bull****, pal
bull****, pal
bull****, pal
blah blah.
Are you done yet?
Good.
Allow me to introduce myself. I'm Tim. I'm the engineer responsible for all technical aspects of PBR and Axxis brake pads in the US market, and all Bendix and Axxis brake pads sold in the Australian and Asian markets.
Before putting on the aftermarket hat, I was the NVH engineer for 4 years, doing nothing but brake noise, with a fleet of test cars and a couple of million bucks worth of brake noise measuring equipment at my disposal.
I know a thing or two about brake noise.
You have almost certainly changed more Volvo brakes than I have. Your hands-on Volvo-specific knowledge is superior. Most of the work I've done has been on current (and future) model OEM brakes, and on the bigger selling references in the local aftermarket, and I spend most of my time in front of a computer or spectrum analyser rather than getting my hands dirty.
DB2, the pad that fits the ubiquitous Volvo rear (and also various MBZ, Alfa Romeo and a Ferrari or two), ranks about 100th on sales volume. It's not a big moving reference. But it's top 10 on noise returns. It's a notoriously noisy brake. There are reasons for this, and I'll go more into that later.
I'll tell you a couple of other notoriously noisy brakes. The 1996-2006 Holden Commodore rear (which you guys got on the GTO). The current model Perodua MyVi in Malaysia. The Mazda3 rear (until they changed the caliper anchor bracket late last year). I shouldn't mention the rear brake of current model Commodore V8s (same as will be on the Pontiac G8 V8s), but I just did.
Other brakes are far less fussy. Whatever you do to them, they're quiet. It's a brake specific thing. The tendency for Volvo rears to be noisy is specific to that brake, but not unique.
Brake noise is started and energised by the friction between the pad and rotor, but it's radiated by the rotor. The top image/animation on
http://www.polytec.com/int/158_427.asp shows a scanning laser-doppler vibrometer measurement of a brake rotor in a squeal mode. I have my own disks full of that stuff of my own pet brakes.
The rotor will only go into resonant vibration - and therefore squeal - if it can modally lock with another component, and go into sympathetic vibration. The two components vibrate together at the same frequency, feeding energy back into each other. They can do this if they have natural frequencies (eigenfrequencies) that line up. All solid objects have several natural frequencies. Rotors (and other things shaped the same - cymbals, gongs, bells etc.) have many of them.
If the modal locking is between the pad and the rotor, it's pretty easy to break by changing the natural frequencies of the pad. Changing stiffness. Simple stuff.
If the modal locking is between the rotor and the caliper, it's nasty. The pad initiates the vibration, and then it's just along for the ride while the rest of the brake vibrates around it. That's where you have a serious noise problem that is very difficult to fix.
I have only done a little bit of work on the Volvo brake, because it's not a priority to fix...compared with the others I've mentioned. We're OEM on the Commodore (I've ordered and analysed more tests on that brake than I care to think of), and it's our #4 selling aftermarket reference. The Perodua is Malaysia's #1 selling car right now. Mazda source most of their "genuine" spares for Australia from us, including the 3, which is their best selling model (and was noisy even with OEM pads, prior to the anchor change).
The Volvo...well...it wouldn't have had a look in, except that I drive one and noisy brakes annoy me. And I'm in the unique position of having an unlimited supply of free pads to play with, and half a clue about the engineering principles involved.
Changing the pad stiffness didn't change anything. Most importantly, the squeal was at the same frequency - indicating that it wasn't modal locking with the pad. Changing the centre of pressure and contact geometry didn't work. Different materials give different amounts of noise, but that's quite normal (different vibration excitation and material damping). A few different shims did some good, and I went with the best of them...which happens to be an off-the-shelf item from our supplier in Sweden, which indicates that it's used in big volume by somebody else, which may be somehow tied in with an OE or a genuine spares contract. I've had our noisiest material on my car for about a year now with these shims, and I occasionally get a very light squeal - the shim absorbs most of the vibration energy.
Anybody supplying pads direct into Volvo will have done a heap of testing and development, in order to meet Volvo's corporate brake noise specs. Contract obligation to meet noise specs aside, when you have that kind of guaranteed production volume (and cost margin), you can afford to spend some testing resource to find a noise solution. So, no question, pads in a Volvo box WILL be quiet, otherwise they wouldn't be in a Volvo box.
By comparison, I have about 1500 aftermarket part numbers to look after. I haven't even tested the noise of most of them, and I'm not going to. Same with every other aftermarket manufacturer. I'm sure some of them are awful noisy. I have no choice but to rely on warranty returns to identify the problem parts, and if it's enough of a problem, source a vehicle and do some testing.
Your comments about doing a decent brake job are valid, but I would consider that a prerequisite. If your calipers and rotors are in crap condition, you have no hope. Who knows how that rotor will vibrate if it only has one pad actively pushing on it? It wasn't designed for that, and nobody ever tested it. Here's a quality write up of how to do a good brake job:
http://www.bendix.com.au/HowToFitBrakePads.aspx . Hey, I think I know the guy who wrote that. Must remember to add some pics one day.
So, this has become an epic post. In summary:
* some brakes are inherently noisier than others.
* Volvo rear is one such brake.
* Solving brake noise on a problem brake takes time and resources.
* OE or OES pads will have been tested and had effective noise fixes designed for them.
* Most aftermarket pads don't get the attention they need.
* Nothing was designed to be quiet on a flogged out rotor and seized caliper.
tim
brake squeal just aint that hard to fix on these cars, boys. believe me, our customers wont put up with it, and therefore we must be able to do brakes on these cars, without noise issues, consistently and reliably. there are bigger fish to fry in the volvo service and maintinance world than squeaky brakes. there is a way... i promise. not complicated, not magic, no special super secret parts needed.
