Since day one after I purchased the TST Model 507 Tire Pressure Monitoring System (TST) (TPMS), I have had to remove sensors to add air when required. On the rear duals this was not so much of a problem since the sensor was sitting on an open valve stem which is connected to a Crossfire System. By means of a proprietary wrench, the sensor is spanned, keyed onto a flat and simply unscrewed. In repeatedly R&R’ing the sensor what happens is that the valve stem seal in the sensor becomes compressed. At some point the sensor can no longer be tightened and the seal will begin to leak.
TST 507 Sensor conventionally mounted on front axle tire. Note that the clearance is not sufficient to apply a removal tool.
Remove the acorn nuts exposes the jam nuts so that the wheel liner can be removed.
Install and Secure a Flow Through Valve Sensor (FTVS) using the provided Allen wrench.
After a year of service, I saw that a low battery condition was displayed on the monitor therefore I had to replace the original batteries using type CR 1632. I found these batteries both in the watch department at Wal-Mart and at the local Radio Shack store. Before attempting to replace the batteries, one will have to get the sensor rebuild kit from TST. The sensor rebuild kit comes with new valve stem seals, O rings and anti-theft housing screws. In order to rebuild the sensors and replace the batteries you will need both flat and Phillips tip “tiny” screw drivers.
The first thing I did was to use a tiny flat head screwdriver and pick and lift out the old valve stem seal. Next, I unscrewed the case from the sensor assembly. The O ring seal on the sensor may come off all on its own and it may look like a curly piece of wire. Look at the shoulder area between the sensor and case and make sure that the old O ring material has been removed. Using a small flat blade screw driver, I simply went around the sensor shoulder using it as a scraper to make sure there wasn’t any of the old O ring that stuck on the sealing surface.
TST Model 507 Sensor
Place the sensor on a flat surface and using a small screw driver, identify and carefully push the back of the battery downward until it just moves and touches the surface. Spin the sensor over in your hand and you should be able to remove the battery. Observing the polarity (as it was removed), insert a new battery and push it in the slot until it is completely seated on the contact toward the rear of the socket. The battery needs to be completely centered inside the sensor. Install a new O ring over the top of the valve and push it down s far as it will go. Using a small screw driver as a lever, work the O ring over the body of the sensor and push the screw driver around the sensor and lift the O ring over the top onto the threaded body of the sensor. Completely seat the O ring on the flat surface just above the threads with the valve facing up. The O ring should be seated up against the shoulder above the threads. Screw the sensor case back onto the sensor, gently, until is stops. Do not over tighten because the case will jump the threads.
The valve stem seal is installed by inserting the new seal inside the stem so it lies flat across the opening. Using a small flat screw driver, push the seal slightly downward and turn the sensor 90° and continue to slightly push the seal downward while turning. The seal will bottom out in the opening. Visually assure that it lies flat. Restore the anti-theft casing and align the screw hole openings. Use 3 new screws, thread and alternately tighten securing the shell and cover together. Do not over tighten.
In the photo you will note that the FTVS stem is too far inside the wheel cover’s valve opening making it impossible to chuck up. Using a short extension which is screwed onto the FTVS stem will allow access for an air chuck.
Using the anti-theft tool, restore the sensor to the valve stem, a slight amount of air will leak as you tighten the sensor. Once installed, pressure reading should come right up on the monitor. Notice that the low battery icon in the display (lower left corner) is no longer visible.
Adding air to my front tires on the other hand was a much more challenging job. The operation required that the wheel covers be removed since there isn’t any room for the anti-theft tool. 3 acorn type nut covers (dimples) need to be removed. I use a 1/2 drive breaker bar to remove the jam nuts that hold the wheel cover in place. Once the nuts are removed, the wheel cover can be removed from the wheel. Secure and place the wheel cover out of the way. At this point, the anti-theft tool can be fitted and the sensor removed. The air pressure can be adjusted and the sensor restored and the wheel cover installed.
TST Flow Through Valve Sensor for Model 507 System
Enter a new product from TST called the “Flow Through Valve Sensor.” (FTVS) The FTVS is installed on an existing metal valve stem like a conventional sensor. The battery is user replaceable. Remove the FTVS from the package and secure the Allen wrench that comes with the sensor. While looking in the valve stem opening back off the Allen screw until it is slightly below the surface of the threads. Screw the FTVS on to the valve stem until seated. A small amount of air will be released which will indicate that the valve stem core has been depressed. Using the Allen wrench tighten the set screw until it’s snug and give it a little bit more twist tightening the screw. Do not over tighten.
Completed installation of FTVS on front wheel end positions. Assure that the sensor bodies and stems have clearance and do not press on the edges of the valve stem opening on the wheel cover.
In my case, I had to thread a short valve extension, 1.5″, nipple onto the sensor since the stem of the FTVS was too short to accept an air chuck. I restored the wheel cover, jam nuts and acorn nut covers. A successful install will show that the sensor sits on the stem without any side pressure on the case from the wheel cover. As shown in the photo, a plastic valve stem cap was fitted completing the install. Once the FTVS is in place, it is live and the tire pressure should be seen on the display. Using the display as an air gauge, you can inflate the tire and watch the change in pressure. I backed up the pressure reading using a DT160 Digital Tire Pressure Gauge that I obtained from TST in Sevierville. The pressure difference was within 1 psi. To verify that the sensors do not leak, make up a solution of dish washing soap and water and using a spray bottle, apply the solution on the valve stems. If there’s a leak it will show up right away.
Going forward, any pressure adjustments that I will need to accomplish on my front axle can be done within seconds using my compressor and the Model 507 display. Since the install, the pressure has held perfectly and the sensors are transmitting pressures and temperature ratings as expected.
Thank you for reading and joining the discussion about the Model 507, Flow Through Valve System installation.Research Campgrounds, Plan RV Safe Routes & Turn your phone into an RV GPS.
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