Replace discs and pads or just pads - 330d

F355 · 11 Jun 2013 at 22:00

After a general check at the weekend I identified on my E46 330d the rear pads are getting low, and look to have just over 2mm friction material left on them (no lights on the dash yet). I'm going to get the pads replaced next week and as I was ordering the parts I thought I should probably replace the discs at the same time.

This evening I took the wheels off and measured the discs with a micrometer and they came out about 21.2mm minimum. There is hardly any lip on disc, the surface is even and not scored so by all accounts they look in pretty good condition. The minimum stamped on the disc is 20.4mm.

I don't want to be cheap and scrimp on brake parts, but I am wondering how worn the discs are in the grand scheme. I can't seem to find for definite what thickness new discs are, but some sites suggest 23mm. Doing some research online, most people recommend that the discs are changed around every second pad replacement as long as the discs do not have an excessive lip or scoring.

Any ideas on the above? In an ideal world I would just replace everything, but it makes an inexpensive quick job into a much longer job, so I would rather replace the discs when they need to be done.

Cheers,
Ian

andy_mk3 · 11 Jun 2013 at 22:04

23mm sounds about right, most discs have around 2mm between 'new' and minimum thickness.

By the sounds of it your discs will happily take another set of pads without an issue.

rodenal · 11 Jun 2013 at 22:11

Unless they've a visible lip or looked otherwise really sorry for themselves I'd be leaving the discs alone tbh

NickXX · 11 Jun 2013 at 22:26

Sounds fine - I would just change the pads. In 7 years of e46 ownership, I've never had to change the discs!

paradigm · 11 Jun 2013 at 22:26

How's your handbrake? If its anything other than superb, you might as well replace the discs and shoes too.

paradigm · 11 Jun 2013 at 22:27

NickXX said:
Sounds fine - I would just change the pads. In 7 years of e46 ownership, I've never had to change the discs!

Which would explain the crap handbrake it had when I picked it up

I replaced the discs twice during my ownership.

Django x2 · 11 Jun 2013 at 22:49

The handbrake on a BMW is no reference to be going by for the life of the discs or pads. All BMWs have shocking handbrakes. It's a fact of life sadly

Clarkey · 11 Jun 2013 at 22:55

Django x2 said:
The handbrake on a BMW is no reference to be going by for the life of the discs or pads. All BMWs have shocking handbrakes. It's a fact of life sadly

No they don't. Mine was pants until I replaced the discs, then was pretty darn good. Position of the lever is hopeless though, way too far back. I use a big silly extension on it for doing drift days, I really should wean myself off the thing though.

NickXX · 11 Jun 2013 at 23:05

paradigm said:
Which would explain the crap handbrake it had when I picked it up

I replaced the discs twice during my ownership.

Haha - that would probably explain why it was crap on my 318 then!

Wilderbeast · 11 Jun 2013 at 23:15

Django x2 said:
The handbrake on a BMW is no reference to be going by for the life of the discs or pads. All BMWs have shocking handbrakes. It's a fact of life sadly

I just bought a 330CiC and have to say its handbrake is 2nd only my A8's electronic one, 3-4 clicks and it simply wont move.

F355 · 12 Jun 2013 at 19:56

Thanks all.

I'll just change the pads this time, and I will adjust the handbrake while I am there. The handbrake has never been fantastic, but where it is an auto it isn't as crucial.

Clarkey · 12 Jun 2013 at 20:10

It will become crucial when it fails the MOT on it even though you never even use it though

acemastr · 12 Jun 2013 at 20:13

I've never used my handbrake

koolpc · 21 Jun 2013 at 12:51

Had 2 tyres changed on my car yesterday and the guy said the front discs need replacing. Now, they had a ridge on the outer rim of the discs. Is that wear? I am no car expert.

Housey · 21 Jun 2013 at 12:55

The disks on my wife's MX5 are scored to **** after we left the pad change a 'bit' to long. I couldn't be arsed to wait for new disks to got them to simply put the pads on. It stops like a ...... and passed its MOT no problem at all. Lot of bow locks spoken around disks in my opinion. In the 'olden days' I can't remeber ever changing disks on a car bar my Fiesta 1.3 Ghia....which was of course very very quick.

paradigm · 21 Jun 2013 at 13:04

Whilst I agree on that Housey, with the E46 they have a tendency to retain water inside the "drum" part of the disc, this utterly mullers the braking surface for the handbrake shoes.

In a car where actuating the caliper forms the handbrake mechanism, then you are spot on. But with an E46 I'd at least be whipping them off to check the inside of the "drum".

Housey · 21 Jun 2013 at 14:22

I did actually put 2 sets of disks on the front and one on the back of my RS4, the rears were utterly embarrassing too

F355 · 21 Jun 2013 at 23:12

koolpc said:
Had 2 tyres changed on my car yesterday and the guy said the front discs need replacing. Now, they had a ridge on the outer rim of the discs. Is that wear? I am no car expert.

My 2p based on my research

A deep ridge on the outer face of the disc is a symptom of wear, and normally indicates you need to replace them. The best way to tell for sure is to take the wheels off and measure the thickness with a micrometer. A safe minimum is stamped on the discs, but it might be easier to look at the manufacturer specs. You might be able to get your garage to verify the thickness for you.

Back in the 'olden days' brake pad compounds used to be a lot softer and were often made of asbestos. This meant that the brake discs rarely wore down, and rarely needed replacing. Modern cars have much more abrasive compounds which will take material from the disc under braking. During my research 2 brake pad replacements per disc replacement should be fairly normal, as long as the discs look in good condition (e.g. even face, no deep scoring, no cracks).

andy_mk3 · 21 Jun 2013 at 23:19

Plus cars these days are twice as heavy and a lot more powerful than cars 'back then', so the brakes do get a hammering!

The disc over drum idea is great but does have flaws. And BMWs are either great or awful, as they like to rust up inside, plus they rarely ever seem to get adjusted properly.