jay827

I'm have the brakes on my 993 done for the first time and have gotten conflicting opinions on the correct course of action. Car has 35K miles and the pads are 75% worn and starting to squeek when hot due to the formation of a lip on the rotor which touches the medal backing of the pad. One mechanic feels I need to have the rotors machined & replace the pads. The other advises against turning the rotors, saying the soft medal combined with the cross drilling gives a surface which is difficult to work with and the results he's had in the past have been disappointing. He's guiding me towards replacing the rotors (note - he has no financial benefit as he's passing along the parts at cost) or simply replacing the pads and doing the rotors next time. Any experienced advice?

Terry Adams

At 48K I had new pads all around, the front rotors replaced and the rear rotors resurfaced, at the recommendation of the shop. They said there is a thickness below which they cannot be resurfaced, but I don't know what it is. They also said that they can only resurface them once, and they will need to be replaced at the next pad replacement. I just had a 60K service, and the rears are still ok.

Chris in Detroit

Jay

If the pads and rotor are worn to the extent that the "lip" on the rotor is high enough, or the pad material low enough to contact - then it is definitely time to replace either or both !

Having said that, I am EXTREMELY sceptical that the lip in your rotor could contact the backing plate of the pad - this would yield a huge screech and lots of sparks and wear on both rotor and backing plate. And a major reduction in braking effect.

More likely, both are fairly worn and as this happens the tendency to squeal is increased.

Porsche doesn't recommend turning rotors and as said above, if your rotors are that worn, you don't have scope to turn them anyway.

Best course of action:

(1) Your pads need replacing - if just for street use, I have had success with Metalmasters rather than OEM as replacement - seem to dust and squeal less. But these do not stand up to track use

(2)Just replacing the pads might fix the problem, but if your rotor is badly worn with v. pronounced lip, you should really replace this also.

(3) If the brakes still squeal, make sure the "anti-rattle" clips in the caliper were replaced as part of the brake job.

Note: all the above is very DIY-able - see Robin's Excellent WebSite under the DIY section.

Hope this helps

Timothy Stewart

I'm having a hard time picturing this.
A new pad is 32mm. The backing plate is
say 5mm. At 75% wear, that leaves
a little less than 8mm, well above
the min of 2mm. The rotor is touching
the backing plate.
Does the rotor have a lip of 8mm?
At 8mm, this would be approaching
1/3 the wear limit of the rotor itself.

FYI - there is a notation in the shop
manual stating "discs may only
be machined symmetrically, ie, uniformly
on both sides.

tim

Ray Calvo

I'm going along with some of the other commenters; idea that there is a lip on the rotor large enuf to hit the brake pad backing plate I feel is ridiculous. Only if you have maybe a mmm or so pad thickness left would I believe it.

If the lip really is a couple of mm thick, then the discs are really worn - highly probable beyond the point of where you can turn them. The difference between new rotors and ones worn to minimum thickness is only a few mm - likely too little to allow disc turning. I'm at work and don't have access to literature so I can't tell you the limit, but it IS stamped into the rotor (either on outer lip or else the protruding "hat" where the wheel bolts to).

I track my car, and I replace rotors largely due to cracking rather than minimal thickness. I have changed pads without changing rotors (I have NEVER had a rotor turned in prob. about a million miles of driving one car or another). The Metalmaster pads are very good street pads, and I don't have any squeal. This is without any of the anti-squeal stuff that Porsche has put on these cars, but I use a common anti-squeal "sticky" spray that is sprayed on the back of the pads before installation (available at any local auto parts store). The Porsche anti-squeal backing I feel adds to a spongy brake pedal feel.

Robin 993DX

Jay,

The Germans don't believe in resurfacing the rotors, they made them to be soft so that the rotor material gives instead of your car's front end when you needed the stopping power. That's why traditionally American cars never had good braking distance, until recent years when they finally accepted German automotive philosophy. (Pop quiz, name one American car that followed the design of the 944 20 later after it was designed by the Germans?)

I replaced my front brakes pads at about the same mileage as your car, 36k. The rotors were showing signs of ridges (rings of ridges). The new pads will eventually bed in to match the ridges, so if you just replace the pads without replacing the rotor the brakes may not feel as strong in the first couple hundred miles, but once it beded in with the rotor it will work better.

But I do not recommend the 993 rotors to be resurfaced (turned).

Simple rule to follow is, replace the rotors every 2nd time you replace your pads in a street driven 993. So the next time you change out your front brake pads at 70k will need to replace your front rotors.

Nol, 95 993 C4

Jay,

I agree with most replies posted above. If it was me, I'd decide on hard facts and measure the thickness of the rotors. Compare what steel you have with the nominal new rotor thickness and the acceptable lower limit. If you're approaching the limit, change pads and rotors. If you've plenty margin left, change the pads only and allow for their bedding in to the worn rotor pattern.

When in doubt, I'd change rotors. Brakes and tires are no compromise safety items in my book. Hence I would not machine the rotors. They weren't designed to be machined, and thinner rotors have less material for heat dissipation. So for the same amount of brake energy generated they get hotter, quicker, which I believe increases the probability of cracking them.

So at 98k kilometers (or 60k miles) my '95 C4 was treated to new pads and rotors all round. There was a definite lip on the rotors and a waviness to the surface, but nowhere the lip was more than a guestimated 1mm. I was also given the advise of changing the rotors at the second pads change by Juergen, our factory trained German Porsche mechanic (who then left us for the bright lights of Dubai). Admittedly, it was part of the purchase negotiations. A win-win deal as it was worth more to me than it cost them to fit.

After some 5000 km I had a bit of squealing, but I've not noticed it for a while now. Must be the weather with 45 degC in summer.

Just my $0.02, Nol

Garey Cooper

I will second the other opinions on the rotors touching the backing plates, not much chance.

As to turning the rotors again you can get into areas of opinion here. My only personal one being that it is okay to turn a few thousandth's off to true up the surfaces. Beyond that it's new rotor time!

Pete911air

Jay,
We at ANDIAL would never do a brake job without machininig the rotors, if they are within specification, or replacing rotors if they are too thin. But then again, what do we know. We only did a few hundred in our 25 years of working on some of the most sophisticated Porsches.
Pete.

DJ

I get my rotors turned also. When the pads are worn, replace them, and turn the rotors, the next time the pads are worn, new pads and new rotors. Seems to work fine. I've got 50k miles, and have just turned the rotors (3rd set), and replaced the pads (6th set) from new. Lots of time on the track, and no problems.

Ray Calvo

A freebie for you welfare clients who are too cheap to buy a shop manual or the little "Technical Specifications" book:

993 brake rotor thickness:
Front - 32mm nominal. Wear limit - 30mm
Rear - 24mm nominal. Wear limit - 22mm

Can always check yours with a micrometer.