Pads not covering entire disc surface

[allymac]

Hi folks,

I have a 130 tdi sport and have just replaced the front discs and pads(old discs were corroded and noisey). They were replaced before at a garage just after I got the car two and a half years ago. At that time I noticed that on the outer face of the new discs(both sides), there was an area, about 10mm+ around the inner circumference that was not being covered by the pads properly, and as such they started to corrode. I put this down to them maybe being cheap parts.(on removing the discs I see that it is only a problem on the outer faces of them)

I have just replaced them again and have the exact same problem and it is annoying me! My nice shiny new discs wont stay shiny for long! Has anybody had the same problem?

Any ideas on what might be causing it? What might solve it? Im thinking maybe worn guide pins and/or sleeves? Or just another little quirk of the A4.

Cheers

[Marco34]

I can only think the new pads require a little bedding in. I've had a smiliar experience and performed a bedding in process. Within a short time they were soon running on the whole of the disk.

[dan.taylor.1]

13856

They are meant to do that, if you mean the front of the disk as you look at it with the wheel off, the bit your talking about is the bit that holds the rotor part to the hub part of the disk and isnt meant to wear or it would weaken the join between the parts allowing them to break off and all hell breaking loose! it is usually about 10mm, and it doesnt happen on the back of the disk as there isnt the same bit to join to the hub part, if you look at the disk side on you will see what i mean.

Pic above is rubbish but you get the idea!

Dan

[allymac]

Ye Marco, I hope so, but thats what I thought when had them replaced the last time, but I wasn't using the car as much then so maybe they got enough of a chance for the corrosion to set in before they bedded in properly.

I understand what you're saying Dan, but Im pretty sure that the area Im talking about is meant to be in contact with the pad, as the pad covers it, it must just be the smallest fraction off covering it properly.

Hopefully it'll come right, cheers guys.

[allymac]

PS Dan, on a different note, did your piper-x panel filter make any difference(is it foam)? I tried a K&N panel filter (oiled cotton)and it Knackered my MAF.

[frankc]

Sounds like the guide pins need cleaned & lubed or replaced. Should ideally be done every year otherwise the caliper body will start to cease in the carrier.
The inner pad is directly contacted to the disc by the piston whereas the outer pad requires the caliper to move freely on the guide pins and the carrier in order to fully transfer equal braking force across both sides of the disc.

HTH Frank.