Air Rupture In Cab - What Is This And How Did It Happen?

[Shakkles]

Attempting to backup and turn my '96 1078 LMTV i had just switched from reverse to drive and when cranking the wheels all the way to the right i heard a POPSHHHHHHHHHHHHH and immediately started losing front brake pressure. It sounded like it was coming from inside the cab.
On inspection, it was this little, firm, black tube previously connected to some kind of brass fitting. I jammed it back in the fitting as hard as i could and voila, the brake pressure restored and i was able to get it home without a massive towing bill.
But... As i mentioned.. "I jammed it in there." Ergo, not a permanent fix.
I tried putting a crescent wrench on the brass fitting and removing it but it would just NOT budge and the assembly itself is screwed into seemed to flex and bend in a way i was very afraid would simply crack off and break itself.
So my questions for any who know are:

1) Any idea why simply having the wheels cranked to make a tight turn would cause that to come out? Was it perhaps "pulled out" by something attached to the other end of it or did pressure "shoot it out"?
2) Is there a special method to removing that brass fitting or should i just "give it hell until it comes loose"?
3) What are those two parts named (the brass fitting and the air line that fits into it?

Thanks in advance and best wishes.

 

[GeneralDisorder]

Oh boy.

This is an air brake vehicle and you're going to want to get familiar with air brake systems and parts, and frankly it sounds like a lot more mechanical concepts to effectively own, operate, and avoid break-downs, etc.

The air system on these trucks runs a LOT of stuff and is one of the more complex systems. Understanding it is absolutely mandatory for owners of these vehicles in my opinion. There's a lot going on. Here's a rundown from Ronmar on some of the rear air brake components - for example:

You should be carrying an air brake fitting assortment as well as rolls of 1/4", 3/8", and 1/2" tubing and all the tools necessary to make repairs to DOT tubing and fittings onboard your truck.

Can't tell the size of DOT tubing or fittings from your pictures. You should replace the fitting once you identify the size. Convert any fittings you touch to PTC (push-to-connect) fittings. Don't buy cheap ones - they leak or they don't function well. Get fittings from SMC if you can. This is who the S&S/BAE used for the A1R trucks:

https://www.smcpneumatics.com/fittings.html

 

[Ronmar]

Can’r tell did it come out of the fitting thru the floor, or the one above that on the 2way check valve a few inches above?

those are called compression fittings. You need DOT approved ones on brake system somponents, I get mine from Napa, as mentioned, they now make push to connect and those are easier to deal with.

nothing inside the cab should have effected it, sounds like it fell apart, or more likley was not assembled correctly. There are 4 parts. The main body, a screwed on outer collar, a brass beveled compression ring around the tubing and a thin inner brass tube to help the plastic tubing maintain its shape when the ring gets compressed around the tube by the thread on cap. The fact you could jam it back in there indicates improper assembly, that and it is so tight you cannot unscrew the outer collar…

Cannot get it free, use a bigger wrench,or cut the tubing and unscrew the fitting from what it is screwed into(blurry pics) worst happens it breaks, then you need to get the whole assembly out and use an easy out on it or put in a new 2way check-valve? and fittings. I would replace the fitting in question at the very least…

as mentioned, a handful of fittings and a tube assortment are not a bad idea, not difficult to carry onboard and way cheaper than a tow…

 

[Shakkles]

Can’r tell did it come out of the fitting thru the floor, or the one above that on the 2way check valve a few inches above?

those are called compression fittings. You need DOT approved ones on brake system somponents, I get mine from Napa, as mentioned, they now make push to connect and those are easier to deal with.

nothing inside the cab should have effected it, sounds like it fell apart, or more likley was not assembled correctly. There are 4 parts. The main body, a screwed on outer collar, a brass beveled compression ring around the tubing and a thin inner brass tube to help the plastic tubing maintain its shape when the ring gets compressed around the tube by the thread on cap. The fact you could jam it back in there indicates improper assembly, that and it is so tight you cannot unscrew the outer collar…

Cannot get it free, use a bigger wrench,or cut the tubing and unscrew the fitting from what it is screwed into(blurry pics) worst happens it breaks, then you need to get the whole assembly out and use an easy out on it or put in a new 2way check-valve? and fittings. I would replace the fitting in question at the very least…

as mentioned, a handful of fittings and a tube assortment are not a bad idea, not difficult to carry onboard and way cheaper than a tow…

Yeah it's that black hose (Maybe 1/4 in?) that's extremely rigid that "popped out of" the brass fitting. In the (blurry) photo i "jammed it back in there to get me home before the cops fined me for improper parking at the UPS store LMAO". It doesn't appear like it broke, more than it just popped out, but it happened when i was cranking the wheels to the passenger side... That's what i find odd and i was wondering if anyone else had that experience with this truck.
Apologies that the pictures were blurry it's a combination of being in an awkward location and it happened after dark to my iphone had to leave the exposure open a long, long time just to take a photo. It's night time here now and i'll definitely be back "in them guts" in the morning to work on it.

Can't thank you enough for the insight because insight is what i was looking for, not "Oh boy... You've got a lot to learn sonny" condescending lectures from pensioners who get their kicks talking-down to strangers asking for help.

 

[GeneralDisorder]

I *wish* I was a pensioner. That's hilarious. I'm a lot of things, and SOB isn't the least of them. Sadly retired ain't one of em.

Helping vs. Hand Holding. Safety concerns may at times be delivered in a condescending tone. To remove the tone robs the speaker of a portion of the message. That message being to educate yourself on the air system in the same manner as is required of commercial license holders, school bus drivers, and other tradespeople for the safe operation of 20,000 lbs of potential wrecking ball. Besides - it's in your interest to avoid 4/5 figure towing expenses - or at least be able to talk to the tow truck driver with a mild grasp of the FMTV technical terminology.

 

[Reworked LMTV]

Yeah it's that black hose (Maybe 1/4 in?) that's extremely rigid that "popped out of" the brass fitting. In the (blurry) photo i "jammed it back in there to get me home before the cops fined me for improper parking at the UPS store LMAO". It doesn't appear like it broke, more than it just popped out, but it happened when i was cranking the wheels to the passenger side... That's what i find odd and i was wondering if anyone else had that experience with this truck.
Apologies that the pictures were blurry it's a combination of being in an awkward location and it happened after dark to my iphone had to leave the exposure open a long, long time just to take a photo. It's night time here now and i'll definitely be back "in them guts" in the morning to work on it.

Can't thank you enough for the insight because insight is what i was looking for, not "Oh boy... You've got a lot to learn sonny" condescending lectures from pensioners who get their kicks talking-down to strangers asking for help.

I think these guys are saying "do your homework, just like we did.." It's ok not to know air brakes, but you need to study this stuff extensively BEFORE you go out on the main roads. I have a map of the air lines in my truck in a binder with lots of other reference materials. These trucks had their "miles" of lines placed in the rails before the engine and trans were dropped in. This makes repairs in the engine and trans areas extremely challenging. Better and faster to run a new line a lot of times in these areas. I labeled pretty much every line and device in the air system with an industrial dymo tape. This helps me figure out issues a lot faster. I use brass re-useable DOT splice connectors at times for these lines.

1996 would be a good year for a wine, but your air lines are Pensioners. If you find oil in them, that oil will tend to dry and weaken them after a while. Oil means you have other issues too. Concur with others, carry spares of each line size. Carry silicone hose for the cooling system too.

 

[Shakkles]

Just getting stranger. So i think i can safely claim to be certain "why" it happened but that just leads me even further down the rabbit hole.
So, that black air line directly comes in contact with the brake pedal. Not only that, it's DIRECTLY in the path, meaning every time you press the brake pedal you're pushing hard up against not just that black line but several others as well.
There's simply no-way the military OK'd this design and i'm trying to find a workaround, but if anyone else with a 1078 or similar would be willing and able to post a picture of that section under the dash so i can indeed confirm this isn't how it's meant to be that would be very helpful.
I tried to find replacement fittings by the hardware store didn't have anything that matches. Despite the fact the largest fitting clearly says "3/8 OD" this fitting IS metric. It just is.
Currently looking through the TM but to no avail so far.

 

[GeneralDisorder]

They are not metric. It's DOT air brake and it's all 100% SAE. Hardware stores are useless. You need to visit a truck/fleet shop - many NAPA locations have this stuff. Fleet-Pride, etc.

That is the correct routing going through the cab body like that *on the older trucks* - they changed it on the A1R trucks to have the hand control lines going through the wiring harness pass-through into the HVAC box but that was likely due to the pedal valve change from WABCO to Bendix.

You just need to re-orient the lines, bulkhead fittings, etc away from the pedal. Make the lines longer so they have a loop in them that keeps them away from the pedal. Someone probably had to shorten them to change the fittings and now you hit them with the pedal. Run new lines.

You may also have excessive pedal travel due to improperly adjusted brake shoes and/or NMC automatic adjusters.

TM will not help you. This is general mechanic knowledge that every Motorpool technician is trained on in school. The manual is a reference guide for people that are already mechanics. It's not a school textbook on how to wrench or the theory of operation of air brake systems.

 

[Ronmar]

Ok, the line that came off is the park air feed-line off of the 2way check valve. Shouldn’t come in contact with anything. I suspect that at some time past something got replaced and new connections had to be done and they nibbled away at the existing cable and pulled out the slack needed to properly route the line…

put in a longer line to route it forward clear of the pedal arm…

Yep, all inch size fittings, absolutely positively NO metric fittings in these brake systems. Stay away from the hardware store, hit the autoparts store and or search DOT approved air brake fittings on line…