What is the best brake fluid to use?

Originally Posted by e46techtuner

I use DOT 4 from the dealer. No, problems on street or track. You can alternate from DOT 4 and DOT 3 but DOT 5 is usually silicone based and doesn't mix well with 3 or 4 brake fluid.

Correct! Do NOT use DOT5. DOT5.1 is the correct upgrade from DOT4 and is miscible with the others.

Chris

I am also looking to do my brakes this weekend and have a question regarding the purity of the brake fluid. During my searches of 'Brake DIY', I generally found consistent info about the process, except one post that pointed out an important part lacking in most other posts (or so it seems to me). I wanted to see if you all agreed or think this is overkill.

The post mentioned that before pressing the calipers piston back to it's initial position (to fit the new pads), you need to pinch off the brake fluid line and open the bleed screw. The reason is that by pressing the caliper piston back, it sucks the potentially dirty brake fluid back up the line and can cause a failure in the system (due to particles in fluid). They recommend allowing the brake fluid to be pushed out of the bleed screw and then top off.

Seems reasonable. Any thoughts?

Originally Posted by tfoxsf

I am also looking to do my brakes this weekend and have a question regarding the purity of the brake fluid. During my searches of 'Brake DIY', I generally found consistent info about the process, except one post that pointed out an important part lacking in most other posts (or so it seems to me). I wanted to see if you all agreed or think this is overkill.

The post mentioned that before pressing the calipers piston back to it's initial position (to fit the new pads), you need to pinch off the brake fluid line and open the bleed screw. The reason is that by pressing the caliper piston back, it sucks the potentially dirty brake fluid back up the line and can cause a failure in the system (due to particles in fluid). They recommend allowing the brake fluid to be pushed out of the bleed screw and then top off.

Seems reasonable. Any thoughts?

Yes, it is always better to expel the old fluid out of the caliper, rather than push it back up towards the master cylinder. This is mostly due to the fact that the fluid in the caliper has seen the most heat and needs to go away. If particulates are in the fluid, you have bigger issues!

Also, if you place a piece of wood between a depressed brake pedal and the driver's seat frame, you won't have to pinch off the brake lines. Once the M/C seal has passed the reservoir port, the fluid cannot go upstream. This is especially important if you have stainless steel braided lines, as they won't pinch so easily.

Chris

Thanks Chris__B. Better safe than sorry.

What about Castrol SRF? Is it safe for our vehicles? A friend of mine worked on F1 brake testing in the university lab. He gave me a few liters of this SRF.

Originally Posted by z_man93

What about Castrol SRF? Is it safe for our vehicles? A friend of mine worked on F1 brake testing in the university lab. He gave me a few liters of this SRF.

That is the best.

Originally Posted by franz

That is the best.

Yes, among just two others. AP Racing PRF has better recovery properties, which is why many NASCAR teams choose to run it. SRF retains retains about 75% of its compressibility resistance once boiled while PRF retains about 95%. Endless also has a fluid in the top category.