with all the brake jobs I do - I always open the bleeder screw before pushing back calipers. put a clear plastic hose onto bleeder screw and drain into bottle so it doesn`t get onto chrome or paint. Pushing old brake fluid into master cylinder just causes problems with seals. On newer units the abs unit can be damaged.
front brake advice needed.
- Thread starter 2001FLHT
- Start date
Etylene glycol swells rubber seals "slightly"...if your system was setup for DOT 5 Silicone based, it is inert, more of a lubricant then a sealer, that is why when you put the DOT 3 in, the seals swelled and basically contaminated the works. Also, DOT 5 does not mix with DOT 3 so the "purple" DOT 5 sinks to the lowest parts and stays there, pumping and bleeding will not necessarily flush it out as DOT 3 is "thinner" floats above it. You may end up rebuilding the caliper/master cylinder seals, as the swelling is done...! May have to flush the entire system with alcohol or Brakleen and hope you got it all out as silicone is kinda like oil, it sticks to everything...
i didnt say they mix, i said dot 5 can be used in any dot 3/4 system,dot 5 doesnt lubricate so when reassembling a dot 5 caliper you must use a lubricant on the pistons.
No...do not use DOT 5 in any braking system not set up for it...! Ethylene Glycol DOT 3, 4 and 5.1 based brake fluids are by design supposed to swell seals, while DOT 5 systems use closer tolerance components because it does not swell seals, its' virtues being not as agroscopic (collector of water), BUT it also is more viscous (heavier) and does not "seep" as readily or mix with EG based brake fluid.
I did a little experiment, had some DOT 3 in the bottom of a bleeder container, then poured in equal amount of purple DOT 5, it just looked like large round purple globules in the amber DOT 4, and eventually settled to the bottom when left alone (after 15 minutes is all it took) for the blobs to merge and settle: purple on the bottom, amber EG based fluid floated to top. Even tried shaking container vigorously, 15 minutes later same result.
I did a little experiment, had some DOT 3 in the bottom of a bleeder container, then poured in equal amount of purple DOT 5, it just looked like large round purple globules in the amber DOT 4, and eventually settled to the bottom when left alone (after 15 minutes is all it took) for the blobs to merge and settle: purple on the bottom, amber EG based fluid floated to top. Even tried shaking container vigorously, 15 minutes later same result.