Leaky CTIS on M35A3

[steve6x6x6]

The wonderfull CTIS on the M35A3, who is the idiot that came up with this retrofit? This is what i found on the rear, the only way to know is in a ( i have some extra rears) destructive test. brake it down, cut the backing plates off. Saw the spindles off, i took a punch and a small hammer bumped the steel shoulder - it moved, bump, bump - what the **** - pulled it off with one hand. The epoxy had no bond at all. What is supposed to had the air back?

 

[ODdave]

Is the epoxy a normal thing?

 

[patracy]

Wow, epoxied? Why wouldn't they have brazed it at least?

 

[steve6x6x6]

Wow, epoxied? Why wouldn't they have brazed it at least?

I thought the steel block, or boss would have been welded to the spindle, but no.

 

[3dAngus]

Steve, Is that the same A3 you had at the Ga. Rally?

 

[doghead]

The term "service life" comes to mind.

 

[motomacguyver]

Mine are epoxied on. This is another point of failure to look into.

It would be very hard to diagnose with the brake drum on. It would sound like air leaking from the brake backing plate... and once the brake drum is off and the hub is apart there is no way to hold air pressure on the hub assembly. Hmmmmm..... a large piece of pipe the same dia as the hub ring, the length of the hub stack up (so the 3 inch nuts could hold it on) and the ends machined flat with a trepanning (grove on the ends to captivate) operation for O rings to make a sealed chamber - the stock threads of the 3 inch nut would have to be sealed also (RTV).... could be bolted on using the stock nuts and some off the shelf O rings to make a pressure test chamber for the spindle to hub junction. This should hold enough psi to see soap bubbles on the epoxy joint.



So without destructive testing, how about putting rtv sealer on the gap between the epoxy and the spindle and putting it back on clean surfaces, or chiseling off the old epoxy Cleaning, Cleaning again. and reglue it? Or possibly braze it. (best)----- big dissasembly, lots of heat. A good med temp solder joint should hold....think radiator shop.

I still would think that any gear lube in wheel bearings is the fault of leaking O rings, cork keyway gasket or thread sealant though. (I know this isn’t your problem, just posting for someone else who may be having issues with CTIS)

Sounds kind of rambling. But I am thinking and typing.

Thanks for the info.

 

[steve6x6x6]

Steve, Is that the same A3 you had at the Ga. Rally?

No, this axle is not from my truck, i picked up one A3 front and three A3 rears. The date on this rear axle is 1999. If this is a problem need to make a sleeve and install it with a spindle nut, turn are the CTIS air and spary this area with soupy water to check for leaks.

 

[rossbart]

Is the epoxy a normal thing?

I just recently expanded my MV collection to include about a 1996 vintage M35A3. Pretty clean truck with 3,100 miles. The tires hold air perfectly and the CTIS appears to be working and complete. However, when I turn the CTIS on it thinks it has a flat. I have just begun trying to diagnose the apparent system leak but did not air seems to be coming from a back axle brake backing plate area?

I've been reading TM's and posts like crazy to try to understand the concept of how air gets from the axle through the hubs and to the tires. It seems that the hub is supposed to isolate air and keep it out of the axle housings otherwise? Anyone with a good grasp please feel free to give me the short course herre.

But, in regard to this thread, I did come across the TM section that details

REAR WHEEL RING ADAPTER MAINTENANCE​

REMOVAL, CLEANING, INSPECTION, AND REPAIR, INSTALLATION, LEAK TEST
It is found at TM 9-2320-386-24-1-2 0347 00

Sure enough, looks like epoxy is he design and there is a procedure for testing and/or repairing the seal.

Hope this helps. Hope that's not my problem...

Ross

 

[sierra117]

If you turn it on and shortly after that does it say flat, mine occasionally does this it will attempt to build pressure and after a little bit it stops trying and then says flat I just hit the on button to stop the auto restart and then push it again to restart it I just keep repeating it till it builds pressure. It only seems to do this when it gets cold

 

[Jbrowning22]

Mine does that when it's really cold......apparently you aren't supposed to use it below 30F until youve been driving for a few minutes.

 

[Rustygears]

I just recently expanded my MV collection to include about a 1996 vintage M35A3. Pretty clean truck with 3,100 miles. The tires hold air perfectly and the CTIS appears to be working and complete. However, when I turn the CTIS on it thinks it has a flat. I have just begun trying to diagnose the apparent system leak but did not air seems to be coming from a back axle brake backing plate area?

I've been reading TM's and posts like crazy to try to understand the concept of how air gets from the axle through the hubs and to the tires. It seems that the hub is supposed to isolate air and keep it out of the axle housings otherwise? Anyone with a good grasp please feel free to give me the short course herre.

But, in regard to this thread, I did come across the TM section that details

REAR WHEEL RING ADAPTER MAINTENANCE​

REMOVAL, CLEANING, INSPECTION, AND REPAIR, INSTALLATION, LEAK TEST
It is found at TM 9-2320-386-24-1-2 0347 00

Sure enough, looks like epoxy is he design and there is a procedure for testing and/or repairing the seal.

Hope this helps. Hope that's not my problem...

Ross

Hey Ross-

Your CTIS system plumbing likely is clogged or has a leak at a plastic joint. The system isolates all the tires and vents the pressure in the lines when shut down. It initializes by blowing little puffs of air to open the wheel valves. It the measures the pressure in the line to get the tire pressure, assuming that the wheel valve opens. If the system can't build 20psi in the lines, the wheel valve doesn't open. It will repeatedly try for a number of times and if it doesn't sense any pressure when 'listening' between puffs, it says 'Flat'. The system will fail to build or hold pressure if one of the plastic tubing joints is loose or the tubing or valves gummed up with oil and snot. The system is very sensitive to dirty air lines and that's why there's a Haldex filter/dryer system added to the air system.

The best way to trouble shoot is to first make sure the air dryer is working properly. Make sure the filter and desiccant cartridges have been serviced recently. The A3s I've seen all had poor air dryer maintenance. That's a cheap fix and will also avoid issues with the air assist steering and air boosted brake system.

Next make sure things are tight at each wheel. The slip on plastic plumbing ends are notorious for having the tubing work loose. Make sure the tubing is seated in each one. Next, never use CTIS until you've driven a few miles, regardless of temperature. This is to give the axle seals a chance to seat. Otherwise you risk blowing a seal and that is a very ugly repair. This instruction is in the TMs. The steps I listed cover the most common issues. It is likely that it will enable your system to work. One last informational item: the CTIS system connects all the tires together when active. On the A3, you cannot measure or fill a single tire or axle. The system will attempt to equalize all of them and fill the combination to the pre set pressures, depending on mode and speed. It will not fill flat tires because the tire must have 20psi in order to pop the isolating wheel valve open.

 

[jaymcb]

Something is leaking so bad on the RF CTIS valave that my compressor can't even keep up with it when the CTIS is on. The buzzer for low air comes on when I try and drive it every time th CTIS cycles.

If I turn it on, it even dumps air if I am filling it from the schraeder valve.

I can feel/hear it dumping pressure/hissing away when i try and fill it past 44PSI.

could I have a bad valve?

 

[motomacguyver]

Something is leaking so bad on the RF CTIS valave that my compressor can't even keep up with it when the CTIS is on. The buzzer for low air comes on when I try and drive it every time th CTIS cycles.

If I turn it on, it even dumps air if I am filling it from the schraeder valve.

I can feel/hear it dumping pressure/hissing away when i try and fill it past 44PSI.

could I have a bad valve?

If your buzzer comes on I think your air priority valve is suspect. The valve shouldn't let the CTIS air demand overide the Brake system PSI. I think at about 60-70 PSI it should cut the air to the aux systems and direct the air only to the brakes. This is a VERY unsafe condition as it will cause your brakes to not work.



It would take a major leak to cause this, check the large lines to the CTIS manifold. Also if you try to fill the tires over 45 PSI and the CTIS knows it.. it will try to vent air.

 

[AMDOOR]

When I picked up my M35A3 at Ft. Riley, all six tires were flat and the CTIS system had been left on. I tried to use the system to help inflate the tires to no avail. I inflated all tires to 20 PSI and the CTIS still reported flat tire. I gave up on it, turned it off, filled the tires, and took it home. All tires held air with no problems, 55 PSI in front and 50 in the rear, Until weeks later when several of my employees decided to "check it out". Among other things, they turned on the CTIS system and left it on when the truck was shut down. I came out to find the tires with about 15 PSI after only about 6 hours. Needless to say I don't turn the CTIS system on and am seriously considering disabling the power to the control panel on the column. Maybe I'll gut it and put a radio in it's place?

 

[Rustygears]

Mr. Moto is right.

Under normal conditions, the CTIS doesn't bleed down the air in a steady stream, but in a pop pop pop fashion as it tries to charge the lines to over 20psi so the wheel valves will open. Between puffs of air, it then measures the line air pressure because if the wheel valves opened, the lines are then pressurized by the tires and the line pressure is the same as the composite tire pressure of all the wheels that have the wheel valve opened. This is why the TMs tell you that the CTIS will not inflate a tire that is below 20psi. It takes a tire with over 20psi and the CTIS fill line also being over 20psi in order for the wheel valve to open.

Additionally, the CTIS has an electrically sensed 70psi (as I recall) cut out that when the service line pressure drope below 70 psi, the CTIS CPU inhibits operation. As a last ditch backup, the truck air system has a 50psi mechanical cutoff for all secondary air systems such as CTIS, air assist steering, cooling fan servo, etc. This is to protect the air supply for the booster for the air assisted hydraulic brakes.

If your air drops below 70psi and CTIS is still running, there are likely problems in the plumbing or the CTIS manifold valve or wiring. This is in addition to any leaks in the plumbing to the wheel valves. I seriously doubt the wheel valves are bad based upon the symptoms that were described.

 

[Jbrowning22]

10psi is the lower threshold, not 20psi. "emergency" mode will drop them to 13psi, and the system will reinflate them fine from there.

 

[motomacguyver]

One other thing to check is on the CTIS manifold, there is a screw in pressure sensor, it has two wires running to it. Mine was physicaly broken off, this would cause the dash display to say "flat"
I called CM automotive and they sent me a new pressure sensor for free. Thanks CM.

 

[BadMastard]

Hey Jaymcb? just a maybe here, but take your tire off and check the air line going to the hub there. Or have soldier b stand by the tire and listen right there. If the hose is loose or leaking heavily, they will hear it when the CTIS starts cycling. It can also be the seals on that hub. Mine does something similiar. If I inflate all the tires to 50 psi, and turn on CTIS, the right rearmost tire drops to 15 psi over 3 or so cycles of the system. I'm checking seals today, so I may find more wrong, but I suspect it's the air line going to the hub. My local carquest and napa have the fittings so yours should too!

 

[motomacguyver]

Hey Jaymcb? just a maybe here, but take your tire off and check the air line going to the hub there. Or have soldier b stand by the tire and listen right there. If the hose is loose or leaking heavily, they will hear it when the CTIS starts cycling. It can also be the seals on that hub. Mine does something similiar. If I inflate all the tires to 50 psi, and turn on CTIS, the right rearmost tire drops to 15 psi over 3 or so cycles of the system. I'm checking seals today, so I may find more wrong, but I suspect it's the air line going to the hub. My local carquest and napa have the fittings so yours should too!

An easy check to see if the OUTER seals are leaking is to check the axle breather, If it is releasing air when the tires are trying to fill one of the outer sets of seals on that axle are bad. I replaced all my axle breathers with fittings and ran the hose up to the back of the cab. When I took off two of the breathers air pressure was released.