Uneven brake wear

[jimyboyle]

My car is a 97 2.5 with 84000 miles

Two questions.

Had this car for 3 years now. The braking has never been good and about 3000 miles ago i had new front discs and pads fitted. Cannot say it really helped. Yesterday I put my finger over the top of the disc to feel the amount of wear on the back of the disc, I expected the usual lip that you can catch with your nail but it is in fact nearly 1/2" wide. The pad has badly worn the inside part of the swept area and done almost nothing at the outside. I have 2 calipers my son bought with the intention of fitting to his old 911,

They are parts 986.351.421 and 422 so from a Boxster. I will get them rebuilt and fit them but any ideas for this unusual wear.

I also noticed that my rear wheels and tipping in at the top, don't remember seeing this before and it is quite pronounced, standard wheels and tyres.

Is this normal or does something need adjusting or replacing

Jim

[ericinboca]

My car is a 97 2.5 with 84000 miles

Two questions.

Had this car for 3 years now. The braking has never been good and about 3000 miles ago i had new front discs and pads fitted. Cannot say it really helped. Yesterday I put my finger over the top of the disc to feel the amount of wear on the back of the disc, I expected the usual lip that you can catch with your nail but it is in fact nearly 1/2" wide. The pad has badly worn the inside part of the swept area and done almost nothing at the outside. I have 2 calipers my son bought with the intention of fitting to his old 911,

They are parts 986.351.421 and 422 so from a Boxster. I will get them rebuilt and fit them but any ideas for this unusual wear.

I also noticed that my rear wheels and tipping in at the top, don't remember seeing this before and it is quite pronounced, standard wheels and tyres.

Is this normal or does something need adjusting or replacing

Jim

Jim -

Hard to say without seeing it. I would want to be sure all the suspension components supporting the wheel carrier and hub, (as well as the hub) including the bearings, are in proper shape.

But, a first guess would be that the caliper pistons are not extending and retracting properly. The push out in a cocked fashion. That can be due to a worn out bore seal or from the piston being scored - possibly both. Could also be some sort of build up of crud in the cylinder.

You can rebuild the calipers you have with new pistons, bore seals and dust boots. It is not too hard. I just did this to my track 986S calipers. Was about $380 including a couple of liters of fluid.

You need to get the pistons out though, to be sure you order the right size bore seals and dust boots. The first bit of the piston is not the same size as the back part that is sealed by the bore seal.

You can take them apart and inspect and reinstall all if they are not bad, as long as you do not damage the bore seal when you remove. The seal and boots are not too expensive - the pistons are the bulk of the cost.

Job requires a very thorough brake bleeding - but I would flush if you are going to do this. (I also bead blasted my calipers and repainted while I had them off.)

I can give more details on how to do a rebuild if needed.

You didn't say if this was a track car. VERY often braking issues on a track car occur because of differnet levels of grip in the four corners, often due to using -- say a new tire on the left front, and on the right front, one with several heat cycles -- in this example, the left one will do more braking and wear those pads out faster. But the symptons you describe don't really match this.

[jimyboyle]

Not been on a track since i've had it and its a tiptronic so probably not been raced. My idea is to rebuild the spare calipers and then give them to my local tyre and brake shop to fit them with new discs and pads. Much easier when its on a ramp.

Jim

My car is a 97 2.5 with 84000 miles

Two questions.

Had this car for 3 years now. The braking has never been good and about 3000 miles ago i had new front discs and pads fitted. Cannot say it really helped. Yesterday I put my finger over the top of the disc to feel the amount of wear on the back of the disc, I expected the usual lip that you can catch with your nail but it is in fact nearly 1/2" wide. The pad has badly worn the inside part of the swept area and done almost nothing at the outside. I have 2 calipers my son bought with the intention of fitting to his old 911,

They are parts 986.351.421 and 422 so from a Boxster. I will get them rebuilt and fit them but any ideas for this unusual wear.

I also noticed that my rear wheels and tipping in at the top, don't remember seeing this before and it is quite pronounced, standard wheels and tyres.

Is this normal or does something need adjusting or replacing

Jim

Jim -

Hard to say without seeing it. I would want to be sure all the suspension components supporting the wheel carrier and hub, (as well as the hub) including the bearings, are in proper shape.

But, a first guess would be that the caliper pistons are not extending and retracting properly. The push out in a cocked fashion. That can be due to a worn out bore seal or from the piston being scored - possibly both. Could also be some sort of build up of crud in the cylinder.

You can rebuild the calipers you have with new pistons, bore seals and dust boots. It is not too hard. I just did this to my track 986S calipers. Was about $380 including a couple of liters of fluid.

You need to get the pistons out though, to be sure you order the right size bore seals and dust boots. The first bit of the piston is not the same size as the back part that is sealed by the bore seal.

You can take them apart and inspect and reinstall all if they are not bad, as long as you do not damage the bore seal when you remove. The seal and boots are not too expensive - the pistons are the bulk of the cost.

Job requires a very thorough brake bleeding - but I would flush if you are going to do this. (I also bead blasted my calipers and repainted while I had them off.)

I can give more details on how to do a rebuild if needed.

You didn't say if this was a track car. VERY often braking issues on a track car occur because of differnet levels of grip in the four corners, often due to using -- say a new tire on the left front, and on the right front, one with several heat cycles -- in this example, the left one will do more braking and wear those pads out faster. But the symptons you describe don't really match this.

[grover]

Why would this have anything to do with racing or tires? It's uneven wear from one half of a single pad to the other half, it's clearly an issue with the brake itself.

Jim, it's normal to have -0.8 to -1.8° of negative camber on the rear wheels (tipped in at the top by up to about 3/4"). Race alignments can go several degrees more negative, which will give you more grip when cornering hard, but your tires will wear out faster than normal. If you're concerned, you can get it realigned.

Edited February 9, 2009 by grover

[Brad Roberts]

Jim,

it doesn't take much to knock out the alignment on the rear of the early Boxsters. The toe adjustment and camber adjustment is done on eccentrics and they are known to slip.

It could also be spring sag. The ChickTronic cars came with different rear springs to compensate for the extra weight. If they sag, the car will go more negative in camber (and the toe will change causing tire wear)

B

[jimyboyle]

Thanks Brad, I will be getting it checked this week, I am sure it was not like this before so maybe the springs are a goner

Jim

Jim,

it doesn't take much to knock out the alignment on the rear of the early Boxsters. The toe adjustment and camber adjustment is done on eccentrics and they are known to slip.

It could also be spring sag. The ChickTronic cars came with different rear springs to compensate for the extra weight. If they sag, the car will go more negative in camber (and the toe will change causing tire wear)

B