Bendix Duo Servo Brake Adjustment – (Mechanical Rod Type) 1930 Willys Six – Paul Young
The braking system on my 1930 Willys Six was showing some signs of wear so I decided it was time for a bit of refurbishment. The first thing I did was take out some of the wear in the linkages. I found website www.mikes-afordable.com to be a good source for clevis pins and brake rod ends.
One of my intermediate drop arms was too badly worn for an oversize clevis pin so I had to remove the arm, drill the hole oversize and then machine a press fit bushing to take it back to standard size.
The front brake arms were worn where they pivot on the front axle. These had to be reamed out to 13/16” and bushed with a 11/16” x 13/16” x 2” bronze bush. Once I had done this, all the up and down movement at the extremity of the brake arm was removed where it connects with the brake rod. That’s a lot of rattle! These brake rods have a spherical end on them to act as a simple universal joint for when your wheel is going up and down. Because these were badly worn and the brake rods themselves were in poor condition, I decided to make up new ones. The rods are 5/16” with a 5/16 UNF thread on them. New spherical ends were made with the same thread and securely attached by screwing them on to the end of the rods with Loctite, then peening over the end. (Other restorers I know have used braze rather than Loctite.)
Now that I had eliminated all play from the mechanical linkages it was time to adjust the brakes. Jack up all 4 wheels. Although the manuals suggest a 1/16” clearance between the front brake rod arm and the brake cam lever, this does not allow for 80 years of wear on the steering arm ball. To allow for this wear, first remove the tapered spring retaining circlips. Then rotate steering wheel full right and check clearance. Repeat with steering wheel full left. Adjust brake rod length so that there is an equal amount of free play at the brake rod spherical ends with the front wheels pointing straight ahead. I found that I needed ¼” of free play in the straight ahead position to give me no play at full left and right lock. Although ¼” sounds a lot, remember this is at the brake rod end of the arm, not the brake cam end. Once you put the tapered springs back in place, you can’t “feel” this gap. Because the length of the brake arm is about 8 times longer from the pivot pin to the brake rod than it is to the brake cam lever, it’s easier to get an accurate measurement and get both sides equal. Fortunately, Willys designed in a compensating mechanism between front and rear so you don’t need to worry about that, just get the gap the same on left and right in the straight ahead position without the brakes being activated on either left or right lock and you’ll be fine!
Now adjust the eccentric wheels as per instruction manual as unless you have shares in an oil company, nobody can afford to have dragging brakes.
Next I clicked the handbrake up 3 notches (which equates to about 2” pedal depression that the manual recommends) and adjusted all the brake shoe notched wheels so as to need 2 hands to be able to just rotate each wheel. Remember to rotate the notched wheel downwards to adjust the brakes up (spreads the shoes further apart) and upwards to slacken them off. Finally, remove the jacks or stands and road test the car. My result was perfect brakes – smooth and equal on all 4 wheels, something that is vital if you are going to drive your vintage car amongst modern traffic.