Master cylinder testing

[Charles Young]

I'm chasing spongy brakes and have
Read myself to death about bleeding and have tried that several times with no success. So now I'm thinking about the master cylinder and trying to find the best way to test it. I read about leaving the lid open while depressing the brake pedal to look for bubbles or swirls. So I tried that. I saw no bubbles or swirls but did have some fluid shoot up out of the back portion of the reservoir. Is that normal?


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[Chuck Leeper]

The squirt is normal.

 

[Charles Young]

Thank you!
Any other suggestions what to look for on the MC?


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[buddy]

Did you bench bleed the master cylinder before you put it in.

 

[Charles Young]

The MC was in the car when I bought it. Should I take it out and bench bleed? For only about $40 I was thinking about just replacing it to eliminate a variable.


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[buddy]

The MC was in the car when I bought it. Should I take it out and bench bleed? For only about $40 I was thinking about just replacing it to eliminate a variable.


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It will never be right if it wasn't bench bled first.

 

[buddy]

Do you still have the cast iron propertioning valve on the car. They are known to corrode and leak also. Kirban sells a nice brass piece to replace.

 

[Charles Young]

Do you still have the cast iron propertioning valve on the car. They are known to corrode and leak also. Kirban sells a nice brass piece to replace.

I don't know but will go check. Thanks!


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[Charles Young]

Looks old and does not appear to be brass. It had this tag on it. Does it mean anything to you?

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[1986 Buick GX1]

The MC was in the car when I bought it. Should I take it out and bench bleed? For only about $40 I was thinking about just replacing it to eliminate a variable.
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The purpose of bench bleeding is to push the piston all the way to the end of the stroke eliminating the air pocket which causes spongy brakes.

When the master cylinder is in the car the brake pedal hits the floor before the piston gets to the end of the stroke.

It may be possible to disconnect the push rod from the pedal and push the piston to the end of the stroke with a long screwdriver, possibly, maybe?? Just a suggestion as I've not tried this, but removing the master cylinder may be easier.

I had the same trouble when I switched to vacuum brakes.

 

[Jerryl]

I'm chasing spongy brakes and have
Read myself to death about bleeding and have tried that several times with no success. So now I'm thinking about the master cylinder and trying to find the best way to test it. I read about leaving the lid open while depressing the brake pedal to look for bubbles or swirls. So I tried that. I saw no bubbles or swirls but did have some fluid shoot up out of the back portion of the reservoir. Is that normal?


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Which brake system?

 

[Charles Young]

Vacume


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