In the process of replacing my brake master cylinder. The directions included with the new master say to use Dot 4. Money as always is tight but I have plenty of Dot 3. Will using Dot 3 harm the brake system?

 

Use DOT4 if that is the spec. They are different.

 

The reason they spec dot-4 is because of its higher boiling point. The brakes on d1's can run very hot(thanks to the awsome non-vented front rotors and almost 2 1/2 ton weight). And unless it's synthetic dot-3, it will not play well with the dot-4 thats in there.

 

If you think you will save money using DOT 3, you are seriously wrong, DOT 3 will ruin your DOT 4 system.
By the way, you will want 2 quarts of DOT 4 for a full flush.

 

All I have available around here (MD) is the synthetic DOT 3-4. I have been using it for 3 years without issue.

But I would NOT use straight DOT 3 for the reasons listed above!

 

In removing the old master cylinder all I did was remove the 2 gas lines from the master, then pumped the brake pedal several times rapidly in order to get the fluid out. Also take into account an unknown amount of brake fluid leaked out prior to any brake work. So my first question is how to I know for sure if all the fluid is out of the system? I already installed the new master cylinder with abs, but haven't added any fluid yet. Not sure how or the best way to bleed the system. Preferably the cheapest fastest method. Can anyone give me some detailed tips? ANd yes Ill just use Dot 4

 

If you have a compressor, I purchased a bleeder kit from Harbor Freight for $15 - and it worked like a dream. (The only better purchase was the 90 Amp Flux Core Welder - but that's a different thread!)

Was able to mount a bottle on the Master Cylinder with a quart of extra fluid while I was bleeding - bled until clean and clear.

And again, I use DOT 3-4, DOT 4 only is not available to me (that I have found) and I have had no issues.

Took like...30 minutes - INCLUDING set up time.

Well worth the $$!!

 

Go down to autozone and get a one man bleeder kit. Theyre like 8$. hook it up pass rear, bleed till new clear dot 4 or syn dot3 fluid fills the bleeder reservoir, repeat on Driver rear, pass front then driver rear. Mike says use two qts, so that's half a bottle per wheel. Maybe less considering you'll want to leave some of that fluid IN the system

 

Sorry. Pass rear, driver rear, pass front, driver front. Only as low as syn dot 3-4

 

Most good quality brake fluid exceeds the specifications for DOT 3 and DOT 4. The reason we see DOT 3 label on some fluid that exceeds DOT 4 fluid specifications is because the company also sells a DOT 4 labled fluid that exceeds it even further. The two fluids are compatible but DOT 3 labled fluids do not *necessarily* meet DOT 4.

Where I don't like the ultra-high boiling point fluids is they can be a lot more hygroscopic. Unfortunately, the DOT specifications and the labeling doesn't tell you anything about how hygroscopic the fluid is. You just get the wet boiling point. So the bottom line is you have to figure the higher the boiling point, the shorter the fluid's life at peak performance is going to be. The DOT3 fluids may have lower boiling points but will probably stay dry longer. The race fluids, I wouldn't keep them in there for more than a year.