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Minimum braking disc thickness
- Thread starter Andrew001
- Start date
SauRoNZA
Honorary Master
I don’t think they mean it’s exactly 10mm.
They simply mean it passed a minimum of 10mm.
Could be different for your exact car. Put your head under the wheel and confirm.
Moneywaster
Well-Known Member
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Is the shudder just at a certain speed? I once had this problem, brakes were inspected and nothing was found wrong. As it was not serious and only at certain speeds I lived with it. When I had to fit new tires later, the problem was gone. Perhaps to be sure ask a local tire fitment shop if it can cause your symptoms and have your tires balanced.
Brieuse
Expert Member
I thought we were not supposed to skim those type of disc
SauRoNZA
Honorary Master
Who said anything about skimming?
Thanks for all the responses - great help l. The shudder is mostly when braking on a steepish hill at about 70kmh. Took it to the Volkswagen stealership and they say its the pads and disk that need replacing. Wish they had picked this up during their 80pt inspection before selling the csry
That would be great. Could you post the link to the thread?
TheChamp
Honorary Master
You do realise it is just a thumbsuck, right? They are just hoping that solves the problem, and for you sake I hope it does. They were not going to cut their profits by fixing that if they can sell it to you as is to carry the costs.
longboy
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Discs and pads are the easiest things to notice if they're worn out during an inspection. Something doesn't add up.
Yeah was thinking the same.
GlassMirror
Expert Member
When I test drove the car I own now, the brakes also shuddered. I informed the salesman of it and he said to be that it just needs skimming but I insisted the discs and pads be replaced before I even buy the car and that discounted from the selling price. You should've made your voice heard as the buyer and picked this up during th test drive
I wish I had noticed it. Unfortunately it was only picked up later on when I was driving down a steep descent at a high speed. Now I know!
GlassMirror
Expert Member
Take it as school fees and never believe the dealer about their so called checks, rather check the car out properly first. I hope you have better luck next time dude
Praeses
Executive Member
You can normally tell the wear on the disc by checking on the "lip" created by the brake pads on the disc. If there's a significant lip on the edge of the disc, it's normally an indication that it's worn and will buckle when it heats up during breaking - which leads to shuddering. It might be that you only feel the shuddering at higher speeds or down hill as this will lead to more heat being produced - leading to more warping. Had my front discs replaced a year ago - fixed my shuddering.
rietrot
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The lip means nothing. You can have the disk skimmed to remove the lip and keep on using them.
Praeses
Executive Member
True, but it does indicate wear. When it's worn too much it can warp when it heats up.
qscwbt
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Brake Tech #01
The final word on brake judder and “warped” discs
In simple terms brake judder is experienced by the driver of a car as a pulsation through the brake pedal and/or side-to-side vibration of the steering wheel under braking. The above symptoms can be frustrating, disconcerting and result in driver complaints about “warped” brake discs. The phrase “warped brake discs” is used almost universally by uninformed vehicle owners to describe the cause of brake judder. The actual underlying causes of brake judder are, without a doubt, the most misunderstood aspect of automotive braking.
While it is possible for a brake disc to “warp” or distort (i.e. change shape) - disc distortion is responsible for relatively few brake judder complaints in our experience. The overwhelming cause of brake judder is a condition called Disc Thickness Variation – period! In other words the disc develops a lack of parallelism between its inboard and outboard friction surfaces. I say, “develops” because even discs that are machined to the very tightest tolerances during production can easily develop Disc Thickness Variation (hereafter referred to as: DTV) due to incorrect fitment or driver abuse.
When the brake pads are pressed up against a disc that has developed DTV they will pass over a series of thinner and thicker areas on the braking surface of the disc in rapid succession. Considering that the brake pads are being pushed together with substantial force they will be forced down into the ‘cavities’ or thinner areas only to be kicked back violently when reaching the bumps or ‘thicker’ areas. The frequency of this ‘bouncing’ action is typically over 100 Hertz when braking from highway speeds of around 130kph. This results in pulses that are transmitted through the caliper pistons, via the brake fluid to the driver, who experiences them as brake judder.
Causes of DTV
Once you understand the causes of DTV it becomes clear that brake judder problems can be almost completely eradicated by following a few simple rules. So, what causes DTV? DTV can be caused by a number of factors including disc fitment errors, driver abuse and poor manufacturing processes. The causes above are mentioned in order of their likelihood of occurrence.
DTV Cause No. 1: Failure to ensure that the mounting surface of the brake disc and hub are perfectly clean prior to disc fitment.
One of the most common causes of DTV is the failure of the fitter to properly clean the mounting surface of the disc and the vehicle’s hub. The smallest fragment of dirt or rust scale caught between the mating surface of the disc and hub is magnified as you move towards the outside diameter of the disc. This results in an unacceptable amount of axial run-out (inboard-outboard movement) at the friction surfaces of the brake disc (the areas of the disc that come into contact with the brake pads). To put this into perspective, the maximum axial run-out measurement that Powerbrake™ will accept on a newly fitted disc is 0.08mm (measured in the centre of the friction surface of the disc). A single spec of rust scale measuring only 0.05mm (50 microns) in thickness trapped between the mounting surface of the disc and the hub can easily cause the axial run-out value to exceed this tolerance!
Once you have a brake disc that is fitted with unacceptable run-out you have entered a downward spiral that will lead to brake judder and irreversible disc damage over time. Every time you apply your brakes the pads will first come into contact with the disc at the point of maximum run-out. In fact, due to the fact that your brake pads retract only fractionally when you release your brakes, excessive run-out often causes a light, continuous rubbing of the disc against the pads at the point of maximum run-out. This is happening when you are off the brakes completely!
To understand what happens next we need to briefly discuss two broad categories of brake pads. The first category of pads relies more heavily on the concept of abrasion to slow your car down. In simple terms this involves the mechanical gripping and breaking off of opposing pad and disc materials at a molecular level. The materials literally wear each other away in the process. The harder material (typically the disc) will wear slower than the softer friction material of the brake pad.
The second category of pads relies more heavily on the concept of adhesion. In this case some of the pad friction material is transferred to across to the contact surface of the disc, where it forms a thin, uniform layer of friction material. Essentially you now have the friction material of the pad coming into contact with identical friction material that has been deposited on the surface of the disc. Under braking, the bonds between the friction material of the brake pad and the friction material deposited on the disc are constantly breaking and reforming. Material crosses the pad/disc interface in both directions as the molecular bonds continually break and reform.
All pad formulations use a combination of both abrasion and adhesion but some pads (such as common semi-metallic formulations) rely more heavily on abrasion and others (such as many high temperature ‘Ferro-Carbon’ fast-road and race formulations) rely far more heavily on adhesion. Abrasive and adhesive pads affect the formation of DTV in different ways.
Back to our brake disc that was fitted without the hub and mounting surface of the disc being carefully cleaned. Let’s assume that the rust scale on the hub caused the disc to have a run-out of 0.1mm. On many vehicles this will NOT be felt as brake judder by the vehicle owner when he collects his vehicle from the fitment centre. He drives off a happy customer. However, after a period of between 1000 and 6000 kilometres of driving the brakes begin to develop a judder, which gets progressively worse. The vehicle owner complains to the fitment centre, who assumes that the discs have “warped”…right…wrong!
Even the best quality discs money could buy would have developed the same brake judder. Here’s why…. As explained above, the disc was continually coming into contact with the pads at the point of maximum run-out first. If abrasive pads were being used this area of the disc would wear down quicker than the rest of the disc surface causing DTV, which is felt as an intrusive judder. If adhesive pads were being run then the pads would have deposited more material on the initial contact point (the area of max. run-out) than on the rest of the disc surface. Again this leads to DTV and brake judder.
for rest of article
http://www.powerbrake.co.za/Articles.asp?ID=253
The final word on brake judder and “warped” discs
In simple terms brake judder is experienced by the driver of a car as a pulsation through the brake pedal and/or side-to-side vibration of the steering wheel under braking. The above symptoms can be frustrating, disconcerting and result in driver complaints about “warped” brake discs. The phrase “warped brake discs” is used almost universally by uninformed vehicle owners to describe the cause of brake judder. The actual underlying causes of brake judder are, without a doubt, the most misunderstood aspect of automotive braking.
While it is possible for a brake disc to “warp” or distort (i.e. change shape) - disc distortion is responsible for relatively few brake judder complaints in our experience. The overwhelming cause of brake judder is a condition called Disc Thickness Variation – period! In other words the disc develops a lack of parallelism between its inboard and outboard friction surfaces. I say, “develops” because even discs that are machined to the very tightest tolerances during production can easily develop Disc Thickness Variation (hereafter referred to as: DTV) due to incorrect fitment or driver abuse.
When the brake pads are pressed up against a disc that has developed DTV they will pass over a series of thinner and thicker areas on the braking surface of the disc in rapid succession. Considering that the brake pads are being pushed together with substantial force they will be forced down into the ‘cavities’ or thinner areas only to be kicked back violently when reaching the bumps or ‘thicker’ areas. The frequency of this ‘bouncing’ action is typically over 100 Hertz when braking from highway speeds of around 130kph. This results in pulses that are transmitted through the caliper pistons, via the brake fluid to the driver, who experiences them as brake judder.
Causes of DTV
Once you understand the causes of DTV it becomes clear that brake judder problems can be almost completely eradicated by following a few simple rules. So, what causes DTV? DTV can be caused by a number of factors including disc fitment errors, driver abuse and poor manufacturing processes. The causes above are mentioned in order of their likelihood of occurrence.
DTV Cause No. 1: Failure to ensure that the mounting surface of the brake disc and hub are perfectly clean prior to disc fitment.
One of the most common causes of DTV is the failure of the fitter to properly clean the mounting surface of the disc and the vehicle’s hub. The smallest fragment of dirt or rust scale caught between the mating surface of the disc and hub is magnified as you move towards the outside diameter of the disc. This results in an unacceptable amount of axial run-out (inboard-outboard movement) at the friction surfaces of the brake disc (the areas of the disc that come into contact with the brake pads). To put this into perspective, the maximum axial run-out measurement that Powerbrake™ will accept on a newly fitted disc is 0.08mm (measured in the centre of the friction surface of the disc). A single spec of rust scale measuring only 0.05mm (50 microns) in thickness trapped between the mounting surface of the disc and the hub can easily cause the axial run-out value to exceed this tolerance!
Once you have a brake disc that is fitted with unacceptable run-out you have entered a downward spiral that will lead to brake judder and irreversible disc damage over time. Every time you apply your brakes the pads will first come into contact with the disc at the point of maximum run-out. In fact, due to the fact that your brake pads retract only fractionally when you release your brakes, excessive run-out often causes a light, continuous rubbing of the disc against the pads at the point of maximum run-out. This is happening when you are off the brakes completely!
To understand what happens next we need to briefly discuss two broad categories of brake pads. The first category of pads relies more heavily on the concept of abrasion to slow your car down. In simple terms this involves the mechanical gripping and breaking off of opposing pad and disc materials at a molecular level. The materials literally wear each other away in the process. The harder material (typically the disc) will wear slower than the softer friction material of the brake pad.
The second category of pads relies more heavily on the concept of adhesion. In this case some of the pad friction material is transferred to across to the contact surface of the disc, where it forms a thin, uniform layer of friction material. Essentially you now have the friction material of the pad coming into contact with identical friction material that has been deposited on the surface of the disc. Under braking, the bonds between the friction material of the brake pad and the friction material deposited on the disc are constantly breaking and reforming. Material crosses the pad/disc interface in both directions as the molecular bonds continually break and reform.
All pad formulations use a combination of both abrasion and adhesion but some pads (such as common semi-metallic formulations) rely more heavily on abrasion and others (such as many high temperature ‘Ferro-Carbon’ fast-road and race formulations) rely far more heavily on adhesion. Abrasive and adhesive pads affect the formation of DTV in different ways.
Back to our brake disc that was fitted without the hub and mounting surface of the disc being carefully cleaned. Let’s assume that the rust scale on the hub caused the disc to have a run-out of 0.1mm. On many vehicles this will NOT be felt as brake judder by the vehicle owner when he collects his vehicle from the fitment centre. He drives off a happy customer. However, after a period of between 1000 and 6000 kilometres of driving the brakes begin to develop a judder, which gets progressively worse. The vehicle owner complains to the fitment centre, who assumes that the discs have “warped”…right…wrong!
Even the best quality discs money could buy would have developed the same brake judder. Here’s why…. As explained above, the disc was continually coming into contact with the pads at the point of maximum run-out first. If abrasive pads were being used this area of the disc would wear down quicker than the rest of the disc surface causing DTV, which is felt as an intrusive judder. If adhesive pads were being run then the pads would have deposited more material on the initial contact point (the area of max. run-out) than on the rest of the disc surface. Again this leads to DTV and brake judder.
for rest of article
http://www.powerbrake.co.za/Articles.asp?ID=253