jinman
Rest in Peace
- Joined
- Feb 23, 2001
- Messages
- 20,387
- Location
- Texas - Wise County - Sunset
- Tractor
- NHTC45D, NH LB75B, Ford Jubilee
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.:thumbsup:
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.:thumbsup:
