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Maybe your brake calibers are locking up on the slides and as the brakes wear the pads have to keep extending out farther and farther to actually apply the brakes. I cannot remember how the corvette calipers are designed, but if the pistons are on one side only, then it is possible that the calipers are locking up and not allowing movement for brake wear which will cause the problem you are describing. What happens is the rotor and mounting hardware deflect under brake application and eventually the deflection is so high that the brakes will no longer come on with one stroke of the pedal. This is probably the case if the breakes work OK with more than one pump of the pedal.
when the pedal goes to the floor, there are a few things that can cause it.
1. an internal leak in the master cylinder.
2. not enough fluid in the system
A. improper assembly
B. pistons all the way out in calipers when assembled, and not topping off the reservoirs.
C. cracked or leaking reservoirs
D. loose or bad brake hoses
E. chafed metal lines under the car somewhere.
That's a good point. Did you buy a new M/C or a reman one? Sometimes the reman units are not assembled properly, a rubber o-ring seal didn't fit properly or is missing, or the cylinder housing has corrosion in the bore and allows fluid to pass thru as the brake pedal is pushed.
If you have the store receipt, take it back for an exchange and see if there is a difference after it's installed.
It's also possible that there is air in the ABS unit. On the C4's, the ABS is bled by using a GM Tech 1 scan tool with the insertable brake module. What the Tech 1 does is to run the ABS pump as fluid is bled out of the bleeder valve. The valve is on the side of the pump and it is a messy job as the fluid drains out into the bottom of the compartment.
Even though teh ABS pump runs a self-test briefly every time the engine is started and the car moves thru 2-4 MPH, that's not enough to bleed the ABS pump. The ABS unit is self-contained and it's very pricey. No reservoir or anything to look at.
having almost the same prob. Out of town now but I am going to change the flex hoses at the wheels. A friend had a problem with his colapsing on the inside. Either way mine are 21 years old. I'll check back after.
if brakes are almost to the floor, it is the positioning of the pedal in relation to the master cylinder.
In order for the master to absorb the proper stroke to port fluid to the lines, the piston has to move a certain amount.
If the pedal pivot, or the linkage rod and pivot are not in the proper relation to the master, the booster in the middle between the pedal and the master may be the problem. There is a spring inside the booster to return the pedal to it's resting place. There is also a spring inside the master. If the master is not returning for some reason,there is no piston travel.
If the spring is broken in the booster, or the diaphragm is not in the right position, you can have a master in the end of the stroke, and the pedal up where it needs to rest, and the pedal will go the length it needs to, and the master isn't actually moving much.
Two questions for you. In your original post I wasn't clear whether the brakes worked ok for a while and the problem started after a month or the problem was always there. Also, by any chance did you replace the calipers?