Question about uneven brake pad wear ....

pkfrdh · pkfrdh's Garage

Anyone ever notice if there is a pattern to the possibility of uneven break pad wear on a '77 911? Do the pads on the inside or the outside wear out faster than the other?

Has anyone noticed that their pads are thicker on one side of a rotor than the other? Or any pattern to calipers on the right side of the car or left side? Or if there is a difference between the wear patterns from front to back? It would be interesting to know to maximize pad wear.

I am rebuilding my rear calipers and noticed that the pads wore differently. I did not think to mark which pad was inboard or outboard. I think the uneven wear was due to a stuck piston that did not let its pad wear towards the rotor. If there is a notorious pattern of wear that anyone knows of such as the inside or outside pads wearing more than the other, it would help me decide which side of the rotor to put these pads back in. They are almost new and I'd hate to toss them if there is a chance they could wear in more normal w/ use. One pad is a little thicker than the other.

Thanks for the input.

JGL
'77 Carrera 3.0

Bill Verburg · Bill Verburg's Garage

If the inner/outer pads are wearing unevenly you have a frozen piston. The fluid must be flushed regularly and the calipers exercized or this will occur. Most other manufacturers use cheaper single piston sliding calipers which either work or don't. The Porsche calipers are a better design which does require more careful maintainace.

Have all of your calipers and m/c r/r'd

pkfrdh · pkfrdh's Garage

Bill,

Thanks for responding. You're right...one of the pistons was frozen. I now have nearly new pads that have uneven wear on them. Should I put the thicker pad on the inside or the outside of the rotor? Is there a notorious side of a rotor that wears pads more than the other? I seem to remember that by the time pads wear all the way down, if the pistons don't stick, there is still some uneven wear that consistently shows up as a slightly thicker pad on either the inside or outside of the rotor. Do you remember seeing this on the rear of your car?

I'm going to call some of the brake shops to see if they have noticed if there is a consistent difference in the way inside and outside pads wear. I want to try to maximize the life left in the pads I have since they are almost new. I don't want to put the thinner pad on the side of the rotor that wears pads faster if there is such a phenomena.

Thanks again for any input.

JGL
'77 Carrera 3.0

Bill Verburg · Bill Verburg's Garage

Porsche used a well designed caliper that just requires a little more attention than some cheaper single piston varieties, both sides of the pad should wear equally, if not there is a maintainance issue. You need a new set of pads! I never had any problems w my Porsche brakes because I am a fanatic about fresh fluid, exercising the calipers and keeping crud off of them. I learned some harsh lesson about brakes from an Alfa that I had. My most recent lesson wasn't about brakes but wheel bearings, I recently had one go bad from inactivity, I could actually see the imprint of the rollers in the races from a few months of inactivity.

pkfrdh · pkfrdh's Garage

Bill,

If you saw bearing imprints after only two months of inactivity, how long till the bearing goes bad w/ the inprints? Does the bearing start to make noise right away? My car has been sitting off and on for up to 6 months at a time without being driven. I may move it back and forth every month or so, and start it up every month, but it doesn't get driven sometimes for up to 6 months. Especially lately w/ the rear brakes sticking...it's been really hard to roll it back and forth the last year. It is up on jacks now going through brake rebuilds. I wonder if I will be soon needing bearings. Is there a definite sound to a front or rear wheel bearing going out? I have had wheel bearings go bad in my Honda and I know that sound. It gets louder as you go faster and has a body harmonic that is sometimes difficult to determine which side it is coming from. My car has no "sound" indicating a wheel bearing problem even though it should w/ the amount of sitting it has been doing over the past 16 years. I think I have only put about 5,000 miles on my 911 in that time.

Thanks for any info.

JGL

Bill Verburg · Bill Verburg's Garage

I don't know, this one was the 1^st in 30yrs of 911 ownership, I drive a bit less these days maybe. Who knows why it happened, the imprints were clear enough, the symptoms were a squeek on left turns, the right front outer bearing was the culprit, both outer fronts required repacking.