987 Boxster S ( 2007 with the 3.4L M97 engine) - rusty rear brakes

Chuckie66 · May 31, 2018

Hi

I'm a newbie to this forum and Porsche - recently purchased a 2007 987 Boxster S ( 3.4 with the M97 engine) with 50K on the clock. Here goes my question:

The previous owner hadn't used it much in the last 3 years and the rear brakes had rusted on the inside disc. I tried to clear the rust with some Italian style breaking which didn't do much, and after a couple of weeks the "break warning sensor" light has come on.

Q1. Short of examining each of the brakes, how can you tell if its front or back pads that have failed?
Q2. The rear disc which is rusty is 24mm thick, looking around various forums the min width is 22mm. Given the rust on the inside face, i'm thinking of getting it skimmed - good idea? see pics of the one disc I removed (NB wear sensor was fine on that wheel).

Any idea on what the cost would be for skimming?

Motorhead · May 31, 2018

Hi Charles,

Rusting of the inner faces of the discs is a very common occurence, often due to water collecting on the discs after washing the car - always best to go for a run to clear the water after a clean.

Most probably the limited usage over the past 3 years hasn't helped re your brake warning sensor issue - there could be a contact issue with the excessive rust build-up. Check the pad thicknesses: I think that the sensors trigger at about 2mm pad thickness, but if they're less than 4-5mm I'd think about changing them.

Disc skimming is perfectly acceptable. If you find somewhere to do the job they'll be able to advise you whether or not it's worth skimming your discs. It's likely to work out cheaper than replacing all the discs but there are plenty of decent quality discs for sale and you may find it cheaper if you purchase a disc and pad package.

Jeff

Ray · May 31, 2018

Motorhead said:
Hi Charles,

Rusting of the inner faces of the discs is a very common occurence, often due to water collecting on the discs after washing the car - always best to go for a run to clear the water after a clean.

Most probably the limited usage over the past 3 years hasn't helped re your brake warning sensor issue - there could be a contact issue with the excessive rust build-up. Check the pad thicknesses: I think that the sensors trigger at about 2mm pad thickness, but if they're less than 4-5mm I'd think about changing them.

Disc skimming is perfectly acceptable. If you find somewhere to do the job they'll be able to advise you whether or not it's worth skimming your discs. It's likely to work out cheaper than replacing all the discs but there are plenty of decent quality discs for sale and you may find it cheaper if you purchase a disc and pad package.

Jeff

I concur with Jeff regarding all his post. I have had the same problem with my Boxster I own. The corrosion is usually on the inside face of the discs. I have in the past just replaced discs and pads as they can be sourced from many distributors at varying costs and quality.

After washing I have run down my driveway with my foot just feathering the brake pedal to dry them off.

As an aside as you are aware the handbrake is part of the rear disc assembly and I have had one stick to the drum because of wetness and then drying onto the drum. This caused the lining to be torn off the metal plate of the drum brake.

Ray

Derek H · May 31, 2018

I would just replace the discs and pads. I just checked and you can get a pair of Pagid rear discs and pads for a 987S from Euro Car Parts for under £100. I've fitted these on four Caymans and Boxsters we've owned and never had a problem with them (road use only).

I don't believe the cause of the inner disc faces rusting is just down to failure to dry the brakes after washing. I did subscribe to this view and religiously dried them after every wash but two years and 12K miles after buying my first Cayman (when I inspected the brakes and they were perfect), the inner faces of the discs were horrible. I swapped them for Pagids and on a hunch, made a point of ensuring I subsequently never ended a journey after driving in the rain without first getting some heat into the brakes at the end of the journey, to dry them off. Four years and 20K miles later, the discs are all still perfect.

Ray · May 31, 2018

Derek,

I must confess that I have the same feelings regarding drying off the brakes. I also bought Pagid and suffered no problems with them.

I did wonder at the time if it was the Porsche discs which were the culprits?

Ray

Contraband · May 31, 2018

Best bet is to replace the discs and pads. You are only buying a short period of grace by getting them skimmed. There is always the chance they might not be skimmed true and cause vibration. They will almost certainly get hotter if they are thinner as well.

Chuckie66 · Jun 1, 2018

Thanks Guys, new discs and pads ordered from ECP, I went for Bembro which was a couple of pounds more.

Would you recommend putting in new brake dampers into the caliper? the old ones looked ok but lost their stickiness. New set of 8 dampers are £50 after ECP discount...

Is there an easier way to figure out which wheel has the brake warning light on, rather than take each wheel off and hunting around?

Motorhead · Jun 1, 2018

Charles,

I'd be inclined to change the brake dampers while you're at it - it would be a shame to do the job, only to find that the brakes are squealing afterwards..!

Other than disconnecting the warning light sensors one by one to isolate the offender, I can't think of any other simple way to check them out. Are you planning to change them all when replacing the other brake components?

Jeff