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When do you replace your brake discs?

B

brendan996

Spa-Francorchamps
Joined
30 Mar 2009
Messages
259
May seem like a daft question, but apart from measuring the thickness, badly scored, cracked,rusted. What else would you consider..?

Mine have about 1mm lip on them and have some pitting on the inside :?: They were replaced about 30k ago
 
Usually I just replace them on reaching min thickness but also if there is a visible defect (crack) or warpage felt as a pulsating brake pedal. From memory I think there is only 2mm difference between a new disc and a worn disc (02 C2)
 
If they are close to min thickness and your pads need doing then change them as you wont get full life out of your new pads (new discs look nicer)
 
matt cooke said:
If they are close to min thickness and your pads need doing then change them as you wont get full life out of your new pads
Click to expand...

When the discs develop a lip. they will cut into the edges of the pads and become less effective.
From memory the min disc thickness is 32mm front and 26 rear.
 
I think I'll replace them when the pads wear out, they have a fair bit of meat left on them though. :thumb:
 
NEW OWNER QUESTION
Hi all, 2 questions, (i have tried to search them out)

WHAT IS THE MINIMUM THICKNESS FOR A 03 996 C4S DISC?

IS THERE A PUBLISHED FIGURE FOR BRAKE EFFICIENCY OR RETARDATION FOR THE 911?

REASON FOR ASKING, OPC GIVING ME THE RUNAROUND ON WHAT I SUSPECT IS SUPPLYING AN APPROVED USED CAR WITH WORN DISCS AND PADS. DISCS FAILED 111 TEST DUE LIGHT CORROSION BUT WERE APPARENTLY SKIMMED AS PART OF THE PDI. OPC HAS REPLACED THE PADS BUT I SUSPECT ARE BAULKING AT DOING THE DISCS AS THIS IS NOT COVERED BY THE POST SALE PORSCHE WARRANTY. GOTTA GET MY DUCKS IN A ROW BEFORE TAKING THEM ON.
THE ALTERNATIVE IS THAT THE C4S BRAKE SYSTEM IS RUBBISH??

THANKS IN ADVANCE
 
HI, WELCOME! :bye:

Can't help with the techie questions around pad thickness, but if you have only been for a short-ish test drive you may come away thinking the brakes on a 996 aren't too hot. Not true; you need to get them up to temperature and you need to stamp on them - they aren't over-servo'd (like VAG brakes, for example), they're old-school so need a lot more pressure on the pedal but believe me they are fantastic brakes (C4S even more so, as they have turbo brakes). :thumb:

ps NO NEED TO SHOUT, WE ALL HEARD YOU FINE... :grin:
 
I agree with Ant, when up to temperature its like throwing an anchor out the back! :thumb:
 
Had car serviced recently, and was advised that with a 1mm lip the disks were 50% worn.
 
OK SHOUTING STOPPED>>LOL
Really, though, thanks for these helpful replies, its a pity the OPC couldn't have put it so. Couple of points though:
Its the disc thickness, rather than the pad thickness that I was after. I have found a couple of references to the disks being 'worn out when 2mm worn from new' Brenden's comment of his discs being 50% worn with a 1mm lip bears this out. But, my discs have been skimmed so without knowing the original thickness, I can't measure them now and find out if they are worn below limits. Now, viz a vis, brake temp, on my daily commute up to Cardiff (50mls) I don't seem to notice that the brakes improve when warmed, or am I not trying hard enough. My impression is a lack of initial bite followed by a feeling of unbalanced braking if I really stand on them. Any thoughts?
 
airbus said:
Now, viz a vis, brake temp, on my daily commute up to Cardiff (50mls) I don't seem to notice that the brakes improve when warmed, or am I not trying hard enough. My impression is a lack of initial bite followed by a feeling of unbalanced braking if I really stand on them. Any thoughts?
Click to expand...

Based on ^^^^^^^^^^ my thoughts = you probably need new discs and pads - assuming of course that your wheel balance, tyres and pressures are all as they should be.
 
Ant Blain said:
HI, WELCOME! :bye:

Can't help with the techie questions around pad thickness, but if you have only been for a short-ish test drive you may come away thinking the brakes on a 996 aren't too hot. Not true; you need to get them up to temperature and you need to stamp on them - they aren't over-servo'd (like VAG brakes, for example), they're old-school so need a lot more pressure on the pedal but believe me they are fantastic brakes (C4S even more so, as they have turbo brakes):
Click to expand...

That has given me a little more confidence as having just moved from a Golf R32 I find the brakes on the 996 a little disappointing (OK, possibly the worst feel of any car I have owned). Having had it for only a matter of weeks with limited quality runs, I'm left cold. There seems to be a lack of feel and initial bite (which is what I do get on all other vehicles I drive), but when I have had to they have retarded me quickly but without the feel, and you are right, with a heavy leg needed. Disks and pads look fine, not new, but nowhere near past it. I'll give it a few more weeks and maybe I'll adjust my senses to this new type of braking sensation. Trouble with suggesting that the brakes need warming up, if you're on a long straight with no braking before a bend then the brakes will be cold. A series of bends may see better feel but it's a shame you won't be able to brake with confidence on that first one.
 
once again, many thanks for the speed of reply and particularly to dodgyfocus for that pdf file. all i need to do now is micrometer my discs and i'll know if the dealer is pulling a fast one or not. the peak-to-valley measurement is particularly interesting, as my discs have some corrosion on them, but how to measure? t8996c4 is probably right, the pads are new, but the discs could probably do with replacing too. The big question is, on my APPROVED 2nd. hand car, which i have had for a month, should the dealer have replaced the discs before delivery.
Thor, there are plenty of comments like ours on this site and pistonheads, so i reckon there is a period of Porsche adjustment to go thru. Although the person who designed PCM and the satnav really needs a talking too!
It has too be said, had I spent I couple of hundred quid on an independant survey, I suspect that I would not be having this confidence crisis in the brakes. Maybe I put too much trust in the APPROVED brand, though to be fair the dealer has sorted other issues out with no hassle.
 
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