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This, from Wikipedia, is worth a read....

 

 

Run-out is measured using a dial indicator on a fixed rigid base, with the tip perpendicular to the brake disc's face. It is typically measured about 12 in (12.7 mm) from the outside diameter of the disc. The disc is spun. The difference between minimum and maximum value on the dial is called lateral run-out. Typical hub/disc assembly run-out specifications for passenger vehicles are around 0.0020 in (50.8 µm). Runout can be caused either by deformation of the disc itself or by runout in the underlying wheel hub face or by contamination between the disc surface and the underlying hub mounting surface. Determining the root cause of the indicator displacement (lateral runout) requires disassembly of the disc from the hub. Disc face runout due to hub face runout or contamination will typically have a period of 1 minimum and 1 maximum per revolution of the brake disc.

Discs can be machined to eliminate thickness variation and lateral run-out. Machining can be done in situ (on-car) or off-car (bench lathe). Both methods will eliminate thickness variation. Machining on-car with proper equipment can also eliminate lateral run-out due to hub-face non-perpendicularity.

Incorrect fitting can distort (warp) discs; the disc's retaining bolts (or the wheel/lug nuts, if the disc is simply sandwiched in place by the wheel, as on many cars) must be tightened progressively and evenly. The use of air tools to fasten lug nuts is extremely bad practice, unless a torque tube is also used. The vehicle manual will indicate the proper pattern for tightening as well as a torque rating for the bolts. Lug nuts should never be tightened in a circle. Some vehicles are sensitive to the force the bolts apply and tightening should be done with a torque wrench.

Often uneven pad transfer is confused for disc warping.[20] In reality, the majority of brake discs which are diagnosed as "warped" are actually simply the product of uneven transfer of pad material. Uneven pad transfer will often lead to a thickness variation of the disc. When the thicker section of the disc passes between the pads, the pads will move apart and the brake pedal will raise slightly; this is pedal pulsation. The thickness variation can be felt by the driver when it is approximately 0.17 mm (0.0067 in) or greater (on automobile discs).

This type of thickness variation has many causes, but there are three primary mechanisms which contribute the most to the propagation of disc thickness variations connected to uneven pad transfer. The first is improper selection of brake pads for a given application. Pads which are effective at low temperatures, such as when braking for the first time in cold weather, often are made of materials which decompose unevenly at higher temperatures. This uneven decomposition results in uneven deposition of material onto the brake disc. Another cause of uneven material transfer is improper break in of a pad/disc combination. For proper break in, the disc surface should be refreshed (either by machining the contact surface or by replacing the disc as a whole) every time the pads are changed on a vehicle. Once this is done, the brakes are heavily applied multiple times in succession. This creates a smooth, even interface between the pad and the disc. When this is not done properly the brake pads will see an uneven distribution of stress and heat, resulting in an uneven, seemingly random, deposition of pad material. The third primary mechanism of uneven pad material transfer is known as "pad imprinting." This occurs when the brake pads are heated to the point that the material begins to break-down and transfer to the disc. In a properly broken in brake system (with properly selected pads), this transfer is natural and actually is a major contributor to the braking force generated by the brake pads. However, if the vehicle comes to a stop and the driver continues to apply the brakes, the pads will deposit a layer of material in the shape of the brake pad. This small thickness variation can begin the cycle of uneven pad transfer.

Once the disc has some level of variation in thickness, uneven pad deposition can accelerate, sometimes resulting in changes to the crystal structure of the metal that composes the disc in extreme situations. As the brakes are applied, the pads slide over the varying disc surface. As the pads pass by the thicker section of the disc, they are forced outwards. The foot of the driver applied to the brake pedal naturally resists this change, and thus more force is applied to the pads. The result is that the thicker sections see higher levels of stress. This causes an uneven heating of the surface of the disc, which causes two major issues. As the brake disc heats unevenly it also expands unevenly. The thicker sections of the disc expand more than the thinner sections due to seeing more heat, and thus the difference in thickness is magnified. Also, the uneven distribution of heat results in further uneven transfer of pad material. The result is that the thicker-hotter sections receive even more pad material than the thinner-cooler sections, contributing to a further increase in the variation in the disc's thickness. In extreme situations, this uneven heating can actually cause the crystal structure of the disc material to change. When the hotter sections of the discs reach extremely high temperatures (1,200–1,300 °F or 649–704 °C ), the carbon within the cast iron of the disc will react with the iron molecules to form a carbide known as cementite. This iron carbide is very different from the cast iron the rest of the disc is composed of. It is extremely hard, very brittle, and does not absorb heat well. After cementite is formed, the integrity of the disc is compromised. Even if the disc surface is machined, the cementite within the disc will not wear or absorb heat at the same rate as the cast iron surrounding it, causing the uneven thickness and uneven heating characteristics of the disc to return.

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88 Esprit NA, 89 Esprit Turbo SE, Evora, Evora S, Evora IPS, Evora S IPS, Evora S IPS SR, Evora 400, Elise S1, Elise S1 111s, Evora GT410 Sport

Evora NA

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This, from Wikipedia, is worth a read....  

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Update on my brake disk problem.

Well after having my local dealer check my disks they confirmed slight run-out issues with my rear disks..

To have the rear disks replaced by Lotus was the best part of £700...

Did some more research and decided to go against the grain and opt for in-situ Pro-Cut skimming for £60 per disk on the basis if I'd didn't work then I would have replaced them anyway! Porsche, Ferrari and BMW are a few players who have these machines in their service centres and skim before replacing for run out issues. Apparently very common on Porsche brakes.

The disks were skimmed and the pads deglazed... Both look and feel like new with more than 70% life left on them :-)

I fully appreciate Lotus's advice but with an engineering background couldn't resist this option as it seemed a waist of expensive metal to just throw away without even attempting to fix.

My brakes are now lip free, smooth across the face and the brake peddle is smooth with no pulses! No vibration or jerkiness at slow speeds :-) Done!

This is the process:-

Here's a photo of my disk immediately after the skim, totally flat to the touch and look clean again with a sharp edge with no lip.

I used Chequers Lane Garage in Tadworth. They had a Ferrari Mondial and 911 in at the same time.. Friendly and careful with my car :-) They charged me £120 for two disks (about an hour and a half).

Hope this helps and is of use if your ever unfortunate to get the same problem.

post-15194-0-73595500-1402447989.jpg

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  • Gold FFM

I concur, had mine done at Christmas for same issue. Also used chequers lane garage, they did a very light skim as didn't need much, more of a clean up. I replaced the pads with red stuff at the same time to see if this would stop the issue recurring. So far so good.

A Lotus is for driving, pork is for breakfast.

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Colin P,

As LooseCannon said, what is it with brakes?!

RedStuff pads ok then? They must be more aggressive then the stock pads? Any squeal?

I'm interested. They look like what I'm looking for... Based on the below I might even have my fronts cleaned up and replace all four pads with RedStuff after my trackday on Tuesday. Won't have enough time to bed the in before otherwise I'd be on it!

So that's two of us that have used Chequers, I like the family business feel there.

Just found this on their website:-

http://ebcbrakes.com/articles/how-to-bed-in-your-new-brakes-for-streeturban-driving-2/

How to bed in your new brakes for street/urban driving

How to bed in your new brakes for street/urban driving

BEDDING IN NEW EBC PADS AND DISCS

Use brakes with minimal pressure for first 100 miles from urban speeds of 30-50 mph only. Brakes will feel very sharp and responsive but this is ONLY the brake in coating working which gives an abnormally high friction level feeling.

Drive a further 250 miles using slightly increased brake pressure and load UNLESS in an emergency in which case apply brake as hard as required.

Clean wheels off as there will be residue from the brake-in coating after bed in.

Look for a full width contact across the pad depth( rotor braking band) from the outer edge of the disc to the inner and if not achieved allow a further 100-200 miles steady driving. You will see a blue-ish band evidencing contact across the rotor face. Until this band goes from the outer to the inner edges of the brake disc/rotor the pads have NOT yet fully seated. When installing new rotors, reduced width banding is quite possible due to various tolerances and slight misalignments in the vehicle chassis and is NOT a warranty defect or a reason to remove and inspect brakes. Many European cars have SINGLE PISTON CALIPERS and these tend to “Flair” open and cause the contact band described above only to be seen at the outer edge of the disc/rotor and work its way inwards taking up to 1000 miles to do so.

After full width contact band is attained make a further 10 stops from 60 mph to 10 mph in succession with a deliberate attempt to get the brakes hot. Some smells may occur even slight smoke during this final heat up stage of the pads in early life. Then coast the vehicle for a mile to allow discs to cool. Do not pull up and park vehicle with brake excessively hot. You must try to get the discs down to below 60-80 degrees C temperature before parking the vehicle.

When parked let brakes cool to a final cool-to-touch point. Before touching discs splash a few tiny drops of water onto the disc to asses its temperature to avoid burning fingers. If the water spots cause a “hiss” you have parked up too soon and should go out and drive slowly allowing the brakes to cool further.

NEW DISCS TAKE LONGER TO BED IN

Fully bedding new pads to decent condition worn discs/rotors may take only 200-300 miles but when new discs are fitted at the same time bed in times to achieve outer to inner edge contact ( full width blue-grey contact band as mentioned under point 4 above ) can be as long as 800-1000 miles due to extra components needed to be aligned to the vehicle. To Short cut this you can ( and EBC recommend should) have EVEN NEW DISCS Pro Cut Lathe aligned to your vehicle. This process removes only microns of new disc material and shortens bed in time by 75% of the time it COULD take giving you better brakes faster and avoiding hot spotting and pad glazing.

BADLY WORN DISCS/ROTORS CAN TAKE AN AGE TO BED IN

Discs/Rotors with more than 0.5 mm ( 0.020 inches) of lip at the outer edge or hollow in the centre of the braking area can take up to 2000 miles to bed in and will for sure cause Noise, brake fade,vibration and pad burning. Bad rotors can RUIN your pads. 95% of brake fade and noise complaints come from poor disc/rotor condition where the pads touch only at the outer and inner edges and have no chance to deliver an effective brake.

Again new Discs/rotors is the solution or a Pro Cut on car Brake lathe re alignment.

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  • Gold FFM

Not had any squeal at all. No pad build up and they seem to stick a bit less when parked up wet. (They have less metal in them). Allegedly less wearing on the discs as well. Mine certainly felt much better after the clean up and the new pads. I don't drive on track though and my driving style means I am quite light on the brakes, which might be why I had the build up issue to start with.

A Lotus is for driving, pork is for breakfast.

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Yup me too being light on the brakes.. Mainly fast A Road and motorway means they hardly get touched.

Interesting point on sticking when wet... I've had to really rev up to free mine on a few occasions when left at the airport for a week or so...

I've got a trackday next week so will see how they fair and then consider the RedStuff.

You need to get that car on a track, it will make you very happy! Not just a great fast road car but sublime on a track!

Thanks for the info ;-)

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I think I'm pretty hard on brakes but I've never had an issue with the Evora.

However, I seem to knacker my family car brakes. The standard brakes went (possibly prematurely going over the Pyrenees) juddery, so replaced with Mintex disc and pads. These have have also gone the same way (possibly prematurely doing the Jura Mountains :)). I'm now looking at EBC discs and Greenstuff pads, so if anyone has experience of these it would be greatly appreciated.

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It's on here a lot mate but greenstuff's are for hatchbacks etc. Stick to yellow or red for performance cars. 

88 Esprit NA, 89 Esprit Turbo SE, Evora, Evora S, Evora IPS, Evora S IPS, Evora S IPS SR, Evora 400, Elise S1, Elise S1 111s, Evora GT410 Sport

Evora NA

For forum issues, please contact the Moderators. I will aim to respond to emails/PM's Mon-Fri 9-6 GMT. 

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RS4, surely?

88 Esprit NA, 89 Esprit Turbo SE, Evora, Evora S, Evora IPS, Evora S IPS, Evora S IPS SR, Evora 400, Elise S1, Elise S1 111s, Evora GT410 Sport

Evora NA

For forum issues, please contact the Moderators. I will aim to respond to emails/PM's Mon-Fri 9-6 GMT. 

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Scanning my cars service history for other reasons.....couldn't help but take note of how many times the brakes have been "done" on the car, turns out it's not just me after all.

 

I bought it in 2003 at 5 years old/24k miles. Turns out the discs had been replaced 3 times before with previous owners; 12k, 16k, 24k with new calipers first time (presumably under warranty)

 

In my ownership;

 

1 year/28k brake skim

4 years/ 38k new discs

6 years/41k brake skim

each time they could probably have done with replacing 1000 miles beforehand

 

They have been pretty knackered for the past 2 years up to 48k, but done so few miles thought what the heck, plus it's not CURING anything.

 

Do we deduce from this that Lotus brakes are just S H I T ? Or is it down to lack of use?

 

Really tempted by some of the PNM conversions, but could get another car for the price.

In the garage no-one can hear you scream 

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  • 3 weeks later...

I used Chequers Lane Garage in Tadworth. They had a Ferrari Mondial and 911 in at the same time.. Friendly and careful with my car :-) They charged me £120 for two disks (about an hour and a half).

 

Add me to the list of owners with skimmed (rear) discs, just driven back from Chequers Lane garage myself in a much smoother fashion than driving there.  Slow speed, light brake pressure "wobbliness" has been eradicated.

Before

photo1_zps9924dc93.jpg

After

photo2_zps29a13a58.jpg

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  • Gold FFM

They seem to be becoming something of experts in Evoras.

A Lotus is for driving, pork is for breakfast.

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Good to hear.

I found confidence in this method after learning that all official Porsche garages have the same ProCut equipment.

Apparently this issue is quite common amongst our German rivals too! :-D

I'm wondering if the extra weight in the Evora makes the pad/disk combination (same as Exige S) insufficient...

Or

The pads themselves from AP are just crap and leaving a build up?

Or

Did the first owner never bed them in properly?

??? Nobody seems to know...

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  • Gold FFM

My guess. Evoras are used more as every day cars so are not driven as hard. The Exiges are likely driven harder for a greater percentage of their use. Porsches tend to be everyday cars so may back up this hypothesis (did I really just use that word on a car forum!) if they suffer as well.

I suspect that the pads need to be abused more in order to self clean the discs and therefore when you use the brakes only lightly the build up occurs. May also explain why only the rear discs on m1lums car had the issue, as they are essentially the same set up and the bias will be toward the front.

A Lotus is for driving, pork is for breakfast.

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  • 1 month later...

i notice this mainly after driving by rainy day or washing the car and leaving it in the garage just after. my position is that the wet pads create rust pitting on the disc if you do not use the car often . then on the next use you feel a kind of jerky breaking .

as mentioned by other the problem is removed by heavy braking or better a track day.

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