BMW Buyers Guide and Problems - Brakes

BMWs have always had good brakes. They were ahead of the game in fitting all round disc brakes and ABS as standard. What's more BMW brakes are easy to work on, parts are cheap and upgrades plentiful on most models.

BMW E32 750i brakes with four pot calipers

E32 750i brakes with four pot calipers.

Wear and Tear

Since the 1970s BMWs have had a pad wear sensor built into the brakes. One front and one rear brake pad have a wire attached, they the brake disc cuts the wire an open circuit is formed and the light glows red on the dashboard. So a BMW with worn pads is easy to spot. Pads are pretty cheap and easy to fit, upgraded pads aren't much more (see below).

BMW brake wear sensor

Brake wear sensor embedded in pad.

You can check the condition of disc brakes by looking through the wheels. Signs of light rust are a sign of little recent use and shouldn't worry you. If there is a pronounced outer rim which is thicker than the rest of the disc then you'll need a new set soon, they aren't dear unless you get them from a dealer. I've become a fan of TRW's discs, they're a bit dearer but the disc is powder coated to stop the centered section and hat from rusting.

If you can get under the car check for weeping master cylinders and damaged flexible hoses. Rusty metal brake lines may need replacing and this can be expensive, get a quote before settling a final price. Brake lines normally run down one side of the car under the floorpan, the fuel lines are often next to them. Genuine BMW pipes and hoses often have a higher pressure rating than aftermarket parts.

If you hear a slight rattle over low speed bumps it could be a badly adjusted or loose hand brake mechanism. The hand brake has it's own pads which grip the inside shell of the read discs, this is known as a Porsche style handbrake.

If you gently pry away the leather handbrake gaiter you'll see a mechanism with two steel cables attached. At the front they're held by locking nuts. As you lift the handbrake both cables should take up slack at the same time if the handbrake is adjusted equally on both sides.

Brake fluid is hygroscopic, that means it'll absorb water at every chance it gets. Water is more compressible than brake fluid so you'll get a softer pedal feel in addition to the possibility of rust and sticking calipers. Fluid needs to be changed every two years, not only for safety but to avoid more expensive repairs.


BMW ABS is self checking. Turn the ignition to position one, most of the dashboard warning lights should come on including the yellow ABS one. If it doesn't the ABS won't work on older cars and may have been disabled rather than fixed! The light should go out once the engine is started. An ABS fault is a UK MoT failure.

ABS can fail due to wiring, control unit or sensor problems. A bad ABS pump relay can also cause a fault. If you're not able to read the fault codes the first fix to try is a new pair of ABS relays. But more often than not it's a bad Hall Effect sensor at the wheel. Only problem with these is that they can rust in place and be hard to remove sometimes.

By far the most common problem on early BMWs such as the E24, E28 and E30s is corrosion of the speed pickup stators. Each wheel carries a toothed ring an inch wide with lots of metal splines on it. These splines are pickup by a magnetic sensor when they move. If the ABS light flickers it's often caused by rusty splines, a ten year life is about right. Sometimes a clean with a wire brush will temporarily fix them. New stators cost my 25 GBP each for the back and 45 for the front as they include the front wheel bearings. Later BMWs have splines with larger splines and are seldom affected by rust.

BMW M-Tech floating rotor system

//M-Tech floating rotor system.

Brake Pads and Dust

BMWs always have dirty front wheels, depressing but true. Cars put more strain on the front brakes due to weight transfer and they're larger to compensate for this. Brake pads produce dust which bonds itself to the wheels.

If this bothers you you can buy low dust pads or fit shields behind the wheel to stop dust getting out. Don't fit shields on cars in very hot climates or which see a lot of hard braking as you'll reduce cooling airflow and cause brake fade. They are OK for commuting and town cars.

Generally you'll want to use pads from a known brand such as Pagid, Textar or Ferodo, they're not expensive at all. Personally I prefer Pagid Fast Road or EBC Red Stuff, they're not much more expensive but improved braking power at the expense of more dust and shorter pad life.

Hydraulic Accumulators

Some older BMWs like the 1980s five, six and E23 seven series use a hydraulic pressure accumulator. It's often known as The Bomb as it's black, the size of a large grapefruit and resembles the kind of bomb the Pink Panther used to throw at people! If it fails the brake pedal can feel dead and offer poor response to emergency braking. New ones aren't horribly expensive and aren't too awkward to fit.

I was driving along in my '85 635CSi once, at a high speed I won't mention, when I heard a snap and saw a drive belt disappear into the distance through my rear view mirror. The steering went heavy and the hydraulic pressure warning light came on. Despite having no hydraulic pump I stopped normally with no fuss thanks to the pressure left in the accumulator. These are the best engineered cars in the world, nothing else has the same depth of engineering effort and I'll never drive anything else.

Sticky Brake Problems

All BMWs were designed to be left hand drive. On some models for the UK and other right hand drive markets a metal bar was added to transfer the braking effort from the brake pedal (on the right) to brake booster (on the left). This bar runs at the top of the firewall in the engine bay and is about 9mm in diameter, on E30s it's on the cockpit side of the firewall.

The problem is that the mounting points and pivots can foul with dirt or mild rust. This causes the brake pedal to stop returning to the normal height once pushed. An early sign is that the brake lights don't go off when the pedal is released. Solution is to clean the pivots. E28 five series and E24 sixes have this mechanism and it's very common on older cars. Sixes seem less prone than fives though and for all I know other right hand drive BMWs may have the same fault.

Brake Judder Problems

Go to 50-60mph and brake hard. Do the brakes judder? If so it could be several things. A common cause on lower mileage (<100.000 mile) BMWs is warped brake discs, new ones are fairly cheap. Before fitting ensure the hub mating surface is completely clean so that the disc is flush and square. Be sure to have the wheels balanced correctly and at equal pressure too.

On higher mileage cars you need to check for worn ball joins and lower control arm bushings. BMW have a habit, even on modern cars, of making the the lower control arm bushings too soft - the E46 was notorious for it. They do this to give a smoother ride but the consequence is that the bushes wear out faster. Generally the //M cars have solid bushings, I have a set on my E30 318iS. You'll also find after market polyurethane bushings which will improve handling and last forever, don't even think of replacing worm bushings with anything else.

BMW F30 three series M-Performance brakes

F30 three series //M-Performance brakes, 370x30mm!


For the four bolt hub cars such as the 2002, the E21 and E30 upgrade options are a bit limited. If you've got rear drum brakes it's possible to get trailing arms from a disc model and convert, highly recommended. But for cars like my E30 318iS there's no easy option. Better pads, good discs and even braided steel hoses help but more would always be welcome. The extreme option is to switch to Z3 trailing arms and front hubs but it's a big job and also means new wheels.

For everyone else with five bolt hubs things are much easier. For a start you can generally upgrade to //M brakes although you'll need wheels big enough to clear them. On the E28 and pre-87 six series the brakes weren't really up to spirited driving. Post-87 E24s used the E34 five series brakes and these are superb, they just bolt on and are truly excellent.

If you feel the need for stronger brakes you'll want to search out someone braking an E38 740i or something of that nature, these will bolt onto most cars and stop a train. If you feel the need for a larger master cylinder the E32 750i is the car to get one from.

Generally brake size increases with engine size. On the E46 the four cylinder cars had the smallest brakes, then the 320i and 325i, then the 330i with brakes that needed 17" wheels to clear them and lastly the M3.

The Z3 1.9 and E36 318ti skimped by having non-vented front discs. The main difference on non-vented discs is the rate at which the brakes cool down after hard use, to be honest for normal driving there's no problem with them.