OK guys, I am getting ready to replace the master cylinder, brake lines/hoses and wheel cylinders on my '61 Lesabre. I am sure this question has been answered before but other than the cost of the brake fluid, is there any reason to NOT use synthetic DOT 5 brake fluid? Since Dot 5 isn't hydroscopic, you can go longer without having to flush the system which appeals to me. Anyone have a good reason why I should stick with DOT 3?
I read somewhere that the DOT 5 silicone fluid is not compatible with any of the other fluids. I saw somewhere that if you ran anything else in your brake system it needs to be flushed out completely. If I can find the info I will link.
Thanks John. Yes I read that too. Link below. I figured since all the parts in the hydraulic part of the brake system will be new, it will essentially be flushed out. https://www.hemmings.com/blog/2013/...different-about-them-and-why-should-you-care/
Personally I wouldn't. I tried it before and had issues with master cylinders and spongy pedal. Once aerated it tends to stay that way. Also it doesn't absorb water so any moisture will be isolated in a pure pocket.. A regular flush thru while bleeding once a year with dot 3 should eliminate any moisture issues. The. Only plus of dot 5 is it doesn't eat paint. The higher boiling point isn't needed
Hygroscopic is a good thing for cold (hard freeze) climates, and/or hard braking application where extreme heat build up is encountered. Water no dispersed turning to steam, or freezing is not a thing one wants when stomping on the "No-Go" pedal. The other issue is the collection of moisture in isolated areas causing corrosion, and problems arising form pinhole leaks and sticking components. If brake systems are drained, flushed and refilled every year or so, it is not a problem, but the majority will not do that. So a good hygroscopic, high temp dot 3 is likely the best for "our" systems.
I contacted a couple shops to rebuild my original master cylinder and they all told me NOT to use DOT5 because it will swell the rubber seals and void the warranty. There is a lot of info online for DOT3 vs DOT5 if you Google it. Apparently DOT5 was originally developed for the Army and even they are now moving away from it. With that being said, I've used DOT5 in my '70 Stage 1 for 20 years. No problems yet.
I have Dot 5 in my GSX and my 69 Electra. Its been in the 69 Electra since around 1985 . At the time it got new wheel cylinders and Master cylinder and rubber hoses . Never have had a problem . My GSX has it in since around 1995 or so . Again the complete brake system was replaced including brake lines . I have never had a problem with it either . When I did them both I had heard about the chance that if aerated it would retain bubbles so I was careful not to shake it and when bench bleeding the master not over pump . I have never had any problems with it.
My military blazer has dot 5 in it and it’s been fine. It’s really not that costly and advance and autozone both carry it. The tech manual for it says to flush the system with denatured alcohol if it is contaminated or someone messes up and puts dot 3/4 in. I chose to use motul dot 4 in my Buick when I redid the entire system.
My friend switched his car and didn't flush it. He then later had problems from two calipers and his master. He flushed it out and changed every component and it's fine ever since. I guess it is all in the process. I do know that what was said about not absorbing moisture is true, but I guess if you do preventative maintenance it can and will be fine.
I ordered new lines, wheel cylinders, master cylinder, etc. last week. I tore into the brake system today so everything is ready to go when the parts arrive. Check out the photo below. the brakes were getting pretty soft but I has no idea how almost non-functional they were. each wheel cylinder was filled with thick, rusty gunk about the consistency of tooth paste. It's a miracle they worked at all.
I have used Dot5 in several vehicles with zero problems. I even flushed the old fluid out of two vehicles using the Dot5. We just made certain to thoroughly get the old fluid out completely.
I had Dot5 in my car from the time I restored it with all fresh components until just a few years back (about 15 years total) and never had any component related failures. A few years back I was trying to firm up the brakes a bit and while working at PRI I spoke at length to a guy from Wilwood and he was not a fan of DOT5 for anything that was going to actually be driven on the road. He recommended some Castrol DOT4 stuff as being his personaly preferred brake fluid so I ordered a quart off of Amazon and used it when I swapped to a 1in bore master cylinder a a few years back. Hard to tell if the new fluid made a lot of difference by itself or not but the combo of the 2 really made my brakes a lot better.
