I have a 1989 928. About 1000 miles ago the brakes were checked and the pads had a thickness of 8/32. I was told 8/32 was good, and I wouldn't need a brake job for quite sometime. Just recently the Service Brake Pads indicator came on. Has anybody had this problem? Don't want to change the pads if its not needed?

 

That warning message is generated when either the pad sensor is worn down and completes the warning circuit, or if the wire or harness to the sensor is cut/disconnected.

The only way to be sure is to pull the wheel(s) and visually inspect the pads. If you have a later style wheel that allows you to easily see the brakes, you probably don't even need to remove them.

 

The sensor is merely a wire that becomes severed if allowed to wear too far, opening the loop and triggering the warning icon. They are installed on the inner pad - so you generally have to pull the wheels to look into the back side of the four piston calipers. As Randy said, a disconnected sensor wire will do the same thing.
In addition to wear, you are checking for symmetrical consumption of the pad material. eg - if the inner pad is half the thickness of the outer ( and the sensor wire is worn through), there is likely an issue with sticking pistons in the caliper. Simple pad replacement is usually all that is required .... if the wear is even.

 

Check them or risk scoring a rotor.

 

I went through the same process: Pads looked good, drove a little, indicator says pads need to be new. !!!! You know you'll need pads, so now the question is which ones. Make a good choice!

The pad sensors, as others have pointed out, are not much more than expensive wire loops that fit into little cutouts in the pad. The wire itself is molded into a little plastic block that is close to 1/4" thick. Wear on the pads allows the sensor block to get scrubbed by the spinning rotor, until the wire wears through. How deep that is probably varies slightly from sensor to sensor, but mine sure did seem to wear through earlier than I thought they should. I'm used to getting my "lifetime" explorer pads swapped when they get down to 1/8". That's what Raybestos says is the wear limit on them. When I took a set down that low, the friction material cracked, and part of it wedged in the part that didn't fall off... It was ugly, especially with the parts sales guy-- he thought they had been abused by taking them that thin.

Back to the 928-- because you may have the opportunity to need a lot of braking in a hurry, even with pads worn, the thicker 'wear limit' on 928 pads is very reasonable. Get ready to spend about $15 per wheel on new sensors from the Big Three. The old ones that haven't worn through yet can sometimes be reused, but those that have any wear on them at all, even if they haven't worn through, they seem to break apart when you try to extract them from the old pads. Give it a try, get --all-- the old brake dust and crud out of the little notch around the sensor. I'm 50-50 so far.

 

Thanks for all of the information!! Good advice. Turns out when I was inspecting the brakes I found on one of them the sensor wire was not on the clip. The sensor wire was hanging loose and had rubbed on the rim. There was enough wear on the insulation that it shorted out the circuit. The light came on after a fast trip of the highway. Quess thats why the warning light was intermittent. I patched up the wire and the warning indicator has not come back on. The brake pads looked good, atleast 8/32. My quess is when they did the brake inspection, they didn't hang the wire back on the clip on the one wheel. A little annoyed with the garage that did the inspection but glad it was a cheap fix....just some electrician tape required.

Again very thankful for all of the help from Rennlist....this site is GREAT! With your help I was able to find the source of the problem.

Thanks
Bruce