Can cross-drilled rotors be turned?
03-21-2008, 04:26 AM
#31
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I'll take a pic of the old pads and you can comment.
The calipers look the same as the ones i saw on Ang's 90 S4. Apparently the Caliper design changed in mid 89.
The calipers on the car look like they were replaced at some point. The rears have faded black paint, it almost looks charcoal or grey colored and the fronts a black and the finish is in excellent shape. So they dont seem to be original. I will pull the wheel and take measurements once and for all.
The calipers look the same as the ones i saw on Ang's 90 S4. Apparently the Caliper design changed in mid 89.
The calipers on the car look like they were replaced at some point. The rears have faded black paint, it almost looks charcoal or grey colored and the fronts a black and the finish is in excellent shape. So they dont seem to be original. I will pull the wheel and take measurements once and for all.
03-21-2008, 09:46 AM
#33
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I agree with Jim, Rod and 69gaugeman - grooves are not usually a problem. Just think of them as extra surface area and extra cooling. The loss of braking with new pads is very, very minimal, and if you use them hard, the pads will have matching ridges pretty quickly. You might lose more braking from losing the thermal mass by turning the rotors.
The first time that I saw this in print, the owner/driver was discussing a C/Modified with metallic drum brakes...
The first time that I saw this in print, the owner/driver was discussing a C/Modified with metallic drum brakes...
03-21-2008, 09:51 AM
#34
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For a FYI only, MB has all their rotors ground and they even spec the angle that the cross hatches the grinding wheel makes. That is taking a detail to the extreme!
I work in the automotive industry designing, repairing, building machines that measure high volume, high accuracy automotive parts. Brake rotors is a large part of that business.
I work in the automotive industry designing, repairing, building machines that measure high volume, high accuracy automotive parts. Brake rotors is a large part of that business.
03-21-2008, 12:52 PM
#35
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I agree with Jim, Rod and 69gaugeman - grooves are not usually a problem. Just think of them as extra surface area and extra cooling. The loss of braking with new pads is very, very minimal, and if you use them hard, the pads will have matching ridges pretty quickly. You might lose more braking from losing the thermal mass by turning the rotors.
The first time that I saw this in print, the owner/driver was discussing a C/Modified with metallic drum brakes...
The first time that I saw this in print, the owner/driver was discussing a C/Modified with metallic drum brakes...
03-21-2008, 01:27 PM
#36
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The grooves on a used rotor like the grooves on a phonograph record have peaks and valleys when a new pad is fitted only the peaks will contact the new flat pad. That smaller surface area will wear down quicker until the pads are fully bedded seated in. That might make it seem like the pads were wearing out quicker but once the face of the pad matches the grooves of the rotors the rate of wear should be much slower. Racing pads should only be run part way down since the pad material helps insulate the piston from the heat.
03-21-2008, 03:27 PM
#37
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A lot of misinformation is getting thrown around here.
Jim, brakes are serious business and to continue with what you are doing is doing everyone a disservice. Especially on a car capable of almost 170mph. The importance of a vehicles brakes cannot be underestimated.
Brakes operate on one principal-friction.
Friction operations when two surfaces are in contact with each other. Agree so far?
When rotors wear over time they not only produce grooves, they produce an uneven surface. Uneven surface results in less contact surface hat friction requires to be limited.
This= more pressure required to stop the vehicle as there is not as much friction material contacting each other. This=more heat!
More heat=less stopping power and eventually more prone to brake glazing until the brakes are bedded properly on both surfaces.
It is very simple physics.
yes, if the rotor is not badly worn or grooved then slapping new pads will work but again it will take some time for the new pads to be bedded into the wear marks on the rotor and the car will not stop as effectively. This does not happen the first day or even week. This can take up to 500 miles or more depending on how bad the rotor is.
The above are facts that every single brake manufacturer will repeat and I know this as I have had dealings with just about every major brake company out there.
I have also had to deal with customers who improperly installed brakes using the above logic as once brakes glaze they make noise/reduce braking and the only solution is sand the lining surface. Again, everything here is ditto what every major brake company will tell you.
Jim, brakes are serious business and to continue with what you are doing is doing everyone a disservice. Especially on a car capable of almost 170mph. The importance of a vehicles brakes cannot be underestimated.
Brakes operate on one principal-friction.
Friction operations when two surfaces are in contact with each other. Agree so far?
When rotors wear over time they not only produce grooves, they produce an uneven surface. Uneven surface results in less contact surface hat friction requires to be limited.
This= more pressure required to stop the vehicle as there is not as much friction material contacting each other. This=more heat!
More heat=less stopping power and eventually more prone to brake glazing until the brakes are bedded properly on both surfaces.
It is very simple physics.
yes, if the rotor is not badly worn or grooved then slapping new pads will work but again it will take some time for the new pads to be bedded into the wear marks on the rotor and the car will not stop as effectively. This does not happen the first day or even week. This can take up to 500 miles or more depending on how bad the rotor is.
The above are facts that every single brake manufacturer will repeat and I know this as I have had dealings with just about every major brake company out there.
I have also had to deal with customers who improperly installed brakes using the above logic as once brakes glaze they make noise/reduce braking and the only solution is sand the lining surface. Again, everything here is ditto what every major brake company will tell you.
03-21-2008, 03:33 PM
#38
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Let me know what you think of the Calipers based on the old pads that I replaced.
Let me know if you think they are late S4/GT or GTS calipers.
Is there a PN on the caliper itself?
Let me know if you think they are late S4/GT or GTS calipers.
Is there a PN on the caliper itself?
03-21-2008, 04:33 PM
#39
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What brand of pads are those Ryan? They look like S4's to me. I've got both back at my shop so I'll take a look for you. My recollection is that with the GTS pads, the indentation for the pad wear sensor seems to barely intrude into the pad surface, with the S4's having a generous U-shaped cut out like what your picture shows.
03-21-2008, 05:32 PM
#40
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A lot of misinformation is getting thrown around here.
Jim, brakes are serious business and to continue with what you are doing is doing everyone a disservice. Especially on a car capable of almost 170mph. The importance of a vehicles brakes cannot be underestimated.
Brakes operate on one principal-friction.
Friction operations when two surfaces are in contact with each other. Agree so far?
When rotors wear over time they not only produce grooves, they produce an uneven surface. Uneven surface results in less contact surface hat friction requires to be limited.
This= more pressure required to stop the vehicle as there is not as much friction material contacting each other. This=more heat!
More heat=less stopping power and eventually more prone to brake glazing until the brakes are bedded properly on both surfaces.
It is very simple physics.
yes, if the rotor is not badly worn or grooved then slapping new pads will work but again it will take some time for the new pads to be bedded into the wear marks on the rotor and the car will not stop as effectively. This does not happen the first day or even week. This can take up to 500 miles or more depending on how bad the rotor is.
The above are facts that every single brake manufacturer will repeat and I know this as I have had dealings with just about every major brake company out there.
I have also had to deal with customers who improperly installed brakes using the above logic as once brakes glaze they make noise/reduce braking and the only solution is sand the lining surface. Again, everything here is ditto what every major brake company will tell you.
Jim, brakes are serious business and to continue with what you are doing is doing everyone a disservice. Especially on a car capable of almost 170mph. The importance of a vehicles brakes cannot be underestimated.
Brakes operate on one principal-friction.
Friction operations when two surfaces are in contact with each other. Agree so far?
When rotors wear over time they not only produce grooves, they produce an uneven surface. Uneven surface results in less contact surface hat friction requires to be limited.
This= more pressure required to stop the vehicle as there is not as much friction material contacting each other. This=more heat!
More heat=less stopping power and eventually more prone to brake glazing until the brakes are bedded properly on both surfaces.
It is very simple physics.
yes, if the rotor is not badly worn or grooved then slapping new pads will work but again it will take some time for the new pads to be bedded into the wear marks on the rotor and the car will not stop as effectively. This does not happen the first day or even week. This can take up to 500 miles or more depending on how bad the rotor is.
The above are facts that every single brake manufacturer will repeat and I know this as I have had dealings with just about every major brake company out there.
I have also had to deal with customers who improperly installed brakes using the above logic as once brakes glaze they make noise/reduce braking and the only solution is sand the lining surface. Again, everything here is ditto what every major brake company will tell you.
If your are in parts distribution I suspect you have fallen for the change every thing at brake change time bull**** that a lot of people out there push.
You are fundamentally wrong in assuming that a grooved surface is an uneven surface.
03-21-2008, 05:49 PM
#41
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Pagid pads
There is something not correct with the setup though. You cant see but the pads have a huge groove on the outer edge because they were never in contact with the rotor. Thats why i replaced them. But the new pads are doing the same thing and what i am now thinking is that i may have a larger caliper but some dumb *** kept the S4 rotors and that would explain why when the pad is in the caliper it dosent get anywhere near the center of the hub like it should, thats why i have a rust strip on the rotor itself close to the inner hub.
I need to solve this once and for all. If i have GTS calipers with S4 pads and rotors i wouldnt be surprised. They should bolt up right? The smaller rotor will fit inside the larger GTS caliper right. This could explain why the pads feel loose in the caliper and why they wear so odd.
I am pulling off the wheel and will see what i can find out.
Where is the PN on the caliper. I recall seeing a number cast into the caliper, is this the brembo number or would it be the porsche number? IIRC its on one end of the caliper close to where the pipe runs under the caliper.
There is something not correct with the setup though. You cant see but the pads have a huge groove on the outer edge because they were never in contact with the rotor. Thats why i replaced them. But the new pads are doing the same thing and what i am now thinking is that i may have a larger caliper but some dumb *** kept the S4 rotors and that would explain why when the pad is in the caliper it dosent get anywhere near the center of the hub like it should, thats why i have a rust strip on the rotor itself close to the inner hub.
I need to solve this once and for all. If i have GTS calipers with S4 pads and rotors i wouldnt be surprised. They should bolt up right? The smaller rotor will fit inside the larger GTS caliper right. This could explain why the pads feel loose in the caliper and why they wear so odd.
I am pulling off the wheel and will see what i can find out.
Where is the PN on the caliper. I recall seeing a number cast into the caliper, is this the brembo number or would it be the porsche number? IIRC its on one end of the caliper close to where the pipe runs under the caliper.
03-21-2008, 06:53 PM
#42
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Good info, thanks.
And I'm fine with maximizing new pad contact right out of the box, risking new pads on my "wavy" cross drilled rotors is not likely to make me happy.
And I'm fine with maximizing new pad contact right out of the box, risking new pads on my "wavy" cross drilled rotors is not likely to make me happy.
03-21-2008, 06:55 PM
#43
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What were your dealings with ' every major brake supplier'?
If your are in parts distribution I suspect you have fallen for the change every thing at brake change time bull**** that a lot of people out there push.
You are fundamentally wrong in assuming that a grooved surface is an uneven surface.
If your are in parts distribution I suspect you have fallen for the change every thing at brake change time bull**** that a lot of people out there push.
You are fundamentally wrong in assuming that a grooved surface is an uneven surface.
Now if you were trying to state that a grooved rotor does not necessarily mean a warped rotor, then yes you are correct.
Just because a few want to save a few bucks does not mean it is the best thing to do.
Take your four fingers face down on a table and push. Feel the friction? Now lift up a finger(groove) and push. Less friction. Does not get simpler than that.
There is a balance here though. These rotors are $$$$$$$$$ as we all know. Turning them thins them out and especially so if some amateur turns them too much. This is why I have had (will again) my own brake lathe as I do not trust just anyone to turn my rotors.
If the rotors are in very good condition with no waves, grooves, warped ,etc... slapping on pads should get you by, just be careful breaking them in until the lining is fully embedded into the rotor surface.
Last edited by pearlpower; 03-21-2008 at 07:32 PM.
03-21-2008, 07:17 PM
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