Advice Sought on Brake Swerve

In the spring of 2022 I was returning home from a "cars and coffee" at the local auto restoration garage, in my '37 Terraplane.  The trip to the gathering had been uneventful, but during my ride home the car swerved violently to the right when I applied the brakes.  When I got home I noticed some sort of liquid dripping from the right rear backing plate, down the tire and onto the ground. "Aha," said I, "my brake fluid's leaking."  But when I yanked the brake drum I discovered that differential oil was leaking, not brake fluid.

I replaced the inner & outer seals on the left and right rear drums, and installed new brake shoes & lining. I replaced the brake drum but at that point got sidetracked doing several repairs to the car.  Then, I had the car towed to a commercial garage to have some other things done.  I never actually drove the car to see if I'd manage to fix the swerving.

This summer I drove the car home from the garage, and found to my horror that the car still swerved violently to the right whenever I applied the brakes!  My "fix" of both rear drums, did not apparently cure the brake problem!

So I pulled both from brake drums, only to discover that there was no problem in either.  No sign of oil or brake fluid on any of the brake linings, and no brake fluid leakage in the brake cylinders.

I did adjust the brakes at 4 wheels, by turning the star wheel, and I even equalized the pressure in all four tires.

So, could anyone please offer some suggestions as to the source of my problem?  I strongly suspect it was something that happened suddenly; not over a period of days or weeks.  When I set off for the cars & coffee, everything was normal.  When I returned home the car swerved all of a sudden.

If you could suggest any explanation I would be most grateful.  I'd be even more grateful if you could suggest a test of some sort that would confirm your suspicions, rather than having me simply replace one part after another, chasing a possible solution!  Thanks in advance for offering your theories!


  • tigermothtigermoth Posts: 558Expert Adviser
    Jon, have you done a sudden stop on loose gravel to determine which (or if) one brake is not functioning properly?

    closest to a skid plate that I could think of.

    regards, Tom
  • cheyenne7271cheyenne7271 Posts: 558Member
    If that’s not feasible, jack the car up, have some one push on the brake pedal while you rotate each wheel to check for operation. You might not have a hydraulic leak but maybe a wheel cylinder that is seized. 
    51 Hornet Club Coupe
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  • GeoffGeoff Posts: 4,714Senior Contributor
    Did  you replace the lining?  It is most likely still impregnated with oil, which will make it grab.  You didn't say if you replaced the inner seal, because that is where the oil will  be coming form. 
    If you're stuck in a hole, stop digging.
  • Jon BJon B Posts: 7,506Administrator
    Thanks for all your good ideas. 

    Geoff, after the initial "swerve" in spring of '22, I pulled rear drums, found rear axle grease leak in right drum, and replaced inner & outer seals and brake shoes in both left & right drums.  I then test-drove car and got same swerve to right.  So I checked both front drums, found no leakage of brake fluid or grease. Wiped off linings with brake cleaner anyway.  Test-drove car and got same swerve.
  • GeoffGeoff Posts: 4,714Senior Contributor
    My Jet was doing the same, and it was the front piston stuck in the slave cylinder.  Look in through the inspection plate and  get someone to pump the pedal, and see if the shoes are both moving.  If swerving to the right it will be the left brake that is not working. 
    If you're stuck in a hole, stop digging.
  • 54coupe54coupe Posts: 1,124Member
    I had a similar issue one time with my 52 Wasp. The flex line to the right front wheel was deteriorated inside, and the hole was closed up. They looked to be in fine condition on the outside. You could apply the brakes, and fluid would pass through, but it did not return as far as the other side, so the next time I applied the brake, the right side grabbed much quicker. If you haven't replaced all three flex hoses in the last five years, I would do them all now.
  • Jon BJon B Posts: 7,506Administrator
    Geoff, thanks for that tip!  That inspection hole trick beats having to remove one or both front brake drums.  Also, if it's too dark to see through that little triangular hole in the drum, I can just stick a feeler gauge into the hole and -- if the brake lining captures it when depressing the pedal -- that means the wheel cylinder piston isn't stuck.  By the way: to what extent would a problem with one of the rear wheel brakes, cause swerving?  In other words, is it usually a problem with one of the front wheel brakes, that would cause violent swerving when applying the brakes?
  • Jon BJon B Posts: 7,506Administrator
    54coupe, according to Geoff, if car swerves to right, the left brake piston is stuck.

    In your case, a defective hose (right front) whose interior had collapsed,  caused that (right) brake to engage sooner than the left front brake, causing a swerve.  So...which way did the car swerve?  Left?  Right?
  • 54coupe54coupe Posts: 1,124Member
    edited September 18
    It swerved right.... Either way, if they haven't been replaced recently, I would do so. All of them.
  • Jon BJon B Posts: 7,506Administrator
    edited September 18
    Thanks for your ideas, 54coupe.  I had replaced the wheel cylinders, shoes and hoses on both front wheels, 5 or 6 years ago, with factory-new replacements.  But I guess anything can fail, no matter how new.
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