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B61 low air pressure


CalebB
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Hey everyone. I just purchased a 58 B61 about a week ago. I’m having some issues with the air system. It will only build up to about 20 psi. There are no audible leaks in the system. I replaced the air governor, but no change. I drained the air tank and it had a lot of water and sludge in it. I’m no genius with air brakes so any help is much appreciated. Thanks!

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It could be that the pressure gauge is sprung and won't read past 20psi. You could purchase a cheap 0-150 psi gauge and connect it to one of the ports on the air tank just to verify you really aren't getting more than 20psi before you start getting real into the weeds. Does it have spring brakes? After idling for 5 minutes or so if you can try to release the spring brakes. You need about 60 - 65 psi to release them. 

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Compressor might be just plum wore out if it has sludge in the air tank.

Mine was pumping oil, it would make pressure, but just slobber the tanks so had it rebuilt.

Yours likely will be a Tu Flo 500 like mine.

IMG-20180116-202556-655.jpg

Larry

1959 B61 Liv'n Large......................

Charter member of the "MACK PACK"

 

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3 hours ago, Freightrain said:

Compressor might be just plum wore out if it has sludge in the air tank.

Mine was pumping oil, it would make pressure, but just slobber the tanks so had it rebuilt.

Yours likely will be a Tu Flo 500 like mine.

I think you may be on to something. There is a small amount of oil coming from the lines but the compressor does pump air. Where would be a good place to get it rebuilt?

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Run the truck for like 10 min then hold a piece of cardboard a few inches from the discharge fitting of the air compressor. If the compressor is passing oil there will be a big spot on the cardboard. Speckles of light oil is normal. This test isn't accepted anymore. However it is an easy field test for owners to do. Bendix likes to use a cup with markings on it now and involves several tank draining’s over a period of time. 

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Not real familiar with how the unloader works, but guessing the govenor feeds air pressure at a specific setting to open the unloader valve so it basically freewheels(at 120 psi).  If the unloader is partially stuck open, then it will never build enough air aince it is basically "leaking" pressure off.

I'd have to look at mine to see if there is easy access to the unloader to inspect it.  Might be an easy fix, but the sludge in the tank means it needs rebuilt anyway.

 

Here is where I got mine done nearly 20 yrs ago.  Not sure they still do them?  It was $500 and like 2 day turnaround.  Mine needed a new plastic coupler as mine was missing a few teeth.

https://www.masontrucksales.com/

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IMG-20180116-202556-655.jpg

Larry

1959 B61 Liv'n Large......................

Charter member of the "MACK PACK"

 

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6 minutes ago, Freightrain said:

Not real familiar with how the unloader works, but guessing the govenor feeds air pressure at a specific setting to open the unloader valve so it basically freewheels(at 120 psi).  If the unloader is partially stuck open, then it will never build enough air aince it is basically "leaking" pressure off.

I'd have to look at mine to see if there is easy access to the unloader to inspect it.  Might be an easy fix, but the sludge in the tank means it needs rebuilt anyway.

 

Here is where I got mine done nearly 20 yrs ago.  Not sure they still do them?  It was $500 and like 2 day turnaround.  Mine needed a new plastic coupler as mine was missing a few teeth.

https://www.masontrucksales.com/

Correct, however for the amount of time this thing has sat theres a good chance the valves could be sticking. Also to add to the fact I highly doubt these have air dryers so all the sludge could just be from no one ever draining tanks and sitting. Compressor will always pass moisture and some oil. Also a good chance the compressor is shit, but there are a few simple checks to do before condemning a compressor. You would know a lot more about this compressor and air system then me though. 

Edited by Onyx610
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32 minutes ago, Freightrain said:

Not real familiar with how the unloader works, but guessing the govenor feeds air pressure at a specific setting to open the unloader valve so it basically freewheels(at 120 psi).  If the unloader is partially stuck open, then it will never build enough air aince it is basically "leaking" pressure off.

I'd have to look at mine to see if there is easy access to the unloader to inspect it.  Might be an easy fix, but the sludge in the tank means it needs rebuilt anyway.

 

Here is where I got mine done nearly 20 yrs ago.  Not sure they still do them?  It was $500 and like 2 day turnaround.  Mine needed a new plastic coupler as mine was missing a few teeth.

https://www.masontrucksales.com/

Here’s a quick vid on how unloaders valves work. 
 

 

Edited by Onyx610
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Yup, kinda figured that is what happens.

Here is picture of typical 500 model.  The upper round port is exhaust pipe to air trank, it is typically a copper line.

The two unloader valves are accessible through the intake port below the exhaust.   My compressor has a small box bolted on with a wire mesh filter screen installed.  Many newer trucks have a feed line from the air filter/turbo inlet pipe.

 

The govenor line inatalls in the port to the right end from the intake.  You can see the bump in the casting that goes to each end.image.png.d71cfe49c59c2d8226cc3790366da44d.png

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IMG-20180116-202556-655.jpg

Larry

1959 B61 Liv'n Large......................

Charter member of the "MACK PACK"

 

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2 minutes ago, Freightrain said:

Yup, kinda figured that is what happens.

Here is picture of typical 500 model.  The upper round port is exhaust pipe to air trank, it is typically a copper line.

The two unloader valves are accessible through the intake port below the exhaust.   My compressor has a small box bolted on with a wire mesh filter screen installed.  Many newer trucks have a feed line from the air filter/turbo inlet pipe.

image.png.d71cfe49c59c2d8226cc3790366da44d.png

So would it be beneficial to check the intake for any trash, gunk, etc? The truck has not been on the road since 1997. Also, Onyx, I did the little test you recommended and it’s not blowing as much oil as I originally thought. It’s still probably a more than ideal amount though.

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7 minutes ago, CalebB said:

So would it be beneficial to check the intake for any trash, gunk, etc? The truck has not been on the road since 1997. Also, Onyx, I did the little test you recommended and it’s not blowing as much oil as I originally thought. It’s still probably a more than ideal amount though.

Yes, check the intake piping to the compressor as well. Start there and then work your way back. You can pry get the unloader valves out and lube them up too 

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51 minutes ago, CalebB said:

So would it be beneficial to check the intake for any trash, gunk, etc? The truck has not been on the road since 1997. Also, Onyx, I did the little test you recommended and it’s not blowing as much oil as I originally thought. It’s still probably a more than ideal amount though.

Every road trip I would drain a oil milkshake from mine.  A good cup at least.  Now it's just some random water.

I would get it functional and see how it does.

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IMG-20180116-202556-655.jpg

Larry

1959 B61 Liv'n Large......................

Charter member of the "MACK PACK"

 

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1 minute ago, Freightrain said:

Every road trip I would drain a oil milkshake from mine.  A good cup at least.  Now it's just some random water.

I would get it functional and see how it does.

Are these cooled by coolant? Possible head gasket failure?

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1 hour ago, Onyx610 said:

How big of circle did you get?

About 1 1/2 in circle. The compressor was blowing well it seems. That’s what’s throwing me off. It gets air to the tank, governor, and toggle switch well. As soon as you turn it off, it’s dead quiet. No leaks.

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What has you thinking it’s not building air? The fact that gauge just says 20 psi? Do these systems have one way check valves at the tank like others and it’s bad? Do you have an air dryer? I’m really trying here with a s system I don’t know. 

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1 hour ago, Onyx610 said:

Even bad compressors will build air. Try what 67rModel said and hook a gauge to the tank and see what it says? 

I’d assume it’s reading correctly because I have no brakes. Also, if it has an air dryer, I can’t find it. This is my first B-model restoration. I’m a wiz with engines and transmissions. I know the basic principles of air brakes, but I’ve never had to work on them before so I’ll admit I’m a little out of my league.

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Welcome,  Caleb. I'm Sure We'll get your Truck issues sorted..

 

3 hours ago, CalebB said:

The truck has not been on the road since 1997.

After sitting for that length of Time the entire Air/Brake system will need a good dose of TLC, to ensure It's safe to use..

I'd see if you can use some "Shop Air" to pump up the Tank & Test if the Brakes ect are working as they Should. 

I'd also ensure that the Brass/Steel line directly out of the Compressor isn't Carboned up. The unloader valve sticking has already being Mentioned..

Just methodically go through all the Basics before spending money on a another Air compressor. would be My advice...Tax free Today..lol

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8 hours ago, Onyx610 said:

Are these cooled by coolant? Possible head gasket failure?

Yes.  Ties into the water pump and returnd to the side of the block.

Typically no air drier on these trucks from factory.

IMG-20180116-202556-655.jpg

Larry

1959 B61 Liv'n Large......................

Charter member of the "MACK PACK"

 

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