Re: 733 brakes locking on

Posted by 32model901 On 2010/6/12 17:01:19

Big Ed,

A few comments:

Check the Perrot units for wear. This unit is a small universal joint. If the pin and coupling inside has excessive wear the two ends of the joint inside the dome shell on the top of the front wheel backing plates will not be on the same axis or center-line.

The more wear you have in this unit the greater the two shaft ends inside will be out of alignment. The more these two shaft get out of alignment the rotation of the end operating the brakes will increase as the wheel is turned, assuming the end the brake cable is attached to is fixed.

You can easily check the play by disconnecting the brake cable and pulling the front drum. Hold the cam that operates the brakes securely and try and rotate the end the brake cable is attached to back and forth.

The working parts of the Perrot unit consists of three shafts and a pin. One shaft goes to he brake cable, one goes to the cam that operates the primary and auxiliary shoe, and the third shaft is the rotating coupling or universal joint. The three shafts are connected by a pin.

These parts were made to fit together closely. I've taken original units apart from cars with 70K miles on them and there has been about .005-.010 play in the whole unit. As long as there has been grease in the unit they seem to stand up well (once again, we can thank the Packard Engineering Department).

Because these Perrot units are not CV (constant velocity) universal joints even in perfect condition there will be some rotation of the joint as the wheel is turned.

I've adjusted the brakes of cars using the Perrot system, and if I had they were adjusted a little tight, the brakes would lock just as you described, even with the Perrot units in good condition.

You may want to try backing of the brake cable adjustment nut to give you a little more play in the front brake system.

Your experiment of disconnecting the cable and looking for rotation of the shaft as the wheel was turned is a good clue. One suggestion, apply some force on the brake shaft to take up any play that may be in the Perrot unit and turn the wheel side to side and see if you can see the brake shaft move. Take up the play in both directions when you turn the front wheel side to side.

If there is play in the Perrot unit you may not see it with the brake cable removed, because as you rotate the wheel side to side with out any pre-load in the system the movement of the Perrot unit could get lost in the play that is in the three shafts and pin (if any).

These brakes can be a "bear" to adjust properly, but when they are, they work great. A thorough, major brake adjustment can take 4-6 hours. I've found the best method is to remove all the brake cables, loosen up the two anchor pin nuts slightly, put a good load on the operating lever and then sock down the anchor pins. Make sure the eccentric adjustment is backed off before you do this. This method centers the shoes in the drum and then allows you to adjust the eccentric to bring the primary and secondary show up to the drum.

I've made up a mechanical foot using some 1/2" threaded rod, a nut, and a few 2 x 4's. When you have all 4 wheels centered they you have to adjust the brake cables at each wheel to get them to operate uniformly. Having a tool you can put against the front seat and adjust to press the brake pedal down and hold it there in one spot will make the 4-wheel adjustment much easier. Just try asking your wife / girlfriend / significant other to keep their foot on the brake with 80 pounds force for a hour, it just doesn't work.

One key point to getting good operating brakes in the position of the brake lever on the brake shaft. With the brakes applied fully you always want to be 5 to 10 degrees before full vertical position to a vertical position. This way you have the greatest amount of leverage applied to the brake shaft.

Good luck,

Dave