rear air brake leaks on new M1078

Just got my 94 M1078 dropped off at the yard and you can hear and kinda feel a massive rear air brake leak when appliing brake pressure by the top of the rear axle assembly, it was really late last night but it looked like it was coming from some distrubition hub block in the center up high or the one that was 2 feet in front of it, air alarm alerts after about 2 seconds of brake pressure then builds back up until appplied again


Thoughts?

Yes, you have a leak that need to be fixed.

Blackmagic94 said:

Just got my 94 M1078 dropped off at the yard and you can hear and kinda feel a massive rear air brake leak when appliing brake pressure by the top of the rear axle assembly, it was really late last night but it looked like it was coming from some distrubition hub block in the center up high or the one that was 2 feet in front of it, air alarm alerts after about 2 seconds of brake pressure then builds back up until appplied again


Thoughts?

Click to expand...

My thoughts are you should wait to start a thread until you have found the leak or at least looked at the TM so you can at least name the part you think is bad . Rather than expect everyone to guess what your talking about . Have you looked at the trouble shooting section of the TM ?

The air should only bleed on release of the brakes correct?

Someone was telling me there is an air brake adjustment on the calipers that can cause excessive venting if not set?

The center valve thing up high leaks from a brass plunger on the right

Blackmagic94 said:

Someone was telling me there is an air brake adjustment on the calipers that can cause excessive venting if not set?

Click to expand...

I really think you need to read the -20p for this truck, it does NOT have calipers, it does have drum brakes all the way around, so who ever told you this is blowing smoke and does not know what they are talking about.

When someone tell me "someone" told them something, I often want to tell them to let "someone" help them then.

Just a random thought.

The M1078 has air wedge brakes all the way around. You need a air pot or a complete backing plate with shoes. I have a lot of new ones here.

The leak is coming from the device to the upper left in the photo from the "relay valve control unit" per the TM, i couldnt find a part name in the TM for it when i was reading it today, but it looks like some kind of air switch and is blowing out of the brass piece on the right side which might be a poppet valve or something.

Find the picture (figure number) that has the item you need(matches your picture), then look a page or two away for the part number.

I can't identify what your picture is.

when i was looking at 2-1639 i didnt see anything that mentioned the other parts adjecent to the valve

What is 2-1639?

Also, a friendly rule reminder, use sentences, punctuation and capitalization.

Page or section 2-1639 in the TM for a M1078

http://www.steelsoldiers.com/upload/M1078/m1078_TM 9-2320-365-20-2.pdf

Use the parts TM, 9-2320-365-24P.

The -20 that you are using is good for service repair but to find pictures, use the parts tm.

Roger

Looks like the inversion valve p/n 12422306. What it does from the Haldex website:
Straight trucks and some tractors use an Inversion Valve which does not function during normal operation of the vehicle’s brake system but operates in the event of a primary (rear service brake) system failure. When the Inversion Valve senses an imbalance of the primary and secondary delivery pressure during an application of the foot valve, it inverts that pressure to release air from the spring brake chambers. This permits the modulated application of the mechanical spring brake chambers on the rear axle(s) to assist the front brakes in stopping the vehicle safely

Hope that helps. Should be an off the shelf part.

Edit: Erik's Surplus has them.
Edit: Looks like it crosses to Haldex RKN 28032

So is that stating there is another failure causing that to vent while the service brakes are applied? I get an air leak down of about 2-5 for 2 seconds of depression on the pedal, so if you apply multiple times to stop it will get to the warning buzzer, but normal course of driving I was able to recover it back to my yard about 10 miles away with max pressure.

Yup, sounds like the valve may be doing it's job, and you have problems with your chambers like Steve said. Let us know how this turns out.

Also if the CTIS box is flashing all modes, what TM should I use to address this issue, does anyone sell a kit with all the seals to make these work again?