Intermitant brake hardens at low revs and brakes fail

[Maggie Bartlett]

Joined site hoping for some help.  My 2007 1 series has developed an intermittent problem on braking when revs are low.  Brake goes really hard and car keeps moving.  AA said it was ABS controller so sent it for checking and no fault found.  Brake fluid ok.  Diagnostic check showed  a bulb but no bulbs out.  Mechanic took car 5 miles without the problem but when slowing right down fault back again.  Would really appreciate your help and advice.

[Greydog]

Morning Maggie and welcome 

Has anyone looked at the Servo? Vacuum in the servo creates brake assistance when the peddle is pushed. As your issue is at  low revs I would suspect a split or perished/cracked vacuum line or failed non return valve from memory there is also a differential pressure sensor on some models. Low revs = low vacuum levels so a cracked or perished line or seal will result in no assistance = hard pedal. If all the vacuum lines .and seals are OK check if you have the pressure differential sensor (there will be a spur off the main vacuum line near the servo to the sensor) it may be faulty, though it should throw a code I would think.

You could look on www.realoem.com put the last 7 digits of your Vin in the search box it's an online parts list but it will show a small drawing and list of parts to help you see where stuff is and make sure you get the right parts for replacement 

Hope this helps

Dave

[Maggie Bartlett]

Hi Dave, 

Thank you so much  for the welcome and fast response .  It's  a huge relief  to have  probable  answers to  this.   Will  send  this  to  the mechanic  and hopefully  my car will be safe  again  soon. 

Maggie  😊

[Bimmer Owners Club]

Hi Maggie....welcome to the Club

I totally agree with Dave's diagnosis of the Servo or vacuum line attached to it.
Also, if it has a Diesel engine then I would also look at the exhauster (vacuum pump) to see if that is performing efficiently.

Let us know how you get on with it all

Cheers,    Trevor

[Maggie Bartlett]

22 hours ago, Bimmer Owners Club said:

Hi Maggie....welcome to the Club

I totally agree with Dave's diagnosis of the Servo or vacuum line attached to it.
Also, if it has a Diesel engine then I would also look at the exhauster (vacuum pump) to see if that is performing efficiently.

Let us know how you get on with it all

Cheers,    Trevor

Dave,

Thank you so much  for the welcome and fast response .  It's  a huge relief  to have  probable  answers to  this.   Will  send  this  to  the mechanic  and hopefully  my car will be safe  again  soon. 

Maggie  😊

[Maggie Bartlett]

Thank  you  Dave and Trevor,   Mark  has  checked  all  the  tubing and there is no wear or leak.   The valve  is fine  too  but there isn't a  sensor on my 118.  Could it be the vacuum pump itself  and how  costly  would it be to replace.   Thank you for your help.

Maggie. 

Edited September 18, 2018 by Maggie Bartlett
Spelling

[Greydog]

Hi Maggie 

Try, engine off pump the brake 5/6 times, then keep pressure on the brake and start the engine, the pedal should feel softer. If it doesn't then I still suspect the servo its pipe work or the check valves or possibly the vacuum pump.

Due to the vacuum created the pipe work may look good from outside but it can collapse internally restricting operation. Particularly if the brakes operate normally at higher engine revs, when your mechanic checked for codes did they use BMW diagnostic software? 

Dave

[Maggie Bartlett]

Thank you for your advice guys, the mechanic replaced the vacuum pump after checking everything else and my car is now back on the road.

Maggie.

[Greydog]

Yay Good news Maggie

Hope it wasn't to painful on the wallet, here's to you enjoying many miles trouble free

Dave  

[Maggie Bartlett]

It was  down  to you  both  that  we got  it sorted  so quickly 😊  I am so glad  I found this forum.

[Greydog]

Our pleasure Maggie, the object of the Forum is always to have pool of knowledge for us all to fish for answers in

Dave

[Bimmer Owners Club]

Glad your car is sorted now Maggie and also that it wasn't too expensive in the end.

On 9/28/2018 at 12:34 PM, Greydog said:

Our pleasure Maggie, the object of the Forum is always to have pool of knowledge for us all to fish for answers in

1

Great analogy Dave....will have to remember that one 🙂