Air Leak Woes

[brock]

Just bought a M923A2 and got it home.

I can hear air hissing in the intake stack after Ive turned the truck off. After an hour or so the hissing goes away.

When I restart my truck, the primary air pressure gauge reads pressure but the secondary gauge shows 0. To verify I started the truck and built pressure in both systems then shut the truck off and watched the air drop in the secondary circuit.

I realize I have a leak coming from the secondary air circuit. What is operated by this circuit?

Any info on locating air leaks would be most appreciated.

Thank you.

 

[Artisan]

Up at the top of the screen there is a link to TECHNICAL MANUALS.

DL all pertinent manuals and look for the section that talks about
air leaks and follow it.

BUT, if you flat out hear a leak TRACK IT DOWN AND FIX IT!
Find what is leaking and look for the parts needed to fix it and buy them
and Viola!

You are lucky you HEAR this leak! Seems to me you should be able to
go right to it, figure out what is going on w/ the TM's and fix it.

 

[Artisan]

PS,

What happened when you do a C.O.L.A. test?

 

[armytruck63]

Soapy water from a squirt bottle is your friend when it comes to finding leaks. Squirt it all over the air fittings until you see bubbles. Don't overtighten anything - just until the bubbles stop.

 

[plode]

My truck does the same exact thing. I've followed the TM's, and the P2P software and I still can't figure it out.

Soapy water hasn't helped as the leak is venting into the intake.

 

[brock]

I tried the soapy water but as stated by plode its venting through the exhaust side of the system to the intake stack therefore no bubbles at fittings.

I looked through the TM's but got impatient. I will read more thoroughly and troubleshoot.

What about the treadle valve? I read another post where someone had the same symptoms as me and found the source to be a faulty treadle valve. I figure these trucks have relavively low mileage and doubt the valve is worn out. Can they be rebuilt?

Thanks for all the info guys.

 

[Coffey1]

Mine does the same thing.
Pass's c.o.l.a but will leak down over time
Works great other than after hour or hour and half I am down to about 90 in both primary and sec.

 

[quickfarms]

When it stops hissing what is the pressure?

An audible air leak is an out of service condition regardless of weather the truck passes COLA.

 

[Artisan]

Can you take out the air cleaner and or it's box and find
what line it is then trace it?

Can you look for a line that goes into the intake and disconnect it to see
if it is the issue?

I have not been faced w/ this issue buts it seems to me that if you
can hear a problem it should not be to big of an issue to at least
find where that sound daylights, then trace it back.

Isn't there a pneumatic schematic in the TM's too? Maybe look
at that and look for a line that heads to the area where you hear
it leaking, trace it back to the problem.

Check valve leaking?

 

[brock]

When it stops hissing what is the pressure?

An audible air leak is an out of service condition regardless of weather the truck passes COLA.

After the hissing stops the pressure showing on the secondary gauge is 0.

Im not familiar with the C.O.L.A test. Whats the procedure?

 

[brock]

Can you take out the air cleaner and or it's box and find
what line it is then trace it?

Can you look for a line that goes into the intake and disconnect it to see
if it is the issue?

I have not been faced w/ this issue buts it seems to me that if you
can hear a problem it should not be to big of an issue to at least
find where that sound daylights, then trace it back.

Isn't there a pneumatic schematic in the TM's too? Maybe look
at that and look for a line that heads to the area where you hear
it leaking, trace it back to the problem.

Check valve leaking?

I am going to pull apart the intake system to isolate which of the three lines venting to the air cleaner.

Does anyone know what TM has the air line diagram is in?

Thanks for all the great info!

 

[quickfarms]

After the hissing stops the pressure showing on the secondary gauge is 0.

Im not familiar with the C.O.L.A test. Whats the procedure?

The COLA test is part of the CDL training.

A class b CDL is required to operate a three axle vehicle that has a GVW over 6,000 lbs, yes 6,000, in California

 

[plode]

I haven't found any diagram or anything in the P2P software that tells you which line connection is which on the air intake. There are 3 connections on the air intake on my truck. I've eliminated the one as it is the vents from the fuel tank etc.
It's one of the two larger lines- both of which I cannot get a wrench into loosen to determine which of the two it even is.

 

[brock]

The COLA test is part of the CDL training.

A class b CDL is required to operate a three axle vehicle that has a GVW over 6,000 lbs, yes 6,000, in California

I am currently prepping for my class B CDL test. Ill research the COLA test.

Thanks

 

[brock]

I haven't found any diagram or anything in the P2P software that tells you which line connection is which on the air intake. There are 3 connections on the air intake on my truck. I've eliminated the one as it is the vents from the fuel tank etc.
It's one of the two larger lines- both of which I cannot get a wrench into loosen to determine which of the two it even is.

I have three as well, one small and two large.

I tried tracing the lines but there are so many down there that I quickly lost the line in the frame rails.

This weekend I will see if I can isolate it.

Thanks.

 

[Artisan]

Brock,

In Arcadia, CA there is a company called DOOTSON TRUCK DRIVING SCHOOLS.
Get signed up there for at minimum a Class B license.
I might even ask for KARL as your teacher.
You will learn in a school bus w/ full blown air brakes just like your MV.
You can get an add on classification of PASSENGER too if you use the bus.
I got TANK also and I already had MC.

In California you have to have a class B license to drive that truck.
If you wreck and people are hurt be prepared to loose everything
you own in a court of law.

I am not being a dick here brock but I am telling you that
you should NOT drive that truck till you get some basic training.
Trying to learn it from guys online is a bad deal. Some of
the Utube videos are ok but there is NOTHING like a seasoned
professional who will teach you right from jump street.
I knew NOTHING about airbrakes and trucks and I did it
in 9 days...piece of cake!
My teacher KARL says I actually
did it in hours. I did all the reading and learning of the Calif Commercial
Drivers Handbook ON MY OWN, and DOOTSON gave me practice tests and I went
from knowing nothing about airbrakes and trucks like these, same boat
you are in, to a Class B in my pocket in 9 days.

Once you learn everything the law demands you know to drive these
types of vehicles on the public roads you will wish you had learned this stuff years ago.

It makes you safe and moreso others around you saf"er". It also
teaches you how to fix things because know you will know how
things work!

You know those Black and White CHP PickUp trucks you see on
the freeways? Well those guys know this stuff BY HEART and it is there JOB
to find the unlicensed and ill equipted drivers and trucks and get
them off the roads or fine them into oblivion.
If you get pulled over and you do not so much as have a Class B
you get to park the truck IMEDIATLY and a tow truck is called.
HUGE MONEY out the door.

If the truck has issues you get fined for all that too and there is
a LOT of it.

the COLA test is the one part of the DMV examination you do in person
in a truck w/ a DMV examiner sitting right next to you and JUST you two.
It is the one part you HAVE to ace or you will FAIL. I mean no exceptions,
you HAVE to know how to test the brake system EXACTLY or you fail.
All other parts of the tests there is a little leeway.

There are some online truck driving schools but you have to have a truck
to take the test in and to the best of my knowledge you can not use
a Mil vehicle to do it in Calif. (Verify that) . If you do use your own
vehicle it has to be PERFECT, no issues or it is an automatic fail.

If you go to a school you learn in one truck and you use that truck to
take your examine in so you are comfortable. You will thank me if you do it I am sure.

 

[doghead]

-20/24 or -30/34 TMs.

 

[zout]

Reading the TM BEFORE you tear apart anything or start shooting soapy water on anything I will tell you this is a normal function to vent out the stack - now you have to go see why in the TM's - use your time reading them instead of trying fix something not broken.

Mine does the same thing - Swiss does the same thing -

 

[brock]

Reading the TM BEFORE you tear apart anything or start shooting soapy water on anything I will tell you this is a normal function to vent out the stack - now you have to go see why in the TM's - use your time reading them instead of trying fix something not broken.

Mine does the same thing - Swiss does the same thing -

I realize systems vent through the stack during operation of the vehicle. What Im looking to figure out is what is leaking when the truck is sitting and shut down. It would fail a COLA test if I had to take it today. I am losing 120 psi of pressure on the secondary side in about 30-45 mins.

 

[brock]

Brock,

In Arcadia, CA there is a company called DOOTSON TRUCK DRIVING SCHOOLS.
Get signed up there for at minimum a Class B license.
I might even ask for KARL as your teacher.
You will learn in a school bus w/ full blown air brakes just like your MV.
You can get an add on classification of PASSENGER too if you use the bus.
I got TANK also and I already had MC.

In California you have to have a class B license to drive that truck.
If you wreck and people are hurt be prepared to loose everything
you own in a court of law.

I am not being a dick here brock but I am telling you that
you should NOT drive that truck till you get some basic training.
Trying to learn it from guys online is a bad deal. Some of
the Utube videos are ok but there is NOTHING like a seasoned
professional who will teach you right from jump street.
I knew NOTHING about airbrakes and trucks and I did it
in 9 days...piece of cake!
My teacher KARL says I actually
did it in hours. I did all the reading and learning of the Calif Commercial
Drivers Handbook ON MY OWN, and DOOTSON gave me practice tests and I went
from knowing nothing about airbrakes and trucks like these, same boat
you are in, to a Class B in my pocket in 9 days.

Once you learn everything the law demands you know to drive these
types of vehicles on the public roads you will wish you had learned this stuff years ago.

It makes you safe and moreso others around you saf"er". It also
teaches you how to fix things because know you will know how
things work!

You know those Black and White CHP PickUp trucks you see on
the freeways? Well those guys know this stuff BY HEART and it is there JOB
to find the unlicensed and ill equipted drivers and trucks and get
them off the roads or fine them into oblivion.
If you get pulled over and you do not so much as have a Class B
you get to park the truck IMEDIATLY and a tow truck is called.
HUGE MONEY out the door.

If the truck has issues you get fined for all that too and there is
a LOT of it.

the COLA test is the one part of the DMV examination you do in person
in a truck w/ a DMV examiner sitting right next to you and JUST you two.
It is the one part you HAVE to ace or you will FAIL. I mean no exceptions,
you HAVE to know how to test the brake system EXACTLY or you fail.
All other parts of the tests there is a little leeway.

There are some online truck driving schools but you have to have a truck
to take the test in and to the best of my knowledge you can not use
a Mil vehicle to do it in Calif. (Verify that) . If you do use your own
vehicle it has to be PERFECT, no issues or it is an automatic fail.

If you go to a school you learn in one truck and you use that truck to
take your examine in so you are comfortable. You will thank me if you do it I am sure.

I greatly appreciate your heeded warning and do not take driving this truck lightly. I will be parking the truck until I get my license.

I picked up the truck on Friday and drove it around my neighborhood over the weekend, its definitely a beast to drive.

Thanks again.