Does your brake pedal slowly sink to the floor?

chrispitude · **Posted:** Thu May 15, 2008 7:44 pm

I noticed something in the CRD today. When the CRD is idling in park, if I press the brake pedal hard, the pedal quickly sinks to where it engages and then will slowly sink all the way to the floor (takes maybe ten seconds). I don't recall this ever happening on any other vehicle I've owned.

Does your CRD do this?

- Chris

valoflyby · **Posted:** Thu May 15, 2008 7:59 pm

Yeah, it happens on mine too. I don't like it either. It doesn't seem to prohibit "normal" braking. It has done this since 2/05 w/ many a complaint to my service manager. The brakes have been bled several times w/ no change in symptom.

Honestly, I don't know what I hope to hear in the replies of others. "Yeah, mine does that too" will make me feel a little better, but I'd prefer a firm pedal.

KeighJeigh · **Posted:** Thu May 15, 2008 8:28 pm

Yep - although not all the way to the floor. But that does not bother me as much as the brake hardening up if you feather it rapidly - which I assume is due to the vacuum not being able to keep up with demand from the power brakes.
I have taken it to the stealer to complain about both issues and, as usual the answer is "Not able to reproduce problem described by customer. No apparent malfunction. Next please."
Either way, I have never had trouble stopping.

tjkj2002 · **Posted:** Thu May 15, 2008 8:59 pm

From the FSM......

Quote:

PEDAL FALLS AWAY
A brake pedal that falls away under steady foot
pressure is generally the result of a system leak. The
leak point could be at a brake line, fitting, hose, or
caliper/wheel cylinder. If leakage is severe, fluid will
be evident at or around the leaking component.
Internal leakage (seal by-pass) in the master cylinder
caused by worn or damaged piston cups, may
also be the problem cause.
An internal leak in the ABS or RWAL system may
also be the problem with no physical evidence.

Quote:

DIAGNOSIS AND TESTING - MASTER
CYLINDER/POWER BOOSTER
(1) Start engine and check booster vacuum hose
connections. A hissing noise indicates vacuum leak.
Correct any vacuum leak before proceeding.
(2) Stop engine and shift transmission into Neutral.
(3) Pump brake pedal until all vacuum reserve in
booster is depleted.
(4) Press and hold brake pedal under light foot
pressure. The pedal should hold firm, if the pedal
falls away master cylinder is faulty (internal leakage).
(5) Start engine and note pedal action. It should
fall away slightly under light foot pressure then hold
firm. If no pedal action is discernible, power booster,
vacuum supply, or vacuum check valve is faulty. Proceed
to the POWER BOOSTER VACUUM TEST.
(6) If the POWER BOOSTER VACUUM TEST
passes, rebuild booster vacuum reserve as follows:
Release brake pedal. Increase engine speed to 1500
rpm, close the throttle and immediately turn off ignition
to stop engine.
(7) Wait a minimum of 90 seconds and try brake
action again. Booster should provide two or more vacuum
assisted pedal applications. If vacuum assist is
not provided, booster is faulty.

Quote:

POWER BOOSTER VACUUM TEST
(1) Connect vacuum gauge to booster check valve
with short length of hose and T-fitting (Fig. 34).
(2) Start and run engine at curb idle speed for one
minute.
(3) Observe the vacuum supply. If vacuum supply
is not adequate, repair vacuum supply.
(4) Clamp hose shut between vacuum source and
check valve.
(5) Stop engine and observe vacuum gauge.
(6) If vacuum drops more than one inch Hg (33
millibars) within 15 seconds, booster diaphragm or
check valve is faulty.

warp2diesel · **Posted:** Thu May 15, 2008 9:01 pm

My '06 has ABS, I don't know if all the '05s had ABS or not. ABS will let the break peddle leak down to the floor under hard braking, this is what it does to prevent locking up the wheels.
Take note and let us know if you notice it more when you are driving near other drivers who act like they took driving lessons from, "Grand Theft Auto" instead of Drivers Education.
The only time mine has done this is when some idiot who wants to prove to the world that their car has ABS brakes is in front of me and stops hard or when I intentionally stomp on the brakes to test the ABS on wet Ice.
My Wife's TDI does the same thing.

tjkj2002 · **Posted:** Thu May 15, 2008 9:13 pm

warp2diesel wrote:

My '06 has ABS, I don't know if all the '05s had ABS or not. ABS will let the break peddle leak down to the floor under hard braking, this is what it does to prevent locking up the wheels.
Take note and let us know if you notice it more when you are driving near other drivers who act like they took driving lessons from, "Grand Theft Auto" instead of Drivers Education.
The only time mine has done this is when some idiot who wants to prove to the world that their car has ABS brakes is in front of me and stops hard or when I intentionally stomp on the brakes to test the ABS on wet Ice.
My Wife's TDI does the same thing.

From the FSM.....

Quote:

DESCRIPTION
ANTILOCK BRAKING SYSTEM
The purpose of the antilock system is to prevent
wheel lockup during periods of high wheel slip. Preventing
lockup helps maintain vehicle braking action
and steering control.
The antilock CAB activates the system whenever
sensor signals indicate periods of high wheel slip.
High wheel slip can be described as the point where
wheel rotation begins approaching 20 to 30 percent of
actual vehicle speed during braking. Periods of high
wheel slip occur when brake stops involve high pedal
pressure and rate of vehicle deceleration.
Battery voltage is supplied to the CAB ignition terminal
when the ignition switch is turned to Run position.
The CAB performs a system initialization
procedure at this point. Initialization consists of a
static and dynamic self check of system electrical
components.
The static check occurs after the ignition switch is
turned to Run position. The dynamic check occurs
when vehicle road speed reaches approximately 30
kph (18 mph). During the dynamic check, the CAB
briefly cycles the pump and solenoids to verify operation.
If an ABS component exhibits a fault during initialization,
the CAB illuminates the amber warning
light and registers a fault code in the microprocessor
memory.

Quote:

OPERATION
ANTILOCK BRAKING SYSTEM
During normal braking, the master cylinder, power
booster and wheel brake units all function as they
would in a vehicle without ABS. The HCU components
are not activated.
During antilock braking fluid pressure is modulated
according to wheel speed, degree of slip and
rate of deceleration. A sensor at each wheel converts
wheel speed into electrical signals. These signals are
transmitted to the CAB for processing and determination
of wheel slip and deceleration rate.
The ABS system has three fluid pressure control
channels. The front brakes are controlled separately
and the rear brakes in tandem. A speed sensor input
signal indicating a high slip condition activates the
CAB antilock program. Two solenoid valves are used
in each antilock control channel. The valves are all
located within the HCU valve body and work in pairs
to either increase, hold, or decrease apply pressure as
needed in the individual control channels. The solenoid
valves are not static during antilock braking.
They are cycled continuously to modulate pressure.
Solenoid cycle time in antilock mode can be measured
in milliseconds.

Your brake pedal should not slowly leak down,it's not normal,if it does you have a internal leak in the brake system.During ABS activation the pedal should vibrate/pulsate not slowly sink.ABS does not make you stop faster either(it actually increases braking distances),just prevents wheel lockup and there is zero evidence to prove ABS has helped decrease accidents,just makes drivers more stupid and taking ABS for granted that they will stop faster.

warp2diesel · **Posted:** Thu May 15, 2008 9:46 pm

....the only way to reduce the pressure to the individual brake is to allow fluid to leak by. Having a piston type high speed actuator controlled accumulator would never make it past the Bean Counters.
ABS will not effect the brake peddle when the vehicle is stopped :!:

But, a faulty leaking solenoid valve in the ABS system can produce the same symptoms as a bad master even when the vehicle is stopped. Plus it may come and go.

What I would do before I shelled out money or pulled a wrench out of my tool box to fix a leaky solenoid is find an open stretch of gravel/dirt road or gravel/dirt parking lot where I can go at least 35mph and stomp on the brake peddle as hard as I can to set off the ABS.

Since Chrysler wants to sell parts, they will not recommend this trick or acknowledge that it may work.

But the way the Laws of Physics apply to hydraulic brakes, one small fiber from a rag used to wipe up a spill on the top of the master cylinder reservoir opening can cause the solenoid valve to leak and the peddle to go down.

1) Try the free fix first. Like the stomp on the brakes method above, the offending fiber can go live in a caliper for a long time and not effect the system.
2) The cheap but not half @$$ed fix next. Like a brake fluid flush, removing contamination may fix it. BMW recommends flushing brake fluid every two years.
Note: A bad master cylinder will not survive a fluid flush and will quit playing cat and mouse games with you.
3) Then test, double check, and be ready to spend the money when the tests determine the proper diagnosis.

Steve

Uffe · **Posted:** Fri May 16, 2008 2:34 am

KeighJeigh wrote:

Yep - although not all the way to the floor. But that does not bother me as much as the brake hardening up if you feather it rapidly - which I assume is due to the vacuum not being able to keep up with demand from the power brakes.
I have taken it to the stealer to complain about both issues and, as usual the answer is "Not able to reproduce problem described by customer. No apparent malfunction. Next please."
Either way, I have never had trouble stopping.

Have you then tried brakes that lost too much power on a parking lot?

My scenario is as follows:

Drive too far from an empty space, put tranny in R, maneouver, brake!, put tranny in D and suddenly I have no braking vacuum to stop me from entering the store itself!

I thought it could be a vacuum leak but I'm sure it isn't just that anymore. After I plugged my EGR vacuum hose the controls in the dash regarding air venting are responding much faster (they are vacuum controlled, so I guess if they are faster the vacuum line is sealed properly).

USNA · **Posted:** Fri May 16, 2008 6:36 pm

Thanks for the tread, and replies. now I have the information to fix mine as well. Hopefully

Does your brake pedal slowly sink to the floor?

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