Quick Tip to Fix Emergency Brake Pedal Position Switch (Not spray!)
#1
01-06-2014, 01:17 PM
Quick Tip to Fix Emergency Brake Pedal Position Switch (Not spray!)
Here's a cheap, easy, and quick "tip" (literally) to fix why the red indicator light doesn't illuminate on the dash when the emergency brake is applied.
The problem isn't just that the little light doesn't come on... the real problem is that other modules that depend on that switch to be enabled won't work until it is fixed. The Auxiliary Powertrain Control Module is one example. It won't work unless it KNOWS that the emergency brake is set, and the only way it knows is via this little switch that is mounted above the emergency brake foot pedal, and is pictured below:
It's a plunger switch... but WD-40 won't fix it. While spraying WD-40 on the spring and shaft may temporarily lubricate the plunger action, that action isn't the problem. The problem is with the bridge disc (see top horizontal washer like disc) having too much play in the reduced diameter of the top of the plunger shaft (see exposed shaft neck down right below the disc) which results in the bridge disc not "bridging" the contacts.
The problem is worsened with generous applications of WD-40, because as the less viscous solutions in the formula evaporate, a sticky guey film is left on the bridge disc and top edges of the contact plates that insulates the two from making electrical contact, like a DIE-electric grease.
Why is it failing to make contact if it hasn't been sprayed? From playing with this switch quite a bit, I believe the contact failure is mechanical in nature, due to the amount of play between the inside diameter of the bridge disc and the outside diameter of the top portion of the plunger shaft, that is turned down to accommodate the disc, and then swedged at the tip to retain the disc.
In action, the disc can get cockeyed at an angle, and hang between a contact on one side, and an angular contact between the ID of the disc hole to the OD of the turned down shaft. This angular hang stops the plunger from travel, and allows the disc to float just above the contact plate on one side, while engaged with the contact plate on the other.
So what is the cheap, easy, and quick tip to fix it?
Yes, a rubber tip!
The above is a facsimile of a rubber bumper I installed over the top of the plunger shaft. The actual bumper I used had a less rounded profile, which works better for stabilizing the bridge disc, but this photo is intended to show why this tip works so easily and well.
The key is that the tip top of the plunger shaft, at the swedged end, fits snugly inside the hole at bottom of the bumper that the photo above depicts. The bumper base seats just as snugly against the top of the bridge disc, and hence reduces the axial play along the turned down annular groove at the top of the shaft.
With the rubber tip installed, the gap is eliminated, which disallows the bridge disc from getting hung up at an angle, or catching its ID with the OD of the let-in portion of the shaft. The elimination of this play results in a decidedly more consistent contact bridge when the emergency brake is applied. Here is what it looks like with the tip in place:
The important thing to look at in this photo is the plunger shaft diameter right underneath the bridge disc. Notice how much thicker it is here, in this photo of the fixed switch, versus how much thinner it is in the very first photo of this write up? The annular groove is observable in the first photo, but it is no longer visible in this photo. This is because the top of the shaft has been shoved into the bottom hole of the rubber bumper, such that the base of that bumper is shoved down on top of the bridge disc, stabilizing it.
The actual "tip" top of the rubber bumper does not "bump" against anything, and can be cut off entirely if not desired. Only the bottom flange of this bumper is used, and only due to the great disparity between its ID and OD, where other available rubber washers and grommets wouldn't work because their ID is too large to fit snugly around the top of the shaft.
Here is what this cheap, easy, and quick tip looks like after being installed back under the dash:
As seen above, the bumper's conical insertion/retention tip doesn't contact anything. It's just sitting up there in black space. Only the base, or the broader "meat" of the bumper, is used to stabilize the bridge disc on the shaft, which results in more consistent contact engagement.
My Emergency Brake Light works now! Which means my APCM no longer has to endure a half dozen button pushes before I remembered that the E brake switch is hung up, again. Time after time, that gets old. Well, this little "tip" fixed the problem, for good!
The problem isn't just that the little light doesn't come on... the real problem is that other modules that depend on that switch to be enabled won't work until it is fixed. The Auxiliary Powertrain Control Module is one example. It won't work unless it KNOWS that the emergency brake is set, and the only way it knows is via this little switch that is mounted above the emergency brake foot pedal, and is pictured below:
It's a plunger switch... but WD-40 won't fix it. While spraying WD-40 on the spring and shaft may temporarily lubricate the plunger action, that action isn't the problem. The problem is with the bridge disc (see top horizontal washer like disc) having too much play in the reduced diameter of the top of the plunger shaft (see exposed shaft neck down right below the disc) which results in the bridge disc not "bridging" the contacts.
The problem is worsened with generous applications of WD-40, because as the less viscous solutions in the formula evaporate, a sticky guey film is left on the bridge disc and top edges of the contact plates that insulates the two from making electrical contact, like a DIE-electric grease.
Why is it failing to make contact if it hasn't been sprayed? From playing with this switch quite a bit, I believe the contact failure is mechanical in nature, due to the amount of play between the inside diameter of the bridge disc and the outside diameter of the top portion of the plunger shaft, that is turned down to accommodate the disc, and then swedged at the tip to retain the disc.
In action, the disc can get cockeyed at an angle, and hang between a contact on one side, and an angular contact between the ID of the disc hole to the OD of the turned down shaft. This angular hang stops the plunger from travel, and allows the disc to float just above the contact plate on one side, while engaged with the contact plate on the other.
So what is the cheap, easy, and quick tip to fix it?
Yes, a rubber tip!
The above is a facsimile of a rubber bumper I installed over the top of the plunger shaft. The actual bumper I used had a less rounded profile, which works better for stabilizing the bridge disc, but this photo is intended to show why this tip works so easily and well.
The key is that the tip top of the plunger shaft, at the swedged end, fits snugly inside the hole at bottom of the bumper that the photo above depicts. The bumper base seats just as snugly against the top of the bridge disc, and hence reduces the axial play along the turned down annular groove at the top of the shaft.
With the rubber tip installed, the gap is eliminated, which disallows the bridge disc from getting hung up at an angle, or catching its ID with the OD of the let-in portion of the shaft. The elimination of this play results in a decidedly more consistent contact bridge when the emergency brake is applied. Here is what it looks like with the tip in place:
The important thing to look at in this photo is the plunger shaft diameter right underneath the bridge disc. Notice how much thicker it is here, in this photo of the fixed switch, versus how much thinner it is in the very first photo of this write up? The annular groove is observable in the first photo, but it is no longer visible in this photo. This is because the top of the shaft has been shoved into the bottom hole of the rubber bumper, such that the base of that bumper is shoved down on top of the bridge disc, stabilizing it.
The actual "tip" top of the rubber bumper does not "bump" against anything, and can be cut off entirely if not desired. Only the bottom flange of this bumper is used, and only due to the great disparity between its ID and OD, where other available rubber washers and grommets wouldn't work because their ID is too large to fit snugly around the top of the shaft.
Here is what this cheap, easy, and quick tip looks like after being installed back under the dash:
As seen above, the bumper's conical insertion/retention tip doesn't contact anything. It's just sitting up there in black space. Only the base, or the broader "meat" of the bumper, is used to stabilize the bridge disc on the shaft, which results in more consistent contact engagement.
My Emergency Brake Light works now! Which means my APCM no longer has to endure a half dozen button pushes before I remembered that the E brake switch is hung up, again. Time after time, that gets old. Well, this little "tip" fixed the problem, for good!
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