The Stovebolt Site Forums The Shop Area Driveline dot 3, 4 ,and 5?

i did a search on brake fluid last night and i decided to use dot 5 over dot 3. i weighed the pro and cons, but when i went in my garage i found out the i have dot 4.(castrol dot 4) so i need advice. it's a 1955.1 3600. my old single master cylinder was leaking and one wheel cylinder failed. ( both of those were about five years old) so i decided to redo the brake system . new double master cylinder ,new hoses, new nicopp lines. all the old fluid is drained away. everything is installed and ready to go. i want to remove the master cylinder for a bench bleed. now i just need a solid answer of what fluid to use because i'm using older wheel cylinders in front newer cylinders in rear and i don't know what type of fluid was in there. am i over thinking this. thank you, brian

Good morning Brian.

You will hear some extreme views on this subject including the statement that DOT 5 always yields a "soft pedal". In order to believe that you will have to believe that what we learned in our physics classes, that fluids are not compressible, is incorrect. This subject is all over the car/truck forums so all the information you can possibly digest is out there.

I use DOT 5 in my restored '36 Chevy pickup and in my '32 Ford roadster street rod. The purpose is to avoid the "paint remover" effect of DOT 3 & 4, especially on the roadster where the front brake lines pass through the exposed frame rails. In my experience successful bleeding of DOT 5 requires waiting a day or so after pouring the fluid in and doing the actual bleeding. On the subject of bleeding I just discovered "gravity bleeding" that makes bleeding a 1 person job if the MC is above the level of the wheel cylinders/calipers. I wish I had discovered that decades ago. It really works!

DOT 3 & 4 advantages- inexpensive, easier to bleed. Disadvantage - removes paint.

DOT 5 Advantages & disadvantages - opposite of above.

If you are into the brakes anyway you might consider using asbestos shoes. They are abundant on ebay and work way better than the "organic" friction that has been manufactured since about 1980.

Good luck with whatever you choose.

I used Dot 5 in my 70 340 Duster. Reason being it sometimes sets for months and I didn't want to deal with rusty wheel cylinders or rust sediment in the 4 piston Kelsey Hayes calipers. Now it you do get moisture in a Dot 5 system, it'll pool in the low spot and.....rust.

I really think Dot 3 is the way to go on our old trucks. If you want to do the best you can for it, buy a power bleeder and change the fluid every year or two. I may add this one to my shop. Price is reasonable and it has good reviews.

RonR

I have used DOT 5 for 16 years in my truck with no problems.

thak you

Some years ago I worked for a company that made Castrol's DOT 4 formulation. It contains an additive that reacts out small amounts of moisture so that small amounts of moisture do not lower the boiling point or cause corrosion. We called it LWS for low water sensitivity, I think Castrol calls it LMA for low moisture activity.

i used dot 3. the top of the master cylinder had a stamp "use only dot 3 fluid from a new sealed container". it may have been an old stamping on a new master cylinder but it sort of made the decision for me. thanks to all that replied , brian