993C4Smontreal

I have Big reds on my 96 4S.
They howl like hell...I have all oem disks and pads....the mech told me the discs were warped and thats why they were howling...he machined them., and said its ok to machine discs...PNA doesnt recommend it cause they rather sell u new ones....They howl less....

THEY HOWL WHEN I SLIGHTLY PRESS THE BRAKES, AS SOON AS I AM HEAVY ON THE BRAKES IT GOESAWAY.....

My 993 buddy noticed that my discs show rust along the inner perimter and outer perimiter as per the photo....is this normal. It seems like the pads are not contacting the discs there, he has the C2 brakes and the whole disc is smooth, no rust anywhere.

help.......

deltawedge

Short answer, no, it is not normal.

Looks like there is a lip on the edge of the rotor where turning the rotor did not reach. This could be lifting the pad away from the rotor until it wears down enough to take away the rust.

chris walrod

For just have turning those rotors, they sure do have quite a lip on them.

MarkD

Yeah, it sure looks like it...

It's hard to tell in the pics. Is the rotor surface flat all the way across? Can you feel or see a lip?

If the rotors HAD an uneven surface, then were correctly resurfaced and reinstalled with the old pads the "old" pad surface is probably not flat yet.

If the rotors are flat, I'd try the "Italian Brake job" first... I can say that because I am Italian
Get up to about 80, brake hard to a stop.
Repeat 2 more times.

Svaha

I was looking forward to new pads quelling the shriek of the banshee if I try to brake slightly. Maybe someday I'll relearn how to brake normally, but for now I only slam on the brakes at the last second, trying to release without squealing. I have receipts for new rotors not long before I got the car 15k miles ago. I tried bedding in by several rapid descents from speed. This didn't seem to effect the heinous scream if I should dare to brake lightly. My pads are all almost shot, I thought that if I went oem the squealing should stop.

AOW162435

My 993 had ~34,000 miles on it at time of purchase. From everything I could tell, the brakes were completely original. They never made noise, regardless of how hard I stopped. Earlier this year I refreshed everything with new rotors/pads/spiders/sensors from Sunset. The car brakes perfectly and without even a hint of noise.

Any chance your rotors are aftermarket? Are your pads fitted with the anti-squeal shims (spiders)?

Andreas

TroyN

Based on the appearance of that lip, it looks like your rotors are done. I think when they wear 2 mm (1 mm per side) you're supposed to replace them. If you want to keep them at least make sure they are flat across the surface. If you replace the pads they are not going to mate to the rotor properly otherwise.

NP993

The 930 brakes on my track car used to squeal like crazy in exactly the manner yours do -- with light pressure. There are several things you can do to reduce the noise. If I were you I'd remove the pads and clean the rotors and pads thoroughly with brake clean/carb clean. Then take a measurement of the rotors and see if they're within spec. Every auto parts store sells a goop product that you paint on the backside of the pads, that dries to a rubbery consistency and dampens the fine vibrations that cause pad squeal. You should also chamfer the edges of your pads so that they seat properly against the rotors. Clean your pads and rotors, check that the pistons in the calipers are oriented properly, chamfer the edges, paint the rubbery goop on the back of the pads, and you may solve the problem.

IMHO, your mechanic's idea of turning the rotors to solve a squealing problem sounds wrong. You turn rotors when they're warped, or when they've been defaced by excessive pad wear. Turning them stop brake squeal, which is caused as I said above by very fine, high-pitched vibration. I'd be a little skeptical of your mechanic.

psychoideas

How were they turned? My Porsche disc has a machined datum surface that all machining must be done to. Because our calipers have ‘live’ pistons instead of a ‘floating’ caliper design, exactly equal amounts must be machined off each side of the disc.

They should be turned in a lathe to the datum reference and not to the hole through the centre like most garden variety brake surfacing machines do.

993C4Smontreal

The rotors where machined becuase they were warped. He showed me that they were warped as they were spinning on the same machine he uses to machines them ( on both sides)....

I felt the edge of my rotors, there is no lip, My guess is that he shaved the edges of the pads to the point where they are not touching the edges anymore....

MarkD

I think the contact area your pads are hitting looks almost normal. If there is no lip on the rotors, your good to go... as long as they aren't out of spec (too thin).
If the pads were used with the rotors prior to resurfacing they are likely uneven and may take some time to wear down to a flat surface... and would likely be more prone to squealing.
So, looks like either re-bed the pads or look at Noah's advice on anti-squeal compound above

I am in a similar situation with my 993tt except I KNOW the rotors are toast. They are on the list-o-stuff-to-do
They squeal like crazy with light braking.

psychoideas

I'm sorry to tell you this but if he has machined both sides at once he is using a standard disc resurfacing machine and as such thay have not been done properly to Porsce Specs. Those machines are for Hondas and toyotas.

993C4Smontreal

from what I understand...porsche doesnt recommend resurfacing rotors, so what exactly is porsche spec as far is resurfacing rotors?...would the dealers have this machine?

psychoideas

Hi,
My car is a lot older than you guys (cars) but Porsche brakes have become better not worse so the principle still applies.

Below is an excerpt from the manual applicable to my car. I’m sure if a brake resurfacing machine is not good enough for my old thing it certainly won’t be good enough for a 993.

Porsche probably doesn’t recommend resurfacing rotors because they know that 99.9% of brake workshops use the wrong process.


When regrinding discs it is most important to preserve the original symmetry. This is the reason for taking an equal amount off each side. To ensure that this may be checked by the operator, the following dimensions are given. Measurement 'a' in FIG 11 :8 is tabled together with the original disc thickness, and a simple calculation will enable the check to be made.
When the thickness of a new front disc is 19.8 to 20.0mm (0.780 to 0.787in), dimension 'a' is 35.0 ± 0.10mm (1.378 ± 0.004in).
With the same thickness of a new rear disc, dimension 'a' is 65.0 ± 0.10mm (2.559 ± 0.004in).




If you just take equal amounts of each side of your disc you are just replicating any symmetry anomalies that have been caused by normal pad wear. Many things can contribute to this, one pad being tighter on the pins that the other, one sticking piston for example.

Good luck

P.S. All you need is a metal lathe, the required dimensions and a good operator.

black ice

Not sure what the hell your mechanic did, but I would put a twenty spot on you not having the anti-squeal shims. I think you need 4 for each caliper and at $5 or whatever a piece they add up, but some 993 guys here have told me that's stopped their squealing cold.

I have no shims on these current pads (PO put em on) and they squealed like a banshee for about 10K miles. I drive it a lot more than the PO and they seem to squeal less now, so I'm not embarrassed anymore, but I do hear a little squeal regularly.

Dave