Help! 1980 Brake pedal going to the floor-getting scared

[Tntruckguy]

OK, I have had this brake system checked and bleed 2 or 3 times now. It seems when I get the car back from the shop the brakes are fine. After a little while the pedal starts getting closer to floor when I go to stop. It still stops but this is starting to worry me. I have checked the fluid and it is full in both reservoirs and has been full. Where am I losing pressure? any ideas or help before I tear into this.

Thanks in advance!

Tntruckguy

 

[Vettehead Mikey]

Did you recently change any of the brake rotors or rebuild the rear wheel bearing assemblies?

 

[Tntruckguy]

Did you recently change any of the brake rotors or rebuild the rear wheel bearing assemblies?

Nope! I checked all wheels and no signs of dripping. I am sure I changed to pads when I bought the car but cant remember changing anything else. I am wondering if there is an air leak or vacuum leak in the booster???

 

[Hib Halverson]

If the pedal is low now, bleed the brakes then report back on whether or not there was air in the system.

 

[Vettehead Mikey]

Nope! I checked all wheels and no signs of dripping. I am sure I changed to pads when I bought the car but cant remember changing anything else. I am wondering if there is an air leak or vacuum leak in the booster???

If bleeding fixes the problem, there's air in the calipers. Rotor runout is the most common cause.

 

[GTR1999]

If the brakes are good after your garage bleeds them and you loose them a few days or weeks later the typical reason is the rotor runout as the others mentioned. If you are new to old corvettes this has been a problem since 1965 and many times is created by the first person working on the brakes - removing the rotors to face or to replace. Once the marriage between the rotor and the spindle flange is disturbed the rotor may have runout. Check the runout in each rotor it should be under 005" but I set them to 0025" or less. Then check the bearing endplay, at 003 you will be able to push/pull the spindle. The spec is 001-008" endplay but it's best to keep it at 0015-002 without any lateral play.

Check the inside of the tires for brake fluid leaks.

 

[tshera388]

I got burned on this one as well. As some of the other posters on this thread can tell you, it was a long and difficult path, but I learned bunches. Take off the calipers and inspect the pistons. More than likely, you will find one or more leaking seals. If you do, check run out and end play as mentioned in earlier posts. Then replace the caliper(s). Be aware that you will have to find a way to hold the pistons back while re installing the calipers. You can purchase a special tool to do this from any of several parts suppliers or you can install the pads in the caliper and use a couple of sockets to hold them apart. When you put the caliper back on, the rotor will push the sockets out allowing the pistons to extend out. Be sure to pressure bleed the system. I tried to vacuum bleed and it didn't work so well. Hope this helps.