Packard Forum Index » Pre-War (1899-1942)

I'm working on a 1937 115C. The rear brakes lock up by themselves at about 10-15mph. As soon as it screeches to a stop, the rear brakes release & I'm good to go until the next time. Any ideas?

Is there any clearance between the brake shoes and the drum? They would do this if they are adjusted too tight.

Lift the rear axle using a jack under the differential, each wheel should spin freely except only to have a slight coasting sound.

One or more wheel cylinders that leak slightly can cause that to happen. A leaking rear axle seal can do the same. Brake fluid or grease may appear at the lower backing plate, but it doesn't always. A slight leak is usually what causes brakes to stick or grab. The brakes get gummy and stick. When the car stops, they un-stick. A bad leak will lubricate the brake.

Other possibilities: I have had a situation where the brakes on a 1947 Plymouth would get progressively tighter with each application until they began to drag and overheat. That problem was in the master cylinder. Somehow, pressure was being applied to the system and retained. If the car sat overnight, the brakes would work normally for several stops, then the problem returned. If your problem is rear wheels only, I would suspect that the parking brake cables or other hardware is stiff and not releasing fully. In some cases, pistons in the wheel cylinders can stick. That usually affects one wheel. Very weak, broken, or missing brake return springs could cause dragging brakes. The first thing to check is the adjustment. There should be no significant drag in the brakes. Another possible issue is lack of free play at the brake pedal. The brake pedal should have about an inch or so of free travel before it engages the master cylinder. Is this a new problem, and has any brake work been done on the car recently?

My experience has shown me that if the brakes are way out of adjustment (that is, way too loose) they will also do this. One of the first, easiest and cheapest things you can do is just give them a standard brake adjustment. Tighten the star wheel till the wheel drags very heavily and then back off ten clicks or so.

If that is not it, then it is on to leaky wheel cylinders or bonded linings having come loose from the shoe.

I once adjusted my brakes too tight and filled my master cylinder too full. It was fine until the car heated up, the fluid expanded, and only needed that expansion to apply the shoes against the drums.

Quote:

Ross, didn’t plug his own video, so I will. I found this video to be very helpful when I was working on my brakes:
Ross Miller - Speedwell Garage - Brake Adjustment Video