Basic info on my car. 89 L98 coupe that is basically stock. Some minor work but still stock cam, crank and pistons, heads all reworked but stock, stock throttle body. Some after market items but as I said, basically stock. I have slowly been going thru the car. All new exhaust. Wheels and tires, shocks, window switch's and window motor. Then I run into a nightmare. The brakes. New master cylinder which I bench bled. New vacuum booster. Good vacuum to the booster and the one way valve in it works as it should. New rotors, pads and calipers. Replaced the wheel brake lines with braided ss and then I started to bleed the system. I have gravity bled them, vacuum bled them and power bled them. With the engine off, I can get a firm pedal that moves a little over 2 inches. The pedal is a good 2-3 inches off the floor. Start the motor and the pedal will go to the floor and only after pumping a few times will it stop the car. Pull it back in and bleed everything again. Now at any one time I have run at least 4 quarts of brake fluid thru the system and I find I can still get small air bubbles out of the front calipers. The rear show no air in them but the front does. There is no leak of fluid anywhere, I've looked. We have spent days, I mean days trying to get rid of the air and I can't. Where it is coming from or where it is, is beyond me. With this soft of a pedal there has to be air somewhere, but where and why does it do it only with the car running. Not running, and you can stand on that pedal and go nowhere near the travel we get with it running. I just measured the travel tonight. Engine off, 2 1/4 in. Engine running, 4 5/8 in. All the brake and abs lights work as called for when starting and running the car. The local garages tell me to bring it in and they know they can find the trouble but can give me no idea how many hours it may take. I'm not crying, but due to a broken back my income is not that much. It took me a couple of months to get all the brake parts and after I had them all we started on them. What am I missing? I couldn't tell you how many brake jobs I've done over my life but this has me going nuts. What's worse, I'll bet it is something simple, something staring me in the face and I can't see it. ANY HELP, PLEASE, and THANK YOU

 

Is the master a reman? It could be bad new out of the box. Pumping 4 quarts via the lines and still air in the system? That tells me the internal valving is malfunctioning. That's were I'd start again. Do you here any air gushing from the booster when the car is running with the hood up depressing the brakes? I think while running the vacuum is assisting the master but allowing air past the masters internal valving. That would be my best guess by reading what you have posted. GC

 

Not a reman. did that once and thought the same thing. Then purchased a new one. Second master cylinder and second vacuum booster.

 

At times I used to have some difficulties like you describe, but I think I have it knocked now.

I use a bleed kit reservoir bottle that clamps to the respective master cylinder reservoir; holds about a quart of fluid and keeps the master from running dry (and sucking air if it does!) as I either force (pumping the pedal) the fluid out, or vacuum with a bleeder tool.

the Russel #639630 speed bleeders are essential to keeping air from getting in via a check-valve AND the thread sealant compound they come with.

I'm doubting the booster is responsible for air getting into the master cylinder; with or without the engine running: it would be a 'new one on me'.

My vote is air is getting in around the bleeders (stock) as you attempt to evacuate the lines, OR the master reservoir is not being replenished before it has a chance to drain, OR, you have a leak in the lines somewhere? (AIR can leak past a tiny breach in the system waaay before brake fluid can get past that breach - enough to be noticed...just sayin.)

 

Me either.. I was suggesting that if he heard no vacuum noise from the booster that the booster is prob ok. I was suggesting while running that some how the internal valveing of the master was sucking in air bypassing the proportioning valve.

All good points I was hoping after pushing 4 quarts this would have been seen

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I had the exact same issue with my 89. The bleed sequence is different because of the location of the ABS unit. I will have to look for the right sequence, but it is not RR,LR,RF,LF. You also might have to activate the ABS pump to clear out any trapped air.

 

Pull the master cylinder to be sure it's not leaking into the booster. Are you certain you didn't pull any air into the lines by letting the fluid get low while bleeding?