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Re: poor functioning brakes
Posted by David Prantl (more from David Prantl) on Thu, 28 Dec 2000 23:28:16
In Reply to: poor functioning brakes, Stephen Hartsell, Wed, 27 Dec 2000 00:22:05
FYI - The Townsend Imports web site is:
http://www.townsendimports.com
Your car has several major ABS components:
Master Cylinder: If this was bad, you would likely be able to see/feel the
pedal drop to the floor under constant pressure. This is similar to a
non-ABS master cylinder failure, and from your description, is probably not
your problem.
Hydraulic Pump: This supplies all the 'power-assist' in your braking
system. If the pump fails to operate, or fails to build the correct
pressure level (being old and tired), one or both brake-related dash warning
lights will illuminate, and more pedal effort will be needed to get the
brakes to work. This may be your problem.
Pressure monitor/switch: This is an electrical part that tells the ABS
brain-box how much pressure there is in the system. If it fails, it may
cause the pump to not turn on, or to not stay on long enough to build the
correct pressure level. This may be your problem.
Brain-box and wiring harness: A fault in either of these could cause your
low-pressure problems. Check all pin voltages/grounds/signals at the box,
pump, pressure sensor, wheel sensors, etc.. You'll need the relevant
section of the SAAB service manual for do this properly. As for
brain-boxes, the '88 does not have fault-code-memory, so once it's
unplugged, it loses the codes it has stored. '88-'89 9000 cars can use the
'90-'91 9000 ('90-'93 900) brain box with a small wiring change at the
brain-box harness connector. This box has fault-code memory, which makes it
easier for a technician to diagnose a problem (like an intermittent warning
light). It is part-number 4002176, and appears regularly on EBay where it's
usually obtainable for about $50.
http://cgi.ebay.com/ebaymotors/aw-cgi/ebayISAPI.dll?ViewItem&item=525988843
I would HIGHLY recommend that owners of ABS-equipped classic-900 cars
('90-'93 3&4-door, '90-'94 convertible) and '88-'91 9000 cars have one of
these brain-boxes as a spare, especially when they're being given-away like
this !
Accumulator: This is a pressure-tank, about the size of a large orange.
It's presence allows the system pressure to stay high for 10 or more pedal
presses before it falls far enough for the pump to kick in and increase it.
The only failure I can think of is if it leaks. If it leaked enough to
cause a pressure drop large enough for you to feel as reduced power-assist,
then all your brake fluid would be on the street within a minute or two.
This is probably not your problem.
Before swapping expensive parts, I would recommend a careful inspection for
brake-fluid leaks and balooning brake hoses, and repair these accordingly.
Then do a very thorough fluid change/flush. Send at least half a pint of
fresh fluid through each caliper, and again, make sure nothing leaks. Then
if you can rule out the master cylinder as described above, look for the
source of inadequate system pressure.
Best of luck.
David Prantl
david_prantlno39sdcx6spamx782hotmail.com
'84 900S, 5M, 210kMi, RIP
'86 9000T, 5M, 182kMi
'88 9000S, 5M, 142kMi
'90 9000S, 4A, 133kMi
'93 9000CSET, 5M, 64kMi
'89 900, 3A, 115kMi
'68 97 Sonett V4, 76kMi, #000467
Posts in this Thread:
- poor functioning brakes, Stephen Hartsell, Wed, 27 Dec 2000 00:22:05
- Re: poor functioning brakes, Cort D, Mon, 1 Jan 2001 14:46:57
- RE: poor functioning brakes, John Cooper, Mon, 1 Jan 2001 14:46:56
- Re: poor functioning brakes, David Prantl, Thu, 28 Dec 2000 23:28:16
- Re: poor functioning brakes, Cort D, Wed, 27 Dec 2000 22:01:12
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