A member of the forum asked so I wrote this up. It some facts I've assembled over the years for when I do the brakes on my vehicles.


Enjoy


-JohnnyO
<H2 style="MARGIN: 12pt 0in 3pt">Brake System Overview and Bleeding</H2>
<H3 style="MARGIN: 12pt 0in 3pt">Overview</H3>
It’s all about boiling points. Racers go for the fluids with high boiling points. They need this because the intense high speed braking creates a lot of heat. Those of us who tow or carry heavy loads should also be concerned. Although we do not go as fast as racers (sometimes) we are heavier, and braking effort and duration may be harder and longer so the heat buildup from friction can be high.
Currently there are three major types of fluids:
<UL style="MARGIN-TOP: 0in" =disc>
<LI class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-list: l1 level1 lfo1; tab-stops: list .5in">Polyglycol based</LI>
<LI class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-list: l1 level1 lfo1; tab-stops: list .5in">Silicone based</LI>
<LI class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-list: l1 level1 lfo1; tab-stops: list .5in">Silicone-ester based</LI>[/list]
<H3 style="MARGIN: 12pt 0in 3pt">The Importance of Moisture</H3>
The amount of moisture in brake fluid affects its performance. The brake fluid absorbs moisture over time. SAE field tests have shown that the average one-year-old car has 2% moisture in the fluid. A random test of vehicles in the U.S. showed on average, a water content of 2.6% for vehicles with an average age of 8 years. And 25% of these vehicles had water content greater than 4%.

As water content in brake fluid increases the boiling point decreases. Fluid with a reduced boiling point (or high water content) can create vapor by boiling in the caliper, or wheel cylinder. The result is brake failure. Water in the brake fluid also contributes to corrosion of parts.

You should really have your brake fluid changed every two to five years depending on the hydroscopic nature of the fluid.
<DIV style="BORDER-RIGHT: red 1.5pt solid; PADDING-RIGHT: 4pt; BORDER-TOP: red 1.5pt solid; PADDING-LEFT: 4pt; BACKGROUND: #ffff99; PADDING-BOTTOM: 1pt; BORDER-LEFT: red 1.5pt solid; PADDING-TOP: 1pt; BORDER-BOTTOM: red 1.5pt solid">
<H3 style="BORDER-RIGHT: medium none; PADDING-RIGHT: 0in; BORDER-TOP: medium none; PADDING-LEFT: 0in; PADDING-BOTTOM: 0in; MARGIN: 12pt 0in 3pt; BORDER-LEFT: medium none; PADDING-TOP: 0in; BORDER-BOTTOM: medium none; mso-border-alt: solid red 1.5pt; mso-padding-alt: 1.0pt 4.0pt 1.0pt 4.0pt">Warning!
Failure of the brake system can cause injury or death. Absolutely! If you do not know what you are doing DO NOT tamper with, change anything, or modify your brake system. Have a professional do it. The brake system is not to experiment with.</H3></DIV>
<H3 style="MARGIN: 12pt 0in 3pt">Fluid Types: DOTS before your eyes</H3>
<P class=MsoNormal style="MARGIN:

Any more info on DOT 5.1? Also some sort of info on cold point info for the fluids would be good. What is better to run in say Fairbanks, Alaska that gets between -40F and -60F below quite often.
Is there a way to visually identify DOT 5 versus DOT 3?

GM does not advise use of DOT 5 fluid. Excellent article

Is't there a special proceedure when bleeding ABS? Or is that only if you replace components and get air in the system? It is time to do mine.

Is it possible to use the Motive Power Bleeder system on our trucks? The Motive system is the pressurized "bud sprayer" with a top that goes over the master cylinder (www.motiveproducts.com (http://www.motiveproducts.com)). I used it on my 70 Pontiac when I switched to silicon fluid (and subsequently flushed it out with Isopropyl alcohol). The system worked great but I didn't know if the pressure would work with our trucks strange system.


Thanks,


Randy

GM does not advise use of DOT 5 fluid.* Excellent article


*

Yeah, that bothers me. I got my truck from Alyeska Service Company (they run the pipeline in Alaska) and on the master cylinder cover it says DOT 5. It could mean DOT 5.1 I guess (I have no way of knowing what is really in there, they could have put DOT 5 in and wrote that, and changed later). Anyway cold weather is the issue up here. We need to have brakes at -65F below. Of note Alyeska is known as awesome mechanics so this does seem strange to put this in if it wasnt recommended.

I have ABS but I never seem to have a soft pedal feel, if anything just the opposite. Some times shortly after I start up and driving slow the brakes are SUPER sensitive and just about slam on.http://www.dieselplace.com/forum/smileys/Dead.gif Not sure why.

Lastly is the procedure to drain and flush GM ABS systems the same as a regular system? I think I might like to put in DOT 5.1 so I know what is in there.http://www.dieselplace.com/forum/smileys/Approve.gif

Is't there a special proceedure when bleeding ABS? Or is that only if you replace components and get air in the system? It is time to do mine.


On the Jaguar I have to pump the brakes a couple of dozen times before starting the regular bleed process. This removes pressure from the power brake booster and ABS. Jaguar has a unique brake system that requres this. The shop manuals for other vehicles I have worked on did not specify this.


There are some cars that have exotic systems and may require a special procedures other than outlined.


It's best to check the shop manual or a Chilton's or Haynes book for your vehicle to see if anything special is recommended.


Thanks for pointing this out.

Any more info on DOT 5.1? Also some sort of info on cold point info for the fluids would be good. What is better to run in say Fairbanks, Alaska that gets between -40F and -60F below quite often.
Is there a way to visually identify DOT 5 versus DOT 3?


I haven't had any experience with the 5.1 brake fluid, that's why I didn't write too much on it. Here in NJ I haven't had to worry about the low temps you are experiencing. Does anyone in the forum know about special brake fluids for extreme cold?


DOT 5 is thicker and does not have the same smell as regular brake fluid.