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farmer52

MH Air Leak

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In June I replaced the RH (dual chamber) air tank because it was leaking air (red needle dropped quicker than the green needle and I could hear air leaking at the step bracket).  In mid-July I noticed the green needle drops to zero (0) within an hour or so but the red needle stays above 100psi (after several days the red needle will eventually drop to zero but that is not my concern).  I have three (3) hand valves - RED (trailer), YELLOW (parking), and BLUE (tractor).  When I am connected to the trailer I only pull the YELLOW parking valve.  When parking just the MH I pull the BLUE valve.  When driving the unit, both needles stay together and drop pressure at the same rate.  IIRC, the compressor kicks in at about 100psi and charges to 130psi.  Using the drain valves, the RH tank secondary side has pressure but the primary side and the LH tank have no pressure.   I also checked the trailer tank and it has pressure.

First am I correct to only pull the YELLOW valve when parking the tractor-trailer combination?

Second, I cannot hear any air leaks.  I would think I could hear an air leak with the green needle dropping pressure so quickly.  The other night I pulled all three (3) valves and the green needle dropped as before and red showed pressure.

I am eventually planning to replace the LH (single chamber) tank but as I mentioned, I cannot hear any air leak.

Any suggestions on where to look or what might be the issue?  Thanks for any suggestions.

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As you stated, losing air that quick you "should" be able to hear it.

take a bottle of window cleaner and start spraying on all air connections. should bubble up

although I do like Vlad's idea too

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Have you pulled off the center panel where the park brake valves are and listen inside the dash for leaks and I buy the stuff where kids blow bubbles with at Walmart and put in a spray bottle.  Also pull panel under the foot valve and ck for leakage. If like me find somebody young to listen.

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Air leak identified - LH air tank between tank and step...duh!

I was not able to drive the "roll hauler" in a deep or cement pond so I got out the trusty water/soap bottle.  Sprayed all the fittings and then soaked the tank at the step bracket (see photo).  I put my ear to the area and even before the bubbles started I could hear a slight air leak.  The bubbles confirmed what I suspected.  So definitely in the market for a nice used LH steel tank.

Still need an answer to my question...when parking the tractor-trailer combination, do I just pull the yellow knob and leave the red and blue knobs pushed in?  The red knob states "Not for parking" so I never pull it when connected to the trailer.

Thanks for the suggestions.

LH air tank leak.JPG

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Does it hurt to pull the red knob or does it just release the air in the trailer tank?

I ask because some times when I pull the yellow the red comes out with it and some times it does not.

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Ken, sorry to see the picture.

By the way I removed both air tanks from my MH being worry they could get holly some day and sandblasted them.

After that the left one went to the paint shop but the right one didn't.

I welded up 5-6 rusty spots I got condensed water leaks from after blasting but not sure it will live long.

Just want you to know any options on getting new tanks you've found to the moment.

And did anyone reskinned air tanks the way people do it to fuel ones?

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Think we had a topic on air tanks before. Welding on air tanks is a bad idea.  Just as I would not weld up brake drums, Brakes and air is nothing to mess with. This is one part I would find good used ones or if new was available opt  for them even at the cost. Bought nice used aluminum 2 tank set for $250, each tank was $625-675 new each. I think if a DOT stop found welded up air tanks they would have it towed on the spot, with special instruction, as the tow air runs though the system too.  I have welded fuel tanks but they hold no pressure with no problems. :unsure:

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12 hours ago, Tbear said:

Does it hurt to pull the red knob or does it just release the air in the trailer tank?

I ask because some times when I pull the yellow the red comes out with it and some times it does not.

if your trailer has maxi-spring brakes yes pulling the red knob is what locks your trailer brakes when you are parked. a properly working system will automatically kick the red valve out when you pull the yellow one. however if you have a really old trlr.which does not have maxi-spring brakes then your trailer brakes will only hold when parked until the air in the tank under the trailer leaks off

Edited by carlotpilot

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Why don't you contact Barry again at Watts Mack with your truck's model and serial number and order another new air reservoir? I'm sure that he'd work with you on price. You'll probably be challenged to locate a used MH air reservoir that isn't similarly corroded.

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5 hours ago, carlotpilot said:

if your trailer has maxi-spring brakes yes pulling the red knob is what locks your trailer brakes when you are parked. a properly working system will automatically kick the red valve out when you pull the yellow one. however if you have a really old trlr.which does not have maxi-spring brakes then your trailer brakes will only hold when parked until the air in the tank under the trailer leaks off

My trailer is a 2005 Great Dane single axle.  When I pull out the yellow parking valve the trailer purges air and the red trailer valve does not automatically pop out.  Also, I notice when I release (push in) the yellow parking valve I cannot move until the trailer brakes release.  There is about a 3-5 second delay.  Is this normal?

New replacement (22QE31179M) tank bought from Barry but has several more ports and does not match exactly.  I can make it work if I can't find a nice used tank.

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3 hours ago, farmer52 said:

New replacement (22QE31179M) tank bought from Barry but has several more ports and does not match exactly.  I can make it work if I can't find a nice used tank.

I got actually three tanks, one for a spare, from, www.truck parts inventory.com  for $125 each. They have the photo and size of the tanks, there are 118 Mack tanks as of this morning. Call them to ask if the ones you are interested in are one or two compartment and how many ports. The ones I got polished up real nice and one had a small dent from a rock underneath that could not be seen until polished. I did have to plug a port or two. Had them in 4 days UPS. It might work for you. :thumb:

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7 hours ago, AZB755V8 said:

I got actually three tanks, one for a spare, from, www.truck parts inventory.com  for $125 each.

Thanks for the link.  I will take a look.  This morning I decided to use the new tank I bought rather than "squirrel it away".  I disconnected the air lines and removed the fittings from the old tank.  I need to install the fittings, plug four (4) ports, and then it is ready for installation.  I was going to powder coat it but will just install with "factory" paint.  Hey the original one lasted almost 25 years.  So the new one will likely outlast me.  As with the RH tank, I will put a rubberized strap between the aluminum step and tank.

6 hours ago, j hancock said:

The red knob should not be popping with the application of the yellow knob.

There probably is a time for brake release but 3 seconds seems OK for the air to overcome the spring brakes.  5 seconds maybe a little long?

My red knob does not pop out with the yellow knob so I think my system is functioning correctly.  I was only guessing at the time delay but it is a few seconds before the trailer brakes release.

Thanks everyone for the comments and information.

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On August 23, 2016 at 10:51 PM, carlotpilot said:

if your trailer has maxi-spring brakes yes pulling the red knob is what locks your trailer brakes when you are parked. a properly working system will automatically kick the red valve out when you pull the yellow one. however if you have a really old trlr.which does not have maxi-spring brakes then your trailer brakes will only hold when parked until the air in the tank under the trailer leaks off

Ok Jhancock says the red knob should not pop out when you pull the yellow you say it should I'm confused!        

My old freightliner the red always come out with the yellow my Mack is about 50/50 my trailer is a2007 Kaufman. I'm thinking the older trucks and trailers are the way JHancock says and maybe the newer stuff is like my old freightliner.The reason I think that is I had a delevery from saia and when that guy set his brakes I heard one pull but saw 2 dust could 1 from the truck and 1from the trailer at the same time. Let me know . 

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11 minutes ago, Tbear said:

Ok Jhancock says the red knob should not pop out when you pull the yellow you say it should I'm confused!        

My old freightliner the red always come out with the yellow my Mack is about 50/50 my trailer is a2007 Kaufman. I'm thinking the older trucks and trailers are the way JHancock says and maybe the newer stuff is like my old freightliner.The reason I think that is I had a delevery from saia and when that guy set his brakes I heard one pull but saw 2 dust could 1 from the truck and 1from the trailer at the same time. Let me know . 

There is a post on BMT about this; newer trucks when pull yellow the red comes out too; & if you hold red 1 in it will mess up tractor protection valve

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7 hours ago, Tbear said:

Ok Jhancock says the red knob should not pop out when you pull the yellow you say it should I'm confused!        

My old freightliner the red always come out with the yellow my Mack is about 50/50 my trailer is a2007 Kaufman. I'm thinking the older trucks and trailers are the way JHancock says and maybe the newer stuff is like my old freightliner.The reason I think that is I had a delevery from saia and when that guy set his brakes I heard one pull but saw 2 dust could 1 from the truck and 1from the trailer at the same time. Let me know . 

FWIW When I pull the yellow knob, I get a "puff" of air from both the tractor and trailer.  But the red knob does not pop out.

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Went to the Shortway Truck Show; Washingtonville, PA on Saturday, nice turnout of trucks and show (great ice cream BTW).  The primary air (green needle) after six (6) hours sitting was down to about 20psi (secondary red needle at about 90psi).  So still have an air leak.  Someone mentioned perhaps the brake "cans" are leaking.  Does this make sense while the truck is parked?  Is there an easy way to check them?  Soapy water?  Any particular area to spray?  I replaced the dash valves last year and there are no leaks there.  Guessing it is outside somewhere since I cannot hear air leaking.  Also while driving the air will drop (both needles at the same rate) from ~120psi to 90psi in 20-30 minutes (then the compressor kicks in and recharges).  Thanks for any suggestions/help.

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Ken, check the trans breather and see if you feel or hear air coming from it, a range piston air leak can cause lots of hours of misery  while looking every place else on the truck. 6 hours to loose 80-100 lbs. will be a pain to find, also does the mh have air operated functions in the heater box? I know my superliner looses air fairly quick because of a leaky piston  for the defroster door.  

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1 hour ago, gearhead204 said:

Ken, check the trans breather and see if you feel or hear air coming from it, a range piston air leak can cause lots of hours of misery  while looking every place else on the truck. 6 hours to loose 80-100 lbs. will be a pain to find, also does the mh have air operated functions in the heater box? I know my superliner looses air fairly quick because of a leaky piston  for the defroster door.  

T2050 transmission so no range piston.  Yes the HVAC doors are air operated.  What about the issue of loosing more air while I am driving (~30psi in 20 minutes =1.5psi per minute)?  Sitting the air leak is way less at approximately 0.27777psi per minute.  Or should I just say "fluff it" and move on?

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I would say that a 4psi drop an hour is Great! I have only been in one truck 25-30 year old truck that could come close to that rate of air lose. The two old truck I have will lose easy 30psi an hour just sitting there. I thing the allowable rate for air lose and not really have to worry about it is 2psi a minute in the State Driver Hand Book for AZ. I tightened up the air fitting to the horns  and my rate slowed by over 5psi and hour. That is a tight air system you got there.  :thumb:

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