Caterpillar 312B Sn-9GR00432- Recently occurring. After starting and waiting for all the 'red warning lights' to go out I flip the safety lever and attempt to use the machine. -Nothing- operates until it runs for a short few seconds then I hear a 'clunk / click' sound like a relay picking coming from what appears to be the area around the left arm rest (where the safety lever is) everything works fine after that. My concern is when a problem starts out small and simple it usually gets worse, never better. Any ideas on what is going on ?
I'll take a bad or corroded connection for $200.
I'm thinking worn out or damaged linkage pieces for the safety.
I've flipped the safety on/off thinking it might be 'loose'. Is there a relay in the area that makes the click/clunk?
My 325B does something similar. When I first start it up and keep it at idle, it takes a few seconds for the hydraulics to kick in when I flip up the safety. The time lag between the safety being flipped up and the clunk/click sound when the hydraulics kick in seems to get shorter if the rpm's are higher, almost like there is dependence on hydraulic pressure. After a few mins of operation, there is little to no lag. Curious to what you find out.
I doubt if it's the linkage. I have flipped the safety several times and beat on the side of the side of it. I was also guessing there might be a hydraulic pressure sensor somewhere involved but don't know enough about it. When I shut it off and quickly restart there is no delay. I start it with the throttle at '6' as the engine runs 'smoother' at that setting. I will do some more 'in depth' investigation after I get some work done in a week should no one offer any insight.
My machine is a ranch machine so it sits a while, sometimes a couple months, before uses so that also might have something to do with it. No idea if this is because of a simple sticky switch/solenoid or if the pilot control circuits are bleeding down or if the pilot pump is weak which then causes the pilot system to take a bit to pressure up after sitting for a while. But yeah, after a few minutes of use, the delay tends to go away. I'll try to play with it again and see if I can mimic your symptoms next time I'm at the machine.
Well, I think I jinxed myself on this one. Went out to my machine over the weekend to see if I could play with that hydraulic safety level but cut couldn't even get the machine to start. With key on, the control monitor lit up but nothing would happen when I moved to key start. After futzing around with schematics, it turns out I had a bad fuze. I couldn't tell it was blown by looking it (had to use an ohm meter) which is why I spent wasted time chasing circuit ghosts. Well, once I figured out how to start the machine, now I can't get the hydraulics to turn on at all. I tested the little micro switch in the hydraulic safety level but need to study my schematics a bit more to understand where to track down a bad wire/connection for the pilot hydraulics. Futzing around with circuits is one of the downsides with old equipment...
Sounds like you may have 'another' problem. Fuses usually blow for a reason. Which fuse?
The DELAY still occurs when first starting. However, after running for a while and shutting down for several minutes when I start it back up everything works immediately after tripping the safety. The DELAY is gone. I don't know if there is some 'pressure' or 'temperature' thing involved. If someone in the know would provide a hint as to where the 'relay(s)'? that 'click' are I would check the wiring connections.
I had a bad fuse on the ignition key (forgot what number) but that's not the problem as it went back to not being able to start. I feel as almost there is a safety switch somewhere preventing the start circuit from activating. Most, if not all of the relays I know are in the relay panel in the engine compartment mounted on back side of cab, right above the batteries. I don't think the click sound is from a relay. I "think" it's from a solenoid that opens the pilot control hydraulic line that feeds the joy sticks...but I don't know where it's located. I'm guessing it's under the cab, accessible via a panel...but of course I can't swing the cab to get to them to see.
CatKC- I definitely think you and I have the same issue with our pilot hydraulic system. I'm sure your 312B and my 325B use very different parts, but I gotta believe Cat basically used the same logic to build the hydraulic and electrical circuits for pilot controls. I futzed around SIS 2.0 and finally found this diagram. The view is looking up from the bottom under the cab; the left is towards the front, right towards rear. The pilot hydraulic lock solenoid looks like it under the cab which might be a problem for me to access it the way I parked it but I'll try. I'm still not sure how the electrical interlocks (relays) work with each other to provide a fail-safe switch to keep the hydraulics inactive during the start cycle. Right now I can't tell if it's an electrical wiring/connection issue causing a relay/solenoid to act stupid or if there is truly a bad relay or solenoid causing this. I'll keep at it and let you know what I find. I'll need study my electrical diagram a bit more to fully understand this but we'll see if Vetech63 gets his $200 or not...
Thanks for the picture. I agree that both probably have a lot of 'common' components and functional designs. I need to get my wiring diagram out and see if I can find the solenoid. While working a while in very hot weather I found that even after running then sitting a long time there is no 'delay' when starting up again. I know nothing about where access panels are located. Is all this accessible from under the cab or from inside the cab? The antenna coax is confusing to me as I don't understand why it would be UNDER the cab.
On mine, there are multiple access panels underneath the cab. Nothing really accessible on top through the cab floor. I think most of the bigger excavators use a single piece cab that bolts onto the frame so they just access the bits and pieces from the bottom. I'm guessing some of the smaller excavators have floor panels to access items below because the cab is more or less integral to frame (ie- doesn't just unbolt and pop off as unit). It'll be a while before i can get back to my hoe to figure out my issue- coming up on a few deadlines that will occupy my next few weeks.
After putting up with this for a couple years I got tired of messing with it and decided to use the K.I.S.S. method to figure it out. My particular problem was the MICRO SWITCH that the safety lever trips. I was making it much more complicated than necessary. Cat = $90 . . . . Chinese knockoff on Ebay = $28
Glad you found the problem. For me, the problem just went away after a couple weeks before I could really troubleshoot it. All works good for me now.
Micro switches like all well designed contact switches are self cleaning. If the contacts weren't burned or pitted it could have cleaned itself, which is not uncommon. If it quits working the part number for the 312B (and several other models) is 111-4799.