How to test a master cylinder?

[Blake]

I have a 1990 Chevy Lumina. I bleed the brakes had a nice firm brake pedal when doing this and once I started the engine the petal went spongy and soft. Is there anyway of testing the master cylinder?

Topic

[619DioFan]

Is this a new master cyl that was installed ? if so was it bench bled prior to install ?

if an old master that was still on the car – pull the check valve on the brake booster and see if any fluid is inside the booster- if so the master rear seal is leaking. also check under the dash were the brake pedal push rod goes through the firewall , check for brake fluid there.

[Mark]

How did you bleed the brakes? If all you did was flush the fluid or perform a bleed after a brake job it may be possible that you some how allowed air to get sucked back up through the bleeder. In this case I would look at your procedure for bleeding and change it as necessary or just re bleed the brakes and go from there. Also I agree with the above post.

[Author]

Replies