Wanted: C15A Brake servo linkage

[Phil Waterman]

Hi Rick

Having a HUP no booster, C60S Pattern 13 large drums, and C60L Pattern 12 small drums I'd like to add a few comments on brake boosters, it is the equivalent of being able to push on the brake peddle with an added couple of hundred pounds of force. Having that in mind the brake system really needs to be up to snuff.

CMPs when the brakes are properly adjusted have better brakes than many if not most trucks of the time period. You can lock the wheels on a HUP at 30 MPH in a panic stop if the brakes are properly adjusted. We are spoiled these days by self adjusting brakes and the result is that we forget that even a little excess peddle travel means it is time to adjust the brakes. Yes you can really tell the difference when the booster is functioning or not. All you have to do to prove that is stop the truck on a hill, kill the engine step on the brakes a couple of time to use up the stored vacuum and you will really know what the booster is doing. I have a hill on the road into the house where I do this little test on a regular basis, just to check the health of the braking system.

Now to the brake booster take the time to bench test and set up the booster before it is installed on the truck. Making sure you have no vacuum leaks is critical, even a few inches loss of vacuum will really impair the operation of the booster. Being sure that you have the booster and linkage adjusted per the manual will make a big difference in the function of the brake unit. The manual tells you to make a little test bushing and gives the dimensions this little bit is critical to getting the booster and linkage to work correctly.

Brake booster on C60S with big brake drums works much better than Brake Booster on C60L with small brake drums. The small drums of the 16" wheels trucks just don't have the same braking force.

I've often wondered if there were C15As fitted with brake boosters and winches in the field particularly in Italy to meet the need for short wheel base trucks in the mountains to tow guns. I've always wondered if this was the origin of idea of putting winches on C15As after the war.

Brake booster on C15A would surely improve its ability to tow heavier loads, at low speeds in steep terrain.

Will look forward to hearing about you progress.

One last tip the boosters need to be serviced yearly with the adding of oil and rotating if the leather seal dries out not much boost.

Cheers Phil