Hello,

I had a leaking old style front brake caliper a couple of months ago. I bought 2 new high quality stainless steel o'ring calipers as well as hoses and pads for the front of my car. I also bought a new master cylinder. They were professionally installed and everything was okay for awhile, but now the brake almost goes to the floor on occasion. It doesn't have that normal firm pedal feel. I don't drive the car much and haven't put many miles on it since everything was installed. There are no leaks that I can see. Before I call the mechanic I was wondering if anyone has run across this issue before and has any idea what the problem might be.

Thank you
Michael

 

Hello Michael,

Have you taken look at the brake fluid level in the master cylinder?

Regards....

 

I haven't done that yet, but I will check in the am. I didn't want to expose the fluid to air. I did use 5.1 brake fluid and had them do a flush and fill.

I hope you are doing well. I was sorry to see you sold your 71 a while back.

 

Hello,
Thanks for the well wish!
It was really time for the car to go.
It was becoming more and more difficult for me to take care of it in the manner it deserved.
Regards....

 

I’m not a brake professional and those who are will have some additional questions answered before they can help you.
Year and model will help.
Your thread indicates you have manual brakes, if so it is information that will be necessary.
What if any modifications have been made to the car, especially modifications to the brake system.

 

Look for a fluid leak at all the wheels. Check the back rotors to see if you have excessive run out. It should be under .005. Best to be under .003. This is a common problem with fixed calipers. Jerry

 

The brake fluid level is full in both compartments.

 

No leaks anywhere and fluid is full in master cylinder. The issue doesn't happen all the time it is random.

 

When it “almost goes to the floor” does the car still stop effectively?
If you pump the pedal at a time when it “almost goes to the floor” does the pedal come up?
I realize you said it is random but does it ever happen when you get in the car cold before going for a drive? Or does it always happen while driving?

Out of curiosity where did you buy your new master cylinder? A friend in North Kingstown went through three new master cylinders sourced from the local parts store before he found one that worked. But that was for a ‘75 Jeep not a ‘72 Corvette.

 

I would bet that your brake fluid still has some air in the system. When installing new calipers it is especially important to gently Tap on the caliper while you are bleeding it to get all the trapped air out of the caliper. I also tap on any brass blocks or unions in the system to free any trapped air.

The O-ring style calipers are better at dealing with the run-out issues. They don't pump air into the system as you drive like the old style seals would.

Find a better way to bleed the brakes. I would go back to your mechanic and tell him that there is air in the system and the pedal is not right at this time. The mechanic should be responsible for getting the air out if he did the work initially.

The problem with faulty components like master cylinders is quiet troubling as you really can't trust the parts anymore like we did when growing up.

Use either a Motive pressure bleeder or my favorite the Phoenix Reverse Bleeding Pump to remove ALL of the air in the brake system. The reverse pump pushes the air UP and OUT of the brake fluid as the fluid returns to the master cylinder. I have found that pushing air up works for me so that is the system I chose to use for the past 3 decades.

Rebuilding the calipers is not that hard to do. As long as there is little to no corrosion on the SS Sleeve then you should be fine rebuilding them at home. I have rebuilt all four of mine with the o-ring style parts.

Best regards,
Chris

 

When the pedal almost goes to the floor it still stops effectively. When you pump the pedal it does sometimes come back up. Only notice the problem when driving. I purchased the master cylinder at CSSB(Corvette Stainless Steel Brakes) where I purchased the calipers and hoses. I see you are also in RI. Have you ever gone to the cruise night at the Beef Barn on Tuesday nights in North Smithfield? How about the large one every other Thursday at Patriot Place in nearby Mass?

 

Do you still have the old master cylinder? Could you put it back on and see what happens. I would also verify that your master cylinder is the right unit for manual brakes in your year Corvette. They made so many variations that maybe the wrong one made its way to your hands.

With the pedal feel like you describe it still sounds like air in the brakes. I have little experience with silicone brake fluid but the one lesson I learned was that it does FEEL different than D.O.T. 3 brake fluid. When I tried it in my C3 the pedal sensation was the similar to my experience with DOT 3 fluid but the feeling changed as the fluid warmed up in my brake system. The pedal sensation was different using the Silicone brake fluids where it never changes with DOT 3 brake fluid. Be very careful when switching back and forth brake fluids as you need to flush the system to clean out the silicone residue before filling it with DOT 3 brake fluid.

Then I switched back to the DOT 3 brake fluids and have never messed around with silicone brake fluid. I did not like the way it felt in my brake system so I will not mess with it anymore. I will stick with what GM suggested we use, DOT 3 and flush it every five years with fresh Pentosin brake fluid. This way the brakes will be there when I need them.

Having the car stop just as the brake pedal hits the floor is not good enough for me. I like the brakes to lock up all four wheels by that point. It might be the length of the pushrod in the master cylinder or even the bore of the master cylinder but something is not right if the pedal goes that far down. I have been fortunate as I had to replace the master cylinder once and it was a breeze.

I did have one master cylinder that locked up and the brake pedal felt like it had a brick behind it. At ~70 mph entering a 20 mph clover leaf it was an exciting revelation and woke me up right away. Thank goodness for the four speed transmission and downshifting. Along with a functional parking brake I was able to make it home. The only smell that warned me of the upcoming event was the smell of asbestos from the brakes and when I touched the pedal it was locked. Prior to this even the master cylinder was extremely sensitive, overly sensitive whatever.

 

DOT 5.1 is not silicone based. I've had 2 instances in the past where the pedal would go to the floor at random and act normal the rest of the time. In both cases, the master cylinder was bad. Air in the system should cause a consistent soft pedal and consistent excessive pedal travel.

 

Agreed - your fluid choice is fine and it’s glycol based (although I ran silicone for 25 years and it was also fine).
And, the only time I had the random almost-to-the-floor events is when my original MC was signaling me that it wanted to be rebuilt. I had the original sleeved and rebuilt by White Post.
With all that you have changed recently I wouldn’t rule out an air pocket that still needs to be bled out whether it is in the MC may want to bleed again to rule that out.
I’m down in Newport county and during the past few years have not been venturing out on the autobahn to get to the get-togethers up your way.

 

There is only one show left at Patriot Place this year, but if you ever get adventurous and venture out of Newport county stop by and introduce yourself. Thanks for your comments. My car is shown below.

 

Totally agree : air in system is constant - doesn't come and go sporadically