Judder under Braking

[timhum2002]

Pete B

Very interesting to read of your experience although I am completely at a loss to understand how it can happen. Surely the same amount of rust forms on the outside as well as the inside of the disc. If the brake pads will then clean the outside after braking why don't they clean the inside, could it be a caliper cylinder problem. I have run a Boxster S and now 2002 C4 and have not experienced this at all. The cars have both been washed with the wheels hosed and then garaged for 4/5/6 days before further use. Yes I do get a coating of surface rust but that disappears after a couple of firm brake applications. Last point, it doesn't seem to happen to any other makes of car, why?

yours perplexed

Tim

 

[Yoda]

Vikash - go and drive your car a bit more and stop washing it so often you freak []

Welcome to the forum.

 

[Mark_Bennett]

it doesn't seem to happen to any other makes of car

It happens to our FIAT...[&:]

 

[Guest]

I was told at the OPC that inspected my 996 before purchase that the 996s are especially susceptable to disk corrosion due
to the compound of the disk.

 

[Rodney Naghar]

For what its worth, I just changed my front pads and disks. I ordered the parts from Eurocarparts.com. I used this link http://www.bombaydigital.com/boxster/projects/brakes/change_pads/ for help. It was very simple, (first pads and disks I've ever replaced myself) and took me 30 mins per wheel. I saved around £412 on my OPC's quote.

Good luck.

 

[Guest]

Vikash

Any further news on your debate with Porsche West London about the rust spots? I have had the same diagnosis from them. The disks indeed look rusty, but the brakes feel perfectly OK.

Higgy

 

[vikash]

Higgy

OPC West London advised that my disks required skimming (normally 375+vat), which has resolved my judder. They also referred me to the Car handbook with specfic reference to disk maintenance.

I will now make a point of driving the car immediately after washing to dry off the disks correctly.

 

[Guest]

Thank you, Vikash and Bruce, for the dilemma you have created for me!

I must say I am with earlier correspondents on this: how can brake disks rust just by washing the car? I can't think of any other product in history that rusts after one night's exposure to water!

 

[38F3E1]

Not unique to the 996 model. The 993 suffers from exactly the same problem to such an extent that it is known as one of the models weaknesses and all OPC and independents see plenty of them. The inner surface of the disks seem to suffer rather than the outer due to the caliper design.

It effects low mileage cars most. Washing / not washing, drying after washing or not etc does not effect the problem. The best explanation I have been given is that the disks corrode at a certain rate due to the material they are made from. As long as you use the car a reasonable amount the disks in effect wear fast enough to remove the corrosion and you reach a point of having to replace the disks through normal use before rust becomes a problem. Low mileage cars however rust faster than they wear.

You might think a harder, non rusting metal would be the answer but that would then have a negative effect on the braking characteristics Porsche have engineered for the car .

Ian.

 

[Guest]

The disks have a very high iron content. As referred earlier in this thread by Rodney, they work in combination with the metal in the pads, causing a complicated chemical reaction at high temperatures (as opposed to generating friction by being very abrasive). This is how carbon brakes work also. The pad and disk are made from the same materials, and when they heat up they chemically fuse. Steel does not work as well, apparently, but corrodes in the atmosphere less quickly. Irrespective of you spraying with water, iron will form a surface coating of rust very quickly, just from the moisture in the air. So not using the car very often will not make your brakes last longer!
Also, when you 'bed in' your pads, you are actually depositing a layer of brake compound mixed with the metals in the disc onto the surface of the disc. It is this that will stop you! If you do not bed in the brakes correctly, you may experience judder, as the coating is not even.
Normally you get one massive build up where the disc stops behind the pads when they are extremely hot. In racing circles, you NEVER apply the handbrake after a race (except on Porsches that use separate shoes in little drums, of course), as this is guaranteed to b*gger the rear discs.
It is cheaper to buy genuine replacement discs from a reputable factor or Porsche specialist than pay for your old discs to be resurfaced, so why bother? Also, you should put the old pads in to bed in the new discs (that is, never replace both components at the same time).

 

[Guest]

I don't know if any of you have picked up this month's (November) copy of GT Purely Porsche, but there's a letter in there about this very topic (from a Boxster owner).

Vikash - you mentioned West London skimmed your disks, was this under warranty or did you fork out the £400?

I take the point that the less you drive the car, the more likely this is to happen, although I've never experienced it before on similar performance car/brake combinations - e.g. previous car was an 02' M3 - with no problems at all.

I seem to be reading more and more on this subject with Porsche's - do Porsche accept this is a problem? I had to perform a high speed emergency stop only this week, and I have to say I was shocked by the poor braking ability - which very nearly caused me to pile into the back of a slow moving Metro[]

 

[vikash]

Thanks Andrew for your in-depth explanation , very interesting. I have since bedded in the brakes, seem ok now.

Justin, with a bit of gentle persuasion I managed to get Porsche west london to foot the bill as a good will gesture. (The car is 18 months old)

Ref "other performance cars" ,I also have a '02 M3 which I use on a daily basis , this stops beautifully !

 

[blease]

With the start of the new track day season, I returned to the scene of the crime, Castle Coombe, running exactly the same car barring one thing...new OPC front discs. Result? Absolutely faultless, stonking braking. FINALLY able to give the old girl the thrashing we'd both been waiting for. Moral of the story? First try new Porsche discs. Probably better than a re-skim and certainly better than pattern parts, which I suspected iIhad on the car because the central bell housing had rusted.

 

[Pete B]

About a year ago I contributed to this thread because my low(ish) mileage C2 had been failed on its DOT test because of excess corrosion on the inner faces of the front disks. Since then I have only washed the car once (filthy b***er) but am pleased to report a complete absence of any corrosion on either side of the disks. The car isn't too bad because Scouser sold me a bottle of RezeX and that seems to stop 99% of the dirt sticking - the only bits I wipe down are the sills and the back bumper.
Regarding the comments about corrosion of the bell housings at the back of the disks - I found that use of acid wheel wash tended to increase the likelyhood of these components starting to corrode. I also run a Golf which seems to have brake pads made from an especially dusty material so they get filthy. At first I used Wonderwheels on a weekly basis and the bells immediately started to go slightly orange. I've stopped the acid and now use non-bio washing powder solution - this serves a dual purpose as the amount of water I spill over myself seems to have a cleansing effect!