Hello When the weather gets better i want to check the condition of my discs. In one of my manuals it talks about 'runoff' is that the same as thickness? There doesn't seem to be a minimum amount specified. It also talks about using a clock micrometer. Does the clock bit mean a digital miccrometer? i can't imagine it does coz the manuals are so old. Or do i use a set of gurnier? guages? (I don't want to buy the wrong tool). In short, any advice on how to measure the thickness of the discs and what the best tool to use is, plus what thickness they should be/changed at, would be very helpful. Thanks so much
Think you may be over complicating things.....if the discs are rusting see if they will clean up, if they are scored and ridged at the edge, bin them and put new ones on.....changing pads and discs seem to be a regular job on most ( modern) cars.
I dont understand why? recently took my car a Honda into the main dealers for a service 4 years old and 32,000 on the clock, they suggested the pads and disks needed changing !! Needless to say when the pads are worn out I'll change them myself and leave the disks alone, cant believe they need changing at such a low mileage ??!!
Thing it's down to the materials used...replaced 2 sets on my Citroen C2 and 1 on the wifes Corsa. Brakes are important and it' not a hard or expensive job even for a basic Diy'er
Thanks BTB. I probably am overthinking it, which is quite reassuring! but i just don't want to replace them if they're ok. IE how do you know if the 'ridge' is significant enough to change them or not?
VW quote 11.50mm as minimum thickness before replacement. A digital micrometer will do for checking...the outer unworn edge of the disc will obviously be thicker so that would give a false reading. Run out is where the disc is distorted and doesn't run true to the axle. A metric clock gauge has to be set up on a solid surface with the tip just touching the face of the disc. Bit of a fiddle...if the disc is badly warped you would feel it when the brakes were operated anyway.
It is because asbestos free pads use more sintered metal in there makup which wears the discs more. With longer service intervals dealer have to try gauge whether the pads and disc will last to the next service which may mean changing them well before they are worn out.
That's brilliant. Thanks very much. Tool station do a micrometer for about £15 its not digital though. It just has lines and numbers engraved. Will this be good enough do you think?
I'll do them myself ... I will measure the disk thickness. I only drive about 7k miles a year in this motor.
Yes thats okay all that really matters is bridging the outer unworn section. As you obviously realised a normal vernier would give you an error. There should be instructions with the micrometer on how to check zero...quite easy to do if needed.
one of the "leading" brake disc/pad manufacturers use a softer grade of Ductile Iron on their brake disks (than those of the 70's & 80's) which has a high wear characteristic over the pad friction material, we got involved in some tests on the discs when they went too far with the material and they suffered from fracturing easily and frequently.
The tool with lines and a knob you turn (a vernier scale) may not have the resolution of a digital instrument but it wont have a flat battery or drift as the battery flattens.
A vernier caliper is a really useful tool, not just for brake discs but pretty much anything. Even daft stuff like checking the size of drill bits or bolts, chuck them in the vernier.
