QuestionQUESTION: Jim- I hads to replace my rear brakes includinghte calipers and I cant get any of them bled now. There are no leaks because the fluid level stays constant. I purcahsed a vaccum to assist in the bleeding and it just draws air with a little bit of fluid. The brake pedal goes all the way to the floor. Any advice?
Thanks, Ross
ANSWER: Ross,
Rear calipers? You mean brake cylinders, correct?
Is the brake warning lamp lit if you start the car?
What was the reason for replacing the rear wheel cylinders?
There are several possibilities for not getting fluid to the wheel cylinders.
No fluid in reservoir (you said it's ok)
Piston stuck in the master cylinder bore
flexible brake lines swelled up internally
hard brake line crimped shut along the frame
PDWA off center due to loss of pressure in the rear circuit
Take another look and see if you can eliminate any of the posibilites from the list. Let me know what you find and we can try to narrow the problem further.
Cheers,
Jim
---------- FOLLOW-UP ----------
QUESTION: Thanks Jim. Yes, I mean cylinders. I will check the warning lamp. I needed to replace them because they were worn out and leaking. I also wanted to have new brakes on this restoration. I was able to bleed them before I changed the cylinders, brake pads, etc... so nothing really changed except for replacing those parts. The frustrating part is that if something was crimped off or shut off, I would not think I would get so much air. I would assume that the vaccum would stay when I applied it. I know air can move through a crimped line, but it is like there is no resistence when I open the bleed nut. Two questions: 1- how do I check to see if the piston is stuck in the master cylinder, 2- what is "PDWA".
Thanks again, Ross
AnswerRoss,
You'll get air from the bleeder via the threads.. there's a bit of clearance between the cylinder and bleed nipple threads that will allow air to come out.
As to your questions:
1) pry the rubber boot away from the brake master cylinder and gently work the brake pedal up and down. If you can hear the push rod (brake pedal into m/c) clicking or tapping the piston.. the piston is stuck. It should move smoothly down the m/c bore and always stay against the push rod.
2) The PDWA is the Pressure Differential Warning Actuator. It's the unit near the m/c that the front and rear brake lines go into and it has an electrical connector for the warning light. If either circuit (front or rear) loses pressure (split rubber hose, badly leaking caliper/cylinder, etc) the shuttle inside the PDWA moves off center and that turns on the warning light.
In order to recenter the PDWA you need to have fluid flowing in both circuits.
From the GT6+ owners handbook (only one I have on hand at the moment ;) the procedure to recenter the PDWA is:
1) Fit a rubber tube to the bleed nipple on the opposite end to the side which was just bled
2) Open the bleed screw
3) Switch on the ignition but DO NOT START THE ENGINE. (the brake warning light will glow but the oil warning light will remain extinguished.)
4) Exert a steady pressure on the brake pedal until the brake light dims and the oil light glows (A click should be felt on the pedal as the shuttle returns to its mid-position.)
5) Tighten the bleed screw.
Are you sure there is fluid in the back of the brake master cylinder? It's easy to look and not notice the rear of the reservoir is dry.
Also, did you replace the flexible (rubber) lines? If they've swelled up internally it'll be difficult to get fluid to the cylinders, and then the brake cylinders may tend to stay locked when you release the pedal.
Cheers,
Jim
