Home > categories > Automotive & Motorcycle > Brake Systems > I have bled the brake lines, replaced wheel cylinders,master cylinder, and booster but still air in system?
Question:

I have bled the brake lines, replaced wheel cylinders,master cylinder, and booster but still air in system?

84 Trans Am, 4 wheel discs

Answer:

I hope you bench-bled the master cylinder before you installed it, and checked all the flex lines to make sure they're not bulging. If you have properly bled the M/C and the flex lines are all right, there's a two-person bleeding procedure that works really well to force air out of non-ABS brake systems. If it's necessary, be sure you have the proportioning valve hold-off tool GM makes for their brakes systems. Install that in the proper place on the master cylinder to make sure the valve doesn't close. If it does, you have to switch to the other brake circuit and start the bleeding procedure over again. Once the proportioning valve is open, have someone pump the brake pedal 4-5 times and hold it down while you crack the bleeder valve. Wait until the fluid runs steady, then close the valve and have the person in the car slowly release the pedal and repeat. Do this for however long it takes to bleed the air from that caliper. I'm assuming you're doing this right, by having a full container of just-unsealed brake fluid in the reservoir for the brake circuit you're bleeding and *bleeding the calipers in the proper order*. If you don't follow the order specified in the repair manual, you aren't properly bleeding the brake circuits and you'll have trapped air. After you've bled with the forced method, you can finish up with gravity bleeding again. It will probably take you a while to get the air out this way, but it's the most thorough procedure. Remember: Never use brake fluid in plastic containers or any kind that's been opened previously, because DOT 3 and 4 are hygroscopic and absorb water for however long their container has been unsealed. Your problem may be wet brake fluid. Good luck!
May 28, 2018
WHAT KIND OF CAR?? YEAR?? MAKE?? MODEL?? More info please. You either have a leak externally, or WORSE a leak INTERNALLY! Check for brake hose FAILURE at all four wheels. Any quickky lube pit can examine it for you! You should use ONLY the factory genuine brake fluid because all brake fluids have different compounds in them. ALSO ALL brake ffluids should be CHANGED and FLUSHED evvery 2-3 years, because the fluid absorbs moisture, and gets acdic, toxic, then turns into liquid sandpaper. If yours is dark brown, it need replacing!! GOOD LUCK!! AS brake fluid thins down, it can take expensive SEALS with it. This is the main reason for caliper and master cylinder replacement over time. GOOD LUCK!!
May 28, 2018
Did you bench bleed the master cylinder before you put it on? also sometimes air gets trapped in the proportioning valve and it has to be bled.
May 28, 2018
read the tire it says it on the side wall example tire size 195/65/15
May 28, 2018

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