Been in car hunting mode and on a ‘33 V12, I saw a front end setup that I’ve never seen on another car that I can recall. What’s the story behind this rod that runs thru the front axle? Is this a V12 only thing? The ‘32 ‘8’ isn’t like this .
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.
Ah, very interesting. Thanks @Jim.
Were there any other makes that used the Stewart-Warner power brake setup? Studebaker, perhaps?
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 understand that Rolls-Royce used it. It is a more expensive unit to manufacture than a more typical vacuum booster unit. In ’36 Pierce went to a vacuum booster. If I remember correctly it was because the new overdrive unit added didn’t leave room for the S-W unit anymore. The whole transmission, freewheel, and S-W brake unit makes for a pretty long assembly.
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.
@Bill, any idea what the rationale was to use the worm drive differential on the ‘33? The ‘32 (at least the model 54) had a conventional final drive. Were there leftover parts in the stockroom to use up?
@Jim, does the S-W per brake setup work better or have advantages over a vacuum booster? I had a ‘35 Packard with vacuum assisted mechanical brakes and they worked pretty well.
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
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
Worm Gears for 1933?
They are supposed to be quieter.
Pierce had used them on trucks since the first trucks in the early teens. Speeds were much lower.
Premature wear was the problem. Interesting that they didn’t use the worms on big 1242 and 1247 chassis.
Most 1933’s were converted either by the factory , dealers or later owners.
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.
@David & Diana Stevens – thanks for the insight on the S-W braking system, Dave. I just figured that all drum brakes on early passenger cars were marginal – they have been on any of the cars I’ve had previously, compared to modern, of course. As a side question, did racing cars of the era have a system like the S-W, super soft linings, or just lousy brakes?
On the worm drive, when did Pierce move away from ring & pinion? Was the ’33 worm drive a one-year change, then back to a conventional rear end?
@Jim Chase – thirty years !?! Yikes – time’s a wastin’. The kick shackle, on the ’35 Packard I had, I think that was called a ‘trunnion block’ – the setup with 4 springs on it, no?
Thanks, everyone, for helping to educate a P-A +noob+. 😏
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.
My ’54 Bentley had a similar system for the rear brakes with hydraulics on the front. Kind of overcame the low speed braking issue.
Yes, the trunnion block is what I call the kick shackle.
Scott Stastny redid the power braking system on my 1933 1236 before he passed away. The brake drums and linings were like new, but the clutch in the power braking system was shot…I virtually had no brakes when hitting the brake tredle. Scott had the power brake clutch relined with Kevlar, but after getting it back from the shop he made circular spirals on the clutch face to keep too much oil from collecting on the clutch face as he believed it would cause some slippage. I can attest to the power of the power brakes, and when switching from one car to another, I really have to be careful with stopping. It is easy to hit your head on the windshield if not careful. I have driven both my car after repair, and Bill Morris’s 1934 roadster, and both have the same characteristics when stopping. Great system.