Dry Master Cylinder - No Sign of Leak

[Phil Waterman]

Hi All

Well spring has finally come to New England, so it is time to check and service the fleet. As CMPs have a single braking system be sure the master cylinder is topped up and the brakes are all working is a priority. C60S no problems only problem was one turn signal that didn't blink clean and replace bulb.

Next up was the HUP, which as you may remember had a full rebuild 4 years ago. Brake peddle went down about half stroke which was not normal as this truck has always had one inch of travel when the brakes are properly adjusted.

Removed the large brake access panel, yes late CMPs have a large removable floor section. Low and behold reservoir was basically dry.
W HUP Brake 3.jpg

Then rolled around on the creeper and could find NO sign of a leak. Refilled the Reservoir pumped the peddle slowly and the peddle level came back up to normal and is nice and hard. Applied the brakes as hard as I could and rechecked, again nothing. Left the HUP sitting on clean dry floor for 24 hours and no drips or drabs. Next step was to let it sit at pressure for couple of hours.

To do this position the porta-power on the peddle and brought the push up to 30lbs. For years I had tried to figure out how to apply 25-35lbs. to the peddle while turning the lower adjustment lugs, as is called for in the Manual. Well it turns out the solution to this is amazingly easy stand a bathroom scale on edge and use the porta-power ram to apply 25-35lbs.

HUP Brake 02.jpg
W HUP Brake 01.jpg

Two hours into the test no pressure drop and no sign of a leak. So I left it for the day and will see what has happened in 24hrs.

Any bets on where or if I'll find a leak?

Cheers Phil