When I apply the brakes (factory power disk) the first part of the pedal travel is ok but about halfway down the pedal becomes really firm and braking continues but only if you stand on the pedal. I replaced the booster thinking it was vacuum related since it seemed worse when there was low engine vacuum. The new booster gives more boost immediately but the same pedal firmness (and poor braking) continues as before, but now it also feels like the pedal is taking longer to return to the resting position and the brakes drag for a second or two after you release the brakes.

I hate to continue replacing parts but does this sound like a master cylinder, proportioning valve, or metering valve? From experience I’ve had master cylinders go bad but those had no pedal for the first half, then braking after half way.

I'm planning on doing the PowerTour in two weeks and need to fix this prior.
Thank you.

Was there work done or parts replaced prior to this condition, or did it work fine before and this just started happening?

Start from the beginning.

Are you running the original rubber flex lines?

No work on the brakes prior to this problem. I removed the steering box and had it rebuild a few weeks prior to this.

The car sat for the winter and did not have a problem when I started driving it again in March. I noticed the problem after about a month of weekend drives this spring. When trying to stop, the pedal was ok for the first half, then it gets really firm. I replaced the booster with a new unit. I have quicker and more responce after the swap but about halfway down the pedal gets firm. I can lock up the fronts if I stand on it.

It doesn't have linear braking since this problem began. And seems to not quickly release the brakes after a quick, hard, application of the brakes. It might be two issues, 1 being the none linear braking and 2 the slow release.
Thanks.

Yes, I am running the rubber flex lines. I won't admit to them being old but they may be nearing the end of their lifecycle. Are you thinking that may be causing the problem?

I have seen the rubber lines go bad in the past. I had a car where one of the front brakes wouldn't release. It turned out to be a bad rubber line. Fluid would go into the caliper but couldn't get back out. The rubber must have been coming apart inside the line, when I got it off I could blow air through it only in one direction.

So you're saying (linear) the vehicle doesn't stop in a straight line. Does it pull to one side only? Based on your description I'd have to point the finger at either the lines or a bad caliper. You can try lines first, the less expensive route but I have a feeling you'll be replacing calipers as well.

Being that our cars sit for lengths of times not being driven funny things can happen to various systems. Also if/when you replace the components, check your rear wheel cylinders replace as/if necessary and flush the system out with good clean brake fluid, I like to use synthetic DOT 3 by Prestone. It tends to be not as hydroscopic (water absorbing) as regular brake fluid. Good for long stints of sitting around.

Good luck!

Sorry, 'linear' meaning, as I apply the brakes the same amount of stopping (force) is not consistant throughout the range of the pedal travel. There is a noticible change when I get halfway to the floor. It does not pull to one side but straight.

I'm going to swap out the hoses next to see if this helps.

Thanks for any suggestions.

I also use the synthetic DOT 3 and so far (4 years) have been very satisfied with its performance. It's nice to open the master cylinder in spring and not see slime in the bottom (water).

Any chance your pads got wet?

I'll have to check the pads. I'm planning to tear it apart this weekend, clean the caliper slides, and replace the hoses.

I know it is bad but I had not flushed the fluid in at least 4 - 5 years. When I take a car to a road course I always prep it correctly, this car doesn't see that kind of action.