A couple of times recently on startup, I've had the brake pedal go soft and the brake light comes on. Pump the pedal a time or two and everything returns to normal. Checked the obvious and brake fluid level is fine and always has been. Any advice on how to diagnose?

Car is a '69 Cutlass and previous owner installed an Inline Tube front disk conversion about 3 years ago. Looks like it was done right and has worked perfectly up to now with weekend type use of 1-2k miles/year. I have limited brake work experience, just changed pads on a few cars over the years but not afraid to dive in.

 

This could be due to a worn master cylinder. What do you know about its history?

I looked just now at the Autozone website, and a remanufactured master cylinder for your car is about $14 plus core charge if you have power brakes and about $40 plus core charge if you have manual brakes. New master cylinders for both power and manual brakes are available as well, but the remanufactured units carry the same warranty (lifetime) as the new units.

Replacing a master cylinder is pretty easy and straightforward if you follow a few simple steps. Go to youtube.com and search for "master cylinder replacement" or something similar, and a number of videos will turn up. I just replaced the MS on my '73 wagon, and it was pretty straightforward. You should get a flarenut wrench (photo below) of the correct size to remove the brake lines from the MS as the nuts can be tight, and a regular open-end wrench will likely just round off the corners.




You'll need to bleed the MS at the bench before putting it on the car. The videos show this as well. I bought my MS at Autozone, and it came with a complete bench-bleeding kit and instructions which worked very well.

 

I agree, though one would assume (yeah, I know...) that a new M/C was installed with the disk brake kit three years ago.

 

Yes, new MC was installed with the brake kit. I was guessing MC also but seemed too new and thought I would ask before throwing parts at it. Does not look expensive or really that hard just never done one before. May get a cap gasket first and see if that helps. Has only done it after sitting a few days, never on a hot start.

 

I agree that it sounds very master cylinder-like, but I would get under the car and look for wet spots, including on the tires (inner sidewalls).
A small brake fluid leak would do this, too.

- Eric

 

Bench bled then installed a new MC, taught my son the fine art of brake bleeding, and started her up. And the brake light came on again. Seems to stop OK but did not push it hard. Problem may actually be a little worse since the light stays on when the pedal is pushed hard at a stop now. What next, proportioning valve?

Not a total bust though. I did swap out the front pads since the ones on it squeeked and seemed to create a lot of dust on the wheels. New ones are quiet and time will tell if less dirty.

 

Finally fixed it yesterday. It was the metering valve that bolts on the master cylinder stud that was only used for a couple of years. Previous owner must have ordered the '69 correct kit from ILT and not a generic kit with the combo valve/block on the frame. May eventually go back to the year correct MC I took off first but tired of bleeding brakes for now.