Weak Brakes

[jaded_tool]

Hi there,

I am a new user on this website and need some advice. I own a 1987 Toyota Corolla (4door sedan, fwd). Recently my car's brakes have been really weak and spongy so I took a look and the front brake pads needed replacement. I a replaced them with new pads and also got new rotors too. That seemed to help a bit but did not fix the problem. I noticed that when I was driving, the initial press of the pedal was weak but when I pumped the brakes I could feel pressure building and that seemed to stop the car. I figured that there may be some air in the lines so I went to bleed the brakes. I then discovered the bleeder screw on the front drivers side was stripped, the passenger side screw was broken, and both the wheel cylinders on the back were leaking!
Since safety comes first I decided to replace the front calipers as well as the two back wheel cylinders. The job took a while but eventually I got it done and was able to bleed the brakes. I read that air is really hard to get out of the lines so I bled them really well, going through more than a few cans of the appropriate brake fluid.
So finally to my predicament....After bleeding the brakes (and I did it by the book) I still have the same problem. I have weak brakes and now the pedal wont even firm up after the first initial pump (while driving). Mind you that when the car is off (and I'm in the process of bleeding them) the pressure is good and the pedal is solid (it pumps up). It is when the car is started that they become weak (I mean straight to the firewall). I also did a check of the power brake booster (as per Haynes manual) and it appears to be functioning well. I could find no signs of leaks or fluid loss anywhere. I assume the culprit is the master cylinder but I would like some opinions before I proceed.

Sorry for the long post but I feel the info is necessary.

Cheers,
Luke

[roadrunner2]

The key to a good informative post is in the details.

You've replaced some possible culprits so perhaps some of my suggestions won't be helpful.

Spongy brakes are usually caused from air in the lines or a defective master cylinder.

A brake pedal that goes to the bottom with little or no resistance may be due to low or no fluid in the master cylinder reservoir caused by leaking caliper piston(s).

Possible loose or damaged brake lines are others.

Did you have a reliable helper when you bled the brake lines?
I mentioned 'reliable' as some helpers will inadvertently pump the brake pedal and suck in air.

Get some other opinions .

[jaded_tool]

Thanks for the speedy reply,

I made double sure that the fluid resovior was topped up at all times. I also made sure to show my assistant how to properly help me bleed the brakes. We went through the Haynes manual and a youtube video just to make sure there was no confusion, lol.

[Monkeytech]

Yeah replacing the master cylinder is the next step on that.. or you can try bench bleeding the master cylinder. look for kinks in the line.

[jaded_tool]

Fortunately I was able to get a replacement master cylinder for a good price so I will be replacing it when I get the part in a few weeks. I'll keep you posted on the progress.

[Monkeytech]

Originally Posted by jaded_tool

Fortunately I was able to get a replacement master cylinder for a good price so I will be replacing it when I get the part in a few weeks. I'll keep you posted on the progress.

DO you know how to bench bleed?

[jaded_tool]

Thanks for the reply. Yes I do know how to bench bleed, still waiting for the master cylinder though.

[jaded_tool]

It's been a while since I posted so I thought I'd update you on the process. I successfully bench bled the replacement master cylinder and installed it no problem. Looks like the master cylinder was the problem all along because now my brakes are rock hard. I took apart the old master cylinder and discovered scoring on the bore and warped rubber piston seals.

Cheers

[roadrunner2]

Thanks for posting back with the results.

I trust the comment "the brakes are rock hard" is just a figure of speech?

[jaded_tool]

Haha, yeah.