Brakes: Stopping is Kind of Important.

The title says it all- stopping IS important. This is a lesson we learned very early on with our truck as soon as we began driving it around our park since our foot brake pedal seemed to be completely unresponsive- luckily our hand brake worked very well. This little issue started us on the path of familiarizing ourselves with the brake linkage system on the Liberty and just how it would work. We quickly found it was in theory a very simple system- but accessing and working on it is definitely not a one-man job. However, we found eventually that the system is about as basic as it gets but ‘simple’ doesn’t always translate to ‘simply fixed’…

Brakes - 1918 Instruction Book, Truck Class B, page 51
Brake drum image from page 51 of the Quartermaster Corps’ Standardized Military Truck, Class-B Instruction Book ca. late 1918. It’s a rather simple system with two brake shoes per drum on each rear wheel. The foot brake applies pressure to front shaft links (left) and the hand brake applies pressure to the rear shaft links (right).

To begin with, I should point out the obvious to anyone reading this: the brakes are fully mechanical. No hydraulics, cylinders or fluids involved whatsoever. This is a huge bonus both in terms of cleanup and also accessibility. As someone who has only recently become mechanically inclined, this was a perfect project to take on and a nice challenge for myself and our motor pool volunteers involved. Luckily the hand brake worked very well, allowing us to still be able to operate and drive the truck safely around the property in the meantime. Most of our issues were related to the brake shoe clearance and linkage adjustments.

Driving set up
The driving set-up for the Liberty is luckily very similar to the standard today-this arrangement was not always a guarantee during the early days of Army motorization. From Left to Right: Clutch, Foot Brake, Accelerator, Gearshift, Handbrake.

The brake system is a simple mechanical shaft linkage and drum system with adjustable linkage shafts, and shoes. From the center of the truck the lines split allowing either the foot or the handbrake to apply pressure to both wheels at the same time- the foot pedal applies to the forward set of brake shoe toggles, and the hand brake applies to the rear set. This means that if you prefer one over the other, you will unevenly wear the brake pads. With the amount of driving we do I’m not *too* worried about this, but its a factor to remember in the future for potential pad replacement. When working on the shoes and adjustment linkages in the drum, there is a convenient work window cut into the drum which allows you to access the system from the outside by just rotating the wheel by hand. This was particularly handy when replacing a broken shoe toggle tension spring.

FDM truck central brake linkages
Central brake linkage elevating the shafts over the center of the frame and the transmission. The foot brake shaft is to the left, and the handbrake to the right 

This broken spring was indicative of one of our greatest challenges working on anything related to this truck: a fear of breaking anything. While no mechanic wishes to break and replace a part, this is particularly worrisome with our truck as anything on it that is original is near impossible to replace. Most of the bolts, nuts and springs on our truck are in fact original, making work on them nail biting. In the case of our adjustment nuts, we are always wary of threading and breakages. Luckily in the process of adjusting we only broke one spring which was easily replaced to standard.

FDM truck foot brake linkage-rear
The brake toggle linkages are to the rear of the transmission and central linkages in the previous picture. It is from the toggles here that brake power from the hand and foot brakes are distributed to both rear wheel brake drums 

Over several weeks of maintenance meetings with our museum volunteers, it took us about 4 sessions of adjusting and testing the brakes and linkages before we got any noticeable result from the foot pedal. The difficulty in adjusting brake shoes to within 1/100th of an inch on a drum that is over 100 years old and slightly out-of-round was not lost on our crew as we eventually settled for best we could get. We have not yet observed any evidence of drag or pad residue from the shoes being too tightly adjusted, but can see one or two spots where there is a gap beyond the 1/100th of an inch stipulate din the 1919 truck manual. We’ve determined this to be unavoidable due to the condition and general age of the drum. Still waiting on Autozone to restock the Liberty drums…

Brake drum interior- rear right wheel
Interior of the brake drum on our truck’s rear right wheel. Note the foot brake (L) and Hand brake (R) linkages and how they apply to the front and back of the drum. You can also clearly see the front shoe adjustment toggles, spring and the clearance adjustment. The pads must be adjusted to around 1/100th of an inch clearance which was our biggest challenge.

 

At the end of the day through trial and error we managed to let out the foot pedal shaft adjustment as far as it would care to go, adjusted the brake clearance nuts and shoe toggles and ended up with a slightly more responsive pedal, which is better than it had been. However, the hand brake remains the most useful of the two. With the shaft adjustment as far out as possible I see no way of getting better leverage at the moment that would result in better applied brake pedal force, aside from fabricating an entirely new shaft linkage which is a future possibility.

This was more technical post than normal, but stay tuned for more historical info coming your way!