Constant brake pedal feel change with disc brakes

[BaBiLuTH]

Hey, I have an '88 gt with a the 94 front and rear 5 lug conversion with disc brakes. I went by all of the instructions that I could find to do the conversion (i.e. gut the prop valve, install an adjustable prop valve, 94 master and booster, and matt's 3-2 port conversion). The problem that I'm having is that the brake pedal feel varies. For example: when I get in the car after its been sitting for a while, the pedal feels spongy. When I press it, the pedal seems to go about half way down until the brakes start "braking". After driving it for a while (happens faster when I push the car hard) the pedal gets to a point where I can just press it on top and the brakes feel like they are "braking". Its almost like the pressure builds up and the brake pedal starts to "brake" with very little movement downward. What can this be. It doesnt feel dangerous but its annoying. Also, I tried adjusting the rod on the booster so maybe fix this problem. I seems to fix the problem, as soon as I got in the car the pedal started to "brake" with very little movement downward. The problem is, as the pressure built up (or what it seems like) the brakes started dragging by themselves because of the pressure in the master. It would get soo bad that I would have so stop and wait like 2 hours for the pressure to drop until I can move it, so I screwed the rod back in. Sorry about the length but I had to get all of this out. Someone PLEASE HELP ME!! thank you.

 

[FixrUpr]

Im having the exact same problem. I put four wheel discs on mine. When I originally did it, I adjusted the booster rod per Maximum Motorsports' website. It was too loose, so I adjusted it to where I wanted while it was cold and it slowly locked up as it got hot. Not sure if it is the pressure or the rod turning out on its own. I never noticed the brakes grabbing any higher before I adjusted the rod out. The pedal used to almost go to the floor before it would grab. Im gonna mess with it today to see if I can figure it out. I know this is an old thread, but maybe someone else can use the info.

 

[93 LX]

sounds like air in the lines. Bleed the brakes again. My Capri was upgraded to 4 wheel disk via T-Bird rear axle and 73mm front calipers with SVO master cylinder. At 1st it was soft but after several bleedings it works great now. I guess I did not bench bleed the M/C well enough.

Allen

 

[superhuaman]

+1 for air. bench bleed the MC. buy & use speed bleeder screws. even if you dont leave them in the calipers.