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Brake fluid preferences.
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Author:  HyperValiant [ Mon Jan 26, 2004 11:40 pm ]
Post subject:  Brake fluid preferences.
What is the advantages /disadvantages of dot5 brake fluid.I would like to use this as it doesnt draw moisture like dot3.What is everyone elses opinion.This will be a daily driver.
HyperValiant
Author:  junkyardhero [ Mon Jan 26, 2004 11:54 pm ]
Post subject: 
Hypester, the DOT5 will weep from the most minute breaks, cracks or perforations. Areas that you thought insignificant or beneath notice will be brought into sharp focus. But on the plus side it won't eat your paint. Also, it's my understanding that it is not at all compatible with any other fluid.

I found it to be good stuff in a race car, but i bled the brakes constantly and flushed the system every three months.

On a street car, i'd go for the DOT3. Inexpensive, easy to find, and easy to maintain.
IMHO, YMMV, results not typical, yadda, yadda, yadda.

-JYH
64 Dart-o-matic, wilwoods? what wilwoods?
69 Cuda, all factory parts.. well factory design... sort of...
SoCal
Author:  Dart270 [ Tue Jan 27, 2004 6:42 am ]
Post subject: 
I use Dot3 or Dot 4+ (Valvoline or similar) that has a higher temperature rating. These are compatible and don't have the problems JYH lists.

Lou
Author:  RG [ Tue Jan 27, 2004 10:01 am ]
Post subject: 
I use Dot 5. Never had a problem. It is not compatible with other types, so if you are thinking about major brake work/upgrading then I would seriously consider this fluid.
My '64 Dart has had it for several years. It is stored in the winter months. My daily driver '79 Volare has had it for three years. The fluid is still clear. Advantages are that it does not absorb moisture, so your system stays cleaner (no sludge in your wheel cylinders/calipers/mastercylinder). If it is more prone to leakage then I would consider that a plus. If the system leaks Dot 5 but not Dot 3 then the system integrity might be questioned.
Author:  steponmebbbboom [ Tue Jan 27, 2004 3:51 pm ]
Post subject: 
I'm going to have to voice dissent here.

The favorable temperature characteristics of Dot 5 will never benefit your street application. Dot 5 is intended for full race, high heat applications and driveline braking systems on industrial trucks. The "hydrophilic" or water absorbing characteristic of conventional brake fluid is undesirable here only in that it lowers the critical boiling point of the fluid, causing fade under normal braking.

In typical passenger car applications, however, hydrophilia is an important characteristic. This prevents any standing pockets of water to form, which can cause corrosion and sticking of pistons and valves in the brake system. It also ensures all water will be removed when the system is flushed, which should be done as part of regular maintenance. Normal brake fluid will not boil under normal braking, however if you have drums and drive enthusiastically, high quality Dot 3 or 4 fluid with a higher boiling point is available. I have no experience with Dot 4 or how it reacts to seals in a dot 3 brake system, but its worth checking out IMHO.

Leakage of Dot 5 in a conventional braking system may be attributed to incompatibility of the seals, but that is just a guess. It could also be due to lower viscosity.
Author:  Pierre [ Tue Jan 27, 2004 4:28 pm ]
Post subject: 
Every master cylinder I've bought for my car so far stated in bold print on the cover "USE DOT 3 FLUID ONLY".....
Author:  HyperValiant [ Tue Jan 27, 2004 7:30 pm ]
Post subject: 
Thanks fellas,its all clear as mud now,LOL.the real reason that I was asking was that when I rebuilt my small bolt calipers I noticed that the first calipers I got was full of rust and had to dig up a second set to rebuild and considering that this car will sit in hibernation during the winters,I didnt want them to rust also but considering that the car will be driven "spiritedly" and often ,Ill probably go with Lou's suggestion.
I appreciate everyones input on this subject.
HyperValiant
Author:  RG [ Wed Jan 28, 2004 7:11 am ]
Post subject: 
I'm confused as to why in one instance water absorbing charteristics of brake fluid is acceptable and in another case it is not.
Why would you want any water/moisture in your brake system? As water is heavier than oil it will collect in the lower cavities of the system(re: calipers.wheel cylinders), the bleeder valves on these componets are not located where the water is. How can you flush ALL the water/moisture out? Moisture+Oxygen (also present in water) = Rust.
The systems that I have installed DOT 5 into do not show any evidence of corrision. The Dart has the original 9" drums. I am not hard on brakes so brake fade is not an issue with me. This auto is only driven in decent weather and is not driven hard (Mash the gas/mash the brake.) The Duster (disk/drum) IS driven daily in all weather. Regular stop/go traffic. No hills, no brake riding. To date I have not experienced brake fade. The Super Bee will be converted when I install front disks. Again this car is only driven on decent days.
Author:  steponmebbbboom [ Wed Jan 28, 2004 8:18 am ]
Post subject: 
Quote:
I'm confused as to why in one instance water absorbing charteristics of brake fluid is acceptable and in another case it is not.
Why would you want any water/moisture in your brake system?
The answer is, you wouldn't.

Most brake systems Ive encountered that were designed to use Dot 5 were exceptionally well sealed, and were an indoor application. Full race cars usually arent together long enough for any significant amounts of moisture to form. And Im not talking about rural circle track race cars.

Driveline braking systems usually use a reduced friction pad, and get quite hot under normal braking. The pads sometimes even have brass shavings in them. If normal organic brake pads were used, the shoes or pads would be ripped from their moorings, and likely bend the mounts. Reduced friction pads are necessary to allow feathering of the brake pedal, because driveline braking takes advantage of the reduced torque needed to slow the wheels when mounted ahead of the final drives.

This is why the boiling point of Dot 5 is so critical here. Wheel end brakes on passenger cars typically dont get nearly as hot.

This is not to say that all driveline brakes stipulate use of Dot 5. It is most commonly used on narrow aisle reack forklifts, which depend on one pair of pads to do all the braking of the truck in an emergency. Some operators erroneously use the deadman brake to stop the truck when they should be switching back the joystick for regen braking. This overheats the pads and this is where the high heat resistance of Dot 5 is critical.

If your car is showing no signs of moisture accumulation with Dot 5, that's great :D Your brake system is obviously well sealed and you arent abusing it. That's not to say though, that if the car belonged to a soccer mom or someone equally ignorant of car care and maintenance, that water would not collect to a dangerous level and cause problems. If you are aware of the shortcomings of the fluid and make allowances for that, it may well be your best choice. I simply dont think its a safe choice to recommend due to that one property.
Author:  Eric W [ Wed Jan 28, 2004 9:11 am ]
Post subject: 
The moisture issue with brake fluid is why I flush the brake system on my car twice a year. Just open the speed bleeders, and go to work for 30 or 45 minutes. Cheap insurance. I always thought the only difference between DOT 3 and 4 was the boiling point. :?: I also use DOT 4 (4 wheel drum, 10").
Author:  RG [ Wed Jan 28, 2004 1:04 pm ]
Post subject: 
I guess I just don't get it. Went to Google and did a search on brake fluid. The following is from "How Stuff Works"..."As a DOT3 or DOT4 brake fluid absorbs water, its boiling point decreases. It can absorb water from the air, which is why you should avoid opening your car's brake fluid reservoir. For the same reason, you should always keep containers of brake fluid tightly sealed.

DOT5 fluid does not absorb water. This means the boiling point will remain relatively stable, but it also means that any water that does get into your brake system will tend to form pure water pockets, which could cause brake corrosion.

Two other important things about brake fluid: DOT3 and DOT4 eat paint, so don't spill it on your car. Also, none of the different types of brake fluid should be mixed. They can react badly with each other and corrode your brake system."

If your system is sealed and full then how could water collect in a Dot 5 system. Dot 5 does not absorb moisture. That is why I use it. It isn't like a fuel tank where the level constantly changes, leaving a large void.
Author:  steponmebbbboom [ Wed Jan 28, 2004 3:14 pm ]
Post subject: 
Eric, I believe you are correct, but I dont want to chance putting my foot in my mouth. :wink:

RG, everything you posted from Google sounds correct to me. The thing is, in a perfect world where everyone is attentive to their car's condition and they maintain it properly, water wouldnt collect in a car's brake system. On a passenger car, this type of person probably makes up about 10% of car owners. Hell, even I neglect my vehicles on occasion for whatever reason. I have been known to roll the odometer as much as 20 miles :!: beyond the next scheduled oil change :wink: But the fact remains, any water that DOES accumulate will not be absorbed into Dot 5 fluid, and it will collect in low areas, where it can seize valves and pit bores.

Truth is, not many owners change their brake fluid on a regular basis. I do, Eric does, and I figure a lot of the rest of us do. And for us, dot 5 might work fine, if not for the fact the seals in the brake system are not designed to handle dot 5. Im just not comfortable using it, especially since I will never ever use regular dot 3 to its design limits. I just dont drive my cars like that. :|
Author:  1969ron [ Wed Jan 28, 2004 8:33 pm ]
Post subject: 
hi, dot 4 and change yearly. also in the new mopar chassis book, dot 5 explained why it's NOT recommended for street or racing. i have other brake books and articles that back it up. ron
Author:  ShivaDart [ Wed Jan 28, 2004 10:18 pm ]
Post subject: 
I have a question. I don't believe that my car's brake fluid has been changed for a very long time(I've owned it two years and haven't changed it), is it something that can be changed without causing massive leaks? Seems like I was told something about leaks(to vindicate myself a little I am very good about oil and filter changes)
Author:  RG [ Thu Jan 29, 2004 4:22 am ]
Post subject: 
I don't regularly change brake fluid. I have no need to. That is why I use DOT 5. If the system is sealed, water absorbsion is not a problem. I have never experienced a componet faliure/leak. To me DOT 5 is great stuff, but, I guess from all the negative feedback, I'm in the minority.
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