and primary tank works. Like you say it would be nice to get a hands on opinion/help. I had a mci 8 at one time. Also check tank drains (pedcocks) known to leak - Cheap to replace. in rear area just forward of step up(inside floor) there is a access engine cover--Air compressor is accessable to check for leaks there. From what I remember and not ...
Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana

Offline Fred Mc

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Re: Mc8 won’t air up past 60 psi
« Reply #5 on: November 02, 2019, 05:11:33 PM »
I would think that a leak large enough to prevent pressure above 60lbs would be VERY evident. Perhaps its the pump that is worn or the regulator. When mine went it wouldn't air up at all.
Regards
Fred

Offline richard5933

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Re: Mc8 won’t air up past 60 psi
« Reply #6 on: November 02, 2019, 05:44:36 PM »
Has it ever gone over 60 since you owned it?
Richard
1974 GMC P8M4108a-125 (Custom Coach "Land Cruiser")
1964 GM PD4106-2412 (Former Bus)
Located in beautiful Wisconsin
KD9GRB

Offline SeanM

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Re: Mc8 won’t air up past 60 psi
« Reply #7 on: November 02, 2019, 07:47:28 PM »
I have only owned it for 4 weeks. But no, hasn’t been up at all. Just recently got it to 60. Been trying to get it off the lot I bought it from since. The biggest leak found what on the tank. Haven’t come across anything else. I agree though preventing it from going above 60 would be i big leak

Offline buswarrior

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Re: Mc8 won’t air up past 60 psi
« Reply #8 on: November 02, 2019, 08:32:50 PM »
briefly, think bad things of previous owner, then accept that as what it is, and move on...

reaching 60 lbs suggests some good things as far as the the core brake tanks, not a guarantee, but at least you got this far, the pressure protection valve opens around 60 lbs, so all the auxiliary stuff now gets exposed, suspension, wipers, shutters, fan dampers, belt tensioners all combine to destroy further air building efforts...

Do you have a gun to your head to get out of there?

You have to solve each source of leak, as you find them, until you get some sort of air integrity.

Go back, go back again, go back until you SCREAM, and find the leaks, fix them, and it will drive out of there.

It is some awful big leaks to defeat the engine driven air compressor, find the big ones, work backwards from those.

happy coaching!
buswarrior



Frozen North, Greater Toronto Area

Offline chessie4905

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Re: Mc8 won’t air up past 60 psi
« Reply #9 on: November 03, 2019, 04:04:42 AM »
If you haven't done already, you need an air source that doesn't  make noise to drown out the leaks. Move aux. compressor away with long hose, and around a corner, place in vehicle, whatever to eliminate it's  noise.
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Offline robertglines1

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Re: Mc8 won’t air up past 60 psi
« Reply #10 on: November 03, 2019, 06:29:50 PM »
does bus rise to drive height? About 12 inches below bottom of Bay doors.  Is gauge any good?  I know your passionate about buses or you wouldn't be trying so hard.  lot of experience on board.. will help as long as you ask questions.
Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana

Offline SeanM

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Re: Mc8 won’t air up past 60 psi
« Reply #11 on: November 04, 2019, 08:57:08 AM »
I plan on trying to move air source further away to see if I can hear any leaks. Also will be using lots of dawn and water.
Bus does not go to ride night. Gauge does seem to work. Can watch it go to 60 psi then seems to stay. This is even with motor compressor. I’ve check all tanks to see if air in them and they do get air.

I have definitely thought bad things of the previous owners. This might even be why they got rid of the bus. I’m trying to be calm and rational with it but I’m loosing patience. If I could just get it to when I will be keeping it I wouldn’t be stressing so much. It’s the time schedule of it being stuck at place of purchase. Tried to have it towed. No one is willing due to air suspension not working.

Offline SeanM

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Re: Mc8 won’t air up past 60 psi
« Reply #12 on: November 04, 2019, 08:59:19 AM »
I do have maintenance manual. However the air line charts are all blurred so can’t understand what is what. Having hard time figuring out what is what and what goes where to even check valves.

Offline Astro

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Re: Mc8 won’t air up past 60 psi
« Reply #13 on: November 04, 2019, 09:06:17 AM »
If you bought it, order up a landoll and take it home and park it.  Relax. Then get to fixing it on your terms. $750 is cheap considering you just adopted a bus.
Ken
Arlington, WA
1971 MC-5B, U7017, S9226 (On the road)
1945 Flxible Clipper (In conversion)
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Offline robertglines1

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Re: Mc8 won’t air up past 60 psi
« Reply #14 on: November 04, 2019, 09:18:05 AM »
watch gauge when it hits maximun (60 lbs you said) push brakes and hold.don't pump. If the air basically drops out of site it's on brake side.... little change say 10 lbs= look to accessory side( air bags ) etc 
Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana

Offline buswarrior

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Re: Mc8 won’t air up past 60 psi
« Reply #15 on: November 04, 2019, 09:27:56 AM »
You have a very large leak, it will not be noisy, big leaks just let air out.

You need a collection of fittings in order to put an air fitting and a quarter turn valve into the drains on your air tanks.

Put air directly into tank under the driver, accessible through the door outside under the driver window, under the electric panel. And report back on what that does for you.

You could have tanks rusted out, burst/aged hoses, valve internals leaking out exhausts.

Go and turn the air supply to the shutters/dampers right off to get that ball of mess out of the picture for now.

You are going to need air schematics, better work on getting that sorted out to. No reference materials, can't help yourself.

Happy coaching!
Buswarrior
Frozen North, Greater Toronto Area

Offline Jim Eh.

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Re: Mc8 won’t air up past 60 psi
« Reply #16 on: November 04, 2019, 12:46:18 PM »
My suggestion would be to remove the compressor discharge line AT the compressor and connect an alternate air source. It may take a few fittings to rig up but since it is a difficult leak to find, start at the source and work your way down stream.

I have had main air lines with holes in them the size of Seattle. It is something that you would think would be immediately obvious but like said above, large holes = little sound. You may even if you have to plug the other end of the main line to find a leak.

The system normally would not leak back out the compressor discharge line when charging the "wet" tank due to a check valve on the inlet of the tank. The check valve may be missing or inoperative between the tank and the compressor line.
"Some days it's just not worth chewing through the restraints"
Jim Eh.
1996 MC12
6V92TA / HT741D
Winnipeg, MB.

Offline SeanM

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Re: Mc8 won’t air up past 60 psi
« Reply #17 on: November 04, 2019, 01:31:23 PM »
Well finally getting her home. Found someone to tow her

Offline SeanM

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Re: Mc8 won’t air up past 60 psi
« Reply #18 on: November 04, 2019, 01:32:32 PM »
Will now have ample time to diagnose her sickness. I will still be asking for help lol

Offline richard5933

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Re: Mc8 won’t air up past 60 psi
« Reply #19 on: November 04, 2019, 01:48:20 PM »
You're way ahead of many starting out. You know the engine runs and you'll soon have it at home so you can work on it at your leisure. Good news on the tow.
Richard
1974 GMC P8M4108a-125 (Custom Coach "Land Cruiser")
1964 GM PD4106-2412 (Former Bus)
Located in beautiful Wisconsin
KD9GRB

Offline buswarrior

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Re: Mc8 won’t air up past 60 psi
« Reply #20 on: November 04, 2019, 04:03:22 PM »
Reaching 60lbs and no further suggests the leak is on the aux side. If a main line or tank was ruptured, the coach might get to 25 lbs at most.

Simulate it on your own coach by opening different tank drain valves and then run it up.

An open wet tank drain valve, used to do this to demonstrate the transit installed emergency air brake release circuit, the gauge on a dual brake system in a GM 5307 wouldn't make it past 30lbs.

With practice, you can set any tank drain valve to simulate a minor failure, to see if the trainees are actually paying attention, or just spewing forth memorised rote...

Nope, never made it into the curriculum, the rest of the trainers would have to know what all this means....

Training course can't be any smarter than the trainer...

Happy coaching!
Buswarrior
Frozen North, Greater Toronto Area

Offline Dave5Cs

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Re: Mc8 won’t air up past 60 psi
« Reply #21 on: November 04, 2019, 04:37:15 PM »
Change the air Governor. They are about 10.00 and lots of times thats all it is if you don't hear or see any other leaks. Check the leveling valves for leaks too.
"Perfect Frequency"1979 MCI MC5Cs 6V-71,644MT Allison.
 1998 Jeep TJ & 2002 Buick Century, Roseville,CA
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Offline SeanM

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Re: Mc8 won’t air up past 60 psi
« Reply #22 on: November 04, 2019, 04:41:43 PM »
When I bought it it didn’t run. Was a stuck rack. Was able to get them all free and turned over no problem. Then came the air problem lol. Always something it seems. Guess I better get used to it.

Agreed now that it’s home I can take my time and go through it without feeling a time crunch. The new tank will be here this week. Will replace that then check everything you all are suggesting.

Offline Jim Eh.

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Re: Mc8 won’t air up past 60 psi
« Reply #23 on: November 04, 2019, 05:13:56 PM »
Reaching 60lbs and no further suggests the leak is on the aux side. If a main line or tank was ruptured, the coach might get to 25 lbs at most.

Could be but it would seem that it would be quite audible at that point. I have had mainline leaks sized so that the system will reach 60 and when the aux valves open it will build no more. This is the reason it drove us nuts trying to find the issue. But you are probably correct and in this case the problem lies in the aux side.
"Some days it's just not worth chewing through the restraints"
Jim Eh.
1996 MC12
6V92TA / HT741D
Winnipeg, MB.

Offline Bus Lurker

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Re: Mc8 won’t air up past 60 psi
« Reply #24 on: November 04, 2019, 08:26:55 PM »
Sean,

Having the coach hauled away was a great solution.  Just out of curiosity what's the going rate to hire a Landoll?

Mike

Offline SeanM

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Re: Mc8 won’t air up past 60 psi
« Reply #25 on: November 05, 2019, 05:22:21 AM »
It cost me 500. Was towed 35 miles. Charged by hour. Took about 4.5 hrs due to traffic. Awesome guy to work with very fair and willing to go the extra mike. Other quotes I git where 900+ and non of them where willing to to it due to it not airing up.

ALFIE'S HEAVY TOWING & TRANSPORT

6408 Causeway Blvd, Tampa, FL 33619
(813) 917-9523


Offline Ed Hackenbruch

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Re: Mc8 won’t air up past 60 psi
« Reply #26 on: November 05, 2019, 08:38:32 AM »
The reason i mentioned checking the ping tank is a few years ago i helped a GM owner who could not build air pressure past 30 or maybe it was 60 lbs.  We spent several hours trying different things looking for leaks. Turned out he had never drained his ping tank and it was plugged full of what looked like reddish sand which was probably really just rust.  Used a screw driver and a piece of stiff wire to get the stuff out....fired up the bus and it built air just fine.  Even though it says right on it to drain daily, or in our case, after anytime you have driven it, most people ignore it. Don't just open the drain, stick something up there and see if anything comes out.
Used to own a 1968 MCI 5A with 8V71 and Allison MT644 transmission.

Offline Boomer

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Re: Mc8 won’t air up past 60 psi
« Reply #27 on: November 05, 2019, 08:03:11 PM »
Nice to see a trucker who isn't afraid of an over height load.
'81 Eagle 15/45, NO MORE
'47 GM PD3751-438, NO MORE
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