The Stovebolt Site Forums The Shop Area Driveline Should have gone to DOT5?

Years ago when I completely rebuilt my brake system (new lines, MC, etc) with not a speck of DOT3 in it, should I have gone to DOT5 which does not suck up water like DOT3 or 4?

In my opinion
You did right, stick to dot3/4/5.1 fluid
Because
Your brake system is not sufficiently sealed up tight from the environment to support dot5 in its intended application
The master is vented to open air where water splashing can introduce serious moisture
And the wheel pistons aren’t super great at being sealed tight either, one layer of protection like mechanical screw threads or a broken boot let’s moisture into the system
So using dot3 technology and replacing the fluid regularly is the way to go (2-3 years total flush is what I aim for)
A dot5 system is meant to be super sealed tight
And no water ever gets in
It is not vented to atmosphere
And the fluid goes a longer time between changes

If you get water in dot5 the wheel cylinders will rust and pit on the bottom inside and the roughness cuts the piston cup seal and then it weeps brake fluid
This problem also happens when you don’t flush the dot3 and it’s ability to hold water is exceeded
-s

I use DOT 5 in my truck and my hobby car. It doesn't absorb water (and we live on the wet coast) and it doesn't remove paint (and I'm sloppy). However, more expensive and not all shops carry it.

TooMany,

Maybe I did something right....by accident.

Hi Gord&Fran
You might want to check if the water is pooling into beads in the bottom of your wheel cylinders
Driving in the rain will splash that master under the truck
The water usually ends up in the wheels at the bottom and that’s always the first place the system rusts out
bleeding won’t get the water out because it’s too heavy for the relatively slow flow rate while bleeding.
It can take years for water to form however if the vehicle only sees dry roads because the dot5 repels water which is desired in a fully sealed system

Absorbing water is a feature of dot3,4,5.1 not a detriment
You want it to absorb that water

Also if your water beads get large enough
They can boil into tiny steam pockets which can easily fill the whole wheel cylinder and lead to no brake action after a seemingly normal and safe stop

A while ago on the forum, There was a terrible and sad video of a guy driving a new restore muscle car and he was even bragging that the engine was so powerful he needed to ride the brake pedal to keep it at 35 down residential roads
Then he suddenly had no brakes and crashes!
This situation could have been water boil off in the wheel cylinders or even the actual fluid boiling if they got that hot from riding the brake
But the effect is the same only difference is the temperature at which it happens

Weird however because no matter the horse power if the engine rpm at idle is reasonable the torque converter should decouple and you won’t have to ride a brake pedal
Also
You should never ride a brake pedal! Something is wrong do not drive
-s

That guy in the video was a complete idiot. He was talking about how the brakes weren't working right the whole time he was driving just before he wrecked. The car was a '63 Comet with a ridiculous 500hp engine with a scoop at roof level.

Look for the phrase "low moisture activity". DOT 4 fluids with that phrase have an additive which reacts out small amounts of water.

My "go to" book on brakes is the Brake Handbook by Fred Puhn. The book discusses various brake fluids. It is now published in the public domain so free and legal download.

https://archive.org/details/BrakeHandbookFredPuhn/mode/2up

My 54 had an incident earlier this year with the brakes not stopping but they felt hard. The mechanic was not able to get it right after flushing the system so I told him to completely flush it again. So far they are working okay. It has been 4 months.