I have replaced my brake cylinders, but the brake pedal goes to the floor

Question

I have a '07 Silverado. Both rear wheel brake cylinders blew apart. I fitted new ones along with new shoes. I have bled the brakes but my pedal still goes to floor. What else can I do?

Answer 1

It's fairly common on GMs when all fluid leaks from the system that you have to bleed the ABS Bypass Modulator Valve. This requires a scan tool with bi-directional controls.

Answer 2

As JPHi1618 said, you'll have to bleed everything, from the master cylinder on down. And the master cylinder may require "bench bleeding". Google it to find out.

Answer 3

I have a 97 suburban. I've replace just about every piece of hydraulic equipment on the vehicle aside from the hoses on the rear axle and the ABS pump. Since replacing a broken line 2 years ago, the pedal hasn't been the same. I probably put about a gallon of brake fluid through the braking system trying to bleed it correctly. I finally was able to get it bleed completely and I can now lock the wheels on dry pavement. Here is what finally worked for me.

Pull the bleeders off, clean them, install Teflon tape so they make a good seal. Bleed the vehicle with the normal 2 person method, vacuum bleeding, or pressure bleeding. If doing the 2 person method, close the bleeders before releasing the pedal. This will get out any bubbles near the calipers/wheel cylinders.

There is a catch, any bubbles near the master cylinder or ABS will want to go up, and there is a good 1 foot drop to the bleeders. I did a reverse bleed. This pushes fluid from the bleeders to the master cylinder. You want to make sure you have a good bleed on the system first, so you are not pushing dirty fluid back through the system. After doing a reverse bleed, do a normal bleed again to ensure there are not bubbles trapped around the caliper/wheel cylinder.

Here is a company that makes a reverse bleeder. http://www.brakebleeder.com/

I was able to build my own with a glass jar, some clear hose, and a connection to the air compressor with a regulator. I took an extra set of bleeders and cut the tip off, so I could screw it in all the way to avoid leaking around the threads. It seemed to work well, but I got brake fluid everywhere.