Car not fully stopping sometimes at traffic lights

droopsnoot

How old is the car? Is it manual or automatic? Is it in gear when it's creeping forwards? If you put it in neutral does it still creep forwards? Do the brakes work normally the rest of the time, and can you do an emergency stop? 

sjaeagle5

Ectophile said:

From what I've seen while waiting at traffic lights, this seems to be a feature of most BMWs and Audis.

LOL.  I suspect the indicators don't work either.

FlorayG

Take it back today. That's a dangerous fault and needs diagnosing

1990xrider

droopsnoot said:

How old is the car? Is it manual or automatic? Is it in gear when it's creeping forwards? If you put it in neutral does it still creep forwards? Do the brakes work normally the rest of the time, and can you do an emergency stop? 

12 years, bought it used nearly 3 months ago, warranty runs out on August 23rd. It's an automatic. 
It's not creeping forwards as such,bit doesn't fully stop.  I haven't tried putting it in neutral yet. 99% of the time when I stop it stops and I just put my foot on the brake it corms to stop. But two times now I put my foot on the brake , it slows down to like to 1-2mph, but still insists on going forward. 

I've noticed one side of the pedal is firmer than the other 

Goudy

Sounds like a brake booster problem.

The brakes are "assisted" so you don't need as much force to operate the hydraulics.
Pressing the brake pedal should cause the booster to assist the master cylinder, easing the effort needed on the pedal.
Without this, you will need to produce all the effort to stop the car yourself with your foot/leg (and probably hands under the steering wheel helping force your leg down)

The booster usually works on vacuum, one side of the booster is held under vacuum, then when you press the pedal the vacuum on one side helps push the master cylinder.

A leak in the system will cause a loss of assistance as it can't hold vacuum.
If it's a fairly small leak you do get some assistance but it'll run out quickly.
A larger leak and you'll lose all assistance.

Does the pedal become harder to press or feel solid?

There are a couple of simple tests you can perform yourself without driving anywhere.
First would be to run the engine up a few minutes without pressing the brakes, then turn it off.
Pump the pedal 6 to 8 times (this gets rid of any vacuum that might be stored), the pedal should stiffen up.

Now hold the pedal down with just enough force to hold it at the bottom of it's current travel and start the engine.

You should feel the brake pedal drop a little as soon as the engine fires up.
If it doesn't you have a booster problem.

Another test would be you run the car up and press the brake pedal down once and hold it.
Turn the engine off and start counting to 30 seconds.
If the pedal moves before you've reached 30, you have a booster problem.

I once had an intermittent booster problem which only happened when raining hard.
Turned out to be a very small crack in the booster pipe and water was running down the scuttle making it worse in the rain.
Not really underpant friendly in the soaking rain!

1990xrider

Goudy said:

Sounds like a brake booster problem.

The brakes are "assisted" so you don't need as much force to operate the hydraulics.
Pressing the brake pedal should cause the booster to assist the master cylinder, easing the effort needed on the pedal.
Without this, you will need to produce all the effort to stop the car yourself with your foot/leg (and probably hands under the steering wheel helping force your leg down)

The booster usually works on vacuum, one side of the booster is held under vacuum, then when you press the pedal the vacuum on one side helps push the master cylinder.

A leak in the system will cause a loss of assistance as it can't hold vacuum.
If it's a fairly small leak you do get some assistance but it'll run out quickly.
A larger leak and you'll lose all assistance.

Does the pedal become harder to press or feel solid?

There are a couple of simple tests you can perform yourself without driving anywhere.
First would be to run the engine up a few minutes without pressing the brakes, then turn it off.
Pump the pedal 6 to 8 times (this gets rid of any vacuum that might be stored), the pedal should stiffen up.

Now hold the pedal down with just enough force to hold it at the bottom of it's current travel and start the engine.

You should feel the brake pedal drop a little as soon as the engine fires up.
If it doesn't you have a booster problem.

Another test would be you run the car up and press the brake pedal down once and hold it.
Turn the engine off and start counting to 30 seconds.
If the pedal moves before you've reached 30, you have a booster problem.

I once had an intermittent booster problem which only happened when raining hard.
Turned out to be a very small crack in the booster pipe and water was running down the scuttle making it worse in the rain.
Not really underpant friendly in the soaking rain!

Funnily enough I did try the first brake booster test yesterday and it did drop down. I'll try the second one 

Car_54

531063 said:

Slow down     

Tricky when the brakes don't work ...

Goudy

Certain BMW's, like the 3 series E90/91/92/93 had an issue with the seal between the master cylinder and brake booster servo.

Brake fluid gets into the servo and causes brake booster issues.
Owners notice it running low on assistance, so the brake pedal firms up and is harder to push the longer the pedal is pressed or if the pedal is repeated pressed in short succession.

Next up is a noticeable fluid leak from the master cylinder up under the dash.
If you follow the brake pedal up under the foot well, you will see it connects with a cleated pin and spring to the master cylinders piston/rod with a rubber cover over the piston/rod.

Quite often if it's leaking brake fluid can be seen on the rubber cover and you have your braking culprit.

The fix is to replace both the master cylinder as it's leaking and the booster servo as it's rotting from the inside.

Mutton_Geoff

If the brake servo is failing, this situation may be like those people who claim "the steering just locked up" when the servo fails (or engine stops) when all that is happening is the driver not realising just how much effort is actually required to operate the brake or steering without servo assist.

Not broken, just need to push harder!

1990xrider

Taken the car for the diagnosis, they say the rear left caliper is getting stuck, and the brake fluid levels are too high and of poor quality, as it was the rear brakepads which were recently replaced I wonder if that garage knocked something