1987 BMW 325E Brake Pressure Build Up

I am experiencing a problem where the brakes lock up after about four
to five miles of travel. I was told that the problem could be
resolved by replacing the master cylinder. I did, but the problem
continues. The only way to get going, is to release the pressure via
the bleeding valves. This works sometimes for an eighth of a mile or
sometimes up to ten miles. I removed all the relays from the ABS unit
with no luck.

Is there someone who has experience this problem? How was it resolved?

On 24 May 2007 07:49:04 -0700, wrote:

>I am experiencing a problem where the brakes lock up after about four
>to five miles of travel. I was told that the problem could be
>resolved by replacing the master cylinder. I did, but the problem
>continues. The only way to get going, is to release the pressure via
>the bleeding valves. This works sometimes for an eighth of a mile or
>sometimes up to ten miles. I removed all the relays from the ABS unit
>with no luck.
>
>Is there someone who has experience this problem? How was it resolved?

Brake vacuum servo is leaking................

> wrote in message
...
> On 24 May 2007 07:49:04 -0700, wrote:
>
>>I am experiencing a problem where the brakes lock up after about four
>>to five miles of travel. I was told that the problem could be
>>resolved by replacing the master cylinder. I did, but the problem
>>continues. The only way to get going, is to release the pressure via
>>the bleeding valves. This works sometimes for an eighth of a mile or
>>sometimes up to ten miles. I removed all the relays from the ABS unit
>>with no luck.
>>
>>Is there someone who has experience this problem? How was it resolved?
>
> Brake vacuum servo is leaking................


Please, tell us more. I've never heard of this, and I'm not sure what
part(s) you are talking about, and how they play with the rest of the
system.

Brake master cylinder would not cause this.

What are the EXACT symptoms you experienced? 'Brakes lock up' is a pretty
vague description.

Going by your current symptoms, it's nothing more that a seized caliper.



> wrote in message
oups.com...
>I am experiencing a problem where the brakes lock up after about four
> to five miles of travel. I was told that the problem could be
> resolved by replacing the master cylinder. I did, but the problem
> continues. The only way to get going, is to release the pressure via
> the bleeding valves. This works sometimes for an eighth of a mile or
> sometimes up to ten miles. I removed all the relays from the ABS unit
> with no luck.
>
> Is there someone who has experience this problem? How was it resolved?
>

Nedavno Haydon napisa:

> Brake master cylinder would not cause this.


I had a similar problem once with my Audi. All four wheels would lock
after about 20 minutes of travel. It seems that a problem was that my
"mechanic" filled up brake reservoir with wrong type of brake fluid,
that caused problem with rubber seals, and return spring was not able
to return cylinder back. I changed master cylinder and problem went
away.




--
___ ____
/__/ / \ ** Registrovani korisnik Linuksa #291606 **
/ / \/ /\ \ ** Registered Linux user #291606 **
/__/\____/--\__\ ** http://counter.li.org/ **

Pretty strange behavior allright. I see that the Bentley manual does list
this condition under trouble shooting and suggests that it may be caused by
the master cylinder although I don't personally understand how that would
happen. If it was a seized caliper it would probably only happen to one
wheel unless the car has been sitting unused for a long period of time. Do
all the wheels get hot or just one?? It seems like you have ruled out the
antiskid controller and the master cylinder so the only thing left is the
vacuum assist. You might try removing and plugging the vacuum line the next
time it happens to see if that fixes it. Just remember that you won't have
the power assist with the vacuum disconnected.
Good Luck and please let us know what the problem turns out to be.


> wrote in message
oups.com...
>I am experiencing a problem where the brakes lock up after about four
> to five miles of travel. I was told that the problem could be
> resolved by replacing the master cylinder. I did, but the problem
> continues. The only way to get going, is to release the pressure via
> the bleeding valves. This works sometimes for an eighth of a mile or
> sometimes up to ten miles. I removed all the relays from the ABS unit
> with no luck.
>
> Is there someone who has experience this problem? How was it resolved?
>

Jack wrote:

> Pretty strange behavior allright. I see that the Bentley manual does list
> this condition under trouble shooting and suggests that it may be caused by
> the master cylinder although I don't personally understand how that would
> happen.

The master cylinder has a relief port in it - that relieves brake
pressure when you let up on the brake pedal. It basically opens the
brake circuit(s) to the reservoir. This same port is also how the system
is kept full as pads wear and the caliper pistons move out.

If this port is plugged up, or the pedal isn't returning fully to the
top position, it will cause the symptoms described.

I would check:

1. Is there anything restricting the movement of the pedal? ie - can it
return fully up? (I'm thinking something like the pedal bracket got
bent, or the brake light switch is binding.) It doesn't take much to
cause this condition.

2. Has the entire system had a fluid flush? If not - it should. It's
possible there is some crap floating around in the system and it's
managed to find it's way back to the relief port.

Other than that - we probably need better diagnostics. When the wheels
lock up - do ALL of them lock up? (Temperature of the wheel is usually a
clue..) If it's all - it's doing this at a point common to all wheel
circuits - which narrows it down to the master cylinder (again) or the
ABS control hydraulic unit.

In article >,
admin > wrote:
> > Pretty strange behavior allright. I see that the Bentley manual does
> > list this condition under trouble shooting and suggests that it may
> > be caused by the master cylinder although I don't personally
> > understand how that would happen.

> The master cylinder has a relief port in it - that relieves brake
> pressure when you let up on the brake pedal. It basically opens the
> brake circuit(s) to the reservoir. This same port is also how the system
> is kept full as pads wear and the caliper pistons move out.

> If this port is plugged up, or the pedal isn't returning fully to the
> top position, it will cause the symptoms described.

I'm not convinced this could cause the brakes to lock on, though. Drag
slightly, yes. I'd be looking at a power assistance fault.

--
*He's not dead - he's electroencephalographically challenged

Dave Plowman London SW
To e-mail, change noise into sound.

On Thu, 24 May 2007 19:04:34 +0100, wrote:

>On 24 May 2007 07:49:04 -0700, wrote:
>
>>I am experiencing a problem where the brakes lock up after about four
>>to five miles of travel. I was told that the problem could be
>>resolved by replacing the master cylinder. I did, but the problem
>>continues. The only way to get going, is to release the pressure via
>>the bleeding valves. This works sometimes for an eighth of a mile or
>>sometimes up to ten miles. I removed all the relays from the ABS unit
>>with no luck.
>>
>>Is there someone who has experience this problem? How was it resolved?
>
>Brake vacuum servo is leaking................

When active in the trade I had a couple of cars in with similar problem of the
wheels (4) locking after a short drive. Releasing the pressure by the bleed
nipple as stated did get the vehicle mobile again but the problem in the first
was traced to a malfunction in the release valve of the brake servo not letting
air into the chamber when the brakes were released. Swapped out the servo and
no further trouble - DID NOT REPLACE THE MASTER CYLINDER.

Second vehicle with similar problems had a leaky master cyl and needed either a
new one or seals. We stuck a new one on and all was well for about 2 weeks then
another tow in for locked brakes so I swapped the servo and no problems with the
brake till the guy sold the car some 4 years later.

I agree there may be other causes but from experience it would be one of the
first places to look as a seized caliper would NOT lock all 4 wheels.

On Fri, 25 May 2007 16:00:36 +0100, "Dave Plowman (News)" >
wrote:

>In article >,
> admin > wrote:
>> > Pretty strange behavior allright. I see that the Bentley manual does
>> > list this condition under trouble shooting and suggests that it may
>> > be caused by the master cylinder although I don't personally
>> > understand how that would happen.
>
>> The master cylinder has a relief port in it - that relieves brake
>> pressure when you let up on the brake pedal. It basically opens the
>> brake circuit(s) to the reservoir. This same port is also how the system
>> is kept full as pads wear and the caliper pistons move out.
>
>> If this port is plugged up, or the pedal isn't returning fully to the
>> top position, it will cause the symptoms described.
>
>I'm not convinced this could cause the brakes to lock on, though. Drag
>slightly, yes. I'd be looking at a power assistance fault.


Thanks Dave..................