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Old 04-26-2008, 08:19 PM   #21
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Found this tidbit in that link above.
Quote:
Also, if a rotor is slotted, the slot should not exit the disk surface. Look at the picture of the power slot below. If both ends looked like the inside edge (with a radiused corner) it may still be alive today. But where it exits the disk is where it will crack, as shown in multiple locations on our example picture.
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Old 04-27-2008, 08:41 AM   #22
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In those links, the Powerslot rotors had cracks too


I wonder if some of this this is the driver'* fault. Even after turning mine I haven't had any crack. Mine aren't Powerslots, they are the drilled/slotted type. I put them to some heavy breaking, sometimes with normal driving and sometimes with towing heavy loads... even had mine turned
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Old 04-27-2008, 08:49 AM   #23
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Quote:
Originally Posted by Bonneville92V688
I wouldn't dare putting drilled rotors on a 92-99. The brakes are undersized enough already.

Now the 00-05s? Not sure, but I surely wouldn't recommend drilled rotors. According to the the records of the 87 BMW 325is I owned, the original owner was replacing drilled rotors on the car every 6 months.
Actually the drilled/slotted rotors I installed on my 95 work better than the oem one that were on it. I never measured how much but I felt a good improvement with them.
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Old 04-27-2008, 03:03 PM   #24
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Quote:
Originally Posted by whitecrystal1
In those links, the Powerslot rotors had cracks too
[img]http://corner-carvers.com/printthread.php_files/crackedpowerslot

I wonder if some of this this is the driver'* fault. Even after turning mine I haven't had any crack. Mine aren't Powerslots, they are the drilled/slotted type. I put them to some heavy breaking, sometimes with normal driving and sometimes with towing heavy loads... even had mine turned
Guys, -the fact that rotors crack has only little to do with cross drilling or slotting. Rotors are made of cast iron and the quality of cast iron is what you need to be looking for. Most imported rotors have bad cast iron alloys and/or are not properly cured. Cast iron needs curing after casting before metal removal. I've used Made in Canada drilled rotors for a long time from a source that supplies them to OEMs. I've never had any problems with my rotors or pad wearing out prematurely. The fact that rotors are casted with the holes in them versus drilled after casting has again to do with curing. If properly cured and drilled afterward the material will not be distorted and therefore cracking will not occur. Also the picture of the cracked rotor looks to me that the rotor overheated according to the scuff lines/marks. Yet another reason why rotors warp and some crack but again this should not occur on quality rotors. China i.e is known for it'* impure iron and low quality iron products...
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Old 04-27-2008, 09:13 PM   #25
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Those cracked Powerslots are Brembo blanks, not cheap china rotors.
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Old 05-02-2008, 10:42 PM   #26
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Quote:
Originally Posted by radomirthegreat
<snip..>...The failure rate one might imagine from reading all the above from willwren and clm2112 is probably higher than what it is in reality.<snip...>
That'* probably true. But, it only takes one failure to destroy the car it was attached to. (and one chunk of metal comming off a rotor under braking will nicely re-arrange the front of the car....possibly with enough force to snap the spindle, ball joints, etc.)

At this point I would suggest a few other, safer, strategies to improve the braking forces available from the car. (this is old hat to folks running roadrace cars, but it offers some great, low cost, approaches.) The order is pretty much how I attack the problem.

1.) Change brake fluid to higher boiling point fluid, bleed the living heck out of them, and keep the resevoir topped off to keep moisture absortion low. Even in an all stock system, new fluid does wonders.

2.) Change the brake lines and hoses. Braided steel hoses offer good improvement in delivering the pressure to the calipers. It'* a small improvement, but it makes them more predictable on repeated applications. (One thing that always is good for a laugh is to look at the hoses connected to those mondo cool brakes on a typical "ricer"-mobile...they are usually cracked and rotten...looser spent all his/her money on the parts you see and ignored the bits that make them work. )

3.) Better pads. The pads do so much for the system. You don't care how clean they run, or how quiet they are...if you want braking performance, go for ones that bite hard and wear away quickly.

4.) Adjustable brake bias valve. The cars leave the factory with a conservative bias that is safe in all conditions. You can tweak it with a bias valve to have more of the pressure put on the front calipers and less on the rear. (Track days for best dry pavement performance at the risk of wet road stability) then go back to a more moderate bias for street driving in all weather conditions (like the factory setup aimed for the best braking performance with a safe margin of stability.)

5.) Bigger master cylinder bore. Braking power comes from the amount of pressure in the caliper pistons. That pressure comes from the master cylinder. Increase the master cylinder bore, even by a fraction of an inch, increases the volume of fluid pumped on every stroke and the pressure pressing the pads into the rotors. Also shortens up the pedal travel...which feels pretty good too.

6.) Bigger calipers and rotors. If you've bumped the size of the master cylinder, then you have head-room to add larger caliper pistons or more of them. This doesn't really increase the braking forces on it'* own, but it gives you more pad surface area, that will make the pads live a little longer. Bigger rotors add more leverage to the brakes...same forces applied a little further away from the centerline of the spinning wheel.

This usually gets it done....and pretty cheaply too (except #5...which is not needed in most cases) It'* not cutting edge cool...but it does work.
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Old 05-03-2008, 01:33 AM   #27
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You guys are perfectly welcome to put any brakes on your car you like. We're not preaching for the sake of excercising our fingers here.

If you pick rotors for cosmetic value, you're putting safety in the back seat. If you buy them because it 'might not happen to me', you're flirting with odds.

Not on my cars.
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Old 05-03-2008, 01:14 PM   #28
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I will ad one more important thing to what clm2112
posted.

Properly bed new pads and rotors.

This is especially important with cheap drilled rotors; slow deep heat soaking will relive stresses and reduce the chance of cracking.
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Old 05-03-2008, 08:16 PM   #29
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Quote:
Originally Posted by popatim
Those cracked Powerslots are Brembo blanks, not cheap china rotors.
The brembo blanks used for H body cars aren't the hi-po Italian made rotors, but just a standard US/Eastern style spec.
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Old 05-04-2008, 10:33 AM   #30
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Since I brought it into this topic, I dug around and tracked down a picture of a adjustable brake bias valve installed in a GM brake circuit.

Name:  Brake_Proportioning_Valve.jpg
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This fellow is using a Wilwood one on an 3rd gen F-Body. However the proceedure is the same for older Bonnies. I've used a Baer valve and it looks the same as this. Newer H-Bodies may need to leave the stock GM proportioning valve in place to keep the PCM happy and not flag any warnings about brake system failure, but the goal remains the same, the valve goes in between the rear brakes and the master (or stock proportioning block.)


Here'* how it works as in the photo:

There are two ports comming off the brake master cylinder. The one closer to the firewall provides fluid to the FRONT brakes. The port further away from the firewall provides fluid to the REAR brakes (The master cylinder is layed out opposite the actual layout of the car.)

The front brakes can provide 100% of the braking forces on dry pavement, so you leave them alone..they always get most brake fluid from the master cylinder without any restrictions. (In the photo, the fellow installed a "T" fitting to divide the fluid in half and feed both front calipers...something the original proportioning block did...but otherwise the front brakes are unmolested..they get everything the master cylinder can put out the port in pressure.)

The rear brakes are now metered by a valve that restricts flow. The more the valve is closed, the smaller the amount of flow to the rear brakes. With the valve wide open, the bias is 50/50 front to rear.

If you leave the original proportioning valve in place and install the adjustable valve in the rear lines after it. In that layout, the bias with the valve wide open is whatever the engineers set up inside the block...i.e. the factory spec bias. Close the valve and you can increase the bias towards the front brakes (which is what you want to increase the front end braking performance on the track.)

Personally, my advice is to leave the stock proportioning valve in on a street car, then add the adjustable valve after it. There'* a nifty little feature the guys with the pocket protectors added to it that can save your bacon (and keep them from getting career-ending visits from the GM legal team) The proportioning block has a slide valve in it that will lock out half of the brake system if it is loosing fluid. So if you cut a brake hose or blow a caliper piston seal, the stock proportioning valve will cut off flow to that half of the system, leaving you with at least two working brakes out of the four. Kinda handy to have...keeps you from having to dive for the cable operated emergency brakes.
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