Brake squeal and bedding-in questions.

[Dan in NZ]

I had the "Brake Linings" message a while back, so ordered a full set of genuine BMW brake pads, wear sensors, and anti-squeal paste. Last week I had the pads fitted by a local mechanic, as I'm about 3 hours drive away from the nearest dealer and we don't have independant bmw mechanics. When I picked up the car I was told to brake gently for the first 200km, and he had put the BMW tag around the gearshift that said the same, "avoid harsh braking for 200km". At first I had poor braking performance and loud squeal, now 500km on I still have a little squeal.

I just read on a couple of websites that new pads should be bedded-in by braking harshly from 100km/w to 15km/h a few times, in contradiction to the advice on the bmw gearshift tag... What's the story, and how do I stop my breaks squeaking???

[pundit]

I had the "Brake Linings" message a while back, so ordered a full set of genuine BMW brake pads, wear sensors, and anti-squeal paste. Last week I had the pads fitted by a local mechanic, as I'm about 3 hours drive away from the nearest dealer and we don't have independant bmw mechanics. When I picked up the car I was told to brake gently for the first 200km, and he had put the BMW tag around the gearshift that said the same, "avoid harsh braking for 200km". At first I had poor braking performance and loud squeal, now 500km on I still have a little squeal.

I just read on a couple of websites that new pads should be bedded-in by braking harshly from 100km/w to 15km/h a few times, in contradiction to the advice on the bmw gearshift tag... What's the story, and how do I stop my breaks squeaking???

Firstly I what type of pads did you have fitted? The original ATE pads have an kind of damping material stuck to the metal backing of the pad. This is designed to dampen the harmonic resonances which can occur whilst braking which leads to brake squeal. Anti-squeal paste serves a similar purpose but shouldn't really be needed unless the pads have no anti squeal backing. Secondly, did they machine the rotors? I would never replace pads on BMW's Mercedes, Porsches, Audi's etc etc. without either machining the disc rotors (or if undersize) replacing the rotors. The reality is that one of the reasons most cars of this ilk have good braking performance is due to the relatively 'soft' nature of the disc rotors themselves. This enhances the frictional 'bite' between rotor and pad. The down side is the rotors wear out faster than 'hard' rotors. I served my apprenticeship (don't ask how long ago) on Mercedes Benz and the rule of thumb was....

First pad change - machine rotors
Second pad change - new rotors
Third pad change - machine rotors
Fourth pad change - new rotors
Etc. etc.

So you can see that generally the rotors can only be machined once before being replaced. There are exceptions to this rule if you were using very soft pads and not hard on the brakes but usually the above is typical.

Even new or machined rotors with new pads require bedding in. If you are in the position to bed them in gradually over 200kms or so I would suggest that over a few hard applications of the brakes. Of course if you are using old non-machined rotors they will require a great deal more bedding in. Just avoid any panic braking situations until the brakes are bed in or you might be replacing more than your brakes!

The bottom line is that if driving a car like this you should budget for new disc rotors on approximately every second pad change. 'ATE' are the OEM supplier of brake components for most German vehicles and should be available from independant suppliers at much less than 'stealer' prices.

[Dan in NZ]

Thanks for that, they were OEM brake pads, didn't check the brand that they actually are. No, didn't have the rotors machined, but sounds like I probably should have.

I'm only planning on keeping this car for the rest of the year, so I really don't care if anything lasts much beyond that... I would rather save a few dollars now, than spend a few to save in the long term.