Spongy Brake Pedals After MC Replacement

[Alex Esenberg]

Hello everyone, have a bit of a problem here. I replaced the master cylinder on my uncles 92 GMC sierra c1500 p/u 1/2ton 4.3L v6. I replaced it only because the donut gaskets that go between the mc and the reservoir were busted so it was leaking brake fluid. No one sold the gaskets separately so I just bought a new mc. I bench bled the mc with lines running from each port back into the master cylinder and kept pumping the piston until there was no bubbles. I put it on the truck, bled the brakes, but I have a spongy brake pedal when I start the car. When the car is off it is nice and hard. There is no air in the system when bleeding the brakes so I don’t feel like air is the problem here. There is now a squeaking noise every time I press on the brakes and brake fluid sprays in the reservoir every time I press on the brakes. Hopefully you smart people can help me out! I blench bled the reservoir twice and bled the brakes like 5 times. :S

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[college man]

check the rear drums are adjusted correctly.
sounds like a bad master out of the box. fluid
should not spray back. did you bleed all four wheels?
Lines are correct?

[Walter Cheryba]

I agree with college mans comments. Fluid spraying in the reservoir is usually a sign of fluid bypassing the seals in the master cyl. spool valve as it travels. The new squeaking noise could be related to this.
Did you notice the fluid spraying in the reservoir during the bench bleeding of the new master cyl.?

[Author]

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