My brakes have multiple personalities...
 

I've had brake issues for a while. Yes, they've been flushed a few times. Makes them better but not the way they were.

There are three distinct feels to the pedal.

1. High and tight. Pedal engages way high, way hard. Brakes work.

2. Pedal sinks down soft, brakes do not work that well.

3. Progressive engagement, pedal tightens up, brakes work.

My shop (Rudtner's) is having trouble replicating the issue. Best diagnosis they have is a faulty brake booster. Apparently NOS brake boosters are $2300.... Not a happy outcome.

Anyone have any thoughts on the matter? Or an alternate source for a brake booster?

Thanks.

do you get 'high and tight' after setting the brakes with the pedal? So brake, lift, then brake again?
That condition can be an indication of pad knock back which could be wheel bearings or pistons, or in aggressive track driving upright flex..

When were the calipers last rebuilt or checked for seals/piston condition? Any corrosion on the pistons or calipers?

What pads are you running?

I would check those before going to the booster... and maybe you can find a take off from a dismantler.

- Yes. The more I pump the brakes, the harder they get.

- I don't understand what you're saying here. Wheel bearings have been checked and are good. Will ask them to look at pistons & calipers.

- Front calipers are new as of a few years ago. Pads were replaced then. Less than 20k miles on them.

- Not actually sure. Not very aggressive.

- That's my thought as well, but want to explore more before shotgunning parts at the car.

My take is, that the more you pump the brake, the more you pressurize the system. If the pedal is then soft later.. you have a fluid issue (could be a leak or a master cylinder) or could be a booster that's failing to keep pressure in the system.

you still have air in the system.

get one of those motive power bleeders and bleed them again.

pull a vacuum on the boost and see if it holds. if it does it is good.
pull a vacuum at the engine on the hose going to the booster, with booster connected of course.

Based on your responses, after you check you don't have any leaks at pistons or a balky dust seal pulling your pistons back, I'd look at the fluid and master cylinder first.

Is your shop bleeding by pressing brake pedal or using a pressure bleeder or a suction bleeder?

Talked to Bill. He's pressure-bled the brakes twice, checked calipers and pistons, and examined soft lines, master cyl, and other parts.

He ordered a used/good brake booster, in an effort to have touched or replaced every possible cause. Should be here in a day or two.

One thing to note - he has not actually felt the issues that I've described. He's taken the car out twice and not encountered the different feel in the brake pedal. So that's fun too.

pull a vacuum on the hose and booster.

Soft lines can swell on the inside so examining the outside isn't very helpful.

I once had similiar issues.
Even though this was with brand new calipers, pads and discs and flushed System after swap to metal brake hoses to caliper.

Got crazy.. I flushed and re-flushed...

Alas issue was the master cylinder of my SC. it was dying.
swapped it for the 2.3 bore MC of the Turbo, swapped the vacuum hose and all is well again.