Sal Lubrano
Active Member
- Joined
- Apr 26, 2002
- Messages
- 1,233
Does anyone know how many ounces is needed to just replace the fluid in the the brake accumulator and reservoir?
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SignUp Now!Richard, thank you for taking the time to share your knowledge. Can you expand on why we should only use DOT 3 as opposed to DOT 4? I recall a post you made years ago where you recommended the use of 3 or 4. What has changed since then? Thanks.As someone that has repaired and rebuilt hundreds of powermasters over the years i will add a few comments. Use only dot 3. The reasons are several and too much for me to type this late at night. Dot 4 is not a better choice in our cars with the powermaster and all the reasons listed in that link are none of them. And don't even think of using Dot 5 or 5.1 unless you really want to regret it later on. I will also promise that with our brake system you will not notice a single difference in the cheapest to the most expensive name brand of Dot 3. If you do its only in your imagination. As for the quantity of fluid it will vary from one brake unit to another as for the exact amount. Reason being that the precharge pressure in any batch of accumulators will vary as much as 50 lbs or more. The brake switch pressure cutoff point will vary even more in any given batch. But what difference does it make? Brake fluid is cheap and the proper amount to replace it with is indicated on the side of the reservoir anyway. No two units are likely to require the same amount.
Richard, thank you for taking the time to share your knowledge. Can you expand on why we should only use DOT 3 as opposed to DOT 4? I recall a post you made years ago where you recommended the use of 3 or 4. What has changed since then? Thanks.
Good stuff. Thanks again Richard.A couple years ago John Norton and I wrote a rather detailed manual on servicing and understanding the Powermaster. In chapter 7 I detailed this subject so the easiest thing is for me to quote some of the book. So..........There are 4 basic types of brake fluid: DOT 3, DOT 4, DOT 5, and DOT 5.1. Dot 3 and 4 are similar with DOT 4 usually having a slightly higher temperature rating. For the sake of classification, the D. O. T. (Department of Transportation) has assigned minimum dry and wet boiling points for each class of fluid. Consequently there are variations from these minimums from brand to brand. There are some DOT 3 brands that exceed the lower-quality DOT 4 brands. Since we are dealing with a 25 year-old car that has at best a marginal braking system (ie single piston caliper disc front / drum rear) brake fluid should be the least of our worries. Our cars came with DOT 3 and simply put, it is still the best for this application. While DOT 4 (depending on brand) can have a slightly higher temp rating, it degrades faster and contains chemicals (borate esters) that affect the firmness of the seals in the Powermaster and has a slightly higher viscosity than DOT 3. If boiling point worries you then shop around for a brand of DOT 3 that has a boiling point close to the 300 F range.The consequence of boiling fluid causing fading brakes can be sometimes confusing. If the brakes fade and the pedal is hard the problem is the calipers and/or rotors are overheated. If the brakes fade and the pedal is soft, its the brake fluid boiling. If remembering nothing else keep in mind that new DOT 3 will always have a higher boiling point than year old DOT 4.
Forget about DOT 5 as it was originally developed for a military specification that has little bearing on what we need in our cars. The specification has been around for a long time and does not actually specify any particular chemistry. The spec is simply performance based and historically has only been met by synthetic formulas, most notably silicone based. While DOT 5 (unlike glycol based fluids) does not absorb water, it does tend to entrain air, making it rather compressible and usually results in a soft pedal even when cold. When it was first introduced many racers adopted it with extremely poor results................if you feel you need to know more get the book............92 pages on Powermaster brake systems