Pulsing brakes...

The Oily Bits S1 Specific Topics
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I think Tut runs MMCs. He has been known to collect them!

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The disk.Actually shatter is not the correct word. Maybe sheared, maybe just broke. Maybe I was just being dramatic.The outside of the disk was still on one piece, but not not attached to the center, all that broke.This happened braking for the hairpin but I don’t know the history of that car (other than it’s a heavily modified+used Elise, giving around 210HP).Cheers,Uldis

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And sticky (Maxsport I think) rubber, which obviously has a large effect braking performance.Cheers

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Guys,the “pulsing” brakes took a new development yesterday at Knockhill.Original pads finally gave out and self destroyed. Total car mileage: 1900 miles. [image]http://www.exiges.com/ubb/NonCGI/images/icons/frown.gif[/image]I commented the pulsing to some people, evaluated the life left in the pads and all agreed that they would last for the day at least (after all, they still had like 7mm left) but braking at the end of the straight I felt the pedal go suddenly “low”.Not right -I thought- and pulled out.The outside front right pad’s backing plate was pressed against the disk (and the disk slightly scored).Good think that there’s guys like Mike Niven, who was there and offered a spare set of EBC greens he had laying around so I could continue, and the Lotus mechanic very willingly changed the pads for me. Otherwise I would have had to test the benefits of AA or something. [image]http://www.exiges.com/ubb/NonCGI/images/icons/blush.gif[/image]The EBC greens stoped better than the originals (surprise!), and Mike tells me that the Pagids will stop even better (at the expense of disk life).But they still juddered (although less than before), so I’m still looking for an answer. I went to the EBC website and found something interesting:"Vibration or judder at low speeds are always associated with rotor run out. Vibrations or judder at high speeds (70 - 100 mph) are what we call hot judder and are normally associated with over heating of the brake disc. This is usually because of a low quality brake rotor casting (in which case the customer needs to be asked who�s rotor he was using). This is only remedied by replacement of the rotor. The other cause of vibration is known as �disc thickness variation� which is a condition generated when the rotor wears thick and thin due to incorrect installation of the rotor by the installing mechanic (in other words not running true from first installation)"I called the Lotus dealer and they are going to see if the rotors would be covered by warranty, since this seems to be the real cause.BTW, I drove another (yellow) Exige yesterday and it didn’t judder (and the sports seats+harness were really nice).So, overall, a very nice day, managed to stay out a long time [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image] [image]http://www.exiges.com/ubb/NonCGI/images/icons/grin.gif[/image], improved my skills, met a nice bunch of guys, used up 2 tanks of Optimax and about 1 liter of Mobil 1 (yes, it happened to me now)Now I really have to get the brakes sorted out. First thing would be the SS lines (I felt like I was inflating a balloon), discs and pads. Lots of choices, let’s see.Cheers,Uldis

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UldisI hope you get your brakes sorted soon.When you get the discs and pads replaced follow the procedure below (info from Nick Adams / Alistair McQueen of Lotus)"With new pads and discs, or just new pads fitted run the car around for 10/20 miles using the brakes gently as normal to bed the two surfaces together. Once this has been done, check the surfaces of the discs and make sure here are no signs of any scoring or damage. Assuming all looks well take the car to an appropriate piece of quiet and straight, well sighted road and perform half a dozen medium pressure stops from 50 mph down to 20 mph to warm the brakes up. Avoid more than a minute between each stop so that the temperatures do not get a chance to deteriorate too much. Once the brakes are warm and the coast is clear, perform 2 or 3 hard stops from 70mph (where local laws allow!) to 20 mph, braking as hard as you can without locking up. Do not come to a halt between each stop, do them as fast as you can to get the brakes really hot. On the third stop come to a halt and keeping your foot on the brake press the brake pedal down as hard as you can and hold it there for at least a couple of minutes, don’t apply the handbrake. This hurts if you are doing it right! This will bed the pistons, shims and pads together and will compress the pad material, giving a hard and repeatable pedal. Once the 2 minutes have passed, release the pedal and go for a short drive, using the brakes as normal to let everything return to normal temperatures. The brakes are now fully bedded in and ready for use in anger. Recompressing the pads once every few thousand miles to the above procedure will help keep the pedal firm, especially if you don’t normally use the brakes hard."Hope this helpsMike

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Certainly. Will follow the instructions and see what happens.Thanks Mike,Uldis

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In my search for the truth about brake judder, I came to find a very interesting link: http://www-personal.engin.umich.edu/~jbarber/animation.html If you click in the link above the animation, it takes you to an in depth analysis of the phenomena, but in my opinion their conclusions are shallow and addressed in theorics terms.But in essence it’s the design of the disk combined with the pad’s characteristics and the rotational speed and pressure applied.If it happens to us, we need just to find a combination of disk/pads that when used at our pressure/rotational speed doesn’t give us any more problems. Easy, right?And that’s what anybody would try to do anyway by buying aftermarket stuff.Trial and error.My guess is that if I get the disks replaced in warranty, the same will happen again.I’ll see.Cheers,Uldis