308 Brake Pedal Occasionally Goes To The Floor

On my 1977 308 GTB I'm chasing a strange problem and thought I would turn to the F-Chat Brain Trust for help.

Occasionally when I go to brake the pedal will go right to the floor on the first application. On the second it is totally normal. The brakes operate 100% perfectly and the rest of the time the pedal is good and hard. It started last year and continues this year after winter storage.

I cannot get it to repeat with any regularity and here is what I have done so far to diagnose:

1. Visually inspected the full braking system. 100% dry and no signs of leaks or problems. The flexible lines are stainless steel and show no visible problems.

2. Flushed the complete system with a full bleed. Found no air pockets to speak of and the fluid (that was only a year old) looked ok.

3. Checked the thickness of the pads and rotors. Thinking that it could be pad kickback I am discounting this theory because the pads and rotors are very thick and you normally need quite a bit of wear for pad kickback to be an issue.

Outside of this the booster system seems to be working fine and the main vacuum line was changed 2 years ago. Also I cannot imagine how the booster could affect the hydraulic system it merely assists.

My inclination is that the master cylinder has gone bad and needs to be re-built. Of course I'd like a second opinion before taking everything apart. Any opinions or feedback would be most appreciated.

 

It certainly caught my attention. I have been endurance racing for years and pad kickback is a very real thing you learn to anticipate. During endurance races I'll tap the brakes with my left foot on the straights to set the pad distance to the calipers. When entering a braking zone on the limit there is no time to press the pedal twice. On the road I leave a lot more margin but even so it is a problem that needs to be fixed before I drive the car any more.

 

Thank you. I'm pretty sure the seals are original and there is no signs that the master cylinder has ever been replaced. I have already ordered a re-build kit and will not be driving the car until this issue is sorted.

 

UPDATE: Turns out it was the master cylinder.

I removed the master and took it apart. The seals looked pretty good but the bore had some wear undulations on its surface. No scratches or pitting but a tiny and gradual differential in diameter due to wear. I assume the master had been re-sleeved at some point because I do not believe that they originally would have had a brass bore as mine did. I tried a re-build kit along with a light hone and polish but struggled to get the master to work properly. Re-build shops were more expensive than a new cylinder with long lead times.

In the end I ordered a new master from Superformance and am very glad I did. It arrived in 2 days and shy of not having the Benditalia marking on it, it is identical to the original and a perfect fit. I'll keep the old one on the shelf to maybe restore sometime later but for now I have a rock hard pedal and no more braking problems.

 

Post edited. Correction made in video tutorial in link a few posts down.

 

I have updated my experiences in the following thread:

https://www.ferrarichat.com/forum/threads/brake-master-cylinder-replacement-bleeding-video-tutorials.625487/