LMTV M1078 not building air pressure

[Seapup]

Just had twin LMTV’s delivered yesterday,
After sorting through a couple issues, ( well Ok a lot of issues) both were non op, got both running, in short, rebuilt one cab latch a couple grumpy air valves, sorted through completely FUBARed relay Panels.
Subbed in two group 31 batteries.
all is well, both are now running
Except, one will not build air pressure,
Any help trouble shooting these systems very much appreciated.
Where to start/ common points of failure/ cures to said common failures .
I plan on starting at compressor checking for air pressure and then working my way down stream.
Where do I check for pressure and how much pressure should be coming out of a healthy compressor?
Thanks in advance

bonus question,
One twin came without a CTIS controller and was wondering if there was a way to inflate tires without a controller on board?

 

[Ronmar]

Just had twin LMTV’s delivered yesterday,
After sorting through a couple issues, ( well Ok a lot of issues) both were non op, got both running, in short, rebuilt one cab latch a couple grumpy air valves, sorted through completely FUBARed relay Panels.
Subbed in two group 31 batteries.
all is well, both are now running
Except, one will not build air pressure,
Any help trouble shooting these systems very much appreciated.
Where to start/ common points of failure/ cures to said common failures .
I plan on starting at compressor checking for air pressure and then working my way down stream.
Where do I check for pressure and how much pressure should be coming out of a healthy compressor?
Thanks in advance

bonus question,
One twin came without a CTIS controller and was wondering if there was a way to inflate tires without a controller on board?

what model/version trucks?

is it making any air at all? If it is I would connect shop air and first look for leaks without the engine running. Way easier to find that way.

without CTIS controller you can inflate with a pair of jumpers. H in the connector is 24V. Place a jumper from H to R, which will power the control solenoid and seal the system. With H-R in place, place a second jump from H to B which will open the inflate valve and feed air to the tires. do this in pulses, 4 tires will lower a full wet tank to the 85psi protection valve cutoff point in about 3 seconds, it takes about 9-12 seconds to refill the wet tank at idle.

When done, Pull the H-R jumper or turn off the main switch to open the control solenoid which will vent the system and close the wheel valves… You will of course have to check tire pressure at the tires…

I use this type manual control in my truck with a pressure gauge connected to the PCU to monitor tire pressure. I am on my second generation now, and I did videos on both of them. Here is the second one.

DO NOT WALK OFF AND LEAVE THIS IN INFLATE UNATTENDED! A 48” split rim overinflated will make a spectacular 4th of july display though

 

[Seapup]

what model/version trucks?

is it making any air at all? If it is I would connect shop air and first look for leaks without the engine running. Way easier to find that way.

without CTIS controller you can inflate with a pair of jumpers. H in the connector is 24V. Place a jumper from H to R, which will power the control solenoid and seal the system. With H-R in place, place a second jump from H to B which will open the inflate valve and feed air to the tires. do this in pulses, 4 tires will lower a full wet tank to the 85psi protection valve cutoff point in about 3 seconds, it takes about 9-12 seconds to refill the wet tank at idle.

When done, Pull the H-R jumper or turn off the main switch to open the control solenoid which will vent the system and close the wheel valves… You will of course have to check tire pressure at the tires…

I use this type manual control in my truck with a pressure gauge connected to the PCU to monitor tire pressure. I am on my second generation now, and I did videos on both of them. Here is the second one.

DO NOT WALK OFF AND LEAVE THIS IN INFLATE UNATTENDED! A 48” split rim overinflated will make a spectacular 4th of july display though

View attachment 872164

Perfect thankyou!

 

[WOT]

Just had twin LMTV’s delivered yesterday,
After sorting through a couple issues, ( well Ok a lot of issues) both were non op, got both running, in short, rebuilt one cab latch a couple grumpy air valves, sorted through completely FUBARed relay Panels.
Subbed in two group 31 batteries.
all is well, both are now running
Except, one will not build air pressure,
Any help trouble shooting these systems very much appreciated.
Where to start/ common points of failure/ cures to said common failures .
I plan on starting at compressor checking for air pressure and then working my way down stream.
Where do I check for pressure and how much pressure should be coming out of a healthy compressor?
Thanks in advance

bonus question,
One twin came without a CTIS controller and was wondering if there was a way to inflate tires without a controller on board?

Not Building Air Pressure - Sometimes, the Unloader Valve on the top of the compressor will get carboned-up or corroded if sitting a long time. Some people hit the compressor with a hammer near the valve, others have put a shot of ATF down the intake side of the compressor to see if it frees-up. Others, replace the valve. There can be many other places that leak enough air to cause air pressure to not reach usable pressure. I had a 2014 Freightliner Cascadia that wouldn't get to brake release pressure and the PEX 90 degree elbow connector on the main tank was leaking around the 3/4 inch plastic hose. $32 Elbow from Freightliner Dealer solved the problem and I drove it for over a year without issues and then, I sold the truck. If you're not getting any pressure at all, it may well be the Unloader Valve in the compressor. If you're getting some pressure, like 50 pounds, it's probably a leak in the system somewhere. Build as much pressure as you can, shut the truck off and get underneath and listen for leaks. Good Luck!

 

[Suprman]

Sometimes the expello valve bottom of the air dryer can get stuck open. On the lmtv you take the elbow off and push the valve closed. If this is the case the dryer needs replacement

 

[Seapup]

Not Building Air Pressure - Sometimes, the Offloader Valve on the top of the compressor will get carboned-up or corroded if sitting a long time. Some people hit the compressor with a hammer near the valve, others have put a shot of ATF down the intake side of the compressor to see if it frees-up. Others, replace the valve. There can be many other places that leak enough air to cause air pressure to not reach usable pressure. I had a 2014 Freightliner Cascadia that wouldn't get to brake release pressure and the PEX 90 degree elbow connector on the main tank was leaking around the 3/4 inch plastic hose. $32 Elbow from Freightliner Dealer solved the problem and I drove it for over a year without issues and then, I sold the truck. If you're not getting any pressure at all, it may well be the Unloader Valve in the compressor. If you're getting some pressure, like 50 pounds, it's probably a leak in the system somewhere. Build as much pressure as you can, shut the truck off and get underneath and listen for leaks. Good Luck!

Excellent reply!
I’ll add it to the list when I get home

 

[Seapup]

Sometimes the expello valve bottom of the air dryer can get stuck open. On the lmtv you take the elbow off and push the valve closed. If this is the case the dryer needs replacement

Good to know,
I’ll give it look when back at the corral

 

[Seapup]

Alright everyone
First of all, huge thank you for all the help and advice from all the guys on steel soldiers!
I got both LMTV’s home safe and sound
It was a baptism of fire journey for sure.
Got a chance to get a little better acquainted with both vehicles.
They did better than I expected for a couple old gals sitting in the dirt for a few years.
The towing company I contracted with actually caused more problems and broke more shit than anything. But that’s why we hire professionals right?
to keep a long story short they will be buying me another set of drive shafts :/

So right off the bat I started experiencing overheating issues, pulled over on the pass to troubleshoot. Traced it to an intermittent fan valve.
It would cycle once or twice and then quit.
Solution- pull access cover And give my son a blunt object and had him tap it every time temp edged over 200.
Had several valves develop leaks and repaired as they developed.
About 130 miles into the trip the fan sheared off the fan clutch
Soulution- pulled fan assembly of of spare truck and installed in towing vehicle…
(Nothing like having a spare everything towing behind you)
both cab locks, air over hydraulic pumps and cab hand pumps blew seals and had to be repaired in route.

some one played musical chair with the relays and many were missing or just in the wrong place…

Now that I’ve had a chance to look them over
I’m very pleased with my acquisitions, to be honest I am easily pleased though , a couple pieces of string and a ball of lent can put a smile on my face…

from What I’m finding, these trucks have had a few hands on them, some good, Some ….well, mechanically challenged let’s say.

So I will be starting from the front and working my way to the back servicing and inspecting every valve and electrical connection…

got both trucks running well and I am going to spend the next few days with a TM in hand and crawl Around a bit.

Thanks again everyone

 

[Seapup]

Truck #2 now named LB has an issue building air pressure.
Compaired out puts of both trucks by removing output lines and both trucks pump same pressure.

attached shop air to wet tank and cannot get system to build air pressure no matter how much pressure or air I pump into wet tank. I cannot seem to locate a leak any where while trying to build pressure either.

has anyone run into to this before?

Is there a way to quickly confirm if this is a unloader or governor issue?

brakes are caged, I don’t know if this will effect anything air pressure related…?
any help will be appreciated
Thanks again everyone

 

[MrMikey4026]

Check the discharge line from compressor to the dryer for leaks.

 

[Ronmar]

Well if you are putting air into the wet tank directly, you can do a few things to eliminate where it might possibly be going. On the side of the wet tank toward the rear of the vehicle there is a protection valve that feeds accessories(looks like a pressure regulator). It stops airflow out of the wet tank below 85 PSI. If you disconnect and cap it’s output, that will eliminate CTIS, fan and cab air suspension. If this was the truck you pulled the fan off of, and you have the fan disconnected, that may be where your air is going, as the system provides air to freewheel the fan until the engine is hot…

if that doesn’t stop it, the governor sense line is the small line attched to the inboard end of the wet tank, you can pull and cap that port to see if that is where it is going. Mind your pressures, as running with the compressor not in contact with the wet tank means there is no sense to tell it to unload at 125PSI. That is why there is a pressure relief on top of the air dryer.

Sometimes the purge valve on the bottom of the dryer gets stuck open, especially if these trucks have set for a while. I would feel the output elbow on the bottom for any leakage while running. If it is, remove elbow and push in on the valve core to re-seat it…

if neither the governor nor the accessory feeds are the leak, well then it is heading out into the brake or air-hydraulic cab/tire/suspension lift system.

 

[Ronmar]

While you are looking at the wet tank you may notice it is plumbed incorrectly on the A0. 100% of the dryer air should flow thru the wet tank on its way to the brake tanks. On the A0 they Td the wet tank off of the dryer output, so only maybe 25% of the air used by the brakes ever sees the inside of the wet tank. They fixed this on the A1…




It is easy enough to fix on the A0…

 

[Seapup]

Check the discharge line from compressor to the dryer for leaks.

Thank you
1st thing I checked -it’s good to go
Just found my issue!

my forward two way air valve underneath the drivers fender well became a pass through valve
New one being installed at the moment.

 

[Seapup]

Update
Replacing that 2 way some what slowed that leak but did not fix it completely…
So I plugged the glad hand and this was enough to make another large leak loud enough for my old ears to hear.
Ther is a large hole in one of the control lines leading to the back of the truck.

so can these lines be repaired ?
And second where can you get replacement hose from?

 

[coachgeo]

One of the front glad hands is also a vent..... you cant just plug it.

there is several threads on here on how to delete front glad hands. Also discussions on which one is a vent. maybe search "glad hand vent"

 

[Seapup]

One of the front glad hands is also a vent..... you cant just plug it.

there is several threads on here on how to delete front glad hands. Also discussions on which one is a vent. maybe search "glad hand vent"

 

[Seapup]

Good call I remember discussing that with a buddy of mine who has one and it’s his front driver side that’s the vent and if it gets clogged Or iced up then its a problem . this one’s the emergency one on the passenger side.
Also this is just a temporary so I can troubleshoot and move it To its new parking place

 

[Ronmar]

Both front glad-hands must be vented. If the red one isn’t , it will store air and prevent you from engaging the park brake. If the blue one is not vented, that will store air and cause the service brakes not to release when you let off the pedal…

it is dead easy to bypass the 2way check valves. the 2ways combine 2 inputs to feed one output. For park brake they combine the red front glad-hand and or the park brake control output to feed the park brake air back to the anti-compounding valve to release the park brakes. To bypass it, you simply take the park brake control output, which feeds one side of the top 2way, and connect it to the line exiting the center port of the 2way(has the air pressure sw on it), which feeds back to control the park brake.

The pair of 2ways below the park 2way, are tied together on one side. That is the service input from the front glad-hand/towing vehicle. The other side are the front/rear inputs into each system(front rear) from the treadle vlave. The center ports are the outputs to those 2 respective systems. If you disconnect the center outputs and connect them to their respective treadle valve output fittings coming thru the cab floor, you can control the sec-pri/front-rear systems from only the pedal. You can also do this with the park control, just move that t fitting off the center 2way port to the park port coming out of the floor. There is another line Td off that feeds the valve that enables the air op hydraulic pump, only when the park brakes are set(no park air applied) keeps the cab from being tilted when driving

you can't really repair the poly lines. You replace them. About the only way to repair a hole in a line is to cut it at the hole and using a tube compression fitting s-lice the now cut line where the hole was.. this poly brake line is available at ny truck shop or stores that sell those supplies, Napa typically carries it and the DOT fittings…

 

[Ronmar]

I did a video showing how to bypass all those 2ways… I also explain a little how all the different air supplies/parts interact.

 

[Seapup]

I did a video showing how to bypass all those 2ways… I also explain a little how all the different air supplies/parts interact.

Thanks again Ronmar
Your knowledge on these FMTV vehicles air systems is legendary!

There seems to be a lot of places on these vehicles where you can simplify the air system To reduce clutter and possible failure points.

also my rear passenger brake spring Canister appears to be leaking at the clamping point.
Can these canisters being aware or the spring of death be rebuilt or is it easier to replace?