Re: Master Cylinder Diagnosis, ABS

[Kneale Brownson <knotnook@traverse.com>]

Sounds to me like your master cylinder is leaking internally if the pedal
will go to the floor gradually.  The hydraulic pressure built up inside the
cylinder has to go somewhere, and if you have no leaks and all bleeders are
running without bubbles, the leak must be inside the MC.  Considering how
inexpensive they are (I got mine last month from The Parts
Connection=Q-List price of $89 vs dealer "best deal" of something like
$260), and how easy it is to change them, I'd swap the MC.  I think I've
read somewhere that a failing MC is one reason for the ABS system to switch
itself off.

Kneale Brownson


At 11:32 AM 8/16/99 -0400, JJK1204@aol.com wrote:
>Hi all,
>
>I would appreciate some help on diagnosing the master cylinder on my 87 5ktq. 
>First, I know that the bomb is bad, 1 pump and the pedal is hard. Engine 
>running I can slowly, or quickly, depress the pedal all the way to the floor 
>where I get the brake warning signal. The pads and rotors are new and the 
>calipers are fine, I bled the system and the brake hoses look in good 
>condition. Normally I would suspect a worn master cylinder but it is 
>difficult for me to confirm this with the hydraulic booster. Are there any 
>signs I should look for, or am I just seeing the bad bomb effects?
>
>As I have said, the pads and rotors are new as are the front wheel bearings. 
>I bought new ABS sensor caps and installed them on all four sensors. The ABS 
>light is off on startup but comes on as soon as I start moving and exceed the 
>4 mph threshold speed. If I stop and recycle the light with the ABS switch it 
>does the same thing as a cold start. Is there anything other than a bad 
>sensor that could cause this behavior? Also, since I don't have a scope is 
>there another good way to check the sensors?
>
>TIA,
>John Katos
>
>87 5KTQ
>Many Alfas