Something occurred to me the other day and thought i'd see what others think. With respect to changing out brake fluid , does the brake fluid 'mix' with itself?By that i mean does the fluid that is in the lines going down to the calipers ever mix with the stuff that is in the master cylinder? Can you just swap out the MC fluid and have it mix with existing and keep doing this a few times and , in essence, change out the fluid? This would be similar to how some go about changing their tranny fluid.Some people are hesitant about bleeding from the caliper for fear of braking the nipple and getting more work than they bargained for.

 

Usually brake fluids can coexist, but please read the label very carefully. I tend to remain within the same manufacturer and brand.

The new and old do mix and cross contaminate, but they do not form a uniform mixture. The one added to the master cylinder keeps creeping down to the slave and back with each application and release of the brake.

Accidents can happen and if you use the wrong tool or apply too much leverage, you can round off/break the nipple. After use the fluid in the slave gets most dirty. So a let out is a must in my books.

Salim

 

technically you can mix DOT 3 and DOT4 brake fluids, they are glycol based however Toyota/Lexus recommends a brake fluid containing borate esters in their older models. Some of Toyota/Lexus brake component vendors had seals that dried out when the borate esters were not present. Siphon out as much of the older brake fluid out of the master cylinder to minimize mixing of old moisture saturated brake fluid with new. Do not mix DOT5 fluid because it is silicone based.

 

Repeatedly changing out the master cylinder fluid will not change the fluid in the lines. There is no recirculation of the brake fluid back to the master cylinder. In order to get clean fluid into the lines especially at the distal ends at the calipers, you need to bleed the brakes. This is unlike the transmission cuz the transmission fluid gets recirculated throughout.