GTS retirement thickness
11-18-2015, 07:03 PM
#1
Rennlist Member
Thread Starter
GTS retirement thickness
My front GTS discs now have a wear lip and when the disc is down to 30mmit is shot as far as Porsche are concerned. I do not think mine are that far gone but will measure them in the next day or two as I do annual maintenance work on the car.
The factory spec is doubtless safe but just wondered if there is any rule of thumb experienced practitioners use to extend the service life of discs a bit. Clearly one does not want to take chances with something so critical but practical experience is also a good performance indicator and wondered whether it is possible to pinch a mm or so over the Porsche spec.
Still have some life left in my noisy Hawk pads and do not want to put new stock pads on these discs if they are close to retirement.
Appreciate this is a sensitive issue and opinions would be considered "for guidance only". Seems to me there is a lot of meat on those discs and experience suggests Porsche do not do things by half.
I also have some new dampers discs to put in- i noticed they have a removable paper cover that reveals a sticky substrate- does this mean they are a "single shot" use item and have to replaced every time you pull the pads [and presumably break the seal]?
Rgds
Fred
The factory spec is doubtless safe but just wondered if there is any rule of thumb experienced practitioners use to extend the service life of discs a bit. Clearly one does not want to take chances with something so critical but practical experience is also a good performance indicator and wondered whether it is possible to pinch a mm or so over the Porsche spec.
Still have some life left in my noisy Hawk pads and do not want to put new stock pads on these discs if they are close to retirement.
Appreciate this is a sensitive issue and opinions would be considered "for guidance only". Seems to me there is a lot of meat on those discs and experience suggests Porsche do not do things by half.
I also have some new dampers discs to put in- i noticed they have a removable paper cover that reveals a sticky substrate- does this mean they are a "single shot" use item and have to replaced every time you pull the pads [and presumably break the seal]?
Rgds
Fred
Last edited by FredR; 11-25-2015 at 05:12 PM.
11-18-2015, 08:21 PM
#2
Rennlist Member
I have a lot of extreme experience with the GTS rotors. in fact, i would take them all grooved up and worn and turn them to about 30mm and use them on the race car. worked great. no issue.
now that they are already worn and you said there is some noise.. run them for as long as you want and as hard as you want.. when the pads get thin.. change them both out.
right now the pads have worn to the grooves of the disc and things are quite safe. those rotors are TANKs compared to what bmw and mercedes run on their cars. again, 3-4 years of racing on 30mm GTS rotors with no issues. the started cracking at the same time that the new zimmerman S4 rotors started to crack, or even the new GTS rotors (that i did buy one time)
you can use the pad dampers again, as many pads dont even come with them. also supposed to inhibit vibration. ive never had an issue with noise, if i bed the pads in perfectly from the start.
now that they are already worn and you said there is some noise.. run them for as long as you want and as hard as you want.. when the pads get thin.. change them both out.
right now the pads have worn to the grooves of the disc and things are quite safe. those rotors are TANKs compared to what bmw and mercedes run on their cars. again, 3-4 years of racing on 30mm GTS rotors with no issues. the started cracking at the same time that the new zimmerman S4 rotors started to crack, or even the new GTS rotors (that i did buy one time)
you can use the pad dampers again, as many pads dont even come with them. also supposed to inhibit vibration. ive never had an issue with noise, if i bed the pads in perfectly from the start.
11-18-2015, 09:53 PM
#4
Rennlist Member
Really?
If they have a lip and pads are worn, replace both pads and rotors, not worth the effort imo.
I don't know anyone who turns rotors, just burn them downand and replace them.
Maybe if they were some super expensive rotors like 1,500 each, maybe.
If they have a lip and pads are worn, replace both pads and rotors, not worth the effort imo.
I don't know anyone who turns rotors, just burn them downand and replace them.
Maybe if they were some super expensive rotors like 1,500 each, maybe.
11-19-2015, 02:40 AM
#5
Rennlist Member
Thread Starter
I will do a bit more measuring before making a final decision.
I feel as though I am on the borderline to fit a set of new pads and get good life out of them or just leave the current ones until they have no life in them.
On the subject of dampers- should there be a thin backing plate over the pads? I am thinking if the sticky contact surface is adhering to the disc pad itself, the pad will be difficult to remove later on [if it still sticks].
Rgds
Fred
I feel as though I am on the borderline to fit a set of new pads and get good life out of them or just leave the current ones until they have no life in them.
On the subject of dampers- should there be a thin backing plate over the pads? I am thinking if the sticky contact surface is adhering to the disc pad itself, the pad will be difficult to remove later on [if it still sticks].
Rgds
Fred
11-19-2015, 03:18 AM
#6
Rennlist Member
they were pretty expensive (GTS rotors are not cheap) these were good with enough meat to turn down for about 90bucks . i think new rotors were in the 300 buck range, each, so thats why i did it.
11-19-2015, 10:40 AM
#7
Rennlist Member
Thread Starter
I would be lucky to get GTS rotors for that price I suspect. they are a bit cheaper in the States but the shipping weight kills any advantage.
any idea what your discs were skimmed to and what thickness they were when you gave up on them?
Regards
Fred
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11-19-2015, 10:52 AM
#8
Captain Obvious
Super User
Super User
You can go down as much as 1.5mm from the backing plate before the pads need replacement. So if the current pads are thick, leave it alone.
11-19-2015, 11:27 AM
#9
Rennlist Member
Thread Starter
The pads at their thinnest are currently around 3.5mm however they are rather squealy and the disc wear rate seems rather high so my thinking was if I can skim and get decent life with stock pads I might go for it.
Must say I am gravitating to leaving them as they are and resign myself to replacing the job lot when min thickness arrives- just hate the squeal under light braking [ yes- I know- just stick with heavy braking and no squeal- ha ha].
Rgds
Fred
Must say I am gravitating to leaving them as they are and resign myself to replacing the job lot when min thickness arrives- just hate the squeal under light braking [ yes- I know- just stick with heavy braking and no squeal- ha ha].
Rgds
Fred
11-19-2015, 02:27 PM
#10
Chronic Tool Dropper
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Fred--
The combination of the SS sliders in the caliper and the clip-in dampers/ that stick to the back of the pads -should- eliminate squeaks/squeals. At my first pad replacement, I decided to experiment some by gluing the old pieces to the back of the pads with a film of hi-temp RTV. I'd purchased a full set of new pieces, but for grins decided to try to reuse the old ones. That worked out fine for the life of those pads. The little SS sliders do get packed up with brake dust underneath. When I rebuilt the calipers, I decided to put a litle more hi-temp RTV underneath them to prevent brake dust accumulation there. It's worked great so far, but the brake system overhaul included new pads and the new dampers I'd saved from the first pad replacement so definitive results to report.
---
At 100k or so, my original S4 rotors were worn to the point where I could safely turn them and still be at or above the min allowable thickness. But going into the third set of pads and looking at the wear history, I decided to replace the rotors rather than turn them and then wear to to below the min thickness. This is of course a judgement call, but my situation sounds a lot like yours. Meanwhile... I get to buy professional liability insurance every year, with premiums indexed to fees. Although that doesn't apply directly to how my car is maintained, it does remind me at least once a year that we live in a society that includes people (and their attorneys) who are constantly looking for that big financial payout, the one that will set them up for life. So I try to think along the lines of what I would expect from a professional mechanic or shop, and what liability they might be willing to accept if they did a job that could even remotely be perceived by a jury as marginal should there be an accident. I replaced the rotors.
Other secondary factors in that decision process include the rapidly-escalating costs of hard parts like rotors, the inevitable replacement need, and the fact that it's quite unlikely that I'll live long enough to put another 100k on the car at the rate it's currently being driven. Ultimately I speculated that it would be cheaper to put new rotors on then rather than waiting.
The combination of the SS sliders in the caliper and the clip-in dampers/ that stick to the back of the pads -should- eliminate squeaks/squeals. At my first pad replacement, I decided to experiment some by gluing the old pieces to the back of the pads with a film of hi-temp RTV. I'd purchased a full set of new pieces, but for grins decided to try to reuse the old ones. That worked out fine for the life of those pads. The little SS sliders do get packed up with brake dust underneath. When I rebuilt the calipers, I decided to put a litle more hi-temp RTV underneath them to prevent brake dust accumulation there. It's worked great so far, but the brake system overhaul included new pads and the new dampers I'd saved from the first pad replacement so definitive results to report.
---
At 100k or so, my original S4 rotors were worn to the point where I could safely turn them and still be at or above the min allowable thickness. But going into the third set of pads and looking at the wear history, I decided to replace the rotors rather than turn them and then wear to to below the min thickness. This is of course a judgement call, but my situation sounds a lot like yours. Meanwhile... I get to buy professional liability insurance every year, with premiums indexed to fees. Although that doesn't apply directly to how my car is maintained, it does remind me at least once a year that we live in a society that includes people (and their attorneys) who are constantly looking for that big financial payout, the one that will set them up for life. So I try to think along the lines of what I would expect from a professional mechanic or shop, and what liability they might be willing to accept if they did a job that could even remotely be perceived by a jury as marginal should there be an accident. I replaced the rotors.
Other secondary factors in that decision process include the rapidly-escalating costs of hard parts like rotors, the inevitable replacement need, and the fact that it's quite unlikely that I'll live long enough to put another 100k on the car at the rate it's currently being driven. Ultimately I speculated that it would be cheaper to put new rotors on then rather than waiting.
11-19-2015, 03:33 PM
#11
Rennlist Member
Thread Starter
Fred--
The combination of the SS sliders in the caliper and the clip-in dampers/ that stick to the back of the pads -should- eliminate squeaks/squeals.
---
At 100k or so, my original S4 rotors were worn to the point where I could safely turn them and still be at or above the min allowable thickness. But going into the third set of pads and looking at the wear history, I decided to replace the rotors rather than turn them and then wear to to below the min thickness. This is of course a judgement call, but my situation sounds a lot like yours. Meanwhile... I get to buy professional liability insurance every year, with premiums indexed to fees. Although that doesn't apply directly to how my car is maintained, it does remind me at least once a year that we live in a society that includes people (and their attorneys) who are constantly looking for that big financial payout, the one that will set them up for life.
.
The combination of the SS sliders in the caliper and the clip-in dampers/ that stick to the back of the pads -should- eliminate squeaks/squeals.
---
At 100k or so, my original S4 rotors were worn to the point where I could safely turn them and still be at or above the min allowable thickness. But going into the third set of pads and looking at the wear history, I decided to replace the rotors rather than turn them and then wear to to below the min thickness. This is of course a judgement call, but my situation sounds a lot like yours. Meanwhile... I get to buy professional liability insurance every year, with premiums indexed to fees. Although that doesn't apply directly to how my car is maintained, it does remind me at least once a year that we live in a society that includes people (and their attorneys) who are constantly looking for that big financial payout, the one that will set them up for life.
.
I am bit puzzled at the "SS sliders" you refer- nothing like that on my brakes - just the pads and the knackered dampers that were in there. I gave the pads to the main dealer to install when we prepared the car some 10 years ago. Never checked what went in other than the pads and new discs. I suspect they reused the dampers [non stick by then presumably] and stuck the pads in. We did not fit wear sensors- saw no point in that. I have seen disc brake set ups with a piece of thin plate between the back of the pad and the pistons- not sure if that was in the S4 or other vehicles of mine. Took a look in the manual and could see no signs of the sliders you refer but maybe the old dampers and the lack of sliders could explain the awful squeal. Much appreciate if you or any other lister can advise what should be inside the GTS calipers so that at least I get the setup correct.
I did note in the W S manual it talks about slipping a sliver of metal to break the seal between the damper and the pad before trying to remove the pads so that explains an earlier query I raised.
On the insurance front I would be equally wary were I in your neck of the woods or any locale that is prone to litigious nightmares. I like to take a measured approach based on experience with some degree of comfort knowing that others have been there safely before.
Mileage wise I suspect we have a similar user profile given I only tend to use the 928 for fun at the weekends. The main difference is the life expectancy of the discs. The hawk pads have great performance but at some expense to rotor wear. Couple that with wide tyres that take advance of the grip and you can imagine why they wear- no idea if our heat compounds matters. Bottom line I have about 50k km on these discs and I reckon they are 3/4 worn. I do like to use the car as and when I can so they do get tested albeit not all the time but a fair chunk nonetheless.
Rgds
Fred
11-19-2015, 04:27 PM
#12
Rennlist Member
i skimmed the rotors to just 30mm (thats the limit that a shop will do)
they cracked out before they had any significant wear.. maybe 29mm as they lasted about 5 race weekends. now, the 2 piece 13" rotors (GTS 12.7") lasted the entire season. 7 weekends.
I wouldnt worry too much about the thickness . if its in the 28 range, sure, toss them. that would be a nasty looking lip anyway!
11-19-2015, 10:38 PM
#13
Chronic Tool Dropper
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Fred,
Take a look inside the calipers where the pads sit, and notice at the ends a little metal piece at each end, secured with a button-head capscrew. The capscrew sits at an angle that makes it tough to get the right driver on it, and there's threadlocker on that screw to keep you from removing it easily anyway. The screw is SS, which places it diametrically opposite of 'tough' as far as resistance to having the screw-head damaged by your tools. Those little metal pads maintain the friction fit that tries to keep the pads secured with no slop fore and aift in the caliper frames. so they get dirty, and more critically they get brake dust packed underneath so the pads are tight. When they are tight they don't retract well, stay in contact with the rotor even when the edal is up, end end up glazed and/or overheated. So a caliper refurb needs to include removing those little SS pieces that the pads sit against, cleaning them and the area under them, then reinstallng with new screws and another drop of threadlocker. In my opinion anyway.
Take a look inside the calipers where the pads sit, and notice at the ends a little metal piece at each end, secured with a button-head capscrew. The capscrew sits at an angle that makes it tough to get the right driver on it, and there's threadlocker on that screw to keep you from removing it easily anyway. The screw is SS, which places it diametrically opposite of 'tough' as far as resistance to having the screw-head damaged by your tools. Those little metal pads maintain the friction fit that tries to keep the pads secured with no slop fore and aift in the caliper frames. so they get dirty, and more critically they get brake dust packed underneath so the pads are tight. When they are tight they don't retract well, stay in contact with the rotor even when the edal is up, end end up glazed and/or overheated. So a caliper refurb needs to include removing those little SS pieces that the pads sit against, cleaning them and the area under them, then reinstallng with new screws and another drop of threadlocker. In my opinion anyway.
11-25-2015, 05:08 PM
#14
Rennlist Member
Thread Starter
Fred,
Take a look inside the calipers where the pads sit, and notice at the ends a little metal piece at each end, secured with a button-head capscrew. The capscrew sits at an angle that makes it tough to get the right driver on it, and there's threadlocker on that screw to keep you from removing it easily anyway. The screw is SS, which places it diametrically opposite of 'tough' as far as resistance to having the screw-head damaged by your tools. Those little metal pads maintain the friction fit that tries to keep the pads secured with no slop fore and aift in the caliper frames. so they get dirty, and more critically they get brake dust packed underneath so the pads are tight. When they are tight they don't retract well, stay in contact with the rotor even when the edal is up, end end up glazed and/or overheated. So a caliper refurb needs to include removing those little SS pieces that the pads sit against, cleaning them and the area under them, then reinstallng with new screws and another drop of threadlocker. In my opinion anyway.
Take a look inside the calipers where the pads sit, and notice at the ends a little metal piece at each end, secured with a button-head capscrew. The capscrew sits at an angle that makes it tough to get the right driver on it, and there's threadlocker on that screw to keep you from removing it easily anyway. The screw is SS, which places it diametrically opposite of 'tough' as far as resistance to having the screw-head damaged by your tools. Those little metal pads maintain the friction fit that tries to keep the pads secured with no slop fore and aift in the caliper frames. so they get dirty, and more critically they get brake dust packed underneath so the pads are tight. When they are tight they don't retract well, stay in contact with the rotor even when the edal is up, end end up glazed and/or overheated. So a caliper refurb needs to include removing those little SS pieces that the pads sit against, cleaning them and the area under them, then reinstallng with new screws and another drop of threadlocker. In my opinion anyway.
I was looking at the rear pads today- they look fine and clean. I did notice that they look to have a stainless shim between the dampers and the pads. I do not have these on the fronts - my question is should I have such in there and if so what are these things called?
Rgds
Fred