Good day fellow HAMBers. Been a few days since we’ve had a Sh Show so here goes. What brake fluid do you all recommend DOT 3,4,5 or 5.1? My understanding is 4 is better than 3 due to higher boiling points but adsorbs water more easily which may cause corrosion and should be changed out more frequently. Is the silicone based 5 the best for our stuff? I believe 5 is easier on paint also. I ask because I will be doing a complete rebuild (mc, wcs , lines, hoses ,shoes and hardware) on the Dirt Cheap Dart this week I have DOT 3 and 4 on hand, but will use 5 if it’s a better deal. The car will be a driver. Thank you Dan
silicone fluid will not absorb water therefore the moisture in any air will turn to droplets of water at low points and cause rust or corrosion your master cylinder will always have air above the fl,id level
I have used DOT5 in two hot rods and my Front Engine Dragster and am completely happy with it. Future builds will get it too. There are a few precautions but I don't fear what some see as downsides. Since DOT5 doesn't absorb water I think the fear of water settling in low spots in the lines causing corrosion and/or ice in cold weather are exaggerated. Just don't pour water in your brake system while you're adding DOT5 fluid and you shouldn't introduce any water. A good brake bleeding and brake fluid flush on a regular basis isn't a bad idea no matter what kind of brake fluid you use. Lynn
there's no "best", as long as you can stop the car safely? 3 and 4 absorb moisture. 5 doesn't. How does moisture get into the system? past cup seals? or through the vent that was used on most master cylinders before about 1960, when they changed to a diaphragm seal? 3 and 4 eat paint, especially non catalyzed paint. 5 does not, but it is really good at keeping paint from sticking in the future. If you plan to paint the car later, don't spill any! I use 3 because it works. Maybe your car is special and needs "the best" fluid.
You can mix DOT 3 and 4 they are essentially the same except 4 has a higher boiling point The “ Book” says you can put Dot 4 in a Dot 3 system but not vise-versa for safety concerns . I use whatever my parts dept has on the shelf , every 2 years I use a syringe and suck the master cylinder reservoir dry , put new fluid in and bleed all 4 corners . never had a brake failure on a system I’ve replaced / maintained like this . the reason I don’t like Dot 5 is if you mix dot 3 or 4 with it you can have issues , 3 & 4 are still the most common brake fluids available, if I do have an issue out in the road it’s far easier to find at a gas station or parts place on the side of the road and get you home .
Correct. You can mix DOT 3 and DOT 4, so if you are in a bind and have to add fluid, no biggie. I don't use DOT 5. I typically use DOT 3 in everything. Plus a lot of aftermarket products like my hydraulic throw out bearing, don't allow DOT 5.
No not special, ran DOT 3 for decades, just looking for input since I’m starting with all new stuff. Dan
This is from experience of what I've seen at work. Had several local guys with old vettes convert over to dot 5, now these cars set alot so keep that in mind. After a couple years the calipers started hanging up due to corrosion in the piston bores. Second, seen people convert to dot 5 OR buy a car with dot 5 unknown to them and later add dot 3 or 4 to top off the reservoir and then all kinds of bad things happen. My personal stuff gets dot 4, easy to obtain, most people still use it so that's what they have on hand at home incase I sell something to them. Dot 4, It's definitely proven itself for many many years too...does exactly what it needs to do.... ...
Thanks all. I will use DOT 4 as I have a brand new jug and don’t see a big gain in going with 5. I will also drain and replace every 2 or 3 years. Dan
Dot 3 in all my cars from 1954 to 2022 and change it every 3 years. It’s cheap, easy to find, and works in all my stuff.
FYI: With Dot 3 or 4, always use a brand new sealed bottle. Dispose of it any remainder. The stuff loves to suck water out of the air, making it less effective. I test with this lovely stuff at work quite often. We have to monitor water % very closely and you would be amazed how quickly an open bottle goes bad.
Dot 3 here. I've never discarded any just cause the bottle was opened as long as it's my own stuff and not some old freebie. Don't have brake problems from that.
I put my avatar roadster on the road in 2009 and have accumulated over 40k miles on the original silicone brake fluid. No problem whatsoever.
I don't have a problem with any type. My issue is figuring out how to keep the line from leaking. I've got two places that are driving me nuts.
usually it requires tightening the fitting, and if that doesn't work, a new inverted flare should fix it. But if it's a banjo bolt, maybe a new washer. And sometimes tapered threads are defective, and brass fittings crack.
I've used DOT 5 when I do a complete overhaul with no contaminated lines etc. New components etc. 25 years on several cars. Pulled a wheel cylinder off one car using DOT 5 20+ years and it looked like new-not muddy/cruddy like a neglected DOT 3 system I believe you gotta drain the DOT rery 3/4 to keep things goin smoothly
Depends on the environment. Warm dry climates DOT 5 will last for years. But in very cold wet conditions it can give issues with moisture in the lines freezing or corrosion problems. This is not helped as moisture on DOT5 systems sinks to the bottom so bleeding does not clear it. Predominantly Cold or wet climates use DOT4 or 5.1 and change every few years.
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