I am rebuilding a 61 unibody. I am to the point of finishing up the brakes. I have put all new parts and am looking for some opinions on what brake fluid to use. Dot 3 or Dot 5 . I have been told both ways. Any suggestions
Thanks

 

My understanding is do not mix. If everything that brake fluid touches is new it is ok to swap, if not, do not.

I still use the old DOT 3 and have no reason to change.




John

 

Actually you have D.O.T. 3 and 4 brake fluid which are both glycol based fluids with the 4 having a slightly higher boiling point. These two can be mixed since they have the same base. On the other hand D.O.T. 5 fluid is silicon based which has an even higher boiling point and used initially for racing cars. The pro of silicon was that it didn't attract moisture like the glycol fluids. Yet glycol in general use neutralizes moisture, disperses the moisture so it doesn't concentrate and changes color proportional to the amount of moisture in it. The attracting moisture is more of a concern for the containers laying around in the garage. The only real problem with it is that it is caustic to paint and silicon is not. Silicon does not disperse moisture nor turn color so it is more prone to corrosion if you don't change it frequently. Now there is a D.O.T. 5.1 available which is glycol based and can match silicons higher boiling point. Plus glycol has lubricating properties that for some ABS systems. To me it is a no brainer and so I use D.O.T. 4 in my four older cars. I don't need to worry about boiling issues in these cars and I routinely change fluid once a year since I now have a pump that sucks it right out of the bleeder. My Focus would get the D.O.T. 5.1 fluid.

 

Do not use silicone fluid. I have yet to meet someone who used it and didn't wish they hadn't.

Clean fresh fluid is more important than the type of fluid. It should be flushed every few years to remove the moisture. If you want a high performance fluid get ATE Super Blue; that's what most of us racers use these days.