Question: 1980 Corvette: Purpose of the Master Cylinder Boot:

[401KVet]

1980 Corvette: Purpose of the Master Cylinder Cap Boot:

I have always wondered and I really don't know for sure, but this is my best guess. What is the purpose, other than helping to make a seal, and proper insulation of the Master Cylinder boot under the M/C cap? My guess is when you put the M/C cap back on the M/C, the two boots, front and rear, should be out, not pushed in. The boots go into the fluid, which pushes the fluid level up toward the top, forcing the small amount of air out rather than trapping it under the cap. Is this correct? I really don't know. To be honest I have always had the boots pushed in. But having recent brake issues it made me think about it and realizing I really did not know the answer. I do realized if this is correct you would have to be carefull not to overfill the reservoirs because the boots will raise the level and maybe overflow. So if this is not right, will someone set me straight. Thanks.

 

[Midnight 99]

The extensions on the gasket should be pushed in. If you have any appreciable brake fluid loss it allows for the centers to pull down so there is some give so the gasket does not pull in from around the edges breaking the seal to the M/C. If yours is pulling in then you have a fluid leak somewhere in the system.

 

[Vettehead Mikey]

One main purpose of the gasket is to prevent external leakage of the brake fluid as you noted. The other main feature is to act as a flexible diaphragm that separates the brake fluid from the atmosphere. The purpose of this is to minimize the amount of moisture absorbed by the fluid over time. The two boots will extend as the fluid level drops with normal brake pad wear.

It's important not to top up the master cylinder between brake pads changes as the reservoir will overflow the next time new pads are installed.