Howdy, new to the forum and hoping someone might be able to point me in the right direction. I have a Catepillar 302.7DCR serial CAT3027CDLJ700810 that I recently had a local Kubota/Yanmar dealer work on to fix an issue with the auxiliary hydraulic control switch/wiring on the right joystick (aftermarket thumb would not retract, though would pulse and would try and close further on same switch). Get it back and the controls are now backwards, I disconnect battery and switch electrical connection under the floor pan and all is right in the world, for an hour or so. Run the machine for an hour or so and get a faint whiff of a burning smell followed by loss of all hydraulics shortly after. Open the fuse box and the 10amp Valve and Horn and 15 amp Power Outlet fuses are blown. I replaced them both and regain hydraulic function/movement for a few seconds before the 10 amp blows again. The 15 amp power outlet fuse does not. Any ideas as to where I should begin to look? Test a solenoid? Relays? I am at best a youtube mechanic, willing and able to replace almost anything if I in fact know what's the issue but I am out of my depth with electrical and or hydraulic diagnostics, so I have come to you fine folks for help. Thank you in advance!
First thing you are going to need is an electrical schematic. Kudos for supplying the machine Serial Number without being asked and check your message inbox. The first thing you need to know is that the implement hydraulic system lockout solenoid and the blade control solenoid are powered from the same fuse. You'll see this from the schematic. Temporarily disconnect the blade solenoid (#15 located on the bottom corner of the main control valve) from the machine harness and see if the problem goes away.
In my 10 minutes of daylight today after I returned from work, I was able to disconnect the solenoid and run the machine. The fuse is no longer blowing and hydraulic function has returned to the arm and remains on the blade. I did not get to check the tracks however before I ran out of daylight/had tools and fasteners sitting on the tracks. I am confused as to how the blade remained running both before the disconnect and after the solenoid was disconnected if they were powered by the same fuse? Thoughts on next steps? Thank you in advance!
I need to clarify something. The solenoid you disconnected does NOT control the dozer blade function, it is for the dozer blade lock. So in all probability the blade will still work even with it disconnected, atlhough the blade might drift down if you raise it and put the control in neutral. Try measuring the resistance of the coil of that solenoid and report your findings. If you can live with this for a while then I would suggest you leave it that way and see how the machine performs - in other words does the fuse-blowing stop. If you confirm everything works OK long-term than the complete solenoid valve will need to be replaced. Unfortunately you can't buy the coil separately. The Part Number is indicated on the electrical schematic.
I am encountering the same fuse problem as goesher and as I read on an earlier thread. I plan to test the solenoids as recommended but, if possible, would appreciate a copy of the electrical schematic. The Unit is a 302.7D with vin LJ7019258. Any assistance would be appreciated.
Check your message inbox for a copy of the electrical schematic.
Thanks again for the elec wiring diagram, just what was needed. I tracked down one problem to a bad safety switch in the left-hand armrest. 12V was not sent to the blade lock out solenoid 386-0880. My question now is whether you are familiar how the solenoid works. When shifting the blade up/down lever, the pin on the bottom of the solenoid does not seem to move into the solenoid when the lever is moved up. Also, the solenoid when test has low ohms. I'm assuming the solenoid when energized pulls in a plunger which allows the shift blade pin to move up in. I would appreciate the feed back.. Cheers
Yes the safety switch controls the power supply to both the blade solenoid and the implement lockout (safety valve) solenoid. A number of people on this forum have gone off chasing implement lockout problems when in actual fact the problem was a non-functional blade lockout solenoid. This question has been asked before and I am afraid there is no information out there regarding the specifications of the solenoid coil resistance. Define "low" please. What was the measured ohm value.?
I failed to write it down but I believe it was in the 8 ohm range
Believe it or not but that sounds in the ball park for that type of solenoid. Generally the resistance of lockout solenoid coils runs somewhere around 10 ohms. Whether it is correct for that paricular Part Number I'm afraid I don't know.
I'm going to recheck the ohms to be certain. I just cringe at the thought of spending $900 (outrageous) for this part. Bypassing the safety switch the hydraulics for boom, bucket and cab work. The unit won't move f/b, but I'm assuming it's because the blade is down and does not move. The blade lever barely moves the cable and the plunger attached to the cable and going into the solenoid. The plunger moves maybe two mms at most. I disconnected the cable from the plunger and tried to move it manually (with the unit running) and it moves no more than when attached. Would you have any info on the interaction between the blade lever/cable/plunger and the solenoid? This is when the test part sitting on the shop shelf would come in handy! Cheers
Question for you. Are you experiencing any issues of blowing the 10A fuse serving the blade lockout/implement system safety circuit.? Regarding the resistance reading of the blade lock solenoid coil see Post #11 of this link. A new one measured 100-120 ohms at the fuse where before it meausred 210 ohms. I'm assuming that the measurement was of the complete circuit fed by that fuse rather than the solenoid valve on its own. If you need any more help I would suggest that you post on that thread and ask the OP to measure the resistance of the blade lock solenoid coil on its own. HeavyEquipmentForums I'm sorry I don't. Maybe someone else can comment.
On the question of the blowing the 10A fuse, yes. That's what lead me to this post and your responses. The link is appreciated. Thanks for the help, you have been most generous. Cheers
No worries. Hopefully one or other of the posters on that thread will come back with a resistance measurement of just the blade lock solenoid coil rather than the complete circuit fed by that particular 10A fuse, which actually contains more than just the two solenoids. You can get more infromation HERE
Update: @guzzi27012 measured the resistance of his blade lock solenoid coil (which was new recently). It came out as 7.1-7.5 ohms.