Problem:
If you’re experiencing premature pad wear, nose-diving, or lack of stopping power on vehicles equipped with a metering valve, this is the right article for you.
Metering Valve Cause:
As you consider the cause of any of the problems above, it is essential to add the metering valve to the list of possible reasons for the above issues. The symptoms produced by failed metering valves will depend on the type of failure and type of vehicle. Here is a description of each type of failure:
1 – Valve stuck OPEN: If the valve is stuck open, the vehicle will have instant-on front brakes (See figure 48.1). The front brakes will apply instantly, while the rear brakes will have to “play catch up.” The long-term symptom of instant-on front brakes is premature front pad wear on all pads. Depending on the vehicle, this condition may also cause the vehicle to nose dive when stopping. This symptom does not always present itself with valve failure.
48.1
2 – Valve stuck where it can’t open completely: if the restriction in the valve’s movement is such that it can only open partway or seized in this position, the vehicle will only have partial front braking. The typical complaint from the driver will be a lack of stopping power.
Metering Valve Solution:
The metering valve should be one of the first things checked when diagnosing the above complaints. The reason for this is it will be one of the easiest things to check. Perform the following steps to verify metering valve function:
1 – Locate the metering valve. It will either be under the vehicle or the hood. Check the external condition of the cap screw–stem area as shown in Figures 48.2 & 48.3.
Figure 48.2 shows an underhood valve. Metering valves located under the hood rarely fail because of the protection they have from the elements. This valve does not need checking. The valve in Figure 48.3 is mounted under the vehicle and receives exposure to the elements. The cap screw and stem have been bonded together by the corrosion.
48.2
48.3
2 – If the metering valve is in question, check it by having someone apply the brake pedal while watching the metering valve stem. The stem should move out on use and in on release, as shown in Figures 48.4 & 48.5.
48.4
48.5
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Excellent information!
At the risk of broadcasting my ignorance, how long have metering valves been a part of brake systems? I’ve worked (DIY) on older, disk brake cars and am familiar with the proportioning valve that limits rear brake pressure, but metering valves are new to me.
Again, great article!