Pontiac Repair: 96 sunfire brake bleed -, disk brakes, wheel cylinder

Question
QUESTION: Hello - 96 sunfire 2.2l rear drum, front disk brakes. I had replaced a broken line to the right rear - bleed them and all was fine. My kid as driving it and said the brake failed and the brake light came on. The reservoir was empty so I filled it and started to look for leaks. I can not find a leak any where. I focused on my repairs and the dbl flare fitting looks good still. When I bleed the system I find that the left front and right rear (repaired line) are working fine - but the right front and left rear are not. I bleed the system from the left rear for over a 1/2 hour with an assistant helping and all I get is air bubbles for a few seconds each time. The fluid in the reservoir did not go down in that time either.

ANSWER: Hi Paul:

sound like the master cylinder failed. when the brake line blew the brake pedal when past the normal amount of travel the cylinder has been over the year and what happens the travle is into an area in the cylinder bore where debris and corrosion is and it more then likley damaged the seals in the master cylinder. The possability is that you have a wheel cylinder leaking inside on of the drums and just don't see it leaking onto the ground yet. Of the master cylinder is leaking it out the rear and into the brake booster which is really bad the fluid will damage the booster for sure.  with out seeing it I can't tell you what happended. good luck :-)


---------- FOLLOW-UP ----------

QUESTION: Hello Todd, Thanks - does the proportioning valve get stuck when this happens? I did pull the drum on the left rear, the one that does not work, and it is very wet inside and I did note too that the rim was very wet. So, I assume that this is where all the fluid went. I did try to bleed the ABS unit on the car as it has 2 bleeders on it. As you likely know one was full of fluid and the other was all air. So at this point I assume that I need to replace the left rear cylinder and the master cylinder? Thanks

Answer
If the wheel cylinder is not leaking then don't replace it. If this is all bound up with air it will be difficult to bleed the air out of the ABS unit. to do it right you acauallt need a scan tool to bleed the air out of the abs unit. it runs the vlaves in the unit and pushes the air out and down stream. A hand held vacuum pump with a bleeder cup on the pump works well for bleeding the brakes on these.The proportioning valve is pary of the master cylinder on these it's interanl to the master. good luck :-)