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Brake Bleeding with ASR

Brake bleeding for ASR proceeds
just like brake bleeding with ABS,
and like that system bleeding is
most often needed to flush the
fluid. ItÕs not that brake fluid has a
shorter useful life with the traction
control systems; itÕs that there are
very expensive machined components
in the hydraulic circuit,
components lubricated internally
only by the brake fluid. You can
buy many drums of brake fluid for
less than the cost of the simplest of
the hydraulic units on any of the
traction control systems, so thereÕs
no economy in stretching the calendar
for a fluid flush. Earlier
vehicles with ASR called for a full
fluid flush every year or 12,000
miles, Òpreferably in the SpringÓ
(at

There is brake fluid under high
pressure in the pressure reservoir,
fluid that wonÕt come out by just
bleeding the brakes through the
wheel calipers. You have to bleed
the reservoir itself and flush the
pressurizing pump to get all the
fluid out.

HereÕs the brake-bleeding procedure
for a vehicle with ASR:
First, with the ignition off, release
any pressure at the reservoir. Do
so by opening the bleeder marked
ÒSPÓ on the hydraulic control
unit. Open this bleeder at least
one full turn and leave it open
until the fluid-flow stops. Then
close it. As with all brake bleeding,
use a hose to direct the flow
of waste oil into a container to
protect the vehicle paint.
Next, with a vacuum pump (or
even a turkey baster, permanently
retired from the kitchen) draw the
master cylinder fluid level down to
within 10 mm of the bottom of the
reservoir. DonÕt draw the fluid any
lower than this, or you risk introducing
air into the system, and
then your flush procedure will be
unnecessarily complicated to
pump the air through and out.
Connect a pressure bleeder to the
master cylinder reservoir (or top it
up with clean fluid, if you prefer to
bleed using the pedal and an assistant).
Mercedes-Benz technical
information suggests a fluid volume
of 80 ccÕs per caliper if there
is no air to flush from the system
and 500 ccÕs per if there is.
Considering the replacement cost
of the mechanical and electrical
hydraulic-circuit components, you
may want to incline to the latter
figure in either case.

ASR systems using a pressure reservoir
(not all!) have a bleeder marked
ÒSPÓ on the hydraulic unit. Step One
in flushing the brake fluid is to open
that bleeder one full turn until all

the brake fluid stops flowing.

Once clear, new fluid flows from
each caliper bleeder, confirm that
the reservoir holds enough fluid,
reopen the bleeder marked ÒSPÓ
on the hydraulic control unit (protective
hose still connected) and start the engine. The pressurizing

reservoir cap is clear.

When you all say "power bleeder" are you just talking about a hand-operated vacuum pump (MityVac)?

__________________
"There are a lot of pebbles on the beach, but there's a Little Rock in Arkansas."

Logan

1983 300D Turbodiesel
1976 300D Rustdiesel

No.
Have a look at the picture in the first post.
We're talking about a positive pressure system, not negative, i.e. vaccum, such as the Mity/Vac.

__________________
2007 C 230 Sport.

Is there a link to that web site for the pressure bleeder???
That would be a great thing for all the bikes that I work on. Motorcycles brakes do thins real fast and like clock work. My ZX14 clutch fluid is all ready dirty and my bike has about 4K on the clock.

http://www.motiveproducts.com/

Seems like a simply idea, simple enough to duplicate in house,,, only question,,, how many psi do you pump up the positive bleeder to and what else do you do??

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There was another recent thread, where Arthur Dalton (Former MB Service Writer or Shop Foreman) recommended 15 psi. I had been using 30 psi. He pointed out that he had seen the plastic reservoirs rupture. I will now be using 15 psi.

Steve

The Motive pressure bleeder instructions states 10psi max. That's what I used and it worked perfect.

Thanks for the link...

At both dealerships I worked at, they required the technician to remove the resevoir and replace the grommets that seal the resevoir to the master cyllinder.

With the resevoir removed, plug the bottom holes with your fingers and fill with clean brake fluid a couple times and shake it up alot to break up any debris, and do that repeatedly till clean.

You can also run the revoir under hot water for a while to remove all residue, and it will look as good as new afterwards, just be sure to blow all the water out with compressed air before reinstalling.

Then we replace the grommets and put the resevoir back on.

The refill with brake fluid.

I always pump up my pressure bleeder to 15 psi not 20 as I have seen resevoir grommets pop and leak at the resevoir at 20 psi.
This is also a good reason to replace the grommets prior to applying pressure.

Also lay a towel on top of the unit and resevoir when pressure is applied in case a hose pops oss the bleeder or a grommet leaks so brake fluid does not get all over the paint and glass if there is a blowout.

I5 psi is plenty pressure to pump out the old stuff.

I always start at the wheel furthest from the master cyllinder and work my way forward.

Then I do them all a second time for good measure.

Always pump up brake pedal prior to driving off into the sunset after this repair, and check for leaks immediately after the test drive.

Keep in mind ,this job can turn into a nightmare on some of the older 107 cars and 126 cars.

I've seen master cyllinder seals blow out, brake caliper hoses plugged up, and caliper piston seals leak during this process, that is another reason to go with 15 psi.

Do you have to pump the brakes or anything like that, or simply build up pressure and open a bleeder?

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No pumping required .
That is what pumping does, it creates pressure to move the fluid.
..but here is the advantage to a pressure bleeder, specially on an older master ..the piston in the master has a travel pattern and that keeps that part of the master well sealed and clean..but when you pump up the brake pedal to bleed the system, the piston/seals go beyond the normal travel in the master and that is when the seals tear and the dirt gets dislodged from the master walls..none of this happen with a pressure bleeder b/c the seals and piston are not required to move..the pressure from the bleeder do all the fluid movement work..much better and no after bleed system damage...

brake fluid flush every 2 yrs is a very good idea - but you probably wont notice a measurable difference in braking performance or feel b4 & after fluid flush.

btw, this is a fantastic DIY procedue to learn, yes brakes are a critical safety issue, but if you go to a dealer for a brake flush, chances are it'll be a novice HS grad kid who'll do the brake flush, master techs wont touch simple things like this.

__________________
Current cars:
2001 MB E55 AMG
2003 Honda S2000
2000 Honda CRV

Gone but not forgotten:
2004 BMW 325i 5sp sport
1999 BMW 540i sport
1997 MB E420
1995 BMW M3 coupe

I dunno. After having replaced the calipers in my 300SD I quite honestly think brake fluid is cheap insurance. Its easy to change calipers and such but in another 25 years when your looking at cleaning or replacing brake lines thats not as easy of a situation.