ilikebig928butts

Happy Presidents' Day weekend y'all!

First time changing the pad sensors...
I got a couple n00b questions:

1) the sensors go on the inside pad or outside? Doe it matter?
2) Which way should the sensor be inserted? The "thick" side facing rotor? or the "thin" side?

dr bob

Grab a small file and get all the coating out of the little notched cutouts in the pad backing plates. Else you'll risk damaging the sensor and making it pretty useless.

The little clips on the sensor hold the sensor in place in the backing plate. From that clip, the thicker bakelite bulge faces towards the friction material on the pad. In service, that bakelite piece has a loop of copper wire running through the face of it. As the pad wears, eventually that section will wear until the wire loop is worn though. The opened loop is what flashes the warning that the pads need replacement. Knowing how it works, the installation might be easier to visualize. Make sure the cables are secured in the notches in the caliper frame, and loop around the wire bales that hold the pads in place.

Rob Edwards

Some later cars have wear sensors both inside and out, early cars have just one on the inner pad.

The thick side of the sensor goes towards the rotor- look at your pic- there's an embedded wire in the thick side. When the pad wears down, the sensor gets ground down and breaks the wire, signaling the brake wear warning.

EDIT: shouldn'ta walked away halfway through my post....

dr bob

The '89 has a sensor for each pad.

ilikebig928butts

Indeed. Upon opening the whole thing up I found a strand on each side.
Is this an '89 only spiel?
I ended up just installing the two I got from 928 International on the inside pads.

ilikebig928butts

Oh, btw, thanks Doc Bob and Rob for the nik-o-time help.

dr bob

The 4-piston calipers made a sensor for each pad a requirement. Prior, the single piston floating caliper would have the most pressure on the piston-side pad, so a single senor was enough.

skpyle

Hi dr bob! Let me throw a wrinkle at you. My 1986.5 has the 4 piston calipers, but only has one pad sensor per caliper. The sensor goes to the inboard pad. There is only one receptacle in the round ABS connector for a pad wear sensor at each corner.
1986.5 only anomaly?

Seth K. Pyle

bureau13

My '86.5 is this way as well.

dr bob

The dual sensors for the later 4-piston calipers have the two sensors wired in series, with one connector to the car. They are electrically interchangeable. I wouldn't go through the trouble of ripping out the singles to put the dual in, that's for sure. But when you replace them next, consider the functional needs as you choose.

Rob Edwards

The front caliper dual pad sensor (928 612 315 02) is for 86.5-88, then the connector end changed for '89-91, then the GTS sensor is different again.

Gratuitous shot of the dual-pad sensor harness routing on a front '90 caliper. The little clippy cable holder on the caliper spring is 928 612 361 00.

bureau13

Wow....I had no idea. I'll have to remember to fix this when I need to do my pads.

Weird that both '86.5 cars mentioned here have the singles...possibly a common kludge with shops that didn't have the dual sensors on hand?

skpyle

Oh ho ho...! That sheds a little light on the subject.
The brake pad sensors on the Red Witch were replaced ar all four corners in the late '90s. They are single sensors now. No idea what they were before.


Thanks!

Seth K. Pyle

StratfordShark

This throwaway remark is so important!

Was struggling to install new sensors recently in new pads, till Dr Bob advised me to file in the notch where the spring clip slides. Literally a few seconds with a needle file, and then the sensor heads slide in positively but easily. I bet they will come out without being destroyed too.

dr bob

I left out the part where the sensors will last a lot longer if you dip them in bearing grease before installation.... (j/k)

A SoCal clinic car arrived with new pads and sensors to install. The owner proceeded to destroy about half of the new sensors before he asked for help. The parts-store pads had a nice thick protective coating on the backing plates. They needed to be hammered into the calipers too. A little attention with the files solved the sensor and the fitment problems quite handily.

For disassembly, the little key slots for the sensors do get packed pretty well with brake dust and crud. Unplug the sensor from the car (open the connector cylinder outer sleeve, then pull the connector out). Then sensors and pads go to the bench for a little cleaning with an old toothbrush and water. With the caked dust removed, the sensors will come out easily after gently squeezing the little clips and withdrawing the sensor straight out, direction radial to the pad as installed. Pull it sideways (towards the back of the pad rather than the edge) and you'll break the plastic part that holds the wire loop.