Question1992 Ford Taurus GL sedan
3.0 liter engine (non-SHO)
230,000 km 4 wheel disc brakes with ABS
Symptom: Left rear caliper fails to completely release
(intermittant).
Hi Eric,
I'll try to give as much detail as possible on this one to help
with your diagnosis.
Have had this vehicle for almost 4 years. I've replaced both
front discs, calipers and pads about 1 1/2years ago. Not
quite a year ago I also replaced both rear discs, calipers
and pads. Brakes were bleed (diagonal as per my Haynes
manual) and fresh brake fluid installed. Somewhere around
that same time I installed new rear emergency brake cables
also. Everything worked fine.
Note: I am careful to avoid contaminants and when working
on items not totally familiar to me I use shop manuals and
go slowly. I'm a licensed marine engine tech so I do have
at least a good mechanical aptitude.
Several months ago a brake line was leaking (rusted), so I
cut out the bad section and fit and flared a new part to the
line. When I went to bleed that Left rear wheel caliper
I noticed discoloration on that rotor and severly worn pads,
in addition when I went to bleed that caliper there was little
to no fluid coming out of the bleeder screw. I removed the
bleed screw to check if it was clear and not plugged. It was
clear. Shortly after I replaced the caliper (figuring it was
seizing up), rotor and installed new pads again.
This rebuilt replacement caliper did'nt want to bleed either,
very minimal fluid going through it, yet it sometimes still
does'nt fully release after braking. I stress not everytime,
but sometimes. Once it got hot enough with the pads
dragging that the plastic wheel cover mounting tabs
actually melted from the transfer of heat. Park it and leave
it set and cool, then it's OK again until problem
repeats itself another time. My manual does not give any
kind of help on this.
I have a code reader, but there are no codes accessible to it
from the braking system that I am aware of.
I have now tried to isolate components. I've removed the
ABS fuses, and pumped the brake pedal about 30 times
without engine on to drop pressure in the pressurized
(accumulator?) to see if that helps. Indicator light for ABS
comes on with fuses out, but nothing else changed.
Problem remains.
A month ago, while leaving a service station that does our
mandatory emmissions testing (it passed with flying
colors), momentarily while leaving the parking lot the ABS
light flickered, just once.
And, a week ago while waiting at a stop, the brake pedal
went way down, like a loss of line pressure. Stopped OK,
never recurred again. No viable leaks, and brake fluid
reservoir level unchanged. Pedal back to normal.
Only other thing was that about a year ago, the brake pedal
seemed to only sometimes not return quite fully after
braking. I installed a spring on the pedal to assist with this.
Ford' TSB's have indicated insufficient vacuum pressure in
the power brake booster as a possible reason for that issue.
I do not know if any or all of these items influence the
current problem.
That's the whole story. I'd like to be organized in the
troubleshooting, and feel I can do a proper job if guided
through this situation. Hope to get this resolved sooner
than later! I don't want to guess and just arbitrarily
replace parts. Seems very stange not to be able to bleed the
caliper, but yet it must be receiving some pressure
(at least at times) to be able to push the pads against the
rotor. BTW, the emergency brake cables are not adjusted
too tightly.
Thanking you in advance, I await your reply.
Rick M.
AnswerHello and thanks for the question...I'll try to help.
It sound like the proportioning/combination valve is frozen.......which is usually the case.
This is located on the rear of the body frame and then attatches to the rear swing arm of the rear suspension.
I would crack the line ope for the feed and see if fluid travels freely......if it does......replace THAT valve.
If it doesn't....the fluid blockage is more forward, towards the hydraulic control assembly.
Erik
