Help me understand the ‘33 front end

That is a torque rod that applies the front brake shoes. There is a bellcrank and cable inboard on the axle that runs back to the unusual power brake system (33-35 only). This is instead of conduit and cables going directly to each wheel on a mechanical brake system. The Stewart Warner power brake uses the torque of the driveshaft to apply the force to the brake shoes via a clutch system on the back of the transmission and free-wheel unit. The brakes are very powerful but often there is a tendency to creep at stoplights.

The ’33-’35 , “8’s” have that also, front and rear. ’33 is different in the rear because of the bevel gear axle vs ring and pinion of ’34-35.

I should add that there is a lot of info available in the Pierce-Arrow Service Bullitens that are key word searchable and downloadable on this website.

There are multiple possible reasons to explain the Power Brake unit vs. vacuum.
1) Mechanical: The power brake unit derived it’s power from driveshaft rotation. The BW Overdrive interrupts that rotation in freewheeling. The sequence of adapting them would be Engine, Clutch, Transmission, Overdrive and then Power Brake unit. This would be an engineering challenge and costly to resolve
2) Cost: The vacuum setup is a lot cheaper
3) More Owner drivers: The Great Depression wore on causing many chauffeurs to be sidelined from driving in local communities so owners would appear less ostentatious. Also more women began driving. The SW Power Brake unit is extremely powerful except when parking. At 1 mile an hour there is not much driveshaft rotation, the treadle pedal goes flat to the floor with no pressure and the car travels another 18 to 24 inches. A shocking experience or worse for those unpracticed with this characteristic.
I have the privilege of having a 1933 1247 and a 1936 1601 so I can describe both systems:
The SW unit is the best braking system by far of ANY until disc brakes. It has the lag at very low speeds, but that is quickly learned. Fade is virtually non-existent. Creeping when stopped indicates that an adjustment is needed. In 21 years I have never experienced that issue. Locking up all 4 wheels at 70 mph with a 6,000 lb. car is possible
Dave Stevens
The Bendix vacuum unit is good compared to other non-hydraulic braking systems on the 1st hard stop. Fade increases very rapidly with subsequent stops. Bear in mind that the brakes at the wheels are the same, in my case right down to the linings. In my 26 years with the 1601 I have had a few scary stops due to fade and have learned to drive this car much more defensively.
The best setup would definitely be the SW unit plus the overdrive if they had gone that route

I have a ’36 Packard with vacuum boost cable brakes and it works well, as far as boost is concerned. The unit has some corrosion inside where the seal sat for decades so sitting at a stoplight it has a bit of a vacuum leak that leans out the mixture and causes a minor stumble at idle. It doesn’t effect the boost. They are a bit grabby when cold but quickly lose that.

My Pierce is still a work in process and I have only driven it in short spurts up and down the cul de sac. I can say that the Pierce brakes work very well and unlike most drum brake systems seem to work as well backing up as going forward.

I have been anxious for 30 years to see how they work on the road. The challenge for any mechanical brake system is to get them adjusted. They all have some degree of mechanical slop in them that is minimized the tighter you adjust them but some level is needed so the shoes aren’t dragging and overheating. Pulling to the left or right is the biggest concern, next is the delay from taking up the mechanical slop. The torque tube on the Pierce I think has the potential to be less prone to uneven pulling, but I don’t know that yet. Both Packard and Pierce are solid front axle cars with an interesting device called a kick shackle on one of the front spring shackles. It is there to reduce the tendency to develop nasty steering shimmy when “balloon” tires were introduced. Packard and Pierce have different designs for these. The kick shackle introduced a new problem, when the front brakes are applied the force gets fed back into the steering arm and the front brakes had to factor this out by tweaking the geometry of the front brakes to pull a bit harder on one side than the other.

There are so many variables that come into play comparing the system on any two cars. One of the main ones that throws things off is the brake lining characteristics. Original linings were relatively soft asbestos which is hard to find. Newer modern linings are often too hard and have very different characteristics which can be extremely grabby one minute and fading the next. I had my Pierce relined with newer material that is supposed to be relatively soft and a suitable replacement for asbestos, but I won’t be able to judge until mine is actually roadworthy. As of a few years ago it was still possible to get asbestos linings for mid ’30’s senior Packards (if I remember correctly Pierce used 16″ diameter and Packard 15″).

Another variable in the S-W system is the clutch that activates the brakes. It is basically a disc brake with a soft lining that is immersed in the transmission oil. When you push the brake pedal you are applying pressure to the clutch to apply the torque coming from the driveshaft to apply the brakes. The original clutch material is no longer available and units that have been rebuilt generally have a Kevlar material that has been found to be a suitable substitute. Although it is clearly suitable, it probably is not an exact match for friction characteristics, so throws another variable into the comparison. I was very lucky on mine, the original material was intact with no significant damage or wear, so should work per original – except for those non-asbestos brake linings.

Adam,

I was always told the worm drive made the car lower. My ’33 has a completely rebuilt worm gear, replete with the bull gear and non sulfur oil to protect the “yellow” metal.

I think Stutz’s or the era had them also.

Bill

Yes, the trunnion block is what I call the kick shackle.

I recall reading that Rolls-Royce licensed their mechanical power-assisted braking system from Hispano-Suiza.