Posted by WOJ on November 26, 1999 at 20:40:22:
In Reply to: Re: 1948 master cylinder posted by Vaughn on November 26, 1999 at 19:11:07:
BRAKE FLUID.
Most old-car owners change oil, coolant and transmission fluid, but never think about brake fluid ....
Of all fluids in a vehicle, brake fluid directly affects safety. ·.. Moisture contamination is the reason that brake fluid gets 'old' and has to be replaced. Glycol-based brake fluid absorbs moisture that bypasses seals, enters through microscopic pores in brake hoses and air introduced into the system." In addition to rusting of the wheel cylinders and lines, this drastically reduces the fluid's boiling temperature, which can lead to vapor pockets under heavy braking. Vapor pockets are bad news; they are compressible and will let the brake pedal go to the floor--no brakes at all! DOT 3 brake fluid starts with a boiling temperature of at least 401°; and is considered unsafe if the boiling temperature drops under 284°. 3% moisture can do this, and brake fluid can absorb 3% moisture in as little as 1.5 years. Therefore, "it is recommended that brake fluid be replaced at least every two years.
DOT 4 brake fluid has higher boiling points, but absorbed moisture is still bad news, since it has a quicker effect.
Old vehicle drivers don't usually experience problems because they drive their vintage vehicles conservatively and don't brake hard. Brake aggressively so the brake system really heats up and you are likely to lose braking efficiency when you need it most. The problem is aggravated in wet climates and where the humidity is consistently high. A reduced boiling point is not the only problem with moisture contamination. Condensation can lead to rust and corrosion, which can pit master cylinders, steel brake lines, wheel cylinders, pistons and other critical brake-system components. I am sure the latter is where antique vehicle owners will experience problems, which is why brake cylinders must be replaced or sleeved. (If you are lucky, honing will be satisfactory.) The prevention is to change the brake fluid, but moisture absorption and damage may be left over from a previous owner--take care.
DOT 5 brake fluid is an improvement, but cannot eliminate the moisture problem. DOT 5 brake fluid is not hygroscopic (does not absorb moisture), but moisture that does enter the system can settle in Iow spots and cause local corrosion. DOT 5 does NOT mix with either DOT 3 or DOT 4. Since diligent flushing of a brake system can leave residues of the old fluid, it is suggested that DOT 5 brake fluid be installed after a complete brake system rebuild.
Moisture contamination cannot be detected by sight unless it has already caused corrosion problems-then the fluid may be brownish. Professional brake shops can test for moisture contamination, and there are test strips that can check it.
All brake fluid is not created equal, so use a premium fluid, not one that just meets the minimum standards. The cheap stuff may not tolerate moisture as well, provide the same degree of corrosion protection, or lubricate as well as a name-brand fluid.
BRAKE LINES.
Stainless steel is great but no one is reproducing them for the PW's as of yet. You can do the reproduction yourself but stainless is a hard metal and is not easy to bend and it destroys the dies of a normal flare tool. The best solution is to make your own from regular parts store brake lines. These come in lenghts of up to 5'. Flare tools are also inexpensive now and done properly, following all the directions with the proper beveling and reaming, you will have a flare which is leak free. Buying lines and having excess line hanging around is not a smart idea as that extra line my get snagged on something and since these trucks do not have a split hydraulic system, you will loose ALL brakes if the line is ruptured, and having a 6000 pound truck rolling down the road with no brakes is indeed a major pucker factor . It also does not look good either. Also after cutting and flaring rinse out the line with 90% isopropyl alchol, available at drug stores, followed by a blowing out with dry crompressed air. This will remove any contaminents and shavings from the flaring process. Also replace ALL the spring guard on the lines. I have found a place that has these in polished stainless for all sizes of brake and gas lines, and they look great (MSC @ 1-800-359-7166).