Brakes for Bing Bong
As I mentioned in the last issue, the drive back to Lincolnshire after collecting my daughter’s VW up! (now christened Bing Bong) from British Car Auctions Blackbushe was essentially trouble-free. I did, however, notice a vibration on heavy braking that was sufficiently serious for me to add a set of front discs and pads to my order for service parts. And when we took the front wheels off, it was immediately obvious my gut-instinct was spot-on. Both front discs were very severely marked on the outward-facing surface, and a significant wear-lip was also present. Having bought the car from auction I wasn’t able to discuss its history with the previous owner, but some of that marking looks to me like it results from the car standing about, quite possibly in a salty environment.
Run-out
In the early days of brake discs, checking ‘run-out’ after fitting, to ensure the disc was sitting correctly, was considered by many to be part of the job. This involved checking in-out movement at the disc edge, as the disc was turned, using a dial gauge. Though no longer generally done on most cars, this is still recommended on high-performance vehicles.
The reason is partly to prevent brake judder after a disc and pad change, but this might not happen immediately. If the disc is fitted slightly off, the brake may still feel fine and, initially, perform as it should. However, if the disc is slightly off-straight, part or parts of it will contact a pad once per wheel revolution. In time, that part of the disc will wear more than the rest, leading to brake judder.
Sometimes when this happens someone will check the disc thickness, discover that it’s off, and assuming the disc is faulty, return it to the supplier for a replacement. In most cases though, the warranty claim, if indeed it gets past the supplier, will be rejected by the manufacturer, as Disc Thickness Variation (or DTV) is very well-known by brake part manufacturers, and well-known as a fitting fault rather than a manufacturing one.
The main way of avoiding it is to ensure that the flange that the disc sits on is clean and rust-free, as shown in the picture sequence. Additionally, new brake dis
