M8 Greyhound Brake Fluid?
 

Hi, I'm working on dragging brakes on a Greyhound. We use DOT 3 in the brake system, based on a Google search saying "HB" fluid should be used. (The 1943 manual we have says "information not available at this time".)

I just dismantled a wheel cylinder and found the u-cup seals in good condition but maybe a bit soft and swollen. They make the pistons quite hard to push by hand through the bore, so I was wondering if we should have been using a mineral oil.

Malcolm

I got the answer from Brian Asbury. It uses dot 3 brake fluid.
Malcolm

always pump the brakes after shut down , that way you will not be looking for where the brake fluid has gone,

Hi Frank,
It looks like you need a couple of seals to leak in the Hydrovac unit between the hydraulic circuit and the vacuum reservoir for this to happen. I haven't noticed our M8 losing brake fluid, so maybe the seals are good? But it may also be because sadly it rarely gets driven. I'll keep an eye out for losing fluid.
Malcolm

M8 brakes
 

DOT 3 is correct for your M8 and for just about any 1940's hydraulic brake system. You should never use mineral oil in a brake system and you should do your best to keep any traces of oil from entering your brake system. Oil is actually a cause of deteriorated brake system seals.

-=BK

Thanks, Rob. I would not have considered using mineral oil in a brake system, until I worked on some CVRTs. They use mineral oil, which rattled me a bit! So now I make sure what is correct before working on any brake system.

Malcolm