Replace all the old rubber. All of it. This applies particularly to the flex hoses to the wheel cylinders/calipers. The master cylinder should be rebuilt with new seals also. You probably cannot get the seals for the PDWA so cross your fingers.
Any old rubber in the system may behave unpredictably. It may swell or it may sluff off black goo into the system. You don't want either to happen.
DOT-5 will not mix with DOT-3/4 so any left in the system will collect in pools. I don't know what really bad effect that would have but I know it is advised against leaving any old fluid in the system.
DOT-5 also traps air easily and can make for a squishy pedal. Two things help. When pouring the fluid into the master cylinder, use a long, clean screwdriver inserted into the MC reservoir. Pour the new brake fluid gently onto the shank of the screwdriver so it runs slowly into the reservoir without splashing. Not only will this prevent a mess but it minimizes any bubbles in the system.
When you replace those flex lines, use the stainless overbraided hoses. They help maintain a firm pedal with DOT-5.
Doug L.
--Previous Message--
: Hi all,
:
: I also started rebuilding the brake
: system this weekend. I'm switching to
: DOT 5 silicon fluid so I'll never have
: to see all that wrinkling paint around
: my master cylinders again. Use of DOT
: 5 requires flushing the original fluid
: out - it's not compatible with any
: other DOTs.
:
: After the system was completely
: disassembled I flushed each length of
: brake line with spray brake cleaner.
:
: For those of you familiar with DOT 5:
:
: - Is this sufficient enough of a flush?
: - What happens when DOT 5
: "does" encounter some other
: DOT fluid in your system?
:
: Got plenty of time to mull this over.
: Won't be able to get to the project
: until sometime next year.
:
: Ciao! - Jim
:
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