Packard Forum Index » General

Well I just rebuilt my Treadle-vac master cylinder and hopefully by monday it will be in the car-I have once question, that little metal box on the bottom rear that contains "hair" what is the purpose of that, and also what kind of brake fluid should I use in it.

The little metal box is on top. Perhaps I'm confused by terminology. The little metal box has two rubber strips that insulate it from the vacuum cylinder. The hair is supposed to be an air filter. Most replace it with open cell foam rubber.

Purpose of the "little metal box" with hair in it is to act as a vent to relieve the vacuum from the power unit when brake pedal is released. Otherwise brake pedal mite stay down and not return when foot is removed from pedal.

NOTE: As RB indicates the "little metal box" should be on TOP of the unit. NOT on the bottom.

DOT 3 brake fluid is used. Many owners are using the modern Dot 5. The DOt3 vs. DOT5 (silicone) is controversial. THus far neither side has proven anything. A few people are even using DOT 4.

Do a search in this forum for the various pros and cons of using DOT 3 vs DOT 5.

Whether to use DOT3 or DOT5 mite depend on what kind of brake fluid the system had in it BEFORE u rebuilt the unit.

Not a good idea to mix DOT 3 with DOT 5. DoT3 has an alcohol smell to it and a slightly sweet taste. Dot5 is silicone and has no particular visual properties nor smell that i can remeber right now. Most DOT 5 i've seen is kind of blue or purple in color.

DOT3 will dissolve paint. DOT 5 will not dissolve paint.

One more question-I noticed after I re-assembled the treadle vac the return action on the plunger/hydraulic part of the master cylinder was extremely slow-I assume its because of all the new parts I put in it-will this action quicken once brake fluid is added to the unit and the vacuum line re-attached?