Detrimental64.
It is recommended that DOT 5 not be used with rubber parts that have already been used with other types of brake fluids.
Also, many people say that rubber used in old wheel and master cylinders is not compatible with DOT 5 fluid (even if the rubbers/cylinders are new old stock).
As has been stated regularly in this forum (recently, too), the best way to change to DOT 5 is when the master cylinder and wheel cylinders are all going to be replaced (rebuilt ?) at the same time.
Various advice has been given on how to flush the lines of old fluid. Not knowing what to do, and wanting a safe, long-term solution, I only use DOT 5 when all brake system parts are new, including brake lines.
You might want to search in this forum on "DOT 5" and "silicone" and "brake fluid". You will find a lot of advice and many opinions (some based on experience, some based on hearsay, and some based on legends). Bob Adler (a professional expert on old trucks) wrote a well-researched article on this subject a few years ago in "This Old Truck" magazine (now named "Vintage Truck" magazine - I forget the year/issue-number).
Tim
PS
AAA gives this information and warning:
"Silicone DOT 5 fluid has some other characteristics that you should beware of. Silicone fluid compresses slightly under pressure, which can cause a slightly spongy brake pedal feel. Silicone fluid also attracts air more than polyglycol fluid does, which makes brake bleeding harder. It also tends to vaporize slightly just below its boiling point; and it will aerate from prolonged vibration. All of these factors mean that DOT 5 silicone fluid should never be used in an antilock brake system."
