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4839Re: [bmw e28] Brakes lockup, Some possible solutions

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  • e34535
    22 Nov 04:47
      --- In bmwe28@..., Gil Thereault <giln1oiw2001@...> wrote:
      >Hi Gil,John and Steve Thanks for the posts guy - a little more
      evidence for you.
      I inspected car thoroughly before auction to check for signs that it
      was not an original garaged 44000 miles vehicle - all points backed up
      the claim, service books would indicate little use over the last
      couple of years. Disc rotors showed NO signs of any heat effects at
      all, at this time - drove/stopped (when cold) beautifully on auction
      test drive. Problem raised its head in traffic after leaving the
      auction house - when I got the car off the road all 4 discs were
      smoking and blue. When the brakes "let go" on cooling, all 4 let go
      together(so I am thinking what ever is doing it is affecting all 4
      discs at once, and probably both brake circuits - (when these babies
      lock on( this happens progressively not suddenly) its back to 1st gear
      (auto), foot flat to the floor/maximum load on the motor/box to creep
      along at walking pace. Obviously this no way to treat a lady, as
      mentioned, if you then lift bonnet and wait maybe 10-15 minutes
      cooling the engine bay down the brakes will slowly release (all 4). I
      have had on one occassion, the brakes suddenly release (with a "clunk"
      from the vicinity of the booster while I had my foot flat to the floor
      against the brakes looking for a pull off spot (very interesting
      effect - like stalling up on the drag strip and sliding your foot off
      the brake pedal - BANG and we are away). I could maybe see problems
      from boiling brake fluid/calipers siezing when hot/overheated
      hydraulic fluid on the booster power side, BUT,and it is a big BUT, As
      mentioned I have tested it on cold start ups, brakes fine (roll car by
      hand, no binding, cold brakes/calipers/fluid (has had 2 brake bleeds
      now)/cold discs etc., and by the time the car has reached operating
      temp you cannot roll the car by hand , and in 15mins you cannot drive
      off at all. Lift bonnet at this time and hose only the booster with
      water and brakes will gradually let go (hosing the
      accumulator/pressure block and the master cylinder do not have any
      effect). Looks like it may be a surgical strike is called for
      (disembowlment of booster for starters). Would a faulty accumulator
      produce a hard high pedal all the time it is pressurised or be
      affected by heat?

      This car is starting to look like a reinCARnation of an old girlfriend
      - well kept, low mileage, great upholstery, tight suspension, but
      temperamental,with a personality (suspect) all of its own - and puts
      the brakes on hard just when your starting to enjoy it!

      > Hello All,
      > From my past experience, the high hard brake pedal issue is the
      brake accumulator. I have replaced mine twice in the past six years.
      You may have an issue with the regulator ?? from the noise you have
      described or it could have been due to the high temperature of the
      brake fluid in the regulator from the overheating of the rotor and
      caliper. I too have replaced the master cylinder as I also was
      experiencing the right front caliper locking up. I thought it was
      from the heat as well. I learned this after needless swapping out a
      good functional right front caliper. Do these things first (the easy
      things) then go further to the calipers and/ or the regulator.
      > Gil
      > 86 535i 192k
      > John Forbey <jforbey@...> wrote:
      > I don't know whether you will work on it yourself, but
      > I say if it has'nt been driven in a while the calipers
      > may have gotten what I call water spot that make them
      > bind. Take the calipers off and they have screws that
      > allow you to separate the halves. You can buy kits
      > pretty easy, maybe price online dealers to find
      > rebuild kits to replace the o-ring seals. There will
      > be an expanding rubber cup that seals the piston and
      > clasps around with wire clip. Clean the parts well
      > and make sure no rust. Use silicon brake fluid to
      > lubricate parts, seals before assy. This is just a
      > start; but if it has'nt driven in while may be what
      > needs to be done.
      > John F. Forbey
      > jforbey@...
      > --- e34535 <e34535@...> wrote:
      > > 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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