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DOT 4 and DOT 5 brake fluid mixed, what to do?

21K views 27 replies 21 participants last post by  ptra1955 
#1 ·
It looks like the brake fluid was mixed and the fluid is cloudy.

SHould I switch to DOT 4 or DOT 5

Can I just bleed it out?
 
#3 ·
I understand that they do not mix

The benefit of the dot 5 is the boiling point but I wrecked some paint on a car and the silicone doesnt affect paint.
Its expensive and I have been puking out a bunch trying to bleed it ou

I was think of draining and just switch back to the Dot 4

Also I heard the combo of the 2 may degrade the seals
 
#5 · (Edited)
Drain it all out and start over, a mighty vac or something similar will make for a speedy process. I would suck all the existing fluid out from all the calipers, refill it with the new fluid of your choice and flush that out too, then refill it and bleed the brakes.

DOT 3, 4 and 5.1 will mix and the Dot 5 is silicone based and should never be mixed with any of the others.

I personally don't like the DOT 5 silicone stuff because of the pedal feel, I'd use either Dot 4 or 5.1.

http://www.advancepetro.com/differentbrakefluid.htm

http://www.opieoils.co.uk/pdfs/tech-articles/Brake-Fluid-Explained.pdf

http://www.afcoracing.com/tech_pages/fluid.shtml
 
#10 ·
OMG No! Don't just flush the system. If you truly had DOT 4 and DOT 5 fluids mixed you have a real mess and a potential safety issue on your hands. You need to rebuild all the calipers, the master cylinder and anything else that has seals in it. DOT 4 and DOT 5 fluids are dramatically different in materials and are not compatible in any way. the 2 types will create a "sludge" in the lines, calipers, MC and everywhere else.

The process should be to remove the calipers, MC, ABS pump/unit (and if a manual transmission using brake fluid as the hydraulic fluid) the clutch slave cylinder and anything else with seals associated. You will need to rebuild all these components with new, fresh seals. For the lines, at the bare minimum blow them out several times with denatured alcohol, then reassemble the system.

Other than the fact DOT 5 will not harm paint there is nothing (IMHO) positive about it. It's highly compressible (can be as much as 19% dissolved air - SAE J1705 Appendix 2.2.8) doesn't swell or lubricate the EPDM seals very well and is NOT hygroscopic.

Good luck with cleaning the mess out...
 
#19 ·
 1. Flush the hydraulic brake system.
 2. If the brake fluid WAS contaminated with an oil-based or a silicone-based fluid, indicated by fluid separation and/or a swollen master cylinder reservoir cap diaphragm and/or swollen reservoir-to-master cylinder grommets, perform the following steps. Refer to the procedures indicated.
2.1. Remove ALL of the following components listed. Each component contains internal rubber seals/linings which have been contaminated.
2.2. Clean out the hydraulic brake pipes using denatured alcohol, or equivalent.
2.3. Dry the brake pipes using non-lubricated, filtered air.
2.4. Repair or replace ALL of the following components listed. Each component contains internal rubber seals/linings which have been contaminated.
■Master Cylinder Replacement
■Brake master cylinder reservoir—Clean the brake master cylinder reservoir using denatured alcohol, or equivalent, then dry the reservoir using non-lubricated, filtered air, or if necessary, replace the brake master cylinder reservoir.
■Replace the brake master cylinder reservoir cap diaphragm.
■Front Brake Hose Replacement
■Rear Brake Hose Replacement
■Front Brake Caliper Overhaul or Front Brake Caliper Replacement
■Rear Brake Caliper Overhaul or Rear Brake Caliper Replacement
■Brake Pressure Modulator Valve Replacement
 3. If the brake fluid was NOT contaminated with an oil-based fluid, but WAS contaminated with water or dirt, rust, corrosion, and/or brake dust, replace the brake master cylinder reservoir cap diaphragm which may have allowed moisture or dirt to enter the system.
 4. Refill and bleed the hydraulic brake system.
 
#21 ·
drain it all. flush with denatured alcohol a few times. fill with fluid of choice and roll cog.
 
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