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Suspension & Braking
Have some questions about suspension or brake setups for your E46 BMW? Get all your answers here!

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Old 04-22-2018, 08:46 PM   #21
bmw9
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Lol this is every driver's nightmare however I think it is unlikely to happen to any of us. If it does, hope you have full coverage and enjoy your crappy 5000 check when insurance totals out your car.
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Old 04-23-2018, 01:05 AM   #22
Viperbcs
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I suspect the DSC activated due to system picking up there were no brakes, so obviously individual wheel braking could not work. Will know today but MC looks to be the culpret.

Brakefluid I did a year and half ago and pads in Nov. Level still right and no chance for contamination.
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Old 04-23-2018, 01:13 AM   #23
Viperbcs
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Quote:
Originally Posted by TobyB View Post
The abs computer monitors pressures and pedal position.
It's quite possible that it saw something out of range, and lit up.

While I agree an electronic failure's not impossible,
BMW (at least in 2002) was horrifically paranoid about
that, and unless abs went into ice mode or something
else odd that we haven't seen since the E30,
the electronics shut themselves OUT of the loop if they
go outside their normal parameters.

The classic failure is that the master cylinder fails- at some point-
so that both circuits are connected, and the system no longer has redundancy.
It still works, but when a sticky caliper boils the fluid in one wheel
or another, now the fluid vapor (usually water) displaces a bunch of
fluid, and now the entire system is useless. The offending caliper cools,
the driver's seat is cleaned out, and suddenly, brakes are back. USUALLY a bit
more spongy, but 80% of their former selves.

It's also not too unusual for an aggressive braker to lose just the front circuit to a cooked caliper,
and go right on through the intersection because the rears alone don't have a chance in hell of hauling
the car down from 80 kph to a stop in 40 meters. And the pedal's drop to NEAR the floor
is interpreted as a complete failure.

But that's all internet conjecture. Someone with some ability will have to diagnose
the thing, and that'll take having a car in front of them.

Mental note- next time I bleed the brakes, stomp on them with one
circuit open, and see if there's still the other circuit there...

t
Thanks, this made me think.
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Old 04-24-2018, 07:49 PM   #24
Metro81
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Quote:
Originally Posted by TobyB View Post
jfoj nailed it- stuck caliper AND probably internally leaking master.

That's about the only way a dual circuit system will totally fail.

t

This.

Had a caliper seize on my M3 while on a track event (of course it was at the end of the front straight), ASC/DSC dumped most all brake pressure to maintain stability and prevent a spin. This is why you get the DSC light and Brake light, and why they can extinguish after turning the car off and on again - until it detects the same fault. U replaced the caliper and the issue is gone.
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Old 04-24-2018, 10:11 PM   #25
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Quote:
Originally Posted by Metro81 View Post
This.

Had a caliper seize on my M3 while on a track event (of course it was at the end of the front straight), ASC/DSC dumped most all brake pressure to maintain stability and prevent a spin. This is why you get the DSC light and Brake light, and why they can extinguish after turning the car off and on again - until it detects the same fault. U replaced the caliper and the issue is gone.
Your seized brake caused lock-up the wheel, or boiling fluid and no brake? I guess you meant that seized caliper locked up the wheel and so the computer released all pressure to prevent spin out. Does this mean the OP's father locked up the wheel(s) and the system detected and released all pressure? This could mean a wheel rotating sensor was bad causing the computer saw it was locked wheel.
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Old 04-25-2018, 11:22 AM   #26
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About dual circuit brake systems. They've been mandatory fitment since 01 January 1968 with some doing diagonal split and most front/rear. Anyway, with my having 40+ years experience of owning European car service/repair shops, sudden pressure loss can only result from failure of a flexible hose, burst metal line, internal seal deterioration. Regardless of type of failure, partial braking should be present. BMW uses the more common F/R split, so my bet is rear braking is still functioning, albeit with considerably longer pedal travel.
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Old 04-25-2018, 03:21 PM   #27
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Originally Posted by FastBlack330 View Post
Anyway, with my having 40+ years experience of owning European car service/repair shops, sudden pressure loss can only result from failure of a flexible hose, burst metal line, internal seal deterioration. .
Read the post again -- it says the brake system was all back to normal after turned off the engine and run again.
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Old 07-02-2018, 01:49 PM   #28
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Had the same scenario with my wife's 2000 323i two days ago. I happened to be driving, and pedal just went 3/4 of the way to the floor and ABS light came on. Eased it home and checked brake fluid, it was full. We had to be at a party soon, so took the E46 Touring and left her car at home, did nothing but check for obvious leaks, etc.
Next morning I went out to further investigate and brake pedal was fine, brakes functioning properly and no ABS light.
Test drove it for like 25 miles and no issues.
Thinking I'll replace master cylinder and flush fluid.
Welcome any advice and will update if any changes...
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Old 07-02-2018, 02:51 PM   #29
Viperbcs
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Originally Posted by TrentW View Post
Had the same scenario with my wife's 2000 323i two days ago. I happened to be driving, and pedal just went 3/4 of the way to the floor and ABS light came on. Eased it home and checked brake fluid, it was full. We had to be at a party soon, so took the E46 Touring and left her car at home, did nothing but check for obvious leaks, etc.
Next morning I went out to further investigate and brake pedal was fine, brakes functioning properly and no ABS light.
Test drove it for like 25 miles and no issues.
Thinking I'll replace master cylinder and flush fluid.
Welcome any advice and will update if any changes...
In our case it was the master cylinder so guess yours the same. The mechanic once had such an issue and a blown internal seal sounds to be the culprit What is your mileage?
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Old 07-03-2018, 10:47 AM   #30
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Originally Posted by Viperbcs View Post
In our case it was the master cylinder so guess yours the same. The mechanic once had such an issue and a blown internal seal sounds to be the culprit What is your mileage?
163k miles
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