I have had an MD-70 for the past eight years and have been very happy with it. I have found it to be pretty easy to work on and very reliable. However, I ran into a recent problem that has totally stumped me and my tech contact at ASV (Tim in Tech Service). Several years ago I removed the service filter indicator on the large (5") spin-on hydraulic filter housing on the right side of the machine, where the roll-over cage mounts. There are three bolts that attach the filter head to a bracket. My machine has a "Change Filter" light on the Main Control Console (left side console) and the light kept coming on even though the filter was not very old. Several years ago, I removed the sensor, which sticks up out of the filter head (housing) and installed a pressure gauge in the 1/4" NPT port. I have gone through several pressure gauges; they just don't hold up to the constant vibration. I now want to go back and install the original sensor. The sensor assembly consists of a 1/2" NPT plug, that has a small threaded stud and nut sticking out the top. This is what the sensor wire connects to. When you remove the 1/2" sensor/plug there is an aluminum cylinder, that is 0.345" in diameter on one end and 0.48" in diameter on the other end (which has an o-ring on it). The cylinder is approximately 1.25" in length. The cylinder is designed to be pushed up into the sensor/plug when there is enough pressure to overcome the force of a spring which is holding it down. There is a drilled hole in the filter head through which the oil flows to exert pressure on the aluminum cylinder and spring. It is my understanding that the bypass pressure for the filter housing is 15 psi; when the difference between the filter inlet pressure and the filter outlet pressure exceeds 15 psi (indicating the filter is getting plugged), oil flows through the bypass channel and applies pressure to the aluminum cylinder, pushing it up into the sensor. This grounds the wire and turns on the light. The problem is that I can't figure out how to reinstall the sensor! The threaded opening in the top of the filter housing is 1/4" NPT (female) and the sensor is 1/2" NPT (male). The aluminum cylinder, which should go down into the port, is just a little too large to fit down the 1/4" NPT port. It doesn't make any sense! I even ordered a new sensor assembly, in case I had lost part of it and it looks just like the one I removed. I called Tech Service and they don't have access to the filter housing or sensor. I sent them pictures and they were not able to figure out how the sensor fits into the housing. What I'm requesting is to have someone that owns an MD-70 look at the sensor on their machine and see how it attaches to the filter housing. If possible, remove the sensor to check the thread size and see how the aluminum cylinder fits down into the housing. The only thing I can think of is that there was some type of adapter fitting that I have lost that went from a 1/2" NPT female end to a 1/4" NPT male end and that was machined to allow the aluminum cylinder to fit down into it. However, I can't imagine that I would lose such a piece or that it would not be included when I purchased the sensor assembly. Thanks, in advance, to anyone who can help me resolve this mystery!
