Weird brake issue, wondering if anyone has experienced this?

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scoTT la rock
Posts: 14
Joined: Thu Aug 16, 2018 2:28 am
Location: New Jersey

Weird brake issue, wondering if anyone has experienced this?

Post by scoTT la rock »

Happy weekend friends!

So Friday I took my car out for a long drive to burn off the old gas, and I noticed something strange with the brakes.

The brakes were working fine for most of my 40mile trip, but twice I had something strange happen. I would be on the highway, put my foot on the brake pedal, and it would be “stuck” and not move down for a few seconds. After some firm pressure the pedal would travel down and the car would brake normally. This happened 3 times during the trip and was a little scary because the car didn’t immediately brake.

Anyone experienced anything like this? As I just recently purchased this car, I had it at a very reputable bmw shop who gave it a once-over a few weeks back and said everything is in top shape.

Any ideas? thanks!
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Brucey
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Joined: Fri Apr 09, 2004 7:17 am
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Re: Weird brake issue, wondering if anyone has experienced this?

Post by Brucey »

I would check the pedal box for cracks. I also would not drive the car until the problem is resolved.

If the pedal box is not cracked the next thing to look at is the servo (booster). If this is faulty, or the hydraulic accumulator is faulty, the brakes can fail to work with servo assistance in the normal way.

Without servo assistance, the brakes still work, but weakly, and feel 'wooden' with much reduced pedal travel and braking for any degree of pedal effort. The servo may still help with the braking but the response will be delayed and if the engine is not turning fast and/or the steering is being turned there won't be a lot of oil from the pump available to operate the servo with.

A simple test for a working accumulator is to run the engine for a few minutes, and apply the brake pedal a few times to get a feel for it. Then run the engine half a minute more and without touching the brake pedal again

a) turn the engine off
b) remove the PAS reservoir cover and check the oil level. There should be no oil visible above the filter screen
c) apply the brakes fully. If the accumulator is working normally the brake pedal should feel 'normal' for 12-20 brake applications.
d) after that number of brake applications the pedal should go hard
e) check the oil level in the reservoir; it should now be almost brim-full
f) run the engine again and check the oil level once more; after the engine has been running for ~30s the oil level in the reservoir should have dropped again, meaning that the accumulator is now fully charged.

If the pedal is hard from the start then the accumulator is probably not working and nor will the brakes, properly. The oil level won't change as described either.

Failed accumulators are commonplace. I think that if the correct oil (Dexron ATF) is not used in the system then this causes failure but they can also die of old age.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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