61 brake bleeding question
Thread Starter
Instructor
Joined: Oct 2020
Posts: 140
Likes: 39
61 brake bleeding question
Hello,
My 61 Vette sat for a few years while kids were growing up and now its time to start driving it again. I recently replaced the entire brake system. New master cylinder, all new rubber and steel brake lines, all new wheel cylinders. I stayed with the original style single reservoir master cylinder. I bench bled the MC, and vacuum bled all four wheels. It took forever to get fluid to all four corners. I kept the MC filled and did not allow it to go dry. After all that I still have a spongy pedal. If I pump it a few times it firms up. During a test drive I noticed the car also pulled hard to the left. I adjusted the pads on the right front and did the two person brake bleed on all four wheels (did not find any air in the lines). I had a good firm pedal and thought I was done. Go for a test drive and have a spongy pedal again. I have bled these brakes multiple times and still not happy. There are no leaks.
Am I still chasing an air pocket someplace or could I have gotten a bad master cylinder?
Thanks for any suggestions.
My 61 Vette sat for a few years while kids were growing up and now its time to start driving it again. I recently replaced the entire brake system. New master cylinder, all new rubber and steel brake lines, all new wheel cylinders. I stayed with the original style single reservoir master cylinder. I bench bled the MC, and vacuum bled all four wheels. It took forever to get fluid to all four corners. I kept the MC filled and did not allow it to go dry. After all that I still have a spongy pedal. If I pump it a few times it firms up. During a test drive I noticed the car also pulled hard to the left. I adjusted the pads on the right front and did the two person brake bleed on all four wheels (did not find any air in the lines). I had a good firm pedal and thought I was done. Go for a test drive and have a spongy pedal again. I have bled these brakes multiple times and still not happy. There are no leaks.
Am I still chasing an air pocket someplace or could I have gotten a bad master cylinder?
Thanks for any suggestions.
Pro
Joined: Jun 2007
Posts: 526
Likes: 260
From: Quebec, Canada
When bleeding brakes, you have to be Verrrrrry patient. The person pumping the pedal should take at least ten seconds to press the pedal to the floor. If you go too fast, the bubble of air coming into the cylinder doesn't have time to float to the top and be purged out. If you create turbulance by going too fast, the bubble of air can be spattered into tiny tiny bubbles that take a good ten or fifteen minutes to rise up and coagulate next to the bleeder valve. If you use a vacuum pump, you're pretty much guaranteed to have turbulance. You absolutely have to have laminar flow. I always let gravity do the work and you can't go wrong. Open each bleeder one at a time and let it drain all on its own. This will always give you laminar flow. It takes time but you only have to do it once.
Le Mans Master
Joined: May 2005
Posts: 7,298
Likes: 2,217
From: Central Maryland
Just a thought - are you certain that the new shoes are adjusted correctly?
Agree that gravity or pressure bleeding tends to work better than vacuum, as vacuum often sucks air through the threads of the bleeders. I use a pressure bleeder.
Live well,
SJW
Agree that gravity or pressure bleeding tends to work better than vacuum, as vacuum often sucks air through the threads of the bleeders. I use a pressure bleeder.
Live well,
SJW
Thread Starter
Instructor
Joined: Oct 2020
Posts: 140
Likes: 39
Thanks for all the suggestions. I did have a small leak at one of the wheel cylinders, but I corrected that and re-bled. I have gravity bled and two person bled several times.
I do need to double check the shoe adjustments.....THANKS
I do need to double check the shoe adjustments.....THANKS
