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Discussion Starter #1 (Edited)
air system/foot pedal brake valve question - THANK YOU FELLOW UNIMOG OWNERS!!

I have an interesting situation:

Just repaired some leaks in the air system, flushed out the tanks, and put it all back together and now another leak.

Everything was perfect while the emergency brake was on, not a bubble in sight. Went for a ride and lost air pressure pretty quick.....

Came back, parked it, put the brake on and no leaks...tanks filled perfectly to 18Bar. Went for another ride, lost pressure.

This time came back, chocked the wheels, and did not engage the emergency brake, found the culprit: air is coming out of the footpedal valve on the firewall via the normal release tube!

Did I do something stupid......

Need help!!

Mogfest....must think Mogfest....
 

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Discussion Starter #4
Thank you BloodyGerman and Nashy!!

I have a new valve (thanks Ben) to install, but was not expecting this type behavior, but perhaps not uncommon when mucking about when the system is so dirty internally.

Seems like two possibilities based on forum searches: gunk in the valve and other modes of failure mostly in the trailer brake system or the aux pump/pto.

Ill be at it this weekend and will post the outcome.

Best,
Marc
 

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Discussion Starter #5
Ok, raised the cab, rebuilt the parking brake, found a broken oring, replaced all rings.

Still leaking air out of the foot pedal exhaust when parking brake is applied.

BUT with the cab up, and parking brake on, I hear a small leak in the "can" at the rear. AND when I release the parking brake, air exits the parking brake vent.

I replaced the 4 way, and pretty darn sure I did not mix up the line- BUT I've done some pretty dumb stuff...!!

Thanks!!

Marc
Help me get to MogFest
 

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OK let's start from here.
Did you have air leak from foot brake valve before rebuilding it ?
How noticeable is the air leak from foot brake exhaust when parking brake is applied ?
 

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Discussion Starter #7
Thanks!

The leak existed and is now debilitating. Replacing the foot valve did not solve issue.
 

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"...with the cab up, and parking brake on, I hear a small leak in the "can" at the rear. AND when I release the parking brake, air exits the parking brake vent.
First - small leak at the canin the back.
If it's on driver side that's your regular trailer 2 lines parking brake valve(18.05),
if it's on passenger side that's old type single line parking brake valve(17.01).
FYI if you don't have trailer and not planning on having one you can disconnect/remove them and just plug the lines.
Now according to diagram, your parking brake and foot brake are connected by 2 line trailer parking brake (18.05) or...if you mixed up lines from 4 way protection valve between 11 and 23.
I'm not sure what kind of silly things you've done over here, but simple mix would cause the problem.
Another thing about foot brake valve.
Did you rebuild it or replaced with the new one.
There is a plastic plug that goes there in one of corner channels, and after rebuilding it I put it in the opposite channel, and sure I had a leak.
It's easy to do that when the valve is taken apart.
I've attached diagram for my 427, if your truck is 18 bar air pressure should be similar.
 

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Well for some reason I'm not able to attach the diagram.
It says: "This is not a valid image file. "
It's jpg format.
 

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Discussion Starter #11
Folks,

Awesome group!!

The fix was....

First some details:

With the help of a fellow bigger we began tracing lines and marking them with colored tie wraps. Check lines to the 4 way, and found one error, with the trailer brake line, jumped with joy!!!

Fired her up and...no change.

Back to the diagrams - with the yellow line as the only possibility source of air in the trailer brake circuit... Once there and thanks to another tread on this topic, we began systematically blocking off trailer brake lines.

First the line to the 4 way, no change.

Then the control line, BINGO!!

Problem solved!!!!

We left on the line from the trailer brake valve to the master air pot. Any issues??

The result- Holy crap, the brakes are now awesome!

Even prior, the brakes were powerful, but sticky, now, smooth as butter!!

Thank you everyone!!

I'll be at the 'fest!
 

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Discussion Starter #13
It's a great feeling having a system that feels so good. Confidence building.

Have a few more brake lines to replace, but not urgent.

I look forward to the drive to Tahoe, but a little concerned about other possible failures although I've gone over just about everything....

See all on Friday!
 
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