just serviced, now the brakes are vibrating?...

[Dr Strangelove]

I've just had my 993 back from a major service. When i picked it up, they said, the front pads are ok, you've had the fronts skimmed, but your discs are getting thin, but are ok until next service. Fair enough i thought. But after driving the car today, i could feel the front discs were really vibrating through the peddle, a kind of wattling feeling. I have never noticed this before, but the difference between the front brake feel pre and post service is stark (under firm braking). I noticed it had had some (test) miles on the clock when i got it back. (next time' i'll insist this is not an option.). Can someone offer a plausible explanation for this?, or are you going to say it's just my imagination.

[verysideways]

Take it back.
Tell them you're not happy, the brakes felt fine before and don't now. Did you ask them to skim the discs?
(I personally believe that you should only skim the discs when there is run out causing vibration).

VS

[tim993]

funnily enough my own 993 (the cause of many problems at the minute sadly) has been doing this. Prior to purchase i had all new pads and discs. Initially there was light shudder on breaking now its really annoying between 30 and 50 mph. Its been back in and matey says its the wheel alignment - which reminds me anyone know where to get the wheels aligned in sussex and how much am i looking at?
vs - on your photos of your old car (A1 OPD) there is a front strut brace in the front boot - how much difference does this make? Have you got the carbon fibre or normal one? Also any problems getting the diy halogens through the MOT?

[verysideways]

Tim,

Which car? My blue C2? A1OPO is on the silver tt now.

The strut brace made no appreciable difference on my standard suspension, 17" wheeled 993 C2. It did make a difference on my previous (low, 18", etc) 993 C4S, and it definitely makes a difference now on the tt (again low, stiff, 18"s, etc).

HID's were at the right height for the MOT so they didn't even mention it.
FYI, not Halogen, they are High Intensity Discharge (xenon). If you get some i have pictures on my site showing install and also a (crap) wiring diagram.



VS

[kevinday]

If the discs were skimmed you will need to bed the pads in again, ideally they should have fitted new pads at the same time as skimming. If you do not bed in the pads properly you will run the risk of pad residue buildup on the discs. This problem is often thought to be warped discs, but is not. Read the manual for pad bedding in, it is some sort of controlled heat cycling, dependent on vehicle type, pad type etc.

[Dr Strangelove]

sorry fellas, I think i could have written that better, because i didn't make it clear that I had already had them skimmed prior to taking car for service. The gist of what i was getting at, was that they had made a point of mentioning that they had been skimmed, and were getting thin (but would last till next service...), and now post service, i can feel vibration through the front brakes. I assume when they inspect them, they take the pads out?, could they have not put them back in properly?

[fabster]

Been there done that on a previous car - did all kinds of tricks (alignment, swap wheels from front to back etc etc) but in the end had to have both the pads and discs replaced and then it was sorted!

[soopdragon]

I had the same problem after having all 4 tyres changed on my Boxster. It was caused by the wheel nuts not being at the correct torque. I re-torqued the wheels and the vibration went away. It's worth a try before you do anything more expensive.

[Pickled Piper]

Dr Strangelove said:

sorry fellas, I think i could have written that better, because i didn't make it clear that I had already had them skimmed prior to taking car for service. The gist of what i was getting at, was that they had made a point of mentioning that they had been skimmed, and were getting thin (but would last till next service...), and now post service, i can feel vibration through the front brakes. I assume when they inspect them, they take the pads out?, could they have not put them back in properly? Some garages take the pads out clean them up, check pad thickness before re-assembly, others just shine a torch through the spokes of the wheel to assess if the pads are worn. It is possible the garage took them apart and didn't re-assemble them properly or it could just be down to a coincidence. Just take it back. pp

[ninemeister]

You cannot blame your service agent for distortion of the worn out discs that you have had skimmed, you are just a victim of false economy, in my opinion.

Sorry to break the bad news, but I do not know of any decent specialist who would sanction compromising your brakes in order to save you money, so my advice is to scrap the warped discs from your car and pay them to supply & fit new discs & pads as required.

Ouch.

[will_t]

My brakes were serviced by 9M and they are .

Will

[Fatboy]

kevinday said:

If the discs were skimmed you will need to bed the pads in again, ideally they should have fitted new pads at the same time as skimming. If you do not bed in the pads properly you will run the risk of pad residue buildup on the discs. This problem is often thought to be warped discs, but is not. Read the manual for pad bedding in, it is some sort of controlled heat cycling, dependent on vehicle type, pad type etc.

Is there anything that can be done to get rid of this residue, or is it just a case of fitting new disks? As my 944 has vibration under braking. At any case new disks are only £70 odd a pair for new cross drilled and vented (IIRC), but I'd like to avoid the outlay if safe to do so...

[bobo]

man u should try having one here in the wild west that is italy!

took mine in for pads and they changed all the disks w/o consent! wenkers!!!! then to make it worse when i asked to see the old supposedly destroyed disks they said they didnt have them!!!!

the disks did not need changing thats for DAMNN sure.

and yes folks that was from the biggest official dealer in lombardia ie milan.

got another 3 examples like this. but hell...its a monopoly over here so what can u do eh?

ahhhh italians.... gotta love em

[Dr Strangelove]

ninemeister said:

You cannot blame your service agent for distortion of the worn out discs that you have had skimmed, you are just a victim of false economy, in my opinion. Sorry to break the bad news, but I do not know of any decent specialist who would sanction compromising your brakes in order to save you money, so my advice is to scrap the warped discs from your car and pay them to supply & fit new discs & pads as required. Ouch.

Putting aside my point that the brakes felt very fine and very not warping just prior to before the service.

your Point(s) well made and taken. But it was pointed out to me by the specialist that skimmed them that there was plenty of life in them, they were just badly lipped. This 'decent specialist' who skimmed the fronts has had plenty of praise heaped on them. The rationale (sales pitch?) seemed plausible and honest, I had spent quite a few quid with them on other things, so said yes, to skimming. I thought this skimming was an innovation that had been well received by the trade. I understand Porsche OPC's offer it too (IIRC)?. Are there any 'Specialists' (apart from 9M) here who would think Skimming is a false economy?.

Colin on a slightly other note. If we are talking about a straight standard service. Do you take the customer cars out on a test drive?. If so, what kind of typical mileage is involved?

[kevinday]

Fatboy said:

kevinday said: If the discs were skimmed you will need to bed the pads in again, ideally they should have fitted new pads at the same time as skimming. If you do not bed in the pads properly you will run the risk of pad residue buildup on the discs. This problem is often thought to be warped discs, but is not. Read the manual for pad bedding in, it is some sort of controlled heat cycling, dependent on vehicle type, pad type etc. Is there anything that can be done to get rid of this residue, or is it just a case of fitting new disks? As my 944 has vibration under braking. At any case new disks are only £70 odd a pair for new cross drilled and vented (IIRC), but I'd like to avoid the outlay if safe to do so...

Take a look at this web page:

www.stoptech.com/faq/data/faq25.htm

and

www.stoptech.com/whitepapers/warped_rotors_myth.htm

[Dr Strangelove]

kevinday said:

Fatboy said: kevinday said: If the discs were skimmed you will need to bed the pads in again, ideally they should have fitted new pads at the same time as skimming. If you do not bed in the pads properly you will run the risk of pad residue buildup on the discs. This problem is often thought to be warped discs, but is not. Read the manual for pad bedding in, it is some sort of controlled heat cycling, dependent on vehicle type, pad type etc. Is there anything that can be done to get rid of this residue, or is it just a case of fitting new disks? As my 944 has vibration under braking. At any case new disks are only £70 odd a pair for new cross drilled and vented (IIRC), but I'd like to avoid the outlay if safe to do so... Take a look at this web page: www.stoptech.com/faq/data/faq25.htm and www.stoptech.com/whitepapers/warped_rotors_myth.htm

Thanks Kevin,

Those articles seem to make a lot of sense, and resolve the disparity between the Service Specialist saying the pads are fine but the disks are warped, however, you won't need to change them until the next service (12 months...). things are beginning to make more sense now. I would still like to hear if any other 'Specialists' that may post here have any comments about the non-merits of skimming, or maybe come to the techniques' defence.

any takers?

[ninemeister]

Dr Strangelove said:

Colin on a slightly other note. If we are talking about a straight standard service. Do you take the customer cars out on a test drive?. If so, what kind of typical mileage is involved?

Vary rarely do we get chance to give a service car a full testdrive either before or after work unless the customer reports an unusual fault that he cannot identify. So, if we had fitted discs & pads for instance, I doubt that we would do more than a couple of miles, if that. All that is required would be to make sure that the initial glaze had gone from the surface of the discs and that the braking effort was safe, probably involving testing the abs at low speed. We certainly would not do enough to bed in the pads fully. The bottom line is that by the time we get out on the open road and back again it takes an hour, but not many customers are happy to pay us an extra £50 to drive their cars for an hour and we do not work for free.

Final thought is that there is no point in measuring discs when they are cold since the judder occurs when they are hot, so if the discs are distorted for whatever reason, a cold skim is unlikely to cure the underlying fault if it only occurs with hot discs.

The only time I would justify skimming is with a disc that has surface corroded through lack of use and is otherwise sound, but I still think back to the problem that the specialist is responsible for the life of the customer when you agree to work on safety items, so when it comes to brakes or steering, the 9m policy is new o.e. parts only unless supplied/specified otherwise by the customer (excluding upgrades of course).

[Dr Strangelove]

ninemeister said:

Dr Strangelove said: Colin on a slightly other note. If we are talking about a straight standard service. Do you take the customer cars out on a test drive?. If so, what kind of typical mileage is involved? Vary rarely do we get chance to give a service car a full testdrive either before or after work unless the customer reports an unusual fault that he cannot identify. So, if we had fitted discs & pads for instance, I doubt that we would do more than a couple of miles, if that. All that is required would be to make sure that the initial glaze had gone from the surface of the discs and that the braking effort was safe, probably involving testing the abs at low speed. We certainly would not do enough to bed in the pads fully. The bottom line is that by the time we get out on the open road and back again it takes an hour, but not many customers are happy to pay us an extra £50 to drive their cars for an hour and we do not work for free. Final thought is that there is no point in measuring discs when they are cold since the judder occurs when they are hot, so if the discs are distorted for whatever reason, a cold skim is unlikely to cure the underlying fault if it only occurs with hot discs. The only time I would justify skimming is with a disc that has surface corroded through lack of use and is otherwise sound, but I still think back to the problem that the specialist is responsible for the life of the customer when you agree to work on safety items, so when it comes to brakes or steering, the 9m policy is new o.e. parts only unless supplied/specified otherwise by the customer (excluding upgrades of course).

Some things are not quite adding up here...

There was no question of the disks being unsafe, the Specialist said they will go for another year!. All i'm saying is that the car had miles on the clock after i picked it up, and it was a standard service with no request from me they need to drive it for faults. The cynic in me is thinking

Prior to service - No 'warp'
Post Service - 'warp' present
+ Miles on clock ...

=Velocity braking.

[tim993]

sorted
paid 25 quid for balancing which had no effect on brake judder but forced my mechanics hand. He rexamined all four pads and discs and tells me the front left one was warped (RHD drive car - sorry vs!). He got a new one from porsche for free as it was only four months old. Just thought i'd let you lot know in case there is a rogue batch (you know like those dodgy 996 rms seals) out there.
also grinding noise was drive belt sensor - now sorted too.
Next project is techart air ducts for front spoiler.