I switched to DOT 5 when I did an engine rebuild in 2022. I did change the front brakes entirely but the rears stayed the same. I did use a different master cylinder. The brakes were not any better than they were beforehand for a few reasons.
It took awhile but after several brake bleeding efforts, I finally got the purple fluid to the back brakes. When I got the car running, I bled and bled and was getting DOT 5 up at the front but the rear calipers flowed a diluted mix. the brake pedal feel was
okay. Not great but not bad. A few months later I went at it again and that time, I bled it until the fluid coming out of the back was as purple as it looked at the bottle. That stuff aint cheap though! $40 a quart???
View attachment 1716378660