Air In Brake System C2

[Bill B.]

I rebuilt a leaky left rear caliper on my 65 coupe about a month ago. Bled brakes and all was fine. Drove the car several times. I took the car to a show today and the brakes worked fine until I was pulling in to my parking spot and the pedal went about 75-80 % to the floor. I pumped the pedal and it built back up felt good again. Several times during the day I did the same thing with the same results. I figured I had air in the system that I didn't get out from the caliper rebuild. When I got the car home this evening I bled the brakes and didn't observe any air come out at all. The pedal doesn't appear to go quite as far to the floor but it still goes further than it should and when I pump the pedal it builds back up. I can't see any leaks in the system and I'm at a loss. I would appreciate any guidance or suggestions.

Thank you in advance.

Bill Bonnichsen

[Don H.]

Re: Air In Brake System C2

Your rotor could be out of round. When you drive it the "whobble" of the rotor pumps air into the system. This is just one possibility. Good luck, Don H.

[William P.]

Re: Air In Brake System C2

Did you bleed all 4 corners or just the 1 you re-built .

Bill

[Jim L.]

Re: Air In Brake System C2

I When I got the car home this evening I bled the brakes and didn't observe any air come out at all.

Bill, the lack of air bubbles when you re-bled the brakes is your clue that what Don wrote about rotor wobble is probably the issue.

When the rotors wobble, they push the piston(s) back in their bores. So, on the first application of the brakes, all of the fluid displacement goes toward just moving the piston back into contact with the rotor. Second application of the brakes, then, actually slows the car.

Get a dial indicator and check your rotors for axial runout.

Jim

[Bill B.]

Re: Air In Brake System C2

Thanks for the replys. I bled all 4 calipers starting with the right rear, left rear, right front and finally the left front and yes, on the rears I bled both sides. The fluid in the master cyclinder got low once while bleeding but it didn't go dry. Do I need to bleed the master cyclinder just in case? The rotors have been on the car for years with no runout problem. Only thing different I did was to leave the springs out of the bores when I rebuilt the caliper. I read in several articles that they are not necessary as they only keep the pads in very light contact with the rotor. I'm starting to wonder. What puzzles me is that for the first 10 or 15 miles after the rebuild the brakes were excellent. Thanks again for the help.

Bill Bonnichsen

[Michael W.]

Re: Air In Brake System C2

Only thing different I did was to leave the springs out of the bores when I rebuilt the caliper. I read in several articles that they are not necessary as they only keep the pads in very light contact with the rotor

I think you've found your problem. The springs are there avoid the very issue you're experiencing.

[Paul J.]

Re: Air In Brake System C2

Bill, while sitting still, stand on the brakes and feel if they lose pressure and the pedal slowly sinks. If so, you need to rebuild your master cylinder. When the seals wear they will allow fluid to pass them and it will feel like there is air in the lines.

This is not an unusual occurrence after all of the excercise that you just gave it bleeding the brakes.

One other thing, 65 calipers are sometimes difficult to get all of the air out of. There are some tips in the archives.

Paul

[Bill B.]

Re: Air In Brake System C2

Just to keep the good folks of the forum updated, I just took the left rear caliper apart again and put the springs back in. Bled the brakes and the pedal feels great. I drove it for 3 or 4 miles with frequent braking and pedal still feels great. If I run into any more problems I'll post. Thank you for the replys to my brake problem.

Bill Bonnichsen