braking fluid

[dave783]

The brake fluid in my Standard 8 clutch and brake system has to be replaced since the existing fluid is over 5 years old.

Can I replace this fluid with any other 4 DOT fluid, you ask? Or should I use a particular brand of brake fluid for vintage cars?

[IrvesBMW]

The use of any DOT 3 or DOT 4 fluid will suffice for this task. Probably, someone does market a "classic-specific" fluid, but it will be nothing more than a pretentious container; the fluid inside will be identical to what you can purchase at Halfrauds or a neighbourhood auto parts store.

[dave783]

Thank you very much for your help. I love the way Halfords is spelt.

What makes 3DOT different from 4DOT? 

[IrvesBMW]

The key difference between DOT 4 and DOT 3 is that DOT 4 has a greater boiling point, which is not a problem for clutch hydraulics. Both of these standards are mutually compatible and may be used interchangeably.

[dave783]

Thank you very much.

[IrvesBMW]

I'm glad To help

Edited June 17, 2023 by IrvesBMW

[dave783]

Since I need to change the brake and clutch fluid because the old fluid is old, I just need to drain the old fluid out of the brake lines, which is simple.

What is the best way to add the new fluid to the system, given that the system also needs to be "bled"? 

[ForumGuru]

Dave, you don't need to empty the system; just bleed it as usual, but keep filling up and continuing till you have clean fresh fluid pouring through. I use a bleed easy kit from Halfords to do mine, which is really simple. I was always instructed to start with the wheel farthest away from the master cylinder, in your case the rear nearside, then the rear of side, front nearside, and front of side. Best wishes.

[dave783]

Thank you....

I'll try that right away. 

[CyberNinja]

As far as I'm aware, not all automobiles can just use the newest Dot fluid. I have been instructed that my Rover P6 must utilise Dot 3 rather than Dot 4. anything to do with producing problems with chemical reactions involving rubber or seals. can't quite remember, but don't use the most recent. dot 4 in my 45-year-old antique vehicle. It would be wonderful to know if anything has changed.

[WiseSage]

Mineral fluids dot 3, 4, and 5.1 are all considered to be "improving" grades.

Because Dot 5 is based on silicone, its improper application will result in the destruction of rubber seals found throughout a hydraulic system.

[TechWhiz]

Never combine dot 5 (silicone) with anything, especially dot 5.1. Glycol fluid incompatible. Silicone repels water. Glycol-based fluids absorb 10% water. 

[PixelMaster]

2 minutes ago, WiseSage said:

Mineral fluids dot 3, 4, and 5.1 are all considered to be "improving" grades.

Because Dot 5 is based on silicone, its improper application will result in the destruction of rubber seals found throughout a hydraulic system.

I once placed some old cylinder seals in a container of silicon fluid; a month later, they appeared identical, which is not surprising given that silicon is a relatively inert substance.

I believe that the reason why people report swollen old seals after filling with silicon is because their systems still contain glycol brake fluid (bleed nipples tend to be higher up, and it is impossible to remove all fluid by simply bleeding). Silicon fluid is less dense than both glycol and water, (and there will be some residue of both in the system). Silicon fluid will repel any moisture, so a glycol mixture with a high water content will be concentrated at the bottom of the cylinders, causing the damage. In a glycol system, water is absorbed and dispersed throughout the system, resulting in a considerably less concentrated solution.