You don’t think about your brake system until it stops functioning. Unfortunately by then it might be too late. The purpose of this short series of articles is to give you the DIY’er a guide to pinpoint trouble spots in your brake system before serious problems develop. The vehicle in this article is a
2000 Audi A8, an early build with single piston vented front disks and solid rears. This vehicle is only driven during winter months and when I test drove the vehicle this week I noticed that I had almost no braking power. The pads felt more like blocks of wood, the car required generous amounts of pedal force to stop and I couldn’t even lock up the wheels despite having no ABS.
These are serious red flags and a car in this condition should not be driven on public roads.
I decided that it was time to inspect all four corners of the vehicle and what I found was quite alarming. When evaluating the brake system start at the fluid reservoir, if you don’t have sufficient fluid you will not have brakes. Remember that you cannot physically have your hands at the four corners of the vehicle providing clamping force to each caliper, that is the purpose of brake hydraulic fluid. This incompressible fluid is an extension of the force you apply to the pedal and provides the pressure required at each wheel to provide braking force.
If the fluid level is sufficient move on to the brake discs. I took measurements at each corner and found them within specification however what I also found were friction surfaces in varying state of decay.
The driver side rear disc had sections of metal missing and the passenger side rear disc was grooved and irregularly textured. This surface condition will lead to a lack of surface area for the brake pads and will also gouge the pads.
Inspection of the brake pads provided an answer for the poor spongy pedal feel and lack of brake force. As a result of the disc condition the pads were wearing very irregularly and less than ½ of the pad surface was touching the brake rotor.
The driver side rear pads were also wearing at twice the rate of the passenger side indicating that the pads were not moving freely in the caliper bracket.
The next portion of the system inspection was the flexible rubber lines. Boy were these things shot!
Cracked and fraying in multiple spots, these 16 year old lines needed immediate replacement. Brake lines will fail in two ways, internal constriction and external failure, neither is ideal for the brake system.
Lastly inspect the only portion of the brake system that touches the road. Inspect your tires!
Check for uneven wear, dry rotting etc. 3 out of 4 tires on this vehicle were in fantastic condition. On an all wheel drive vehicle it is imperative to verify similar tread depth on each axle.
Significantly different tread depth across axles can wreak havoc on center differentials in certain all wheel drive systems.
In the next installment we will discuss remedies for all of the problems observed.
Kyle is the Mercedes Catalog Manager at FCP Euro and has been with the company since 2014.