Could somebody tell me what type of brake fluid should be used? I have a 1954 3100. Is there any way to know what type is in the system?
You would have to taste it to be shure..... Nah, just empty it all and flush the system if you are working on it, and fill with dot 3.
It also depends on how much you think you will drive it and whether or not you have good, uncorroded brake lines. If you use it on a regular basis, use dot 3 like Russ says. If it's a fair weather or trailer queen truck, think about using a silicon based brake fluid, which will keep the lines relatively corrosion free. If using the silicone type, make sure that you flush the system first.
DOT ratings DOT 5 is silicone and should not be mixed with other brake fluids. The higher the DOT numbers equate to higher boiling points. Higher DOT numbers cost more. DOT 3 can be mixed with DOT 4 but not 5. I have been told that if 5 is mixed with 3 or 4 that it will gell up and the lines and cylinders will have to be replaced. Never have been curious enough to try. Besides DOT 5 cost a lot. If you are going to replace the complete brake system; go with DOT 5 as it wont adsorb water. Still will need to bleed the brakes to keep out water on schedule. I understand that DOT 5.1 is not to be mixed with DOT 5 for the same reason.
Brake Fluids This is REALLY important ! . Use DOT 4 as it has a higher boiling point . Be SURE to get a quart or two of it and bleed untill perfectly clean fluid is coming out of each cylinder . if you decide to go with DOT 5 , you'll have to take the ENTIRE hydraulic system apart and hand wash each and every part with alcohol and flush out the open steel lines and flex hoses with it too , BEFORE re-filling with DOT 5 or you WILL have gelling and CATASTROPHIC BRAKE FAILURE ! . If the three rubber flex hoses show _any_ cracks or swelling , no matter how small , replace them RIGHT AWAY .
