Just finishing my brake system and don't want to ruin the paint on my frame if I have a leak. Is Dot 5 brake fluid a good way to go? The master cylinder and wheel cylinders have been blown out with compressed air. All of the lines are new. Thoughts? Mollydog
Nothing personal but isn't that kind of a lame reason to go to DOT 5. If you did the job right, it wont leak. The new corvette comes with DOT 5 but I doubt it has anything to do with leaks and paint removal.
I have been using Dot 5 for over 35 years with very good results in two different rods BUT if you are going to replace Dot 3 you need to flush out your old system. If there is any residual Dot 3 in your system it will not mix well with Dot 5.
Dot 5 has been in the 37 for 31 years before using I rebuilt all caliper , wheel cylinders and master cylinder . Still has solid pedal and no leaks .
33 years driving my 3W with Dot 5, started with a complete new system, wheel cylinders, calipers, master cylinder and all stainless lines with AN fittings. Never any leaks or blown seals.
I completely rebuilt the brake system in a '68 Corvette I had. Everything the best, so I went with DOT-5. I had a hell of a time getting it bled, but finally got a firm pedal. It was fine for about 20 years and I then sold the car. I have never used it again. These days I use DOT-4 on all my current cars. Brake fluid is like any other fluid in your car; it needs maintenance and occasional changing. The problem with DOT-3,4 is that it is "hygroscopic", meaning that it picks up moisture from the atmosphere. With our cars, which are usually used in stored in the best of conditions, this is not much of a problem. I also have a device that tests the moisture content of brake fluid in a car. I test mine annually, and have found that regular DOT-3,4 will go about 10 to 15 years before it even starts to show signs of moisture. I use "Speed-bleeders" on my cars, so changing the fluid is a quick, one-man operation. I have done my '51 once (I have owned the car 32 years) and my '67 Corvette (which I have also owned for 32 years) once. In the final analysis, I came to the conclusion that DOT-5 is not worth the extra effort and expense involved. Think about all of the old "beaters" that you see on the road everyday that probably have their original brake fluid; if it were a problem, don't you think there would be all kinds of rules and regulations requiring it to be changed regularly? As to spilling it on the paint and ruining it, I have never had that problem.
Conventional brake fluid is hygroscopic, but that's not really a "problem", this is why it was chosen over other fluids to begin with. In a relatively open master cylinder system as used in those days small amounts of moisture can get in through condensation or other means, the question is what happens next. The characteristic of absorbing small amounts of moisture prevents it from either boiling at high temperatures or freezing solid in the winter either of which means "no brakes". It isn't as if the engineers were stupid.
It is difficult to get a firm pedal with dot 5. Use dot 3 or 4, and before you start your bleeding operation wet the area down with a spray bottle filled with water. If you spill any brake fluid, spray water all over the suspected area immediately. Dot 3 or 4 absorbs water, and water kills brake fluids ability to eat paint. Bleed your brakes, and wipe off the water with a soft cloth.
The issue with switching to dot 5 from day one has always been contamination from old fluid still in the system somewhere. That happened a lot years ago when it became a hot lick street rodder item after a magazine article or two on it and that it didn't eat paint and all the sudden guys were fighting brake issues because they hadn't properly flushed the system or started with a completely new system Never heard of a guy with a totally new system having a problem though. On the beeding thing. I'm going to say it is a hell of a lot more of the skill and patience of the person doing the beeding and proper procedure than it is what fluid you use.
I like DOT 5 a lot, and convert all my old cars to it. (unless they have mechanical brakes) I've had it in my Olds since 81 with zero trouble. If you flush your system out with brake cleaner, then air, it should be ok to switch to the DOT 5. Disassembling the cylinders and cleaning and reassembling with dot 5 is even better. Dot 5 is 100% compatible with DOT 3 as far as that the brakes will still work fine if they are mixed. But if you do not have 100% pure dot 5, you will loose the moisture proof and high boiling point benefits of it.
Dot five and dot three will not mix and are not compatible, dot 3 and 4 and 5.1 are glycol based and mix fine, all three are hygroscopic, which is good, they keep moisture trapped in them. Dot five is silicone based and is not hygroscopic which means moisture is not absorbed and will settle to the low points and can cause corrosion. Most oem applications do not use dot five because it requires service more often and cannot be used with abs systems. There is no need for it. Sent from my iPhone using H.A.M.B.
... dot 5 for me, was attainable ONLY because I replaced ever single piece of brake system. From the master down. Dot 5 and dot 3 mixing, makes a very corrosive mixture. I guess one could flush their system, but I didn't.
I originally used silicon (DOT5) however the pedal never felt right and was spongy so I drained and flushed the system installing all new seals and replacing fluid with older style fluid which is still there today. Are you using a particular type of fluid or mixing different types? FYI, silicon fluid is not hydroscopic and does not absorb water, originally introduced to give higher temperature performance over DOT4 fluid. Whatever you do, don't mix DOT 5.1 (Glycol-based) with DOT 5 (Silicone-based) or any other DOT brake fluid as each has a different boiling point.
Dot 3, 4 or 5.1 can be mixed, it will affect the boiling point, as far as paint damage, why is brake fluid on your paint? Modern paints with hardener are far less susceptible to it. Sent from my iPhone using H.A.M.B.
I read up on using DOT5 fluid when I was re-doing my T roadster a few years ago. What I learned agrees that all that the old fluid be flushed out as completely as possible. I had also read that the pedal can seem a bit spongy if not filled and bled properly. I was carful not to shake the bottle of DOT5 fluid around which would introduce tiny air bubbles which are slow in coming to the top. Also pour it into the MC slowly also to keep from introducing air bubbles. To bleed, I just cracked all 4 bleeders and kept the MC full until I had fluid at all 4 wheels. I followed that with a "normal" pump-and-bleed procedure. I'm not saying this is the final word on DOT5 brake fluid but I've been pleased with the brake feel on the T. Lynn
Yes, absolutely not a problem. Like @Mr48chev said, it depends a lot more on the skill and patience of the person doing the work than it does the type of fluid used. As @lake_harley said, DOT5 is VERRYYY SLOOWWWW when it comes to allowing air bubbles to migrate out of it to a high spot where it can be bled out. DO NOT shake the can, DO NOT pour it quickly, don't do anything that will allow tiny bubbles to be introduced into the fluid. Those tiny bubbles are why so many people think the use of DOT5 will result in a soft pedal. Tiny bubbles belong in beer and champagne, not brake fluid. @57 Fargo mentioned the inability for DOT5 to absorb moisture, and this is the only drawback I see with DOT5. Any moisture that is in, or gets into the braking system will settle to the low spots and lay there, possibly causing rust and corrosion. I use DOT5 in the two old Harley Shovelheads that I have because the front master cylinder on those bikes are notorious for seeping fluid, and I have had one very nice paint job ruined over the winter due to a couple drips of DOT3 which I previously used. Those bikes get their brake systems drained and flushed every couple of years because they're easy to do. In the cars, it's all DOT3 because it's more of a PITA to completely flush them.
When I bought the DOT-5 fluid for my Corvette, I swear that it came with instructions to heat it up (I imagine to drive the air out of the fluid) just before installing it. I bought a cheap tea kettle and did just that. It also made pouring the fluid into the master cylinder easy, which also cut down on the air entrapped in the system. I have searched the internet high and low to try to find some definitive information about this, but came up empty. Anyone else heard of this? It seemed to help, and I eventually did get a nice firm pedal.
Thanks to all who replied to my question on Dot 5 brake fluid. This is my first complete build and my first attempt in double flaring brake lines. I still have a long way to go before I need to add the brake fluid. Thanks everyone... Mollydog
No do not use that . That stuff is specific for certain types of seals. 5.2 is comparable but MUST BE Changed often . I found out the hard way. Good DOT 3 is best all around and DOT 4 is a synthetic that is also very good and seems to less prone to moisture corrosion. All the 5’s are high temp for racing but must be changed regularly. Some may disagree but after having failure I did research into the subject . Sent from my iPhone using H.A.M.B.
All brake fluid is "synthetic" as a matter of fact, it just looks better on the label. Advertising wankery. A quality DOT 3 is pretty good stuff, it will have a lot higher boiling point than the minimum required by law. It bleeds real easy too because of its viscosity.
Dot five does not require special seals, that’s false. Any glycol based fluids are compatible. The boiling point will be affected by mixing them. Sent from my iPhone using H.A.M.B.
I have a really large syringe you can usually find at veterinary supply type places. I use it to pull the fluid from my brake and clutch reservoirs on my old cars. I carefully wipe out any dirt or debris laying on the bottom and replace with fresh fluid. I use it on power steering reservoirs also. The fluid that comes out even if it is only a year or two old can be pretty nasty. The syringe trick works good to if you are changing a master or power steering pump and want to pre-drain them.
Somebody local sent out an advertising flyer in the mail a while back for the standard routine automotive services and related "specials"; oil changes and tire rotations and the like. One of them caught my eye though, was called a "Brake Fluid Exchange", for $79.95 I didn't ask, but it doesn't sound like an actual brake bleed or flush. Maybe, but I doubt it. Just a little too weaselly in the title. I think some wanker found something that sort of sounds like a total brake fluid replacement but they just swap out a few ounces of fluid out of the master. Basically I just doubt they could pencil it out at eighty bucks bleeding all four corners.
I used Dot 5 Silicone brake fluid in my '56 truck when I built it in 1991. All brake components were new at the time. In 2016, after 26 years, I had to replace the rear brake cylinders because one of them was hanging up due to corrosion on the ends of the bores, not in the center where the fluid is in contact. For a new build, I would highly recommend using Dot 5. John U
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