CTIS spewing gear oil but controller not connected.

[aw113sgte]

Noticed a rear tire was down on pressure a bit so refilled to 80psi. Also replaced the quick release valve near the muffler as it was missing. Then after a drive, gear oil sprayed out of the discharge from the quick release valve on the forward rear axle(connected to the tire that was low). Taking off the CTIS banjos, both had gear oil in them. So can back pressure from a tire cause the QRV to trigger? I haven't looked into the logic of how the QRV can be triggered. Tire pressure on that tire dropped by 20 psi to 60. Maybe pressure leaking through the CTIS manifold?(if that would trigger a QRV)

 

[Ronmar]

Noticed a rear tire was down on pressure a bit so refilled to 80psi. Also replaced the quick release valve near the muffler as it was missing. Then after a drive, gear oil sprayed out of the discharge from the quick release valve on the forward rear axle. Taking off the CTIS banjos, both had gear oil in them. So can back pressure from a tire cause the QRV to trigger? I haven't looked into the logic of how the QRV can be triggered. Tire pressure on that tire dropped by 20 psi to 60. Maybe pressure leaking through the CTIS manifold?(if that would trigger a QRV)

The QRV/dump valve is a remote pressure regulator. Whatever it sees on its input port from the PCU, it copies on its output ports to the wheels. Put 60 psi on the input it will feed air from input to output untill output matches input. Lower the input side from 60 to 30, it will vent air from the output side out the vent until it = the input 30 PSI. Have a tire valve leaking? it will send pressure back to the qrv outlet port but since the input port is at 0 it will vent that tire air out the vent…

the tire valves compare the truck side port to atmospheric pressure. When it sees ~5 psi on the truck side it pushes a diaphragm toward the atmosphere side. This movement opens a port to the wheel connecting the truck side port to the tire.

You obviously have a bad CTIS hub SEAL allowing gear oil into the air passage that connects stationary spindle to rotating hub. It may also be that you have a clogged axle vent, so as the axle warms it pressurizes, or when CTIS tests pressure it pressurizes the axle and this in turn forces oil back into the air passages.

if you have a leaky seal, CTIS air should leak out the axle vent whenever the system pressurizes…

 

[aw113sgte]

The QRV/dump valve is a remote pressure regulator. Whatever it sees on its input port from the PCU, it copies on its output ports to the wheels. Put 60 psi on the input it will feed air from input to output untill output matches input. Lower the input side from 60 to 30, it will vent air from the output side out the vent until it = the input 30 PSI. Have a tire valve leaking? it will send pressure back to the qrv outlet port but since the input port is at 0 it will vent that tire air out the vent…

the tire valves compare the truck side port to atmospheric pressure. When it sees ~5 psi on the truck side it pushes a diaphragm toward the atmosphere side. This movement opens a port to the wheel connecting the truck side port to the tire.

You obviously have a bad CTIS hub SEAL allowing gear oil into the air passage that connects stationary spindle to rotating hub. It may also be that you have a clogged axle vent, so as the axle warms it pressurizes, or when CTIS tests pressure it pressurizes the axle and this in turn forces oil back into the air passages.

if you have a leaky seal, CTIS air should leak out the axle vent whenever the system pressurizes…

Thanks for the info, I looked at the vent lines but didn't have time to follow their routing as it went up the frame rail to somewhere, so many lines there it will take a bit to trace.

 

[aw113sgte]

Okay looked at the vent lines from the axle, both were completely blocked. Enough that when pulling the fill plugs, both rear axles let out a fairly significant hiss. Truck hasn't been driven for a few days.

 

[aw113sgte]

After digging though TMs and posts on here, found the two axle vents and the 2 hub CTIS vents all connect together and vent is located near the bellhousing vent. Verified that one by blowing into it and could feel the air compression(like blowing up a balloon), air flowing back tasted horrible but indicated it was clear.

 

[KN6KXR]

Make the tool from the TM and check all the hub seals. My bet is some are totally shot. I carry the test tool and a blank off cap on the truck so if one goes I can identify, blank it, run with 5/6 operation and hand manage the failed one. I recommend anybody that runs with CTIS operational do the same. I really like my CTIS and I use it but you should be prepared like the rest of the truck.

 

[Ronmar]

After digging though TMs and posts on here, found the two axle vents and the 2 hub CTIS vents all connect together and vent is located near the bellhousing vent. Verified that one by blowing into it and could feel the air compression(like blowing up a balloon), air flowing back tasted horrible but indicated it was clear.

CTIS vents? The only CTIS vents I am aware of are the horns on the dump valves themselves. The dump for the front axle is on the right side of the transmission. The dump valve for the rear axles are located on a crossmember above the axle near the center of the chassis… on mine it is on the back side of the crossmember where the brake components Are located. On the 6X there is another crossmember to the rear and that is where I have seen the rear axle ctis dump valve placed on the trucks I have worked on… So what are you meaning by CTIS vents?

I have not seen the axle housing breather/vents remoted But I am not very familiar with the 6X6. On my 4x4 the axle housing vent connects up to a bulkhead fitting on the bolt in crossmember plate that has all the airbrake components on it. The front axle is a little different. It has 2 vent ports on the top of axle housing, and each hub has a vent. The two hub vents are T’d together and tie to one axle port. The other port has a line that runs up to a vented fitting attached to the right side of the cab suspension arch on my truck…

lip seals are usually good at sealing in one direction. In the case of the CTIS hub seals that would be to resist air at tire pressure in the CTIS passage, from escaping into the axle housing. Since the axles should be vented they should only ever have to resist oil at atmospheric pressure from the other direction. Now if the axle vents are plugged and a little air escapes into the axle, it could pressurize it as high as tire pressure. When CTIS finishes a run and depressurizes and closes the wheel valves, the seals are now presented with gear oil at pressures as high as tire pressure on the wrong side to provide a good seal…

 

[aw113sgte]

Ronman: Yes, you have it all correct, I was just wording the CTIS vent as describing the front hub vents

 

[aw113sgte]

Make the tool from the TM and check all the hub seals. My bet is some are totally shot. I carry the test tool and a blank off cap on the truck so if one goes I can identify, blank it, run with 5/6 operation and hand manage the failed one. I recommend anybody that runs with CTIS operational do the same. I really like my CTIS and I use it but you should be prepared like the rest of the truck.

I'm not finding a refence to that tool for testing hub seals? This is the closest I found:

 

[KN6KXR]

Because I'm working from a different truck. That said the systems are the same (or similar enough to not make a difference).

Look at TM9-2320-272-24-2 section 3-462 "Hub air seal leak test". It's for the M939A2 series.

 

[aw113sgte]

Because I'm working from a different truck. That said the systems are the same (or similar enough to not make a difference).

Look at TM9-2320-272-24-2 section 3-462 "Hub air seal leak test". It's for the M939A2 series.

Here are the pages. I'm not super familiar with the 939, but it looks like blocking both sides of the seals, then pressurizing to 80psi and checking that no more than 10 PSI leaks out in 1 minute.

 

[KN6KXR]

All the QRV's, the controller, the sensor, etc.. are VERY similar. The basic idea is trace the line back from the inside of the axle up to wherever it's mounted on the frame rail. The ones on my M936A2 are JIC fittings to the distribution block. Take the line off and plug in your "special" tool. Mine is a gas pressure tester I got from Home Cheapo, a 100psi gauge swapped to it, a tee with a blow off valve to release the pressure and a male JIC fitting. Use shop air and pressure test. This will open the QRV at the wheel and the whole thing will be at tire pressure from your gauge to the tire. When you open the blow off valve fast it will shut the QRV. If you open it slow it will drain the tire down. That's how the system controls the pressure. It has pre-programmed parameters and timers and stuff depending on the truck tire size, pressure target, etc, etc...

If you have the truck off and use shop air (creating a QUIET environment) then all of the sudden it becomes super easy to find a leak. I chased them all over until I did this and as soon as I did I identified 4/6 bad hub seals straight away. You'll wonder why you didn't do this sooner. The follow up part of this is when you get your tool made then get a blank cap for it. Not only will this keep crap out of the tool but if you do get a leak you can cap the line and run one tire short on CTIS (hand manage it) but still operate the rest. That's the shitty thing about the CTIS when you lose one you lose them all (at least on the M939 maybe they fixed that?).

Lots of folks give up on the CTIS. I think it's pretty simple. I use it quite a bit on my wrecker as it weighs 36,xxx pound and going from tarmac to potholes at 80psi isn't going to work unless you want to rattle the truck apart. I also appreciate the periodic checks going down the highway it's peace of mind.

Sorry I don't have exact advice since I don't have the same truck but I hope that helps. If you are computer savvy find the "P2P" simulation program posted in the M939 section it's pretty cool!

 

[Ronmar]

Basically you disconnect the axle vent line and screw in a low pressure gauge. Then pressurize CTIS(you can do this with jumpers at the controller connector, or disconnect the outlet line at the PCU And connect an air pressure regulator set to tire pressure to pressurize the system. If you dont have any pressure buildup, the seals are fine. Move the gauge to a different axle and check there… If you have pressure buildup on the gauge you have a leaking CTIS axle seal. You can then disconnect the regulator at the PCU, disconnect the CTIS line at a wheel and apply regulated air at each wheel end of the axle individually to see which side the leak is on…