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Re: Missing Brake Fluid

Subject: Re: Missing Brake Fluid
From: (Denise Thorpe)
Date: Fri, 22 Mar 96 11:06:00 PST
Michael Lytton asked:

>      Several weeks ago, I attempted to take my 70B out for a quick spin 
>      after it had sat in my garage for two months or so.  The brake pedal, 
>      however, failed to inspire confidence by quickly pushing all the way 
>      down to its stop.  After the customary bouncing of the forehead 
>      against the steering wheel as a gesture of supplication, I checked the 
>      master cylinder fluid level.  There was very little fluid left.
>      After this, I checked the brake cylinder for each wheel, plus checked 
>      brake lines under the car.  I could find no evidence of leakage.  A 
>      check underneath the master cylinder both in the engine compartment 
>      and under the dash also revealed nothing.
>      So can MGB's "use" brake fluid?  I must confess I haven't checked my 
>      brake fluid level in over a year (wince).

As the front pads wear away making the pistons live farther out of the 
calipers, the total volume of the brake hydraulic system increases, however, 
the difference shouldn't be enough to make your reservoir run dry.  I 
suspect that this increase in volume is taken into account when a master 
cylinder reservoir is designed.  Your system has to be leaking somewhere.  

If you have a brake booster, the fluid may be leaking from the master 
cylinder into it.  If brake fluid is leaking from the other end of the 
master cylinder, it would run down the brake pedal.  Is the surface rust on 
your brake pedal darker than the surface rust on your clutch pedal?  Also, 
when you looked at your rear wheel cylinders, did you pull back the dust 
covers on either end to make sure there was no fluid inside the covers?  It 
takes a while for enough fluid to leak for it to get outside of the dust 

The wheel cylinders are the most likely suspects because they're at the 
bottom of the system where water collects because it's heavier.  Now that 
I no longer anal compulsively bleed my brakes once a year, I've given up 
on rebuilding wheel cylinders and just replace them because they're always 
pitted from rust by the time they start leaking.  However, both the brake 
and clutch master cylnders on my car have been there for 15 years. 

For the people out there who are compulsive enough to replace their brake 
lines, I saw a slick trick on a '67 Cadillac I once worked on.  Where the 
brake line travelled along the differential, in one spot on the back side 
of the axle housing, it dipped below the level of the wheel cylinder.  Any 
water in the system would collect in this dip instead of in the wheel 

BTW, no one is allowed to say anything about 1100's until next Friday 
because that's when I'll be back from skiing.

Denise Thorpe

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