U1300l air pressure problems om352 - Page 5 - Mercedes-Benz Forum
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#41 (permalink) Old 11-22-2012, 05:46 PM
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I had a problem with my air system as well, not building up pressure maybe 1 bar max. I have 2 compressors. One is a engine block compressor and the other is an aux. belt run compressor. I got my Mog(1974 406 Doka) stuck in 3 1/2 feet of mud and water....on my Aux. pump the air intake hose came off at the pump unbeknown to me. I lost pressure...so I changed the air reg.to a new one....then I took off the engine block comp. Head off(4 bolt) to make sure that valve were working...was not to sure about the rings, so I ordered a new set(for spare)....Then I disconnected the air intake going to the air reg.....no air getting to it, then I disconnected the engine block union and closed the hose from the aux. air compressor and had proper pressure. I then checked the output of the aux. air compressor and no air....that was my problem. When I got stuck and the air intake hose came off I sucked mud and clay/water into the Aux.air compressor, I caked the piston head and valves full of mud and clay. So what had happened was the engine block compressor was working properly but was back feeding through the aux. compressor out take hose because the valves were stuck open and was not sealing so all the air was going out the intake port of the aux.compressor. I ended up changing the air regulator, taking off the cylinder head of off the engine block compressor and cleaning the intake and out take valves, taking the cylinder head off of the aux. air compressor and clean and polish the reed valves and head, put it all back together and it works great.Hope this helps.
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#42 (permalink) Old 11-23-2012, 04:49 AM
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DX,

The valve is pointed to in red. I have made so many changes to the pipework under here that it is hard to trace what is what, without spending ages.

There are two bango ended pipes on the side (facing you) in the pic ,I am sure that the first pipe where I have joined clear pipe to is the feed. It maybe this pipe goes to the locker switch and not branched off as I said previously.

Rob
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#43 (permalink) Old 11-26-2012, 09:58 AM
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OK.

Seem to have gotten to the bottom of this. It's the unloader valve.

What's been making me think that it's the 4wd system is the location of the silencer for the unloader. DokaTD covered this in a thread about a year ago :/

If I undo the unloader valve on the bottom of the air dryer it starts dumping at 8 bar. I've pulled the air dryer apart and cleaned what I can to no avail.

What I did notice is that on a plate on the side of the dryer where there's the adjuster (don't know what it's for but it's <not> the unloader adjuster) there's a ball bearing in the casting which was pretty dirty looking. The bearing doesn't want to come out, so I presume that it's to seal the line for a different application?

There doesn't appear to be any carbon build up in the unloader valve, and the air just dropped one day.

What issues am I going to have winding the adjuster up on the unloader valve to get back to 18 bar pressure? I feel like if I do this I'm missing what the original fault was and just bodging to get it working again?

I've just put a call into the local truck factors for a price on a new dryer - I'm expecting stooopid expensive.


edit :-

Part no longer available. That's bosch 1 487 417 912 The BW fitted air dryer with purge canister.

Looks like it's coming apart again for a <very> good clean and tinker.

Last edited by dxmedia; 11-26-2012 at 10:02 AM.
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#44 (permalink) Old 11-26-2012, 10:46 AM
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T Modler---what is the part number of the water cooled compressor unit? I went to the wabco site and could not find it. Is it a direct bolt in and just add water hoses for cooling etc?
Tlane
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#45 (permalink) Old 11-26-2012, 11:41 AM
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Unloading valve is built into the air dryer. If its unloading at 8 bar then you have solved your own problem. Unloading valve is buggered or plugged with particles. I assume you have the typical military air dryer. I would take the air dryer out, disassemble and clean it out. Put in a new cartridge.

On my 1300L I had a problem with the solenoid valve on the air dryer getting plugged with small particles or grit and oil causing it to bypass and leak air. I disassembled it, cleaned and reassembled. Solved my problem.

However the problem reoccurred several times. Had oil coming out of the air dryer when it was unloading. Turned out my compressor was shot and engine oil was bypassing the compressor piston rings. Explains the particulate too. Also there was carbon steel lines in place of original stainless lines that were in poor condition and were also most likely a source of the particles. New compressor, new stainless lines, new cartridge will solve my problem.

On my 1300L the silencer/muffler for the air system is for the compressor unloading so the " enemy " doesn't learn your whereabouts in combat and it also silences the air from the deep fording option.

Just my two cents on what I learned from my experience. Hope it helps.
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#46 (permalink) Old 11-26-2012, 11:53 AM
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I should also add that I too had a big problem with my compressor. It would not build to 18bar at idle around 900 rpm. It would only go as far as 13-14 bar tops. Barely maintained pressure when driving around town and built 18bar pressure when driving full out on the highway at 2600 rpm in 8th gear.

Yup, my compressor was shot to hell. Lol Brand new Wabco unit from Atkinson Vos only cost me about 1100$ Canadian landed in Vancouver air freight.
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#47 (permalink) Old 11-26-2012, 12:46 PM
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I had an air pressure problem last winter. Ran it one day, fine- ...ran the next and virtually had no brakes because of the regulator. Tore it apart to find it FILLED with water. Pulled it completely down, cleaned and reassembled with marker oil. Not a problem what so ever since!

My 406: XM-47's, hydraulic driven Garwood 10,000lb pin-on front winch, custom bumper, small jib for front or rear, PTO driven 20,000lb Garwood rear winch w/ level wind, (super secret) forward-N-reversing unit for rear winch/PTO operation, 8 speed 2x4 conversion...+2, front 3pt hitch, HT11-A1 backhoe.

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#48 (permalink) Old 11-26-2012, 02:57 PM
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Stripped and cleaned the air dryer / unloader again. It looked like the smaller conical rubber valve had quite a bit of carbon around the seat.

Is the electric heater standard figment on the bw mogs?
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#49 (permalink) Old 11-26-2012, 04:50 PM
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Quote:
Originally Posted by tlane View Post
T Modler---what is the part number of the water cooled compressor unit? I went to the wabco site and could not find it. Is it a direct bolt in and just add water hoses for cooling etc?
Tlane
Terry,
You want a 411 142 168 7. PM me your email and I will be happy to send a copy of the invoice to you. It was plug and play for me, transferred the fittings off the old one and done. I have a bosch compressor before.

I disconnected the heater lines and used them for water supply and return. Damn heater is nt worth a hoot anyway....

C.

I believe in the United States of America as a Government of the people by the people, for the people, whose just powers are derived from the consent of the governed; a democracy in a Republic; a sovereign Nation of many sovereign States; a perfect Union, one and inseparable; established upon those principles of freedom, equality, justice, and humanity for which American patriots sacrificed their lives and fortunes.

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#50 (permalink) Old 11-26-2012, 06:24 PM
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Quote:
Originally Posted by dxmedia View Post
Stripped and cleaned the air dryer / unloader again. It looked like the smaller conical rubber valve had quite a bit of carbon around the seat.

Is the electric heater standard figment on the bw mogs?
To the best of my knowledge all BW Unmogs had the air dryer with electric heater. Standard refit item I believe.

I forgot to mention that when I had the electro valve/solenoid valve apart I checked the inside and outside of the electromagnet for cracks. With my experience working with electromagnets, you see a crack even hairline it's garbage and needs to be replaced.
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