A friend of mine has a 1st gen 3000GT with very low pedal response on the brakes. The problem is as follows:
--Problem: Pedal goes all the way to the floor and produces very little braking power. --History: Pedal response had varied before; one moment the pedal would engage firmly near its top position, and then at the next stop it would have to be pushed further in to generate the same power. This would alternate several times in a short trip. I didn’t look at the car during this time, but he seemed to think it had something to do with the ABS (ABS light was on). He replaced a fuse under the hood for ABS and the light went out. --Work so far: When he brought it to me, he noted the pedal issue so I suspected air in the brake lines. I vacuum bled the brakes, and sure enough, got tons of air on the first pump, and the second, and the fiftieth. I was getting out exactly as much brake fluid as was going down in the master cylinder, but with a ton of air added in at some point. The master cylinder was kept full at all times, and the car has never had a history of leaking brake fluid. --Questions so far: (1) Where is all this air coming from? (2) How can I get it out of the system? (3) How can I keep it out of the system? (4) Is there an overarching problem (like with the ABS) that I should be more worried about here? --Possible handicaps as a mechanic: I only have experience working on older German cars. The only car I have with an ABS system has the option on the dash to turn it on and off.

 

well air is getting in from somewhere that is for sure. And if air is getting in most likely fluid is getting out somewhere. Do you have anywhere where you can see any leaking out. If not then it is most likely not the lines or anything. Maybe the master cylinder or could be the ABS Pump. Is the car a turbo or non turbo?

 

The 3000GT is a non-turbo. Also, I figured brake fluid would be getting out somewhere, but as I noted, apart from normal fluid use from pad wear, this thing doesn't seem to be losing a single drop of brake fluid (At least in the master cylinder reservoir, surely to get that much air in the lines some had to come out). The calipers and all visible brake lines look great. This had lead me to believe that there's some sort of one-way valve open in the system.

Also, I forgot to mention this: When bleeding the brakes, after a good amount of pumping, one line was actually successfully bled of all air and gave us only brake fluid; however, halfway through the bleeding (after taking out and putting in about 2 pints) it had done the same thing, then put out more air. A pint or so later it stopped again (gave straight fluid for a full cycle) and I just left it like that. The master cylinder was kept full through all of this.

I'd almost like to try pressure-bleeding this system to test that one-way valve theory, but as I've never worked on a car with a standard (and possibly malfunctioning) ABS unit, I don't know how successful that would be.