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Old 09-07-2009, 09:59 AM   #1
SalemCat
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Default Brake Pad Wear Sensor - Up or Down ??

Do the Wear Sensors go on the Leading Edge of the Pads (Up), or on the Trailing Edge (Down) ?





Alldata explains they should be Up (Leading Edge),







then in the very next picture shows them Down (Trailing Edge).







I am confused.

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Old 09-07-2009, 11:03 AM   #2
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Default Re: Brake Pad Wear Sensor - Up or Down ??

They go up in the S-series front brakes.

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Old 09-07-2009, 11:24 AM   #3
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Default Re: Brake Pad Wear Sensor - Up or Down ??

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Originally Posted by ssicarman View Post
They go up in the S-series front brakes.
Thanks ssicarman !

That's how I installed them.

But do you agree AllData shows them installed Down in the second pic ?

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Old 09-07-2009, 12:00 PM   #4
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Default Re: Brake Pad Wear Sensor - Up or Down ??

Yes second picture is not right.

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Old 09-07-2009, 12:22 PM   #5
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Default Re: Brake Pad Wear Sensor - Up or Down ??

They are installed down in the second picture. The descriptions are backwards though. "Up" is considered the trailing edge of the caliper. There was a thread regarding this not too long ago. One poster said it doesn't matter, the rest of the posters said the sensors should go up, on the trailing edge of the caliper. All the disc pads that I have come across installed by the factory had the wear indicators installed in the trailing edge position. If only two pads come with the wear indicators (one per side) the pad with the indicator is installed in the inboard position. This is the pad that normally wears the quickest.

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Old 09-07-2009, 12:51 PM   #6
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Default Re: Brake Pad Wear Sensor - Up or Down ??

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Originally Posted by Spaz View Post
They are installed down in the second picture. The descriptions are backwards though. "Up" is considered the trailing edge of the caliper. There was a thread regarding this not too long ago. One poster said it doesn't matter, the rest of the posters said the sensors should go up, on the trailing edge of the caliper. All the disc pads that I have come across installed by the factory had the wear indicators installed in the trailing edge position. If only two pads come with the wear indicators (one per side) the pad with the indicator is installed in the inboard position. This is the pad that normally wears the quickest.
That was me The entire pad touches the rotor. However I agree that if only one pad had the sensor it should go on the inside.

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Old 09-07-2009, 01:27 PM   #7
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Default Re: Brake Pad Wear Sensor - Up or Down ??

Yes, I see. Up is the Trailing Edge.

Before this I figured if you put a mark on the Rotor, and then rotated it as if the car was travelling forward, the mark would reach the Sensor first, hence the Sensor would lead. But that is wrong.

I'm not sure why Up is called the Trailing Edge. Perhaps I'd better quit trying to figure that out, and just remember to install the pads with the Sensor Up.

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Old 09-07-2009, 01:45 PM   #8
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Default Re: Brake Pad Wear Sensor - Up or Down ??

Ok, it's a little convoluted, but if you put a mark on the Rotor, then turn it, the first thing it hits is the Sensor. Hence the Sensor leads to the Rotor.

But we're not talking out the Rotor, we're talking about the Pads. It the Pads are rotating, which they are relative to the Rotor, the Sensor is on the Pad's Trailing Edge.

Hence the Sensor is on the Pad's Trailing Edge (whew).

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Old 09-07-2009, 01:55 PM   #9
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Default Re: Brake Pad Wear Sensor - Up or Down ??

The illustration is misleading. The caliper is postioned perpendicular to the ground in it. In reality, the top of the caliper is canted to the rear. This puts the bottom of the caliper more towards the front of the vehicle, thus making it the leading edge, and the top, the trailing edge. (Unless you drive in reverse all the time!)

Last edited by Spaz; 09-07-2009 at 02:06 PM..

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Old 09-07-2009, 02:16 PM   #10
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Default Re: Brake Pad Wear Sensor - Up or Down ??

Quote:
Originally Posted by Spaz View Post
The illustration is misleading. The caliper is postioned perpendicular to the ground in it. In reality, the top of the caliper is canted to the rear. This puts the bottom of the caliper more towards the front of the vehicle, thus making it the leading edge, and the top, the trailing edge. (Unless you drive in reverse all the time!)
The Leading and Trailing refers to the Vehicle itself. This is a good way to remember it.

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Old 09-07-2009, 02:23 PM   #11
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Default Re: Brake Pad Wear Sensor - Up or Down ??

I see your line of reasoning. Don't make your head explode. The leading and trailing edges aren't determined by the the rotational direction of anything in this case. It just refers to the position of the item. The area that is most towards the front is the leading edge, and towards the rear, the trailing edge.

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Old 09-07-2009, 03:17 PM   #12
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Default Re: Brake Pad Wear Sensor - Up or Down ??

The reason for this confusion is this:

Some cars mount the calipers forward of the axle, some mount them behind. This makes no difference in terms of rotational action; the leading edge is ALWAYS that edge which, if a mark were made ON THE ROTOR, would meet that mark first when the vehicle is rolling forwards, while the trailing edge is always that edge it would pass last.

Let's look at a car from the driver's side; rolling forward, the rotor is turning COUNTER-CLOCKWISE. This means that if the calipers are mounted on the REAR side (BEHIND the axle), the BOTTOM edge is the leading edge, while the top edge is the trailing edge. If the calipers are mounted on the FRONT (AHEAD OF the axle), then the top edge is the LEADING EDGE, and the BOTTOM edge is the trailing edge.

Now here is the fun part; while it has held for AGES that the correct place for the wear indicator/squealer IS on the trailing edge, and in MOST cases this IS TRUE; not ALL manufacturers build their cars this way.

When I worked in the Dodge Garage, we had certain models (I believe they were all Mitsubishi imports, bu they could have included the US K-cars... it's been a long time) where the squealer HAD TO GO on the leading edge, or it would bind up between the caliper and the pad recesses. The BEST PART? They had the SAME EXACT DIAGRAM you posted above IN THE FACTORY SERVICE MANUAL.

Another thing I've run into is... ALL 4 pads IDENTICAL, with the squealer on the same corner. You don't get a choice there, bub.

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Old 09-07-2009, 03:32 PM   #13
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Default Re: Brake Pad Wear Sensor - Up or Down ??

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Originally Posted by rc1488 View Post
That was me The entire pad touches the rotor.
I agree that the entire pad contacts the rotor, but they don't necessarily wear uniformly across the pad. During my last front disc pad change, I noticed that the pad was worn down more on the trailing end. I've found this to be the case on other vehicles as well during my time as a tech.

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Old 09-07-2009, 05:00 PM   #14
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Default Re: Brake Pad Wear Sensor - Up or Down ??

Quote:
Originally Posted by Spaz View Post
I agree that the entire pad contacts the rotor, but they don't necessarily wear uniformly across the pad. During my last front disc pad change, I noticed that the pad was worn down more on the trailing end. I've found this to be the case on other vehicles as well during my time as a tech.
Then there is something Majorly wrong. The pad sits flat in the cradle. The entire pad should contact the rotor at the exact same pad as there is even force across it. You should see no angle in pad wear across the material. Now pad to pad is a different story.

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Old 09-07-2009, 05:14 PM   #15
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Default Re: Brake Pad Wear Sensor - Up or Down ??

Yeah - spaz is right. some SMALL variation from edge to edge is normal... but any more than just enough to tell is evidence of something faulty.

If the pad tapers along the leading edge-trailing edge axis, it usually indicates issues with the caliper; a damaged piston can cause this, as well as a binding slider bolt. If it tapers along the perpendicular axis, this is usually brake hardware - sliders, bolts or shim spacers - that are SUPPOSED to keep the caliper square with the rotor.

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Old 09-07-2009, 05:33 PM   #16
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Default Re: Brake Pad Wear Sensor - Up or Down ??

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Originally Posted by mnementh View Post
Yeah - spaz is right. some SMALL variation from edge to edge is normal... but any more than just enough to tell is evidence of something faulty.
That is the case. The variation is just enough so that you can see it. I agree that anything more than that would indicate a problem.

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Old 09-07-2009, 05:37 PM   #17
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Default Re: Brake Pad Wear Sensor - Up or Down ??

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Originally Posted by mnementh View Post
Some cars mount the calipers forward of the axle, some mount them behind. This makes no difference in terms of rotational action; the leading edge is ALWAYS that edge which, if a mark were made ON THE ROTOR, would meet that mark first when the vehicle is rolling forwards, while the trailing edge is always that edge it would pass last.
Arrghhh !!

Then I placed the Wear Sensors on the Leading Edge, which is Up on the SW2 Front Discs.

This is obviously a source of disagreement among even the experts. Heck, even AllData has it shown both ways for the SW2.

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Old 09-07-2009, 05:44 PM   #18
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Default Re: Brake Pad Wear Sensor - Up or Down ??

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Originally Posted by SalemCat View Post
Ok, it's a little convoluted, but if you put a mark on the Rotor, then turn it, the first thing it hits is the Sensor. Hence the Sensor leads to the Rotor.

But we're not talking out the Rotor, we're talking about the Pads. It the Pads are rotating, which they are relative to the Rotor, the Sensor is on the Pad's Trailing Edge.

Hence the Sensor is on the Pad's Trailing Edge (whew).
I wrote this post earlier. I must admit it makes no sense at all to me now.

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Old 09-07-2009, 05:44 PM   #19
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Default Re: Brake Pad Wear Sensor - Up or Down ??

Don't drive yourself crazy overthinking this. Whether you call it the leading edge or the trailing edge, the general consensus is to have the wear indicators at the top of the caliper.

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Old 09-07-2009, 05:52 PM   #20
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Default Re: Brake Pad Wear Sensor - Up or Down ??

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Don't drive yourself crazy overthinking this. Whether you call it the leading edge or the trailing edge, the general consensus is to have the wear indicators at the top of the caliper.
Does this apply to the Rear Brakes of the SW2 as well ? For that matter, will they be Disc Brakes on a SW2 DOHC ?

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