Brake fluid recommendations? Dot 3 VS dot 5

[GHOST RUSTERS]

Hello FABO.

1965 Barracuda 273/904 auto, 10” drums front and back.

we’re planning to finish up our brake system and I’m curious what brake fluid y’all might have experience with or recommendations?

Current status:
Upgraded to a Dorman M71258 manual dual master cylinder (which reads use only dot 3 fluid) all new brake lines front to back, new hoses from the hard lines to the wheel cylinders, new distribution blocks, new breather bolt in the distribution block on the axle, original wheel cylinders have been cleaned and honed with new springs and new rubber soft goods, bleeders cleaned out, front and rear brake shoes cleaned up and rebuilt, parking brake hardware and cables cleaned and lubed.

In my homework and research I’ve seen healthy points to pros and cons of dot 3 vs dot 5… mostly with concerns for dot 5 preventing harm to any painted surfaces if I’m understanding correctly, and also the idea of one or the other adsorbing moisture… but also conflicting stories that dot 5 isn’t kind to rubbers and soft goods and being thinner finds places to leak a little easier…

Having said all of that, with a whole “new” brake system and completely empty… any suggestions would be greatly appreciated. Once we’ve decided on a brake fluid most suitable for us, we’ll start with bench bleeding the master cylinder and moving down the line from there.

Thanks everyone!

 

[RustyRatRod]

It's not that DOT 5 is unkind to rubber parts. That's not it at all. It will MAKE an unkind mixture IF it is mixed with DOT 3 or any of the rest. That's where the problem comes in. So, in short, IF you go DOT 5, you really need to start from scratch with all new parts that have not seen DOT 3 or anything other than DOT 5. If that makes sense.

 

[harrisonm]

Plus, there is absolutely nothing wrong with DOT3.

 

[Kern Dog]

I switched to DOT 5 when I did an engine rebuild in 2022. I did change the front brakes entirely but the rears stayed the same. I did use a different master cylinder. The brakes were not any better than they were beforehand for a few reasons.
It took awhile but after several brake bleeding efforts, I finally got the purple fluid to the back brakes. When I got the car running, I bled and bled and was getting DOT 5 up at the front but the rear calipers flowed a diluted mix. the brake pedal feel was okay. Not great but not bad. A few months later I went at it again and that time, I bled it until the fluid coming out of the back was as purple as it looked at the bottle. That stuff aint cheap though! $40 a quart???

 

[RustyRatRod]

I switched to DOT 5 when I did an engine rebuild in 2022. I did change the front brakes entirely but the rears stayed the same. I did use a different master cylinder. The brakes were not any better than they were beforehand for a few reasons.
It took awhile but after several brake bleeding efforts, I finally got the purple fluid to the back brakes. When I got the car running, I bled and bled and was getting DOT 5 up at the front but the rear calipers flowed a diluted mix. the brake pedal feel was okay. Not great but not bad. A few months later I went at it again and that time, I bled it until the fluid coming out of the back was as purple as it looked at the bottle. That stuff aint cheap though! $40 a quart???

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Obama phone?

 

[GHOST RUSTERS]

It's not that DOT 5 is unkind to rubber parts. That's not it at all. It will MAKE an unkind mixture IF it is mixed with DOT 3 or any of the rest. That's where the problem comes in. So, in short, IF you go DOT 5, you really need to start from scratch with all new parts that have not seen DOT 3 or anything other than DOT 5. If that makes sense.

That makes perfect sense and I’m glad I asked… thank you for clearing that up for me, so in the application that I’ve described, everything is new and bone dry… would that be safe to start with dot 5 and ONLY dot 5? No intentions of ever mixing it up after… just curious on the benefits of dot 5 other than it not being harsh on paint… which I’m not too awfully concerned about, our barracuda fits more of the DNA of a rat rod (patina, nothing pretty, minimal chrome, made safe and road worthy) and being that dot 3 is affordable in comparison to dot 5… is there any specific reason that dot 5 is safer and or superior to dot 3? (Sorry for the 21 questions!)

 

[RustyRatRod]

That makes perfect sense and I’m glad I asked… thank you for clearing that up for me, so in the application that I’ve described, everything is new and bone dry… would that be safe to start with dot 5 and ONLY dot 5? No intentions of ever mixing it up after… just curious on the benefits of dot 5 other than it not being harsh on paint… which I’m not too awfully concerned about, our barracuda fits more of the DNA of a rat rod (patina, nothing pretty, minimal chrome, made safe and road worthy) and being that dot 3 is affordable in comparison to dot 5… is there any specific reason that dot 5 is safer and or superior to dot 3? (Sorry for the 21 questions!)

Yup, perfectly fine. I would make dang SURE no one like a quick lube place or any other got under there to top fluids off....if you get my drift.

 

[Kern Dog]

The only advantage that I see for DOT 5 is that it won't damage the paint.

 

[GHOST RUSTERS]

Yup, perfectly fine. I would make dang SURE no one like a quick lube place or any other got under there to top fluids off....if you get my drift.

Agreed. This vehicle will be home and family maintained as long as I can turn a wrench and when it’s time to pass it onto my girls or whomever, they’ll get the “bible” of documentations of everything that’s ever been done to and for it and the dos and donts of fluids, services and so on… the family technical service manual if you will haha. But very good point and thank you.

Do you have a preference yourself for dot 3 or dot 5?

 

[GHOST RUSTERS]

The only advantage that I see for DOT 5 is that it won't damage the paint.

I might have misunderstood but I’ve read there’s some consideration between the two with moisture in mind… water displacement I’m assuming? I do live in the Midwest and it’s mighty cold, I certainly don’t PLAN to for the car to be out and about at negative temps, but it will spend its downtime during the winter in an insulated garage… would that be a concern with moisture in mind between dot 3 and dot 5?

 

[RustyRatRod]

I might have misunderstood but I’ve read there’s some consideration between the two with moisture in mind… water displacement I’m assuming? I do live in the Midwest and it’s mighty cold, I certainly don’t PLAN to for the car to be out and about at negative temps, but it will spend its downtime during the winter in an insulated garage… would that be a concern with moisture in mind between dot 3 and dot 5?

One absorbs moisture (DOT 3), the other does not (DOT 5). So, what does that mean? It means that with DOT 5, the moisture will not mix with the fluid. So the moisture will be "wherever it is" in the system and OUTSIDE of the DOT 5 brake fluid. So, rust and corrosion "CAN" be an issue. I know, we're now gonna get all the "I've been runnin DOT 5 147 years and never had problems" crowd, but that's the FACT and there's no gettin around it.

Conversly, DOT 3 will absorb moisture, since it is water soluble. That means that the fluid will become more diluted over time. How much time? Crapped if I know. A LONG time I guess, since I've seen 50 plus year old cars with the same brake fluid and same brake system and the brakes still worked.

I'm not advocating for one or the other. I'm just stating facts. The DOT 5 is REAL nice if you have a really nice paint job and don't want it to be possibly damaged.


In the end, BOTH fluids should be flushed and changed with new over a period of time, just like all service manuals say. So if done correctly, that would get any moisture out of the system anyway, theoretically.

 

[Dana67Dart]

I would switch to Dot 5 in a heart beat but it is not super available at auto parts stores near me and I can't say i have seen name brand fluid.

 

[GHOST RUSTERS]

Well that sounds like the long and short of it, I knew I came to the right place… thank you for the education… sounds like I need to make a decision on a fluid and move forward…

My plan was to bench bleed the master cylinder, double check ALL of the brake lines and hardware and then double check again, then mount the master cylinder and starting at the passenger side rear bleeder while my oldest pumps the foot brake for me and top off as needed as we go… driver side rear, passenger side front then driver side front… does that sound like a fair plan? Anything I’m overlooking or missing? (The car is up on jacks, no wheels or tires mounted)

 

[Kern Dog]

Years back I was doing a service interval on the Wife's Honda and listed right there was Flush and replace brake fluid.
Whuuut?
I took a turkey baster and drew the fluid out of the master cylinder, then poured in fresh DOT 3.
The old fluid was dirty looking and to my surprise, the brake pedal feel actually improved by a noticeable amount. The fresh fluid didn't compress like the old stuff so the brakes felt better.
I use DOT 5 in just one car for now and that one has a paint job that I want to keep nice. The other cars that I have here are ratty so who the heck cares if I get a spill on them ??

 

[RustyRatRod]

Years back I was doing a service interval on the Wife's Honda and listed right there was Flush and replace brake fluid.
Whuuut?
I took a turkey baster and drew the fluid out of the master cylinder, then poured in fresh DOT 3.
The old fluid was dirty looking and to my surprise, the brake pedal feel actually improved by a noticeable amount. The fresh fluid didn't compress like the old stuff so the brakes felt better.
I use DOT 5 in just one car for now and that one has a paint job that I want to keep nice. The other cars that I have here are ratty so who the heck cares if I get a spill on them ??

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Send me that truck. lol

 

[GHOST RUSTERS]

Years back I was doing a service interval on the Wife's Honda and listed right there was Flush and replace brake fluid.
Whuuut?
I took a turkey baster and drew the fluid out of the master cylinder, then poured in fresh DOT 3.
The old fluid was dirty looking and to my surprise, the brake pedal feel actually improved by a noticeable amount. The fresh fluid didn't compress like the old stuff so the brakes felt better.
I use DOT 5 in just one car for now and that one has a paint job that I want to keep nice. The other cars that I have here are ratty so who the heck cares if I get a spill on them ??

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Well said and I can absolutely appreciate that point. Nice lookin rides there! Thanks for sharing!

 

[Kern Dog]

That truck....
Oddly enough, it is pretty rare. It is actually a 1975 but I put a '78 grille on it. Original 440/4 speed sold new in California! My the early 70s, getting a manual transmission V8 in California was getting difficult. Like a dummy I converted it to an automatic.
To top it off, it was a somewhat rare color originally...

I am thinking of taking it back to the stock orange paint but to look like a "Macho".

 

[RustyRatRod]

That truck....
Oddly enough, it is pretty rare. It is actually a 1975 but I put a '78 grille on it. Original 440/4 speed sold new in California! My the early 70s, getting a manual transmission V8 in California was getting difficult. Like a dummy I converted it to an automatic.
To top it off, it was a somewhat rare color originally...

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I am thinking of taking it back to the stock orange paint but to look like a "Macho".

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You went the wrong way with the grille. The 73 is the best lookin grille. I'll take it like it is though. lol

 

[GHOST RUSTERS]

Good lookin trucks, kinda reminds me of another package similar to those, I think it was called a Warlock but I could be mistaken… love the orange!

 

[RustyRatRod]

Good lookin trucks, kinda reminds me of another package similar to those, I think it was called a Warlock but I could be mistaken… love the orange!

Yeah the Warlocks were awesome. As were the Midnight Express trucks. Dodge has always made badass trucks.

 

[GHOST RUSTERS]

Yeah the Warlocks were awesome. As were the Midnight Express trucks. Dodge has always made badass trucks.

Speaking of badass trucks. I got to drive my uncles power wagon for a few years (1953 if I recall correctly) when we used to go play in the snow and gather up Christmas trees. The kids LOVED it, probably not the smartest safest thing but they would sit on the front fender with my wife and their legs wrapped around the headlight while moseying through the snow at very very slow speeds… gotta have some fun…

 

[66fs]

Dot 5 and be done. Now is the time since you are starting fresh. Been running DOT 5 since the 70's.

 

[abodyjoe]

been running dor 5 for a decade +.

people claim that it doesn't absorb moisture so it kills calipers and wheel cyl. if you are that worried about it just bleed the brakes in the spring. dot 3 absorbs the moisture so now ya have it throughout the entire system. i originally went to dot 5 because it doesn't strip paint if ya get a leak.

 

[CFD244]

My thoughts only.......

Dot 3 absorbs moisture from the air. Checking the level introduces moisture to the fluid and it ends up in the system. The longer between fluid changes, the more potential moisture. Dot 5 does not absorb moisture. If there was none in the system to begin with, it shouldn't end up there.

 

[340six]

I would switch to Dot 5 in a heart beat but it is not super available at auto parts stores near me and I can't say i have seen name brand fluid.

Napa has it or should be able to get it for you