another hydrovac question!

[tom]

hello everyone,

Here I am again with my hydrovac questions! What type of oil should i use in the hydrovac it has to lubricate the leather piston seal. In the bendix catalogue they tell to use bendix vacuum piston oil.But what kind of oil is this? or what is a good alternative?

thanks

tom

[motto]

Hi Tom.
I'm sure that the manuals tell you to add a small amount of brake fluid to the vacuum chamber and that would be the safe bet. The push-rod passes through a seal between the air and hydraulic sides of the unit and you wouldn't want to contaminate that seal.
David

[RANGER]

The manuals do not tell you that.

[motto]

You're right Ranger.
On taking a closer look at the lube chart inTM 9-801 April 12 1943 where it refers to oil, hydraulic it is not refering to brake system hydraulic oil but something else as the code given for the hydrovac cylinder is OH and the master cylinder HB. It doesn't specify exactly what hydraulic oil that may be.
TM 9-802 23 Feb 1945 is more specific in calling up, Fluid, shock absorber,light. Both manuals recommend starting the engine and giving 3 or 4 severe brake applications to distribute the oil which seems to me to run the chance of bringing mineral oil into contact with a vegetable oil seal?
David

[Gordon_M]

I used a small amount of hydraulic jack oil in mine, same as I used to fill the shocks.

I do remember seeing somewhere recently that vacuum cylinder oil was still available over the counter in some places?

[RANGER]

I hope I'm right after 50 years. I've had a lot of good training by some who helped develop brake boosters when they first came out.
Use Permatex Hydraulic Jack Oil, Midlandand Bendix endorse the use of this oil. It only wets the seal in the air chamber and does not contavt the brake fluid. No need to second guess the use of the fluid, it just creates hype and home fixes which are dangerous.