Dodge: '97 Voyager - Brakes

Who put on the Master Cyl.?

"MamaB" <com> wrote in message
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Hi Harry.

A licensed mechanic (Dodge background) replaced the master cylinder; the
vacuum gasket for the power brakes is okay.

Is that why you asked? Have you a suggestion?
MamaB

Harry Balzak wrote: 

make sure there isnt a problem with boiling the brake fluid, if a rotor or
drum is locking up, it could cause excessive heat and boil the fluid,
causing air in the system
"MamaB" <com> wrote in message
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Thanks for the suggestion but the pads and routers were replaced also.
Any other ideas? The stick of dynamite is starting to look mighty good.
MamaB

maxpower wrote: 

Is the mechanic using a pressure bleeding system?
Did the bleeding include cycling the ABS?
By chance do you have a Traction Control System? Unlikely but could be.
I recomend and use www.alldatadiy.com online manuals

Thoughts,
For NON-traction control:
If the master cylinder seal is leaking it would effect the primary pump thus
air in RF+LR. Look familiar?

Didn't sound like the dealer was involved so I assume the mechanic did not
have a pressure bleed system or the diagnostic controller needed to cycle
the ABS in order to bleed it. Sometimes the dealer is expensive but they get
the job done. OTOH your mech may have done all this.

Your description of peddle to floor, and ABS pump stopping it, plus air in
..., leads me to a faulty master cylinder or at least one that was not bled
properly before being mounted on the booster. Note that the service bulletin
is specific re: the bleed procedure for the master cyl replacement.

I suspect the ABS is fine and likely does not need bleeding. given that it
stops the vehicle then the air is not btw the ABS and the slaves(wheels) so
it must be at the Master! I'd pull the master cyl and mount it in the vice
(by the flange) and bleed it IAW service bulletin.

info from alldata below but it you pay you get the rest and pictures<g>

Master:
NOTE: Two different size bleeding tubes are used depending on which type of
master cylinder the vehicle is equipped with. Vehicles equipped with
traction control use a center port master cylinder with a larger diameter
brake tube. Vehicles not equipped with traction control use a compensating
port master cylinder using a standard 3/16" diameter brake tube. Be sure the
correct size bleeding tubes are used when bleeding the master cylinder.
2. Install the Bleeding Tubes, Special Tool 6920 for a non traction control
master cylinder or Special Tool 8129 for a traction control master cylinder
on the master cylinder. Position bleeding tubes so the outlets of bleeding
tubes will be below surface of brake fluid when reservoir is filled to its
proper level.
3. Fill brake fluid reservoir with brake fluid conforming to DOT 3
specifications such as Mopar or an Equivalent.
4. Using a wooden dowel, depress push rod slowly, and then allow pistons to
return to released position. Repeat several times until all air bubbles are
expelled from master cylinder.
5. Remove bleeding tubes from master cylinder outlet ports, and then plug
outlet ports and install fill cap on reservoir.
6. Remove master cylinder from vise.
7. Install the filler cap from the master cylinder filler neck, on the
master cylinder fluid reservoir.
8. Install the master cylinder assembly on the power brake vacuum booster.
NOTE: It is not necessary to bleed the ABS Hydraulic Control Unit (HCU)
after replacing the master cylinder. But, the base brake hydraulic system
must be bled to ensure no air is entered the hydraulic system when the
master cylinder was removed


OPERATION
The master cylinder primary outlet port supplies hydraulic pressure to the
right front and left rear brakes. The secondary outlet port supplies
hydraulic pressure to the left front and right rear brakes. Note: primary is
closest to the booster.

Bleeding order
The use of this wheel sequence will ensure adequate removal of all trapped
air from the brake hydraulic system. (1st) - Left Rear Wheel (2nd) - Right
Front Wheel (3rd) - Right Rear Wheel (4th) - Left Front Wheel

Hi bobQ.

Comments are interspersed below........

bobQ wrote: 
Not sure; maybe just foot pedal 
Not sure 
No 
Thanks for this tip 
Very familiar .... however .... There were absolutely no signs of any
leaks..... NOwhere. Air is always in LF + RR ..... even after master
cylinder was replaced 
The local dealer WAS one of the 3 mechanics who have worked on this
problem .... he had his turn, too. 
2 of the 3 mechanics were qualified & experienced mechanics specializing
in Chrysler products. 
Air was bled at the wheels each time - it had to pass through HCU 
[this section snipped]

Given that the original MC was okay (since the problem continued after
replacing), all 4 wheel cylinders are okay, there's no evidence of leaks
anywhere and the problem surfaced immediately after hard-braking (at
slow speed) where ABS kicked in ..... can you suggest HOW the air was
getting into the system?

Further developments ..... after failing to solve the problem, with new
MC installed, have now installed a replacement HCU & controller for the
ABS. One day-trip out and everything seems okay BUT I'm keeping my
fingers AND toes crossed!!

THANK YOU for your interest and your valuable time in explaining the
bleeding procedure. I have every intention of passing this along to my
mechanic for review & comment (will let you know). Thanks for coming to
the aid of a "damsel in distress".
MamaB.

Sounds like the abs system is somehow letting air into the system IMO.

--
Mark
"MamaB" <com> wrote in message
news:v5Lrd.189451$nbnet.nb.ca... 

With the HCU (Hyd Cntr Unit) & ABS controller replacement (on this vehicle
that is a single system) you can be assured that the HCU got bled.

Could air get in a faulty HCU as in a loose fitting or seal. Not to likely
IMHO. If you didn't see a puddle of brake fluid under the drivers feet then
I'll assume no leak. If air gos in, fluid can come out.



Replacement flat rate on the HCU is 2.1 hrs so the total cost well over
$600. Ouch.



My theory. Since the brake pads/shoes got replaced after the incident then I'll
assume they needed replacement. Meaning the pads were worn. When this
happens the calipers expand and contain additional fluid leaving the Mater
Cylinder reservoir low. In your case two low. Perhaps on the verge of
allowing air into the MC. Now you stomp on the brakes and the ABS kicks in.
The ABS HCU has two reservoir chambers of 5cc each that come into play. This
allows the MC to pump additional fluid to the wheels in a cycling period.
Although a short time. After the emergency is over the HCU electric pump
returns the fluid to the MC reservoir. In your case the MC ran out of fluid
and pumped air in while the ABS was active. The HCU never got properly bled
thus leading to the replacement of the MC. When that didn't work they
replaced the HCU and bled it.



It is likely that the MC and HCU were both fine, and that they needed to be
bled properly.



You'll never know.



How would I do it differently? I likely would have made the same mistake
after adding fluid and finding that standard bleeding failed. But I'd have
removed the MC and disassembled and inspected it. If I didn't see damage I'd
have been in the book looking for the next cause. Also I can buy rebuild
kits for MCs and calipers that are inexpensive. OTOH no reputable mechanic
will rebuild alum MCs. Mainly for cost, safety and liability reasons. So you
cant blame the mech there.



I doubt the HCU was ever properly bled before it was replaced. Even if the
MC ingested air it goes right through the HCU and bleeds out in a typical
repair. Of course yours was not typical. You had an air ingestion problem,
likely before you had the slow speed ABS action. Let me guess, the road was
wet or slick. This led to the ABS kicking in when you pressed down on the
brakes hard. You may also be a little implicated yourself if you let the
fluid get that low in the first place. This is all speculation. And I don't
want to blame the victim (to much<g>). From now on it's a good idea to check
the brake fluid level. Also, Low fluid is a sign of a leak or worn front
break pads.

Good luck. Your system should be fine thought the bank account took a hit.

BTW about what were the costs involved? City/rural? Just curious.