Brakes locked up on a drive

Out for a drive in my 51 and was noticing I had to down shift on the hill sooner than I normally would. 
Why am I losing power was my thought.  On a flat spot I put the clutch in and came to a stop. 
I thought then I had a sticky brake. Quickly drive home suspecting a rear brake because it steered fine. Touched the rear hubcaps and both were hot. 
And to my surprise both of the fronts were as well. 
I’m now guessing I need to rebuild my Master Cylinder. Are these rebuildable ? Any thoughts ?



  • When was the last time the wheel cylinders and the master cylinder were rebuilt and the brake fluid changed?
  • Geoff
    Geoff Senior Contributor
    Check for a little free play before the rod contacts the cylinder piston.  Also check that the breather hole in the cap is not blocked. If the pedal is not fully back, holding the piston slightly forward, pressure can build up.  
  • Ol racer
    Ol racer Senior Contributor
    edited May 2022
    If determine the Master Cyl is at fault suggest replacing rather than rebuild
  • paulrhd29nz
    paulrhd29nz Member
    edited May 2022
    thank you all. Brakes and wheel cylinders have all been done. That’s why I suspect the master.
    I’ll get it up on hoist end of the week for look see.  I should add that the pedal has been getting noticeable harder over the last few drives. 
  • Jon B
    Jon B Administrator
    Paul, there's an interesting discussion over at the AACA Forum about the same problem happening to another fellow.  A lot of people chimed in with suggestions.  One suggestion (not yet mad here at your discussion), is that the bypass hole in the master cylinder, is plugged.  I had a similar problem with a car I owned 55 years ago.  The further I drove, the more the brakes dragged.  When I got the car to a mechanic he told me that the bypass hole had clogged, thus putting pressure on the hydraulic system, which tightened all the wheel cylinders slightly, which produced more heat through out the system, which in turn produced more pressure in the system, and....well, you get the picture.

    In the end, the owner of the car (at the AACA Forum) determined that the former owner had incorrectly assembled the master cylinder after rebuilding.  (Parts designed for a different M.C. had been used.)  The car's braking system had never worked correctly since he bought the car a year or two earlier, but he'd never had it out on the road, so didn't discover this.
  • Thanks Jon. Geoff had suggested to check the breather hole earlier. With luck I’ll get time to have a go over this weekend. 
  • All. We’ll I thought I had solved the problem by clearing the the two vent holes that were plugged. I removed the vent cap and went to go find a wire to clear the plugged holes and when I went to reinstall the cap there was break fluid all over the carpet. The master cylinder had burped. Topped it up, reinstalled the cap. Went for a drive. No brakes. No peddle. Thank goodness for Hudson’s back up system. 

    I think I’ve broken the springs in the master cylinder  by pushing the peddle hard to attempt to clear a blockage. I had the car up on the hoist and no leaks anywhere. 
    Conclusion, master cylinder is toast. It’s only 8 years old and still looks brand new. It was part number M3081. 
  • 50C8DAN
    50C8DAN Senior Contributor
    The Hudson Triple Safe system saved my car one time and it was and remains a great setup.  Not sure why it was never copied by others?  A Hudson original!