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4828Brakes lockup, siezing with under bonnet heat

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  • e34535
    20 Nov 17:53
      Hi, I am a new member and a BMW fan (tragic)from Australia, I have
      another e28 (aus delivered) among a stable of other BMW models (1x e34
      535i manual,2x 3.0si, 2x 3.0L) and have just bought at auction a UK
      spec 1986 e28, the car is low mileage (44000miles original with all
      books and service). I was wondering if anyone has had the problem this
      car is exhibiting before (my high mileage rather ragged aus spec e28
      has never given me any brake trouble like this). Being a UK spec the
      ATE hydraulic booster is on the drivers side(RHS above the exhaust
      manifold) - the aus spec car has the ATE booster on the LHS (US/Euro
      Left hand drive style)

      Problem: When I picked the car up I suspect it had been not used very
      regularly prior to its sale - brake discs showed no overheating, on
      driving it home I noticed that stuck in traffic the brakes started to
      squeal and bind - this got worse with a hard, high brake pedal(no real
      brake usage just stop start traffic) until the car was labouring
      against locked brakes, in 1st gear under full throttle to just keep
      moving. Bonnet up on roadside and many expletives/+*?@#%$_BMWs later
      I heard a series of metallic "clunks" from the area of the brake
      booster (this sound is easily heard inside the cabin), at this point
      the engine bay had started to cool down. I found then that the brakes
      had "let go" and the car could be driven again - until you applied the
      brakes (still some temperature in system)- lock up again - car can
      only be driven cold.

      Long story made short - 1. Had brakes professionally bled and took off
      that night to drive home (550kms) at country speeds (100km/h) - no
      brake troubles at all! (cold night/cool engine compartment) - thought
      it fixed, but next day same problem with engine heat again - bonnet
      up/ cool down / "clunk" / brakes free again ???

      Tested car by letting car heat up at idle for 15-20 minutes from cold
      (good pedal/brakes OK when cold), car not driven, no brake pedal use,
      result:- rock hard brake pedal again and locked brakes - placed trans
      in drive but car would not move at idle, ran cold water on the
      hydraulic brake booster(not master cylinder)and heard the light
      "clunks" brakes slowly let go in unison with "clunks" and car started
      to move under its own power.

      I am suspecting a faulty booster (or maybe Bomb/pressure unit), there
      is what appears to be a pressure valve on the return line on booster
      to the power steering reservoir - having never had the need or
      pleasure of dismantling a booster before I only guessing what is
      inside it.

      Has anyone had this problem before? - any help appreciated before a
      costly "suck it and see" replacement program is commenced. As I
      mentioned before the car is in 1st class condition for its 20 year
      vintage other than this problem.

      When things go wrong with an e28 they go WRONG! big time
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