Dot 3 or Dot 5 for a 55

[Bob Kielar]

Hello all,
                       I am going to replace all my brake lines can I use dot 5 brake or does this effect the power brake booster. Is there anyway to tell what kind of fluid that I am currently using ? It seems that the hoses and brake cylinders have been replaced.

Happy Holidays,
Bob

[Steve Passmore]

I run Dot 5 in all my cars with or without booster.  Works great, remember not to fill the reservoir up as it does expand when it gets hot.
The fluid has a different feel, colour and smell but that doesn't help unless your not familiar with the different types.

[CEC #20099]

DON`T USE DOT 5 in a 1955 Cadillac with a Hydrovac power booster. These units are known to consume small amounts of brake fluid, which is sucked into the engine thru the vacuum hose. DOT 5 turns to gritty sand in the cylinders, & ruins the engine. Use DOT 3 or 4, which is a polyglycol, & will not ruin the engine, if ingested.
c chleboun #20099

[william_b_noble]

no opinion about "turns to sand" - I'd expect its' more like a synthetic oil - howerver there are two other issues with DoT 5 -

1. because it's hydrophobic, it can leave pools of water in low spots of the system and if you are in a location where freezing can happen, the water can freeze and leave you with diminished (or no) brakes.  or under hard braking it can flash to steam and also leave you with no brakes.  If you live in a mild climate, I wouldn't worry -

2. when I bought Dot 5 fluid some decades ago, it didn't have the swelling agents, so it wouldn't work in some cars - it leaked out of my 51 dodge and 36 cad, it's fine in my morgan, 59 cad, and 356 porsche - I don't know any way to tell whcih cars can tolerate it.  maybe new formulations now have a swelling agent.

I have Dot 5 in my 59 cad, no problem, but it leaked out of my 36

[D.Yaros]

Seems to me I just saw a tv show hyping test strips which one may use to determine the DOT # of brake fluid.  My recollection is the strips were readily available at local auto parts stores.

[Alan Harris CLC#1513]

Conventional brake fluids have a distinct smell. Silicone (DOT 5) fluids, to the best of my recollection, have no smell at all.

Years ago, I used DOT 5 in a 69 Cadillac, 50 and 51 Cadillacs, and an MGB. I never had any problems.

In more recent years, I have stuck with the DOT 3 fluids. I recently had a Bendix Treadle Vac unit rebuilt by White Post Restorations. They have a lifetime warranty as long as DOT 5 is NOT used in the unit. There must be a reason.

If you are really worried about brake system corrosion, it is probably better to use DOT 3 and replace the fluid every few years.