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Username Post: Master Cylinder Fluid Evaporating        (Topic#361042)
Posts: 7

Reg: 01-16-07
05-20-20 10:53 AM - Post#2794282    

Every late fall I park my 55 Chevy in a heated and conditioned garage all fluids are topped off and fine. The car doesn't run until spring. When I open the hood to get it ready to start in the spring I have small yellowish crystals all over the master cylinder and the brake fluid is down to where the level is approximately half full. The crystals are not sticky and wipe off falling below the master cylinder which I blow off. Does anyone else have this problem or have any ideas as why this occurs?


Senior Member
Posts: 1534

Loc: North Coast, USA
Reg: 12-19-01
05-20-20 01:36 PM - Post#2794295    
    In response to buker55

read this link:


Member #409
Posts: 27736
Loc: Katy, Tx, USA
Reg: 07-06-00
05-20-20 04:16 PM - Post#2794308    
    In response to buker55

Brake fluid isn't going to readily evaporate, particularly when the car is in storage - because the boiling point is so high. Also, any liquid is going to evaporate more readily at higher temperatures, which are only going to occur when the brakes are used.

Brake fluid does expand and contract with rising or lowering temperature. If you fill the reservoir to the top when it's cold, it's going to expand when the brakes are used and this may cause the reservoir to overflow. Another cause of a lower fluid level in the reservoir is a leak that you can't see. You might have a leak at the rear of the master cylinder, or more likely, a wheel cylinder.


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