This is my second post on this subject. I’ve got a 79 XLS. Rebuilt the front master. I asked what kind of brake fluid to put in and was told that only DOT 3 was in use in 79. And you’ve all got real honest looking faces so I believe that. Also was told the cover should tell what kind of fluid to use so I looked and it said DOT 5. I assume it's not OEM even though the kit parts matched what I took out. My dilemma: How do I determine what kind of fluid is in there now. I would expect that my rebuild kit and possibly the slaves were made for DOT 3. Will DOT 5 rot the rubber? The bleed fittings are at the top of the calliper cylinders. How do I flush all the fluid out? I’ve got a bottle of something called DOT 5.1 that says it’s compatible with DOT 4. Anybody had any experience?
Any superior knowledge greatly appreciated.
You run whatever ya want ....PROVIDED ya flush it properly..
dot 3 , 4 and 5.1 are the same family and are compatible the higher the number the higher the boiling point
dot 5 is silicon fluid and wont attack your paint like the others and is compatible with nothing.........
Use a fresh bottle of a different coloured fluid to what's in there and remove the brake line from the caliper and drain the fluid out......
then reconnect and fill the master cyl and keep bleeding till well past the fresh stuff comes out of the caliper
Havin a few beers in the shed with my mates.
Dot 3 is more of a solvent based and moisture mixes with it. It also has a lower boiling point than 4 and or 5. 4 is a sort of blended fluid that has properties that resist collecting and mixing with moisture. 5 is straight silicone than they claim won't mix with moisture. Reverse bleed from the bottom up using a syringe and tubing, or if you have patience, take the lines apart and flush them out. There are web sites that explain the brake fluid properties fully. Dot 4 or 5 should work fine. I feel the main concerns are moisture collecting over time and causing the system to corrode and fail and boiling point due to the heat in the calipers. If you are a worry type, flush and inspect every spring