Greetings all...
Car in question is my 89 with 53,000 miles. Its in great shape.
I was driving home the other day when I noticed the brake went half way to the floor at a light. Continued to the next intersection where the light went red and I applied the brake...almost went to the floor....brake light came on. I limped the car home. Did a little checking...no leaks..at the wheels or under the hood. Assumed a master cylinder failure. Replaced master cylinder and did a brake job while I was at it. Bleed entire system. Brake light will not go out and when I start the car I have full travel of the petal to the floor with no resistance. No leaks.....??????? The only other possibility would be the booster...anything I possible missed?? Can pump brakes twice while car is off...very firm! Once I turn the key it goes to the floor.......

 

A booster won't cause the problem you're experiencing. Either there's an external leak, there's still air in the system or the new master cylinder is bad.

 

with what you've described the seals inside your MC were bad. Rebuilding or replace the master cylinder was the right move. Now you've got to get the all the air out of the system to fix the "soft" pedal problem. Glad to hear that you got the car stopped safely -

 

with both previous posts. Did you bench bleed the master cylinder before installing it?

 

Thanks guys....!
Upon further research i have realized it would have been to my benefit if I had read the directions which came with the new master cylinder!!!
I did NOT bench bleed the master cylinder! This is likely the problem. Now I will have to go back to work on this thing....I will post my results.

 

Did you check the ABS?

How did you bleed it?

There's a sequence to follow

Certain years have a bleeder on the ABS unit.

Also, there's a seal separating the two circuits on the MC

 

I did not check the ABS and I did not bleed it.

I bench bled the master cylinder then bled the 4 calipers in the suggested order in the maintenance manual. Absolutely no results. Like I did nothing to the car at all....same problem as before i started work.
Got new fluid to the rears no problem. Fluid coming out of the front is still old in color. Good pressure to the rear...not so good to the front. Cant get the fluid to shoot out like the rear.

Still air in the system i suspect..but the system is not leaking! It looks like I should investigate the ABS?? Bleed it if possible?? What about bleeding the MC again then gravity bleed everything....except the ABS...?

 

Keep bleeding until the fluid is clean at all 4 corners.
If the pedal is still soft - start the car but do not attempt to put it in gear and let it idle sometimes the vibrations will "shake" the lines to help if you still have an air pocket(s)within the MC.

 

Need to find the procedure for the ABS specific for your year.

Went through this before, if not done right it will drive you nuts!

 

Bled the system again with no luck. The ABS system is behind the drivers seat. The maintenance manual for the car says nothing about bleeding the ABS. Followed the proper sequence...back left then back right then front left then front right.
I think the master cylinder I bought is bad or there is air in the master cylinder as a result of me not bench bleeding it the first time.

 

According to to the '89 FSM, the correct sequence for manually bleeding all four corners is:

1. RIGHT front

2. RIGHT rear

3. LEFT rear

4. LEFT front.

The FSM cautions that the M/C must be free of air before attempting to bleed the individual brake calipers. If you have another person to help, have them depress and hold the brake pedal to the floor. Using a flare wrench, crack open the forward brake line at the M/C. If there is air in the system, you see it bubble out. Tighten the brake line fitting, and then have the assistant release the brake. Do this sequence over and over with both brake lines coming from the M/C until you only have brake fluid escaping (no bubbles) from either fitting.

I've found two things that help while manually bleeding my brakes. With the engine off, depress the brake pedal to bleed off any residual engine vacuum in the brake booster, and release the parking brake to allow the rear brakes full travel.

You cannot manually bleed the ABS system in an '89. The only thing that you can do is bleed all four corners and then start the car moving it forward until the ABS system cycles during its start up mode. I alternate going forward and backward during multiple starts to cycle the new fluid through the ABS.

Hope this helps!

 

I'm using Haynes Chevy Corvette auto repair manual which is different than what you quoted...what is the difference between the 2 manuals?

 

It is night and day between the 2

Haynes was done to cover "general" repair/maintenance for a specific generation of 'vettes (C4)

The sequence mentioned above from mr.beachcomber is from a year specific vette FSM (Factory Service Manual) ...it is what the d(st)ealership use...it is the most accurate source as many thing changed from year to year.
New FSM "reprints" are available ($100+) or sometimes you can find a "used" one that is still in good shape for much less. Check the C4 F/S section or ebay (buyer beware) you might find a deal on one.

 

Use the Haynes for when you go out in the woods and forgot the TP.

The factory service manual for each specific year is the manual to use.
There are lots of errors and omissions in the Haynes, mainly because its so thin. I could stack 2 Haynes manuals together and it still wouldn't be as thick as one of the two volumes in the FSM set.

 

You most likely kicked the combination valve. This valve is used when the system detects a pressure differental between the front and rear and blocks the low pressure side. If the wireing is correct your brake light should also be on. All you need to do is get the valve to go back to center. Here is the way I do it and it should work. pump your brakes up lightly., once you have pumped them then hit the pedal hard not a pump but a hard jab. may have to do this a couple of times for it to set. look to see if the light is off. When the light go off the valve is reset. Do not push on the brakes!!!!! Now fill the master cyl and gravedy bleed one wheel at a time. I usaly bleed run about a full load of fluid threw each wheel. You can pressure bleed later if you want but usaly not nessary

 

To everybody who has posted on this thread pertaining to my brake issue. Thank you very much. It seems air is a good thing for jet engines and our bodies...but not brake systems.
I have since fixed the brakes on my 89 corvette. With the new master cylinder and reconditioning of the calipers I got a lot of air in the system. It took extra patience and a very helpful wife to spend so much time in the drivers seat pumping those brakes.