The Stovebolt Site Forums The Shop Area Driveline Which brake fluid

I have a 53 Chevy 3100 that I completely rebuilt the brake system with all new lines and parts about 15 years ago. However, I seldom drive the truck and probably only racked up about 5,000 miles. Recently , the master cylinder seemed to be locking up and the brakes would not entirely disengage after release of the pedal. A teardown of the master cylinder and wheel cylinders revealed a rusty colored sludge , water, and pitted sections in the wheel cylinders that were too bad to hone. I have ordered a new master cylinder and all new wheel cylinders along with new hoses. I blew out the hard lines with brake cleaner. My question is which brake fluid to use this time around. What I had used was synthetic dot 3 . A friend of mine who has a Packard that he seldom drives told me to use dot 5 silicon based . I would hope that the dot 5 would not attract moisture as dot 3 evidently did. I hope for advice on choosing dot 5. thanks

Every car you see in my signature line uses DOT 3.

DOT 3 will hold up just fine, even if the car isn't driven very often. Everything has to be sealed up tightly so no moisture gets into the lines.

DOT 5 doesn't always play nice with rubber seals and hoses and may disintegrate rubber seals in your old wheel cylinders. It's also more prone to foaming which will give you a soft pedal.

Unless you've replaced every single component in your system, there will likely still be DOT 3 in the system which doesn't mix with DOT 5. ERvena small amount of DOT 3 will cause serious problems in a DOT 5 system - gunked up lines, sticky mess, etc.

The only parts being retained are the hard lines which I have blown out with compressed air and brake cleaner. Damage to my system seems to have been done by moisture as noticed by the rust colored goo inthe master cylinder and brake cylinders. The brake cylinders were also heavily pitted in the central parts where fluid is compressed. Too deep to hone.

I agree with Otto....and with problem you had I'd definitely change lines as well because they rust fron inside. SVe yourself a lot of future problems and replace them.

As you might imagine, we have had this discussion before. e.g.

Brake fluid discussion

I use DOT 5 in my truck and project car.

I have had the same dot 5 in my truck for the last 25 years, I have had zero issues with it and only topped it off once in all those years. I don't drive all that much, 15K since rebuilding the truck. Mine does stay in a garage thats semi climate controlled ( no freezing or above 80 ).

Do not mix DOT 5 with any other brake fluid. DOT 5 is silicone based; DOT 3, 4, 5.1 are glycol based. Mixing 5 with any glycol based fluids will result in a gelled mess with no braking. DOT 4 has a higher boiling point than DOT 3, but 4 absorbs more water and needs be changed more frequently. Same goes for 5.1 over 4. DOT 3 is probably fine, but all brake fluid absorbs moisture and needs to be flushed. If you really want to use DOT 5, you will have to totally and completely flush out any traces of DOT 3.

Geoff: Flush with what?

If it were me, I would disassemble all brake lines and clean them with brake clean, then run multiple flushes of new fluid through. I really wouldn’t recommend switching between glycol and silicone based fluids though.

Pits in a wheel cylinder that are in line with the hole for the fluid to enter don't necessarily need to be completely honed out. The rubber cups never get pushed that deep into the cylinder because of the spring and the tapered metal expander cones that are included in any rebuilding kit worth installing in the first place.
Jerry

I always use denatured alcohol. (methanol) The stuff is sold at most Walmart and big box hardware stores as "shellac thinner". Any residue that's not eliminated with an air pressure purge will evaporate when the brakes get up to operating temperature the first time.
Jerry

I've had Dot 5 in my 1939 Chevy Stake Truck for 25+ years. Never a problem. If I stomp on the brakes hard it'll put your nose into the windshield. Before I used it I replaced all lines, wheel cylinders and master cylinder. If the rubber flex hydraulic brakes hoses are bad on the inside they can keep the pressure from releasing in the system.

Rick G.