You don't choose. The manufacturer of your brake equipment specifies what to use. Follow their recommendations.
Castrol GT/LMA Dot4, it's a lot safer if there's any natural rubber in your braking system. In daily stuff I change it every year.
For over 20 years I have run Dot 5 exclusively. Mainly to protect the paint on my suspension and brake components, but also because it just works fine for me. Last year I drained the brake system when I redid my 27 and the 20 year old Dot 5 came out like the day I put it in. I've never had a leak and even run it in my hydraulic clutch setup. Don
That applies to late model cars built in a factory. I am sure the original poster is asking about Traditional Hotrods which are assembled at home using ordinary parts which are probably made in China and which are from parts stores as available. QUOTE=rld14 Castrol GT/LMA Dot4, it's a lot safer if there's any natural rubber in your braking system. I seriously doubt if there is ANY natural rubber ANYWHERE in a car. America quit using real rubber during WWII QUOTE=Donshotrods For over 20 years I have run Dot 5 exclusively. Mainly to protect the paint on my suspension and brake components, but also because it just works fine for me. Last year I drained the brake system when I redid my 27 and the 20 year old Dot 5 came out like the day I put it in. How can anyone argue with success? Like Don I have used Dot5 from Advance Auto and other part stores with enormous success for 20 years. Dot5 does not absorb moisture out of the air and thus does not turn into rusty mushy sludge in the brake systems of the many ol cars I drive. When I drain it out years later, it looks as good as new and there is no sludge, no stuck pistons, no deteriorated soft seals or boots.
Or, or, how about the new DOT 5.1, not silicone, alky base as DOT 3 & 4 but higher boiling point yet. I have used DOT 5 good and bad, hard to get air out.
Dot 5 isn't better in every way. Like many things, there are pluses and minuses. - Dot 5 doesn't absorb moisture, which in some ways is a plus. - Dot 5 doesn't absorb moisture, so it cannot remove moisture from the system. - Dot 5 tolerates higher temps. - Dot 5 doesn't damage paint. - Some Dot 5 is incompatible with some seal/hose materials. - Dot 5 is harder to bleed because air tends to stay in suspension more than with Dot 3. - Dot 5 is not as good a lubricant as Dot 3. - Dot 3 does not prevent rust as well as Dot 3. - Dot 5 is not compatible with "regular" fluid, so you can't mix them. - When switching to Dot 5 the system should be thoroughly and completely cleaned/flushed of "regular" fluid.
I highly advise against the use of dot 5 on anything that will get driven. I have had cars in here and ended up rebuilding the entire systems due to incompatability of the silicone and the seals in the master and calipers/wheels cylinders. As stated Dot 5 does not absorb water but when water gets in the system (it does) it "pools" together. In a worst case scenario that pool ends up in the caliper/ wheel cylinder and will boil. When that happens it turns to a great big air pocket. Use a quality dot 3 or 4 fluid. if you don't fill your master cylinder with a squirt gun and spray it all over your firewall you wont have any problems.
It's best to do some research on DOT 3, (4) and 5 fluids before you make a decision, along with making sure your brake components are compatible with your choice. Your driving habits, car storage, maintenance and location play a role in what fluid you should or should not use, and while some have good results with a certain fluid, like #5, you may not. BTW, my choice is DOT 3, factory recommended by all our daily late models, and chosen for my "toys".
I've been running Dot 5 in one of my 71 ford truck's for 2 or 3 years now. Never had any probs! I just put Dot 5 in a 71 F350 flatbed last year, Dot 5 in a 66 galaxie, 1966 F250 4x4. I was talking to a friend of mine that was in the army a few years back and he said they use Dot 5 in there stuff! YES!!! IM talking about 'TRADITIONAL" Hotrods which are assembled at home using ordinary parts which are probably made in China and which are from parts stores as available!
DOT 5 only in old cars. PERIOD I have been using Dot 5 for over 30 years in old cars 40 Fords, 57/62 Chevys, 68 Olds-you name it I use it in it. Sure air is a little harder to get out but there are a few tricks that make it easy. I began using DOT 5 when you could only buy it at the Honda motorcycle dealer. Allsystems still clean, no rust or lost paint.
Been using dot 5 for also over 20 years trouble free. Most of the brake systems I've used them on are brand new systems ( fresh builds ).
dot 5 has been in my vette for over 30 years now and it's like new when I check it, and trouble free (was installed along with the new system)( this car is run hard too!!)
If you drain your MC and push out the brake fluid which is DOT3 can you then put DOT 5 in? Or is it one of those things that's like once you start you better just keep using what you did?
I put the Dot5 in the day I build the car or when I replace all the cylinders. The guy at the parts counter told me if you mix dot3 and dot5, it will gel so of course I immediately poured both into a cup and watched it for weeks. nothing happened
I have never had good luck changing fluids, without replacing all cylinders and flushing the lines thoroughly first. New system, use what you want, old system, use whats there, that's my experience anyway.
I've never flushed the system either as I start out with Dot 5 on a fresh system and stay with it. On my cars that have Dot 3 in them I just stay with that. There is a way to flush it, but I don't know what it is or how many times you would have to do it to get out all the old fluid. Don
I ended up with 5 a few weeks ago, but at Advanced Auto, there was some fluid with huge letters saying it was "New - Synthetic" but I think it was classed as DOT3? Will that new Synthetic brake fluid eat paints?
No, its great. A person can get any answer they want to hear. There actually are cases of that happening. The fact some people have one problem or another while others have good results indicates that Dot 5 is not all the same. Dot 3 was always a synthetic product. Manufacturers are now saying so on the can to make it cooler. Unless there is something available I don't know about you are looking at regular DOT 3 with a marketing enhancement.
What he says - DOT 5.1 is Polyethylene based. DOT 5 is silicone based and comes with a safety warning on the can - and for good reason. I had total brake failure - sudden and without warning - with DOT 5 Silicone - not to be confused with DOT 5.1 which is NOT silicone. Here from the Vintage Triumph Registry: DOT3 DOT3 brake fluid is the "conventional" brake fluid used in most vehicles. One of the most familiar brands is "Prestone." Advantages: DOT3 fluid is inexpensive, and available at most gas stations, department stores, and any auto parts store. Disadvantages: DOT3 will damage natural rubber brake seals and should not be used in any car suspected of having natural rubber seals (most Triumphs prior to 1968). DOT3 fluid eats paint! DOT3 fluid absorbs water very readily. (This is often referred to as being hydroscopic.) As such, once a container of DOT3 has been opened, it should not be stored for periods much longer than a week before use. Since DOT3 fluid absorbs water, any moisture absorbed by the fluid can encourage corrosion in the brake lines and cylinders. DOT4 DOT4 brake fluid is the brake fluid suggested for use in late model Triumphs. The most familiar brand is "Castrol GT-LMA" Advantages: DOT4 fluid is available at most auto parts stores, and at some (but not all) gas stations or department stores. DOT4 fluid does not absorb water as readily as DOT3 fluid. DOT4 fluid has a higher boiling point than DOT3 fluid, making it more suitable for high performance applications where the brake systems are expected to get hot. Disadvantages: DOT4 fluid eats paint! Small leaks around the master cylinder will eventually dissolve away the paint on your bodywork in the general vicinity of the leak, and then give rust a chance to attack the body of your car! DOT4 fluid is generally about 50% more expensive than DOT3 fluid. Since DOT4 fluid still absorbs some water, any moisture absorbed by the fluid can encourage corrosion in the brake lines and cylinders. DOT5 DOT5 brake fluid is also known as "silicone" brake fluid. Advantages: DOT5 doesn't eat paint. DOT5 does not absorb water and may be useful where water absorption is a problem. DOT5 is compatible with all rubber formulations. (See more on this under disadvantages, below.) Disadvantages: DOT5 does NOT mix with DOT3 or DOT4. Most reported problems with DOT5 are probably due to some degree of mixing with other fluid types. The best way to convert to DOT5 is to totally rebuild the hydraulic system. Reports of DOT5 causing premature failure of rubber brake parts were more common with early DOT5 formulations. This is thought to be due to improper addition of swelling agents and has been fixed in recent formulations. Since DOT5 does not absorb water, any moisture in the hydraulic system will "puddle" in one place. This can cause localized corrosion in the hydraulics. Careful bleeding is required to get all of the air out of the system. Small bubbles can form in the fluid that will form large bubbles over time. It may be necessary to do a series of bleeds. DOT5 is slightly compressible (giving a very slightly soft pedal), and has a lower boiling point than DOT4. DOT5 is about twice as expensive as DOT4 fluid. It is also difficult to find, generally only available at selected auto parts stores. DOT5.1 DOT5.1 is a relatively new brake fluid that is causing no end of confusion amongst mechanics. The DOT could avoid a lot of confusion by giving this new fluid a different designation. The 5.1 designation could lead one to believe that it's a modification of silicone-based DOT 5 brake fluid. Calling it 4.1 or 6 might have been more appropriate since it's a glycol-based fluid like the DOT 3 and 4 types, not silicone-based like DOT 5 fluid. (In fact, Spectro is marketing a similar new fluid which they are calling Supreme DOT 4, which seems less confusing.) As far as the basic behavior of 5.1 fluids, they are much like "high performance" DOT4 fluids, rather than traditional DOT5 brake fluids. Advantages: DOT5.1 provides superior performance over the other brake fluids discussed here. It has a higher boiling point, either dry or wet, than DOT 3 or 4. In fact, its dry boiling point (about 275 degrees C) is almost as high as racing fluid (about 300 degrees C) and 5.1's wet boiling point (about 175 to 200 degrees C) is naturally much higher than racing's (about 145 C). DOT5.1 is said to be compatible with all rubber formulations. Disadvantages: DOT5.1 fluids (and Spectro's Supreme DOT4) are non-silicone fluids and will absorb water. DOT5.1 fluids, like DOT3 & DOT4 will eat paint. DOT 5.1 fluids are difficult to find for sale, typically at very few auto parts stores, mostly limited to "speed shops." DOT 5.1 will be more expensive than DOT3 or DOT4, and more difficult to find. General Recommendations: If you have a brake system that doesn't leak or show any other signs of failure, but has old seals in it, don't change fluid types as a result of reading this article. If it isn't broken, don't "fix" it -- you may simply break it instead! Flushing of the brake system every couple years to remove any absorbed or collected water is probably a good idea to prevent corrosion, regardless of the type of brake fluid used. DOT3 is dangerous to use with natural rubber seals, and thus should not be used in such cars, except as a temporary "quick fix to get me home" solution. (If this is used as a "get-me-home" solution, bleed the system as soon as possible, and be prepared to replace all your seals.) DOT3 is an adequate brake fluid, although it is rarely preferred. My recommendation would be to simply not use it. DOT4 fluid, for a slight increase in cost, will give significantly increased resistance to moisture absorption, thus decreasing the likelihood of corrosion compared to DOT3. DOT4 fluid has a higher boiling point than DOT3, making it preferable for high performance uses such as racing, autocross, or excessive use of the brakes in mountainous areas. For even greater braking performance, consider going to DOT5.1 or a high-performance version of DOT4 fluid. DOT5 is a good choice for the weekend driver/show car. It doesn't absorb water and it doesn't eat paint. One caveat is that because it doesn't absorb water, water that gets in the system will tend to collect at low points. In this scenario, it would actually be promoting corrosion! DOT5 is probably not the thing to use in your race car although it is rated to stand up to the heat generated during racing conditions. The reason for this recommendation is the difficult bleeding mentioned above. When changing from one fluid type to another, as a minimum, bleed all of the old fluid out of the system completely. For best results, all the seals in the system should be replaced. As always, your experiences may vary.
I was having problems with my Hydraulix throwout bearing leaking when it sat with Dot 3. I changed to DOT 4 and that problem went away. Great post Weasle and good thread. I was wondering why DOT 4 wasn't an option in the poll.
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