Technical brake fluid issue

i am plumbing my ch***is brake lines,on my 32 ply all new disc brakes all around.i have always used dot 5 on custom motorcycles,is dot 5 good to go on my hot rod. opinions?

 

You might get some pretty heated opinions on this. All I'll say is that I've used it in all my "speciality" vehicles (cars & bikes) for 30 odd years and never had an issue. Love that it's non hydroscopic and doesn't damage paint.

 

i appreiciate the input,i really prefer to use dot 5,the choppers i built got pretty heated brakes with no issues. thanks

 

I vote Yes on dot 5 brake fluid. I've used it in two hot rods and a front engine dragster without issue. To me it seems like a no-brainer if you're plumbing from scratch. You don't have to worry about contamination or mixing with other types of brake fluid.

Lynn

 

Just wait till you're done painting, before you put it in the car. It's a ***** to remove silicone, when prepping for paint!

 

I use DOT 3 in all my stuff other than the dailies; they are new and get whatever the factory says to use. I have a hydraulic clutch in the roadster, and you cannot use DOT-5 in that so why carry 2 different types of fluid and chance using the wrong fluid when topping off a M/C? I used DOT-3 in the pickup that I built from scratch as well. Of course, the muscle cars and the dune buggy get the same. I only need one bottle in the cupboard. Works for me.

And DOT-3 does not remove paint...If you build and flare your lines correctly.

We almost made it to the end of 2025 without asking this one. So close. Oh well, thems the "brakes"!

 

NAPA has a Dot 3-4 Synthetic that we started to put in the cars at the collection I work at.

 

I prefer dot 4, any moisture is absorbed by the fluid, dot 5 the moisture pools together and can create a rust area where it pools.

Dot 5 has more compression ability than dot 4. There's a reason dot 5 isn't used in new vehicles or motor cycles anymore or in hydraulic clutches.

Dot 4 is easy to find anywhere. Again as stated above don't have to carry 2 separate brake fluids if you run a hydraulic clutch.

Dot 4 is easily washed away with water should you get it on anything.

Dot 5 isn't as popular as it once was, and I see they have come out with 5.1 that isn't compatible with 5. But going back to dot 4 compatibility.

I expect 10 yrs from now dot 5 will be an orphan.

..

 

I've used Dot 5 for over 40 years in our fun cars and motorcycles without a problem. We live on the Pacific coast in a high humidity area and no problems with water buildup in the systems.

Use what you believe is best for your vehicle is my recommendation. There are pros and cons to both...

 

Dot 3 and 4 are virtually identical fluids , only real difference is boiling point ( just like “ super dot 4 “ higher boiling point . You can mix dot 3 and 4 fluids with no ill gains . ( “ The book “ states you can top up 3 with 4 but not 4 with 3 , simply due to boiling point being lower on 3 .

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I prefer dot 3 and 4 brake fluid , simply because it’s easy to find if you’re in a jam .

Dot 5 is great fluid , does not harm paint if you have a slow drip and don’t see it . Not a fan of dot 5 , seems to leak more on the stuff I service at work over dot 3 or 4 fluid .

the “ new “ super dot 5.1 glycol based fluid , seems cool . Can be mixed with dot 3,4 fluids not with dot 5 synthetic.

I like simple and what’s easy for me to get when on the road .


Also want to add dot 5 not being hydroscopitic is a bit of a misnomer .

regular dot3 and 4 fluid the water it absorbs is distributed evenly in the fluid , that’s why when the fluid is contaminated with water , the water can boil and introduce air bubbles in the fluid and cause issues .

dot 5 all the water will collect in the low points of the system, if you live someplace where it freezes you now have the possibility of ice forming in lines or other parts of the system creating a blockage , and also a big ol chunk of ice grating across seals and bores creating havoc .

 

DOT-5 is already an orphan. It started as a military only item and spread to the mainstream. Unfortunately, it is incompatible with anti-lock brake systems, so none of the current manufacturers use it. This means it will die out or become a very expensive specialty item. I had it in my '68 Corvette, and once I got it in and bled correctly, it was great. Bleeding that system was one of the most frustrating experiences I have ever had.

 

Put dot 5 and all new or rebuilt brake parts in 39 chev 36yrs ago, haven’t needed to add more yet. Followed directions from Russell Eng, bleeding can be a pain.

 

Dot5 (silicone) has 2 significant weaknesses

1) its compressible so can't be used in ABS systems. It can also lead to more brake pedal travel

2) water/frost. If moisture gets in, and it can it has nowhere to go. Its heavier than the brake fluid so s*** in the bottom if the cylinders and can't be removed through conventional bleeding. If it freezes in cold weather, no brakes. It can also corrode the cylinder and piston. I have seen this in Harley brake calipers.

These are the reasons its hardly ever used in OEM applications.

If you can live with these issues, its fine.

 

JFYI, DOT 3 and 4 brake fluids are all technically "synthetic". Adding synthetic wording is just marketing.

 

I'm using Dot 5 and agree that bleeding can be agonizing. I've constantly fought a leak at the regulator, still unable to pinpoint precisely where the leak is occurring. It's not much, just enough to taunt me every time I climb under the frame to search for the problem.

 

There will be lover & haters on this. I'm in the lovers camp as not a single issue with Dot 5 in over 40 years. I think the key is to have really well done flares, I bleed them as a one man job with a pressure pot bleeder.

 

I think (the) bigger issue than the moisture debate is whether or not the (type) of rubber in any given brake system will be compatible with certain brake fluids.
I'm not articulate enough to explain the pros/cons of it all so I'll let the real chemical experts put their stamp on it.

 

I put dot 5 in my 62 pickup in 1992, when I restored the brake system this year all I needed to do was run a light honing in the cylinders and replaced the seals. This truck sat for 28 years mostly out side.
I put dot 5 back in.
but
On all my other cars I’ve switched to dot5.1, which is compatible with 3&4 but not 5!

 

Given the comments about soft pedal and bleeding issues, just make certain you don't shake the can of fluid and pour it in very gently so you don't introduce bubbles. Micro bubbles can take a while to rise to the surface in dot 5 fluid.

Lynn

 

A bit of a myth. ALL DOT fluids are compatable with the rubber used in brake system components. The issue is swapping fluid. Rubber absorbs a tiny amount of fluid so changing to an alternate chemistry can lead to contamination issues. Flushing with isopropyl alcohol can help if you want to swap.

 

Any idea of exactly why it is incompatible with anti-lock brake systems?

 

You can't use DOT 5 brake fluid (silicone-based) with anti-lock brakes because it foams easily when agitated by the ABS pump, creating air bubbles that lead to a spongy pedal and drastically reduced stopping power

 

Interesting. Thanks for that info.