Have a Cat 312. Recently, the auto throttle control (idle down portion) as quit working regularly. Sometimes it does idle down fine, but will speed back up on it's own like the controls are being moved. Have also developed what seems to be a few leaks, so I'm curious if they are related. One leak is the pilot line to the left travel pedal. The other leak seems to be hose connections to the swivel joint. Anyone have any thoughts on the Auto Idle Down and what to check? In regards to the swivel joint hose connections, do these have o rings where the hose connect on top? How about a breakdown of the swivel joint itself? What does it take to rebuild this joint? Thanks.
Anyone?
Regarding auto-idle...not 100% sure but it is very possible that auto-idle engages via pilot pressure drop. If you have a line that leaks, I would repair or replace that line (left side travel). Regarding the "swivel joint". I believe you are referring to the rotary manifold. This rotary manifold is basically a hydraulic swivel joint. It allows the travel (propel) hoses to reach the motors and still maintain ability to swing the house 360 degrees. Most hydraulic hoses today that are used in quality built machines use O-ring face seals. That would be where I would first check. If the rotary manifold itself is leaking, there are rebuild kits available. Good luck.
Auto idle is controlled by pressure switches in the pilot circuits for the functions and travel. If its kicking up the idle on its own you probably have a bad pressure switch. The switches can leak too if they get broken or bumped. If a hose is leaking wash it off and inspect it while running to see where its leaking. Cat does use oring face seal lines and also straight thread oring boss fittings into the swivel all of which can leak but are easy to change once you know where its coming from.
Finally got around to replacing the leaking pilot line...no change to the auto throttle. I'm aware of three pressure switches on the center bank, as I had already replaced one because it would not auto up in travel. But how do you check these things to see if one may be the cause of no idle down?
actually, the way those pressure switches receive pressure is via a split path logic circuit. One path of the logic circuit pressurizes anytime a spool moves off center. If a centering spring retaining bolt is loosening, that can allow a spool to drop a couple mm and that will trigger the switches. If the travel alarm is also beeping it's in the travel path of the logic network. If no tvl alarm, it's in the implement path. One thing that can sometimes be the issue is when someone removes an attachment and plugs off the attachment pilot lines instead of looping a hose end to end. Pressure builds in one cap and shifts the spool slightly. Or a restricted return hose back to tank from the logic network.
Ok. Lost me a bit, so what do you suggest I check? The arc seemed to be fine till the line got a hole but since the hole has been replaced still does not work.
I think if you unplug the switches it will send a signal to idle down. Unplug them one at a time until you find the problem.
I can't make any connection between a leaking hose and this system acting up. Unless it was your attachment pilot line that was leaking and someone capped it off instead of replacing it. I have seen that before where someone says "hey we aren't using the attachment -let's toss this hose" Or they remove some plumbed up attachement and don't put the jumper hose back to original. When it's idling, you can short across the switch contacts of either of the pilot logic switches and the engine should rev up - that will test the AEC and the wiring right to the switches. As I recall the switches have bare terminals which would make shorting them simple - green plastic switch body... You can't harm anything shorting them. It's a pull up type voltage out of the ECM to those switches. One of them should also make the travel alarm beep. That will identify which one is travel. You can leave one switch disconnected for a while, then the other to see which half of the logic circuit is causing issues. Then whichever side has issues, you can replace the switch with a pressure gauge. Watch for the pressure creeping up. It should stay at less than 30 psi when no functions used. If it climbs over 30, a spool is shifting off center in the DCV. A spool could be shifting due to pilot pressure leaking through to the cap (maybe from a joystick) which would require a pressure gauge teed into each one of the dozen or so pilot connections to figure out which it is, or the bolt could be loosening. You'd have to remove all the pilot caps including straight travel and verify the bolts are tight Also, as I recall, some 311/312's had the pilot switch for travel logic under the cab plumbed into actual travel pilot, other serial number prefixes had it in the logic network of the DCV, so if there's only one on your DCV it will be implement, the other will be under the cab.
The hoses going into the manifold are not o ring. If the suddenly started leaking check the locating bolt that stops the top half of the manifold from spinning. It can become loose or break . If that happens the upper section will turn when you swing causing the hoses to leak. If that has occurred carefully check the rubber boot for cracks. My 311 did this and over time water built up in the swing gear. When the weather turned cold it iced up and tore the seal out of the bottom of the swing drive. Not that ice should be an issue for you.