I spoke too soon, brakes still FUBAR
Group: alt.autos.4x4.chevy-trucks Date: Fri, Sep 26, 2003, 8:42pm
(CDT+5) From: firstname.lastname@example.org (Doc)
Ok, here we go. Took her out yesterday for a healthier test drive
(previous drive was <2 miles), maybe 10 miles and my gosh what an
adventure. I though I was a gonner...........................
Here's what we have now:
1) LOTS of air in the rear lines with virtually no pressure
2) Front calipers will NOT let go after pedal application until 30-45
seconds later as the pressure bleeds off. You can actually hear them
"creaking" as the pressure bleeds off.
I likely cooked my wheel bearings as they were smoking when I pulled
back into my driveway. I bled another 2 quarts through the rears last
night and was still getting air (total of around 4 quarts pumped thru
the rears). There is no air in the fronts. There are no leaks in any of
the rear lines.
It MUST be the combination valve. It's the only thing that would have
the ability to let air into the rears and hold the pressure in the
fronts. I think one of the internal seals took a dumper.
I picked up a new combo valve today (AC Warehouse 45 minutes north of
me) as well as some front wheel bearings (plus another 3 quarts of brake
fluid) and am heading out as we speak with a 12-pack, 1/2 a pizza, two
packs of smokes and a really bad attitude.
Doc (who is EXTREMELY PISSED OFF at this point in time).
with all respect,
I know you been fight'n this thing, and you've
thrown every thing at it but the sink....
(including....by my count....close to a case of beer)
If that thing has good pedal with the rear hose
clamped down, you really oughta peel the dust
boots back on the wheel cylinders and make sure you don't have "seepage"
from the internal seals. I have seen it many, many, many times.
Guys bleed and bleed and bleed, without getting all the air out.......or
all the air comes out
and a good pedal is achieved (for awhile)...and
the prob all along is a wheel cylinder "sucking air".
The front calipers "MAY" be seizing from doing
all the work , getting hot, and expanding the
fluid causing the pads to apply. You may also have the master
overfilled....not giving the fluid
anywhere to go when it gets hot and expands,
and again applying the front pads.
Here's the deal...........
Post repair, pre-test drive = good pedal feel
Post test drive
Hot rotors, pads applied till cool off a) pads doing all the work...
b) fluid expansion due to heat...
c) overfilled master, not letting hot fluid expand
d) binding claipers
e) restricted hose (hoses)
Spongy Pedal a) brake fade (fluid boiling)
b) air in system
Air in both (?) rear cylinders...no air at front a) out of round drums, combined with weak
cylinder seals allowing air to "suck" in.
b) master cylinder bore "rear" seal failure
c) master cylinder reservoir to bore seals bad
(at rear seal)
d) "pin" hole in "over the axle" steel line (lines)
e) bleeder screws not seating at rear cylinders
f) poportioning valve front seal bad
I know you've got the kitchen sink ready to install already, and you
have the entire NG eagerly wait'n to see if that's the fix.
" if " it isn't..........common sense can negate a majority of the
above causes, you being the
one working on the truck and knowing what
you've replaced, and what the chances are of
the respected parts being bad.
a suggestion to a fellow technician of high calliber...........if the
sink don't fix it, and you
still have the same results after the test drive,
as soon as you park it......1) clamp that rear
hose and see how the pedal feels 2) pop open a front bleeder and see
if the caliper releases on its own.
with all respect to the Doc,
the NG is waiting the results of the free brake seminar......
Scrib Abell (brake tech)
~~passes the Doctor a beer~~