Brake issue 1984 733i

[jim5723]

Hello all. I have a brake issue. When I hit the brakes suddenly with force, no stop (heart attack)! However, if I gently press on the brakes, I have stopping power.

My steering is also a little wiggley(loose). Are these related?

Brake Booster?

Please advise.

Thanks,
Jim

[mechy1barry]

if pedal goes to the floor, suspect master cylinder,or very loose wheel bearings.

[jeffreyb4me]

from your description you 'brake pressure accumulator' is bad. this unit stores boost pressure for at least 10 pedal applications if the engine stalls. to be sure, with the engine idling quickly JAB the brake pedal.....you'll see a 'BRAKE' warning lamp flash on the R/S of the cluster. this is warning you of low boost pressure. the reason it fels good on 'slow' pedal braking is because the steering pump can keep up with the pressure/volume demand. on 'quick/hard' applications the system needs the stored pressure of the 'accumulator' to keep up with the system's sudden requirement for pressure [+100bar] and volume......this isn't an easy do-it yourself job and ypur steering sounds like a linkage wear issue that should be checked SOON.......jb.

[jim5723]

I dont recall seeing the brake light come on. But from you described, it fits the accumulator broblem. I'm just wondering if I need to replace a $350.00 booster AND the $150 accumulator? I guess I'll try the accumulator first and see if it corrects the problem.

BTW, my brakes dont go to the floor (mechy1barry).

Thank you,
Jim

[jim5723]

I forgot to ask...
Could it be the Pressure Regulator ($450.00)? God, I hope not!

And how can I test these parts to MAKE SURE it's that particular part thats bad. I dont like trial and error (too expensive).

Thanks again!
Jim

[mechy1barry]

if not already tried.take the pipe of the brake servo that supplies vaccuum to it start engine and see if you have a good vac at the end,if not trace back to inlet.

[jeffreyb4me]

NOTE : DON'T PULL ANY LINES ON THE HYDRAULIC SYSTEM ** UNTIL ACCUMULATOR PRESSURE IS EXHAUSTED ! ! ! !
now, your symptoms are classic for a 'dead' accumultor, i.e., the metal diaphram eventually fails and it looses it's nitrogen charge [>1,500 psi] into the 'steering' fluid "harmlessly". htere an expensive gauge manifold and elaborate procedure for testing and diagnosing the system but an early understanding of these boost/hydro. systems fairly common in some euro makes let me develop an accurate testing method by symptom alone.
******in short:
a.] a boosters only failure will be leaking.

b.] you're experiencing an accumulator failure.

c.] the 'pressure' regulator or D/S Regulator can
fail but is rare and usually causes other symptoms your not experiencing.

I BELIEVE YOU SHOULD REPLACE YOUR 'ACCUMULATOR' AND THE TWO SWITCHES ON THE 'PRESSURE REGULATOR'.....[ both can be done on the car ]...........................jb.

[jim5723]

1. Are there any tricks to replacing the accumulator? Or does it just unscrew?

2. Should I wonder why I need to replace the two switches on the Pressure Regulator, or just do it?

Thanks for all your help!
~Jim~

[jeffreyb4me]

for #2], they leak and they fail, you mentioned you didn't see a 'BRAKE' warning lamp flash when you 'jabbed' the pedal, this is probably why, IT SHOULD HAVE [ failed 'low press.' switch ] which is the most important.

for #1] well, yes, uhhh, okay. i developed a 'trick' many years ago. it works on most any well mounted [ like yours and other BMW's exept 750iL ] high pressire 'hydro' boost sytem, peugoet, maserati, citroen, etc...

++ THE ACCUMULATOR MUST BE KNOWN 'DEAD' ++
++ I REPEAT ! ! KNOWN 'DEAD' ++

+ LOST IT'S NITROGEN CHARGE BY TESTING +

Okay, warning given, it's not really dangerous, it won't ex- or implode but, well you know, anyway,

you've done the 'testing' i.e., run the engine to build system pressure then shut it off. step on the pedal. IF it doesn't 'sink' on the FIRST application the ACCUMULTOR is 'dead', [ lost it's charge ] A GOOD accumulator will allow you to pump the brake pedal 10 -20 times before you notice the pedal height rise up AND the pedal becomes very hard........this also tests the master cylinder but thats a different issue you've already addressed.

PROCEDURE: note: it looks hard to get to but i've done this over a hundred times and on every model.
1] engine off
2] pump the pedal HARD 25 - 30 times to expell any
residual system pressure [there's always a little]
3] from the top and at an angle to loosen the
accumulator [counter-clockwise], with a long
heavy & sharp chisle, [ i use an air-hammer ],
smartly smack the 'ball' a few times until it
loosens from the D/S Regulator, [ it will ]. then
finish unscrewing by hand a remove.
4] lube the new units threads, lube and install the
o-ring [lubed well with ATF] and install it onto
the D/S Reg. 'til almost hand tight. clean the
entire area with 'brake cleaner' and dry for a
good grip, then with one twist of your wrist, spin
it up tight. if you don't get it right [tight] the
first time, readjust your 'starting point' and do it
again 'til tight in one motion. you'll see what i
mean.
5] fill the reservior to the top, run the engine a few
min's lightly pumping the pedal, then shut it off.
pomp the pedal 20 -30 times and top off the
reservior and repeat+DON'T OVER FILL IT !+
level is always checked engine OFF and after
pedal has been pumped 'UP' ! !

sounds harder and 'trickier' than it really is and you'll
smile all the way to the bank.....................jb.

[jim5723]

Thank you very much!

I'll let you know how it turns out. I've got to order the parts...

~Jim~