Replacing DOT4 break fluid with DOT5 silicon fluid

[Schulmann]

I was wondering if there is anything particular about replacing DOT4 fluid with DOT5 silicon fluid. Especially is there a chimical incompatibility problem ?

[GTS Dean]

Just don't go there. It's not worth debating.

[Ron]

Absolutely. Stay with DOT4, example Valvoline synthetic, change annually (more if you race) and live happily ever after.

[Schulmann]

Okay I will stay with DOT4.

[Iceman]

Motul 600.

[95Viper]

Replace with Motul600 RBF Dot4. Check out the boiling points and you'll understand. Only about $10 a bottle.

[JonB - PartsRack]

Just don't go there. It's not worth debating.

"PEOPLE WHO THINK THEY ARE ALWAYS RIGHT,
REALLY PI$$ OFF THOSE OF US WHO ARE "

I agee w/ Dean, as Usual. Remember this:

"SILICONE IS FOR BREASTS, NOT BRAKES"

[Hostile]

What JonB said X2

Skeeter

[Warren S]

Schulmann,

First, I agree with everyone here, definitely stick with DOT 4. Cars with ABS (’01 and newer Vipers) should only use DOT 4 or DOT 3 at the least. Due to the hydroscopic nature (compressability / sponginess brake feel) of the DOT 5 silicone fluid, it is not intended for use on cars with ABS. So which DOT 4 brands to use? This debate can arguably go on forever like a discussion about motor oil. I like Neo 610 because it the highest "dry" (no % moisture absorbed) boiling point, and a lot of track junkies swear by the Castrol SRF because it has the highest "wet" boiling point which leads to better consistency. Others like Motul RBF 600, Valvoline synthetic and so on...they’re all good. Unless you track your car often, it’s not critical to go with the top brands, but it’s much more important to flush out the old brake fluid when it gets dirty (dark tan to grayish color). Contaminants and moisture are corrosive and wreak havoc to the brake system, can seize master cylinders at the worst case scenario.

DOT 5 silicone brake fluid is better suited for older collector muscle cars and classics. The benefit of not absorbing moisture for prolonged storage time and consequently not having to change the fluid as often is more beneficial for these older cars that are occasional boulevard cruisers and show circuit cars that do not see spirited driving sessions. Generally, DOT 5 has the highest boiling point of all brake fluids. BUT the BIG DRAWBACK is a noticeably "SPONGY" pedal feel. Your brake pedal may travel twice the distance to get the same clamping force to the rotors. I’ve not seen a technical report of performance results with DOT 5, but I’m willing to bet it will increase stopping distances by some margin. That’s not good. Is it worth sacrificing some safety margin in an emergency brake situation? Of course not. In addition, any moisture globules will find it’s way downwards into the calipers and since water boils at 212 F (at sea level, even lower temp at higher elevations), you can get vapor lock very quickly. In addition X2, the two types of brake fluids are not compatible. I’ve also heard seals going out because when owners switched to DOT 5, they used some petroleum based solvent or alcohol to flush out the brake fluid...not good.

So flush your brake fluid often and stick with DOT 4. Even if you don’t drive it often, flush it because brake fluid will still absorb moisture over time. Flush it more often if you see track use. Remember, brake fluid is corrosive on paint, will eat paint. So be careful not to spill it if you’re a DIY’r and wipe off any excess and rinse off with water. Sorry for the long explanation, but you can see why the overwhelming majority will say stick with the DOT 4. Good luck.

[Schulmann]

Just bought 4 bottles of Valvoline synthetic Dot4 ...

[Tom, F&L GoR]

As an added comment, when I disassemble the old rear calipers sent in as cores for the 40mm resizing, it is obviously many do not flush their fluid. The needle bearing and load-bearing washer that support the parking brake arm are inside the caliper, bathed in brake fluid, and often rusty. Luckily they are are at the far end from the piston and piston seal, so I've only seen perhaps two or three where it would cause a fluid leak or stuck piston. While the rears may not get as hot as the fronts to cook the fluid, you should bleed them occasionally to dry the fluid.

[Janni]

Hey Tom,
How were Stuart's old calipers? Did we train him well?

[Tom, F&L GoR]

Stuart:

Others that insisted on getting their exact calipers back because they were in such good shape:

Calipers that were thought to be good spares: