Have any of you replaced a clutch disconnect solenoid on an LB75b or similar? There should be two of them on top of the transmission. I keep popping the fuse after using either one of the buttons a few times. It could be a short in the wiring, but I've heard the solenoids are prone to failing. I'm trying to figure out if there's access to the top of the trans. I wish there was an access in the floor. It'd make it a lot easier...
I found this posted on another site from 2012 and some of the testing will help me, but maybe or maybe not his solution. The poster "jinman" has since passed apparently so messaging him won't help... I'll post this to help anyone that comes across this. Knowing how the circuit operates tells me that it's more than likely the relay or the fuse connection etc. not the solenoids. There's no "disconnect solenoid" and my shuttle shift solenoids work perfectly. I added pics of the shift solenoid set up. edited for relevance: "One of the things I find extremely convenient on my LB75B TLB is the Transmission Disconnect switches on the joystick and gear-shift lever. Pressing that button and shifting gears is so easy. When using the loader, approaching my dump trailer or the pile and pressing the button on the joystick makes holding my position while dumping just a simple operation. With the button still depressed, I can flip the shuttle to reverse and be ready to roll away. Suffice it to say, it's a feature I really like. Earlier this week, I noticed the gearshift came out of gear, but would not shift into the next higher gear. I suddenly realized my disconnect switch had stopped working. I tried the switch on the loader joystick and found it also was not functioning. However, when I placed the shuttle to neutral, the transmission disconnects as it is supposed to. The shuttle switching is working perfectly while the switches on the shifter and joystick are not operating. I have a maintenance manual and electrical diagrams. The way the transmission works is a dual solenoid valve sits on top of the transmission. The valve has forward, neutral, and reverse positions. The neutral position is just a centering of the valve with neither solenoid engaged. The forward solenoid, when energized, sends hydraulic fluid to the forward clutch in the transmission. The reverse side does the same thing to the reverse clutch. When either of these positions are engaged, pressing the disconnect button simply interrupts the electrical path to the forward or reverse side of the solenoid and lets it return to neutral the same as putting the shuttle switch to neutral. It's a pretty slick setup and the electrical circuit is pretty simple. The disconnect buttons have their own supply of 12 vdc through a dedicated fuse and either switch energizes one relay to interrupt flow to the shuttle solenoid. That's it. The switches are wired in parallel so their operation does not depend on the other one. After locating the proper fuse and relay on a diagram, I went to the TLB and removed the fuse/relay cover. I pulled the fuse (10 amp) and found it was blown. A blown fuse always gets my attention because I worry that just replacing the fuse without finding a short may just immediately blow the fuse again. To partially disconnect the circuit, I removed the disconnect relay from its socket, replaced the fuse, and started the tractor. I tested both disconnect switches and the new fuse didn't blow, so I turned off the tractor and put the relay back into its socket for normal operation. After starting, I tried the disconnect switches again and nothing happened. The relay did not energize and the fuse did not blow. Hmm . . . I exchanged the relay for a known good one and tried again. Same results! The fuse is not blowing, but the circuit is also not working. Next I slid under the tractor and looked for broken wires. Except for dirt and hyd oil, the wires look fine and no damage is visible. I previously had a leak from a hydraulic hose in that area, so things are a bit messy. My next move will be to get my voltmeter and start looking for the open circuit. I should have had my voltmeter yesterday, but didn't have it with me. I may also just jumper 12 vdc to the disconnect relay to make sure it works normally when energized. Of course, whatever is wrong is common to both switches but does not effect the operation of the shuttle lever. I can still use the tractor just fine, but can't shift on the fly. I have to stop and shift to neutral before I can shift gears. I'd guess that hydraulic fluid got into one of the connectors and caused an open circuit, but that's a real stretch. I have been working in/around water in my ponds, so my guess is water may also have splashed into the connectors and shorted a wire. That seems the most likely issue since the fuse was blown. I've pretty much reached the limit of what I can do without a voltmeter. I'll troubleshoot a bit with it and hopefully trace down the problem. It's comforting to know that the problem is electrical. The fact that the shuttle lever works normally tells me there is nothing mechanically wrong with the transmission. This problem just keeps getting more strange. Yesterday, I got my digital VOM and printed out the circuit diagram so I could troubleshoot. What I found only adds to my confusion. On the attached diagram, fuse 4B is the 10 amp fuse that I previously found blown. That fuse is replaced and is holding fine now. Tracing the 12v at the fuse and down to switch S26 is normal with +12v. However, when I pulled relay K1 and measured at the terminal socket for it's coil, pressing either transmission disconnect switch produces -12v on my meter. Of course, if it is -12v, the coil diode is conducting all the current away from the coil. My guess is that when I get to the circuit board level, I'll find it is burned up and open. Now, I made all my measurements using the ground lug where it attaches to the circuit board. I measured the positive voltage coming in at that point and it is fine. I have two batteries bussed together in parallel, but my system is not a 24V system. Only +12 is supplied to this circuit. The only thing this can be is somehow the line to the relay coil is now ground and pressing the disconnect switch puts +12 on what should be ground. The same as swapping leads on the meter so that it reads -12 vdc. Of course, I left my ground lug attached to the input ground terminal, so I don't how reversal would be possible. I'm just not seeing what would make my voltmeter read negative voltage in a circuit only supplied with +12v.:confused2: I experimented with the shuttle operation by pulling the relay K1. Exactly as I suspected, the transmission disconnects when I pull that relay. When I replace the relay, the shuttle lever works normally for Forward-Neutral-Reverse. I can monitor the switch closures at the relay, but instead of them sending +12, the switching is to -12v. I ran short of time and closed everything back up. I think the next move will be to remove the circuit board completely and start testing components. Something really weird is going on here. Well, my problem with my LB75B TLB got fixed today. I've been putting off working on this solenoid clutch circuit since mid-July. Today, I went back to troubleshooting and found the problem. It was a dirty fuse socket. Previously, I had a blown fuse. I put in a new fuse and it didn't fix the problem. Today, I removed and re-installed the fuse. Like magic, the solenoid clutch started working. The fuse was new and clean, so the fuse socket must have been a bit dirty. I used the tractor all afternoon and it's working perfectly."
Have found over the years that relays that have 5 pins, when you push them into the receiving harness it is very difficult to tell if one socket receiver is loose. Have tightened up many with a sharp pick that I have, and things were better after. Have found loose receivers for ATO fuses tthat needed to be tightened up also. Thanks for the story on how it works and how you fixed it. Simon C
Thanks Simon. I wish I could say that was my story for the repair, but it was a story from another guy I found online. Hopefully mine will end up with a similar ending for my backhoe soon. I'll be going through the relay and fuse pins soon. It's a pretty simple circuit so I should be able to sort it out knowing that it's more than likely not the solenoids now.
Power goes into a fuse and out of a fuse. If a person can get access to the receptacle side of the fuse on both sides with a meter while load is applied, you should not read more than 0.1 volt loss or it tells you the connection is not tight enough or is too dirty. Simon C