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Now, given that the Dakota (like most trucks), are very light in the rear end when unloaded, it might not be surprising that losing one of the braking paths might feel like you only have 25% braking.
would have placed me at fault. Ok, as far as I have been able to trace on
my 1998 Dakota with the 318 V8,the brakes are configured as follows:
Master cylinder reservoir has 2 separate compartments..one for the back
and one for the front. So below a certain brake fluid level, the compartments are separate there.
The master cylinder has a dual piston (one for the front system and one for the back).
The o/p of the master cylinder goes to a combination valve that has separate
inputs and outputs.
The lines are crossed going into the input of this combo-proportioning valve with the REAR of the master cylinder going to the FRONT of the combo valve, and the FRONT of the MC going to the REAR of the combo valve.
The combo valve has a (two wire) fluid pressure switch fitted. so when the piston inside the combo valve moves from one side to the other, (due to more pressure on one side than the other, in case of a leak) the difference in pressure will activate the dash board BRAKE and ABS light.
The combo valve has two output lines coming out of it.
Combo valve: the FRONT line o/p goes to the HCU (hydraulic
control unit) that is controlled by the ABS controller. The HCU has a dump
valve solenoid and an isolation valve solenoid on it. The o/p of the HCU goes
down to the distribution block (on the frame) and a line goes from there to BOTH rear wheels. There is a flexible line that goes to middle of the axle and two lines come off it to each rear wheel cylinder. These are the ABS controlled
drum brakes. The front disc brakes are just normal brakes.
Combo valve: The REAR o/p line goes down to a distribution block (on the frame) and then two lines go off from it, one to each front wheel.
Since the only common place for fluid to be transferred between the front
and rear braking systems is the Combination valve, the fluid loss had to
be there, because the piston inside didn't move all the way(sticking?) and repeated brake pedal applications forced more fluid to be transferred from
the front (disk brake) system over to the ABS controlled system..which had a split line LEAK on the front to back line.
2000 dakota 3.9l 4x4 standard transmission
driving down the road one day the vss sensor went out: engine light on, no speedo, abs light on, brake light on but the brake wasn't on, shift light told me to shift into a higher gear when already in 5th. engine started stalling and backfiring. got it home, and replaced the sensor ($40).
all is good, except now the brake pedal is soft, and pulsates a bit(but it doesn't feel like the normal pulsating from the normal warped rotor problems) it feels more like a clunking in the pedal if that makes any sense. checked all the rotors and pads and have new rear brakes(shoes and drums) nothing looks bad that way....and this only started after the vss sensor was replaced... what else should I look into?
thanks in advance for any ideas
driving down the road one day the vss sensor went out: engine light on, no speedo, abs light on, brake light on but the brake wasn't on, shift light told me to shift into a higher gear when already in 5th. engine started stalling and backfiring. got it home, and replaced the sensor ($40). [/quote]
The ABS controller WILL set the ABS light and Brake light if it detects
a fluid leak/loss of braking pressure in the rear lines from the HCU (hydraulic control unit) which pulses the rear brakes, or loss of fluid pressure at the proportioning valve.
So it sounds like you had some sort of brake issue already,
but that shouldn't cause stalling and backfiring..that is something else
entirely.
The Vehicle speed sensor (in rear differential) sends pulses to the PCM
for the Speedo and to the CAB (Controller Antilock Brake) for RWD antilock
brakes. So if you have complete failure in the VSS, the PCM doesn't
get the pulses and it can't calculate the vehicle speed. The CAB can't
perform the ABS function, BUT you would still have regular braking power.
On the Dakotas, the rear brakes are drum brakes and they use
a RWAL (rear wheel anti-lock) system to prevent the rear drum brakes from locking up on you, causing a skid when you jam down on the power brakes hard.
[quote]
all is good, except now the brake pedal is soft, and pulsates a bit(but it doesn't feel like the normal pulsating from the normal warped rotor problems) it feels more like a clunking in the pedal if that makes any sense.
checked all the rotors and pads and have new rear brakes(shoes and drums) nothing looks bad that way....and this only started after the vss sensor was replaced... what else should I look into? [/quote]
The clunking is a mechanical issue with either the front calipers or the
rear shoes. If the pedal feels soft and there is brake fluid in the reservoir
up to the fill mark, then some possibilities are:
- Master cylinder leaking and air is getting in the lines somehow.
-one of the rear wheel cylinders is leaking fluid
- pinhole leak in the front to rear long brake line somewhere.
it needs to be checked thoroughly and the rubber line that connects
it to the axle lines. That rubber line could be abraded from wearing
on the axle and have a small pinhole leak
-ABS system (rear brake line and wheel cylinders have possibly got some air in there somehow.
-Front pads ok? If not, more fluid has to be transfered from the master
cylinder to the caliper pistons to achieve front braking and the pedal
WILL travel further to the floor to achieve braking power in that case.
Solution: a) Check pads for wear, replace if necessary.
b) bleed all 4 wheels at bleed screws on calipers/ wheel cylinders.
If the new shoes/drums were replaced recently, was the wheel cylinders ever bled?
That may be a challenge however, if the bleed screws
are seized from brake heat over the years.
c) Try resetting the CAB by disconnecting the positive battery cable for
10 seconds. If the CAB still thinks there is a brake issue, it won't
reset itself until the actual problem is cleared.
Yes the rear brakes were bled when they were changed a month before all that went down, we had to change the one cylinder at that time, and the brake line to it as well. front pads and rotors still looked good as well. no loss of fluid either. Should I maybe try to bleed them again even tho all we did was change the vss sensor?
I probably should say that my dashboard isn't light up like a christmas tree anymore, that was fixed with the new sensor also. no lights on at all. I still drive it, just not when there is a lot of traffic as I don't trust others to not pull out in front of me as I don't have much confidence in stopping quickly at the moment.
thanks for the help
That would introduce air into the braking system and it doesn't take much air to give
you a soft pedal.
I agree that the VSS sensor going bad and being changed has nothing to do with
a soft pedal. It would only give you a ABS and BRAKE indicator coming on as well
as a check engine, since the CAB requires the pulses coming in from the VSS to
function. IF the brake lines and brakes are free of air, you would get a normal
pedal feel and the hydraulic brakes would still function normally.
The soft pedal means that air has entered the system somewhere, it can
get in through the threads of the loose bleeder screw or the master cylinder
sucking in air when the fluid is too low.
Did you add fluid to the master cylinder and check it constantly while bleeding the rear
brakes? When bleeding, you must not allow the brake fluid level to get down to the point
where the master cylinder sucks in air...if it did, then there is now air trapped in the front calipers
and they must be bled to get rid of the air in the front lines.
When bleeding brakes, you need lots of brake fluid. You need a rubber tube fitting
tight on the bleeder screw going into a container of brake fluid. The end of the
rubber hose cannot be exposed to air..otherwise air will get in via the bleed screw
as soon as the fluid stops flowing when the pedal is down. As soon as the pedal
is released, the system starts sucking air wherever there is any tiny exposure to air.
If one person bled the brakes, then there is some likelyhood that air did manage
to get into the lines, and trapped inside the front calipers. If you didn't bleed the
calipers, then there is a good possibility that there is some air in one or both
of the front calipers which do 70% of the braking on the vehicle.
With two people , one pumping the brake pedal and the other checking the master cylinder
fluid level and operating the bleeder screw with a hose on the bleeder screw going into
a sealed plastic bottle containing brake fluid, there would be less chance of getting
air introduced back into the system.
(Instructions to person pumping pedal)
1. PUMP!
2. HOLD (dont release pedal until instructed)
Other person opens up bleeder screw and fluid and air go into a closed container
Other person QUICKLY CLOSES BLEEDER SCREW.
3. Ok (RELEASE
repeat the proces)s 6 to 7 times for each caliper/wheel cylinder
NOTE: You will require 2-3 containers of brake fluid for this, Do not pour old
fluid back into mastercylinder as it may contain moisture which will boil inside
if the brakes get too hot!
So to summarize: with one person pumping and holding the pedal down WITHOUT RELEASING,
the other person operates the bleed screw and fluid/air released into a bottle
containing some brake fluid.
Here is a youtube video on a spongy pedal tough brake bleed job.
Calipers incorrectly installed on this car. They ended up using
the reverse bleeding method and note the last section where the caliper bleed screw was
elevated to allow trapped air (still in the caliper) to finally make it's way out and allow
for a firm pedal.
http://www.youtube.com/watch?v=giENZskoE6w&feature=related
Tomorrow is supposed to be a pretty nice day here in NE Ohio, will try to bleed them tomorrow health permitting(my brother has some troubles)
I will let you all know if your ideas help thanks!
rear drum brakes. The convential split master cylinder has two lines that
go to the proportioning valve (which has the brake light PRESSURE switch),
then it goes to the HCU (Hydraulic Control Unit) which has the ABS isolation
solenoid and the ABS dump solenoid.
CAB operates both solenoid valves on the HCU.
The Normally open isolation valve blocks brake pressure from the Master
cylinder during anti-lock braking and a Normally Closed dump solenoid
valve is there to release pressure in the rear brake circuit when the
anti-lock operation is initiated. This is done at a fast speed so the
action of both valves basically "pumps" the brake fluid at a fast interval,
preventing the Bendix type drum brakes from (at least in theory),
locking up.
On the RWAL Dakotas, the CAB (Controller Anti-lock Brake) receives a speed signal from the VSS in the differential, to determine whether to initiate anti-lock action if the VSS is no longer providing pulses.
The speedometer is also driven (by the PCM) from pulses derived from
the VSS.
Code 65..main relay open (ABS) (open/shorted, poor electrical contact
or even a faulty relay)
Code 51 ..Rear isolation solenoid open
Code 52 ..Rear dump solenoid open
There can be internal CAB faults as well.
Brake light warning indicator on:
possible causes: (assuming no problem with dash indicator itself)
- pressure switch in proportioning valve out of position
(proporting valve issue or fluid leakage to rear brakes)
- faulty CAB
ABS indicator set (by CAB)
(assuming here that the indicator itself does not have a problem.)
open or short condition
condition in hydraulic system/lines to rear brakes that needs to be
checked out
or
defective VSS sensor
or
possibly a faulty CAB..try removing ABS fuse for 5 seconds or
disconnect negative on battery and see if it clears first
to Dodge RWAL..it has nothing to do with any kind of relay.
Looking at the the 2000 wiring diagram for RWAL brakes, there is NO
relay associated with the CAB. I checked the PDC on my 1998 Dakota
and confirmed this,
The CAB is fused by a 40amp fuse in the PDC. So obviously if the lights
are coming on periodically, the CAB is getting battery power through that
fuse to operate. It has it's own separate ground connections G101.
There is also a 10amp fused ignition- run going to it. This would be coming
from the ignition switch I believe.
The rear wheel speed sensor comes into it and so does the CCD +/- data bus that it communcates with the PCM.
The brake pressure switch has it's own separate ground and comes in from
the proportioning valve. The CAB also senses the brake switch.
The ABS specific codes (read from the ABS controller diagnostic connector)
are: 21 to 90. Some are generic. Some are applicable to 4W ABS systems,
some to RWAL (like the dakotas) and some to internal ABS controller issues.
I don't have any specific wiring information on the K-H RWAL HCU..
but this link will give you a pretty good idea of how it works on the Dakota.
http://www.aa1car.com/library/abs_kelseyhayes_rwal.htm
I had an answer all typed up and lost it.
Anyway, the K-H ABS control codes are NOT integrated with the OBDII diagnostic connector, as it was a proprietary RWAL ABS that most NA
vehicle manufacturers use. To read the ABS codes, you need an expensive
shop scan tool. ($2500). The CAB has it's own diagnostic connector for
that.
As far as the ABS codes..the link below will give you a explanation for
each code once you enter the make,model, year and abs code.
(ABS codes 21 to 89)
http://www.wellsve.com/custom_searches/abs_troublecodes.php?make=Dodge&model=Dak- - - - - - - ota&year=2000&code=51&confirm=1&submit.x=21&submit.y=23
As far as I know the solenoid/valves on the K-H HCU are not individually
replaceable, and these are pretty expensive units, so you would want
to make sure that is what is faulty first.
from these used parts places..they offer a 1 year guarantee..that's
what I would do if it was mine.
http://www.automotix.net/usedautoparts/2000-dodge-dakota-abs_control_modulepump-- inventory.html
be sticking or faulty. Probably some corrosion from moisture in the
brake lines. This will occur over time if the brake fluid is not replaced
periodically (every 2-3 years). Time to replace it I would think.
I've never tried reading the ABS codes, because all I have is the elcheapo
OBDII code reader and it doesn't pull the codes from the ABS controller
like the more expensive shop scan tools. I'm not going to invest $2500
for a more extensive set of tests, when I rarely have an ABS fault on mine.
My only time was when the rear brake line failed this summer after 13years, and after replacing it and both wheel cylinders,
bleeding the braking entire system, it's been fine No ABS or Brake indicator.
have a brake fluid level sensor. It uses just a compartmentalized front/rear
standard master cylinder used for many years with a dual braking system.
The ABS controller senses only two inputs. Pulses from the the VSS sensor
in the diff and a brake pressure switch located on the proportioning valve
provide input to the ABS controller (CAB)
If the rear wheels lock up, the differential is no longer turning and their
will be no pulses coming into the CAB, so it starts to initiate ABS
braking on the rear wheels for a RWAL system.
If the VSS is no longer functioning and the ignition is still on,
it may think that that is a wheel lockup if the vehicle is moving and continue with ABS. The speedometer not working or erratic would be another indication of a VSS problem.
If there is a fluid loss in the front or rear brake system, the differential
fluid pressure switch will activate and it will turn on the ABS and Brake
indicator.
Lifting the battery and resetting the controller only works if there are
no faults present. If the brake pressure switch is still operated one
way or another, signifying an open brake line somewhere, the
ABS and Brake light will stay on until the braking system is repaired and
bled.
ABS/Brake indicators being on. As long as the fluid doesn't drop down
inside the reservoir to the point that the master cylinder is sucking in air, the possible
reasons for the ABS/BRAKE light coming on..could be:
1. You have a pressure leak somewhere in one of the lines, or calipers
or wheel cylinders
2. Proportioning valve is stuck in one position?
3. VSS sensor not providing adequate pulses to the CAB. If this was the
case, the speedometer gets affected as well, since the same sensor
is used to calculate Vehicle speed by the PCM.
4. HCU (ABS pump) fault in either the isolation or dump solenoid valves.
5. ABS controller itself..although this is much lower probability.
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