Ive got a customer with what seems to be an air leak but i cant find air leaking. Air keeps going down and alarm keeps going off but i can turn engine off and cant hear anything leaking with pedal mashed or not. Any ideas? Also operator said it was building up too much pressure a while back and they did something to the compressor to fix it but now its doing this. if that helps any.
Is The Compressor pumping ?
Yes, it will pump up to right pressure and as soon as it gets low it kick in like it should.
Its been my experience with these machines that an air line under the engine packed with dirt around it so you cant hear the leak
sounds like a good possibility! I'm gonna check it out again in the morning. Does anyone have a pdf. of the system?
Possibly the governor on the air compressor. They do go bad and are cheap to replace. Can you hear any air leaking from the air dryer.
I dont even know where the air dryer is on this machine...lol. Which is why i could use some paper work on it, but i didnt hear any air leaks at all. Im gonna take another look at it tomorrow.
The dryer is in the left rear compartment. It is controlled by the governor to control the max pressure. When the system reaches the max pressure the air dryer purges. This blows the water off the desiccant inside and down a hose to exit under the machine. This is where you look for a leak if the dryer is bad. I have seen the check valve in there stick and wear out. There are service kit for the dryers. The governor that controls the pressure isn't mounted directly on the compressor, it is emotely mounted under the air tanks behind the dryer. At the shop we put a coupler on the tank and feed shop air to the system and look for leaks without running the engine. it is easier to find them when it is quiet.
Bobin your right on the mark . Those air lines under the engine can give you more grief trying to locate the leak than any other air leak.
It might depend on how old your customers 140H is. The "early" H had compressor-governor-tank in location about the same as the G-Series. The "late" H changed things. Tanks and dryer inside engine enclosure, not sure about governor location. I'm many miles from my stash of old literature, so I'm not sure if the air dryer came standard or as an option on the early H. All of our early H's had Aerofiner-II dryers mounted on the left side of the radiator/fan housing. Air leaks can be very difficult to find. Air hoses running next to hydraulic hoses sometimes get holes rubbed in them from the vibration of pumps or valves. Same with engine vibration. Some conditions should be checked out first. Turning the key to the "off" position normally causes a solenoid controlled air valve to vent, and set the spring applied brake pack located internally at the front of the transmission. Does this stop the drop on your pressure gauge. Does one of the two circuits leak, or do both? You might need to replace the foot brake valve under the cab. Old age and moisture messes up o-rings and aluminum alloy parts in the valve. Kits are available, but we haven't had real good luck with them. Another place to check-the parking brake has a large diameter o-ring which can fail, and cause leaking air to vent into the transmission/differential housing. If this gets real bad, you will end up with a no release parking brake, and smoke coming up through the shift console. If you are lucky, it is just the air governor, and I have overthought the entire situation. But I have seen all of these things happen, so I know they are all possibilities. Serial number and year of machine might help someone find the answer for you. smoothoperator
Funny you mention air into the transmission cause i did find a vent where transmission filler tube is blowing out air. I figured it was just pressure from trans. but machine was just running never moved it. So youre saying air can get in transmission from bad oring in park brake...cause the park brake control valve is leaking a little. Where is this oring located in park brake valve in cab? Ill get some more info this morning for ya.
just had a 120H the with same problem. One half of tank would drop 40 psi in ten minutes and to nothing in an hour. Could hear nothing even with workshop closed up in dead of night. Checked every valve and solenoid I could think of but in the end the old soapy water found a cracked drain valve extension on the air tank.The tank sections are small and only need a tiny leak to cause trouble. Another easy check is to pull off delivery hose from compressor.(engine stopped and air at max) If any air comes out you have a bad check valve on tank, There is one on each side. When this happens air will leak back through engine intake and you wont hear it. Also check unloader valve on top of compressor which can cause the same problem. Dont forget difflock is air operated and can also leak air in tranny.
Caterpillar recognized a problem with the materials used in the original parking brake o-rings. If your dealership has a good service department, or a sharp parts person, they can find the parts you need, and their parts system should handle the change from original part numbers to the improved o-rings. In our shop, when we do any kind of repairs, the parts books get speckled with highlight marker, and the spaces get filled with p/n updates, and dates when repairs were performed. The repair is quite easy, but use a few common sense steps. Drain the air system, support heavy p/b housing with a couple of threaded guide pins, order any other related parts that might get damaged or need replacing during the repair, and be as clean as you can when assembling. You may also need a repair sleeve on your output shaft yoke. Your call on that one. Hopefully you will have access to a good parts book, and a service manual to match the machine. They always seem to make things a little easier. 50+ years ago, Caterpillar used to send out product updates in a little newsletter called "Service Bulletins" or something like that. They have a history of recognizing that no machine is perfect, and the real world finds problems that never show up on a drafting table. smoothoperator
Thanks for the info. i told the shop foreman what the problem is now its up to them to get it in the shop and fix it. Thanks again.
mine also got the same problem its a 140g