Auto Service Professional

FEB 2018

Magazine for the auto service professional

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39 | ASP February 2018 Technical alloy but is susceptible to long-term corrosion, similar to other aluminum vehicle compo- nents. Aluminum tire pressure monitoring valves must be inspected during every tire- related service, as they may corrode over time, leading to potential failure. While some OEM sensors cannot be retro- fitted with a new valve, note that some OEM aluminum valve stems are not permanently attached to the sensor and may be serviced without the need to replace the sensor. ese two-piece sensor and valve stems must be replaced during tire service or replace- ment when corrosion is evident, allowing the continued use of a good sensor. Dodge, Chrysler, Jeep, BMW and VW, as examples, feature sensors equipped with a replaceable aluminum valve stem. Service kits are available that include the valve stem. e valve stem attaches to the sensor body by inserting the valve head from the bottom side on the front of the sensor before installing into the wheel. e hex nut is then installed and tightened to a torque value of 58 in.-lbs. e most common type found on makes such as Audi, BMW, Mini and VW is installed into the wheel first in order to obtain the proper alignment of the sensor. Using a mounting pin to hold the base of the stem, tighten the hex nut to a value of 40 in.-lbs. Next, attach the sensor to the base of the stem and torque the screw to 35 in.-lbs. Kits are available that include a locking hex nut that features a shear ring internal to the nut that will shear off as the hex nut is tightened short of full torque value, ensuring that the valve stem and sensor are locked together. e ring is sheared prior to reaching 35 in.-lbs., after which the nut is then final tightened to 35 to 40 in.-lbs. Some OE designs feature an easy to replace valve stem. e stem should drop into the clip at the narrowest section of the threads, and then pulled into place. Once you install it into the wheel, align the flat surface of the washer to the underside of the sensor body. Slide the rubber grommet on the stem with the angle edge up and straight edge down. Install the hex nut while adjusting the valve to the wheel angle and torque it to 71 in.-lbs. If the grommet and washer are of the one-piece design, there will be no flat side so alignment is not important. is simple to install OE stem is found on numerous European, Asian and domestic vehicles. Kits for Dodge six-wheel dually applications with alloy wheels may feature inner duals equipped with a rubber valve stem. During replacement, be sure to torque the sensor to the valve stem first with the hex screw at 12 in.-lbs. After inserting into the wheel hole, install the nut and torque between 80 and 125 in.-lbs. Always verify the proper part for the appli- cation you are working on before installing and follow all instructions that are provided with replacement TPMS components. Editor's note: It is critical to pay attention to the specified torque values listed for any given TPMS sensor. Under- or over-tightening can easily result in leaks and/or sensor damage. NEVER guess at torque value. Be sure to carry the inch-pound torque wrenches that are dedicated for TPMS service. Editor's note: Do not be tempted to apply any type of lubricant to aluminum stems or hex nuts or any threaded connection on the Note the cracking and deterioration of this TPMS sensor stem-to-wheel grommet. This may have occurred as a result of age and temperature or by over-tightening, or a combination. Even if a grommet appears to be in good condition visu- ally, never assume condition,. Always replace the grommet whenever the sensor is serviced. Photo courtesy Dill

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