Dry Master Cylinder - No Sign of Leak

[rob love]

I was going to say the same thing: the fluid will be more likely to leak at rest than at pressure, as the tension is not on the cups.

The leaked fluid will dry eventually, but will usually leave some staining to let you know where it left the system. Question is, was your system full in the fall, or near empty to begin it's winter rest.

Not all brake systems have the residual check valve. I know I have to remove them on the M135 when I use a M35 master cylinder, otherwise the brakes drag for 2 or 3 seconds.

You can also have cup expanders in the wheel cylinders to help prevent the seepage. It uses the spring pressure in the wheel cylinder to force the lips of the cup outwards.

I have always said the sitting is worse for these vehicles than using them. In my location, the temperature over the year will vary by almost 80°C over the year (we see almost -40 in the winter and almost +40 in the summer). The miracle is that the systems work at all. The other miracle, when I think about it, is that anyone chooses to live here.

[Lynn Eades]

Good points Rob. Especially the last one
The general rule for residual line pressure valves is;
Drum brakes have them and disc brakes don't. (not directed at you Rob )

[Phil Waterman]

Hi Rob

As things happened the trucks just got driven into the shop after the Summer Rally and sat until the end of November before I could do anything on them. So no they didn't get a fluid check before going into storage this year.

Well the system in the HUP sat at pressure for 24 hours did leak down a little 41 to 30 lbs still no sign of any leakage. With out re-stroking peddle increased the peddle pressure up to 55 lbs and then left for an hour. There was no sign of the peddle having creeped down.

So tomorrow when the weather is better I'll take the HUP off the jack stands and take it for a drive and see how the brakes feel. Taking each of the trucks for a nice long drive is part of my spring ritual, got to burn up all that stale gas in the tank and then get fresh.

Cheers Phil