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Account deactivated by owner's request
  
Location: On this barrel | Hello,
I need to replace the master cylinder and one of the brake lines on my 61 Dodge. Since I'll be bleeding out the old fluid I'm wondering if I should start fresh with new DOT 4 or 5? Maybe this would improve the life of the master cylinder since it isn't driven very often?
Thanks!
Edit: I think I found my answer here:
http://www.forwardlook.net/forums/forums/thread-view.asp?tid=32962&...
Edited by 56royaldodge 2012-01-10 7:21 PM
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Expert
Posts: 3403
Location: Chestertown, NY ( near Lake George) | I use Dot 4, it specs out to absorb less moisture but has a lower boiling point, not an issue with our cars, Dot 5 can be tricky to use, I would only recommnend it's use when all the components are new, as any trace of 3 or 4 can cause problems mixing with 5. |
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Extreme Veteran
Posts: 520
Location: Colorado Springs, Colorado | Dot 4, i use ate type 200 in all of my cars. It has a high boiling point and is not overly hydroscopic unlike many of the high boiling point fluids. Don't bother with dot 5, in a pinch you won't be able to find it as easily as dot 3/4 |
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Expert
Posts: 1530
Location: ZH, Switzerland | I use DOT 4 as well. It's because the brake light switch is still at it's original location (at the main brake cylinder).
Happy Motoring!
Dieter
Edited by di_ch_NY56 2012-01-22 7:41 AM
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Veteran
Posts: 204
Location: St. Louis, MO. USA | DOT 3-4 Verses DOT 5. Which brake fluid should I use?
"With regards to the DOT 3-4 verses DOT 5 brake fluid controversy, here is an article sent to me by Mr. Steve Wall. It is one of the most professional treatments I have seen on the subject".
[I had to condense this article from 6 pages to 1 due to space limitations.
Brake Fluid Facts
by Steve Wall
As a former materials engineering supervisor at a major automotive brake system supplier, I feel both qualified and obligated to inject some material science facts into the murky debate about DOT 5 verses DOT 3-4 brake fluids. The important technical issues governing the use of a particular specification brake fluid are as follows:
1. Fluid compatibility with the brake system rubber, plastic and metal components.
2. Water absorption and corrosion.
3. Fluid boiling point and other physical characteristics.
4. Brake system contamination and sludging.
Additionally, some technical comments will be made about the new brake fluid formulations appearing on the scene.
First of all, it's important to understand the chemical nature of brake fluid. DOT 3 brake fluids are mixtures of glycols and glycol ethers. DOT 4 contains borate esters in addition to what is contained in DOT 3. These brake fluids are somewhat similar to automotive anti-freeze (ethylene glycol) and are not, as Dr. Curve implies, a petroleum fluid. DOT 5 is silicone chemistry.
Fluid Compatibility
Brake system materials must be compatible with the system fluid. Compatibility is determined by chemistry, and no amount of advertising, wishful thinking or rationalizing can change the science of chemical compatibility. Both DOT 3-4 and DOT 5 fluids are compatible with most brake system materials except in the case some silicone rubber external components such as caliper piston boots, which are attacked by silicon fluids and greases.
Water absorption and corrosion
The big bugaboo with DOT 3-4 fluids always cited by silicone fluid advocates is water absorption. DOT 3-4 glycol based fluids, just like ethylene glycol antifreezes, are readily miscible with water. Long term brake system water content tends to reach a maximum of about 3%, which is readily handled by the corrosion inhibitors in the brake fluid formulation. Since the inhibitors are gradually depleted as they do their job, glycol brake fluid, just like anti-freeze, needs to be changed periodically. Follow BMW's recommendations. DOT 5 fluids, not being water miscible, must rely on the silicone (with some corrosion inhibitors) as a barrier film to control corrosion. Water is not absorbed by silicone as in the case of DOT 3-4 fluids, and will remain as a separate globule sinking to the lowest point in the brake system, since it is more dense.
Fluid boiling point
DOT 4 glycol based fluid has a higher boiling point (446F) than DOT 3 (401F), and both fluids will exhibit a reduced boiling point as water content increases. DOT 5 in its pure state offers a higher boiling point (500F) however if water got into the system, and a big globule found its way into a caliper, the water would start to boil at 212F causing a vapor lock condition [possible brake failure -ed.]. By contrast, DOT 3 fluid with 3% water content would still exhibit a boiling point of 300F. Silicone fluids also exhibit a 3 times greater propensity to dissolve air and other gasses which can lead to a "spongy pedal" and reduced braking at high altitudes.
DOT 3 and DOT 4 fluids are mutually compatible, the major disadvantage of such a mix being a lowered boiling point. In an emergency, it'll do. Silicone fluid will not mix, but will float on top. From a lubricity standpoint, neither fluids are outstanding, though silicones will exhibit a more stable viscosity index in extreme temperatures, which is why the US Army likes silicone fluids. Since few of us ride at temperatures very much below freezing, let alone at 40 below zero, silicone's low temperature advantage won't be apparent. Neither fluids will reduce stopping distances.
With the advent of ABS systems, the limitations of existing brake fluids have been recognized and the brake fluid manufacturers have been working on formulations with enhanced properties. However, the chosen direction has not been silicone. The only major user of silicone is the US Army. It has recently asked the SAE about a procedure for converting from silicon back to DOT 3-4. If they ever decide to switch, silicone brake fluid will go the way of leaded gas.
Brake system contamination
The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some BMW owners changed to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. BMW brake systems should be flushed only with DOT 3 or 4.
If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.
New developments
Since DOT 4 fluids were developed, it was recognized that borate ester based fluids offered the potential for boiling points beyond the 446F requirement, thus came the Super DOT 4 fluids - some covered by the DOT 5.1 designation - which exhibit a minimum dry boiling point of 500F (same as silicone, but different chemistry).
Additionally, a new fluid type based on silicon ester chemistry (not the same as silicon) has been developed that exhibits a minimum dry boiling point of 590F. It is miscible with DOT 3-4 fluids but has yet to see commercial usage.
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Veteran
Posts: 168
Location: SD | I use DOT 5 in my old cars, and recommend it. Doesn't absorb moisture, doesn't damage paint.
Here's some info from Rick E. of Mopar Action: http://www.moparaction.com/Tech/quest/BINDER_JUICE.html |
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Extreme Veteran
Posts: 409
Location: Tampa, Florida | I rebuilt the brakes in my 58 Fury back in the 1980's and used silicon brake fluid. When I got the car out of mothballs in 2007 to take it to Tulsa, I bled the brakes and have been driving it to cruise nites and car shows at least once a month since and the brakes still work fine. I highly recommend silicon fluid and use it in all my antique cars. |
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Expert
Posts: 2519
Location: central Illinois | I started using DOT 5 silicone fluid when it first became available to me in the early 80's. Didn't rebuild anything, just removed all I could from the master cylinder, filled her with DOT 5 and bled the brakes. I've used it in probably 10 or so cars and have never had a compatibility issue. The one negative that some may point out is the old fluid or moisture that was previously in the system might gather at a low spot in the lines and cause a line to rust. Bah humbug. If it concerns you then bleed them every couple of years. And it won't hurt your paint!
My only concern on a FL car is what it might do to the inline brake light switch. |
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Veteran
Posts: 168
Location: SD | b5rt - 2012-02-14 4:53 PM
My only concern on a FL car is what it might do to the inline brake light switch.
I rebuilt my brake system in around '04. I installed a new hydraulic switch at that time, and it's been fine with the DOT 5 so far. |
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DOT 3/4/5
