Dot3 or Dot4

[yody]

I have a 100% brand new braking system, everything is new, should i fill it up with dot3 or dot4? what are the pros and cons?

[Travis B]

we use all DOT5 because if you spill it won't eat paint.....
Just an idea for you!

[MuscleRodz]

I know DOT 3 makes a dandy paint stripper. I would use a silicon brake fluid. Won't eat paint.

Mike

[deadcarny]

hmmmm... where do you get the 5?

[Travis B]

hmmmm... where do you get the 5?

Now you have me wondering

I am pretty sure it is 5 I will check tonight!

[CarlC]

If you plan on using the car for track days you may want to re-think using the silicone fluids. Check the archives, there's some not-to-good stories.

The NAPA fluid is great. It used to be sold under the Heavy Duty label and may still be found, but the newer version is their Premium brand, DOT 4, both with a wet boiling point of 311*F. This is the same fluid as the HD Ford type.

[rockdogz]

I am by no means an expert on this, but the research I did said to use synthetic fluid but not silicone fluid. I'm pretty sure DOT 5 is all silicone, so I went with DOT4 synthetic...

[deadcarny]

oh, NM then about the 5...

[wick]

Have any of you heard of Motul? They make alot of products for bikes and they are very good. I raced motorcycles off road for many years and would boil the fluid in the rear especially in long two hour muddy race. Once I switched to Motul I it only boiled once.

[MuscleRodz]

I am by no means an expert on this, but the research I did said to use synthetic fluid but not silicone fluid. I'm pretty sure DOT 5 is all silicone, so I went with DOT4 synthetic...
Synthetic is what I meant, not sillycone! :slap:

Mike

[rockdogz]

Mike,
I think you were right the first time though - silicone won't damage paint, but I believe synthetic still will. Silicone (DOT 5) however will give you a mushier pedal though. (is that a word?)

[yody]

So carl, do i want the new premium version, or the old version?

[68BNUT]

Whats the heat rating on that DOT 5 fluid??

[rockdogz]

500 degrees F

[CarlC]

So carl, do i want the new premium version, or the old version?

I believe they are the same fluid.

NAPA has a so-called "new" DOT 3 Heavy Duty fluid that has a 284* wet boiling point fluid. This is the less expensive fluid that has in big red letter "450 boiling point" on the front of the label. It also says "Heavy Duty". But it is not the better DOT 4 fluid.

The older labeled DOT 4 Heavy Duty fluid and the new labled DOT 4 Premium fluid, I believe, are the same. Check the label, they will both have a 311*F wet boiling point. I just went through all of this on Saturday while buying fluid to flush out the "old" DOT 4 Heavy Duty fluid.

The main reason that I like the NAPA fluid is that it is inexpensive, it works very well, and can be purchased in every small town in North America. I had to replace the caliper dust boots on the PBR calipers because they melted, but the fluid did not boil.

[yody]

okay, hopefully the brakes will bleed with no probs tomorrow. So close to driving it!! out of curiousity, why does the not so good stuff does it say in big red letters; 450 boiling point if it is only 284?

[CarlC]

Dry vs. wet boiling points.

[yody]

is all dot4 synthetic?

[MarkM66]

I've seen even the el cheapo DOT 3 says synthetic on it now. I think all brake fluid can technically be called synthetic.

[jy211]

we use all DOT5 because if you spill it won't eat paint.....
Just an idea for you!

I use DOT 5 in my chopper....I'd go with that!

[Joe_Rocket]

I painted everything in my engine compartment the same blue as the rest of the car. The frame, the block, the booster, the master, the ps pump and steering gearbox, etc. Everything that wasn't blue, was chrome. It looked real sweet.

The first time I drove it, I discovered the nice new chrome lid and hold down bracket on the master wasn't tight enough to really seal. The fluid splashed over the back top edge on acceleration and got on most everything that side of the engine eating the paint off. It even dripped down the length of the front subframe on that side. What a pain to redo that!

When I repainted, I got new stainless lines, flushed my calipers and have been running DOT 5 for a few years now. I haven't noticed anything odd.

I heard horrors of sludge like build up due to moisture, but don't know if I believe that. So, I search around and found the following info on another site which I summed up below.

1) DOT 5 is silicone-based brake fluid with a wet boiling point of more than 500° F.

2) DOT 5 does NOT absorb any moisture, so any mositure in the system could come in contact with any exposed metal and cause rust.

3) DOT 5 silicone fluid contains more absorbed air than DOT 3 or DOT 4 glycol, and it will aerate much more easily which is why most manufacturers DON"T recommend it for ABS. THough, I have heard of people using it anyways without problems.

4) DOT 5 is recommended for vehicles that sit for long periods such as antiques and classics that are stored all winter, and, of course, for racing due to its high heat tolerance. But conditions within the hydraulic system MUST be monitored.


I still haven't completed my C5/LS1 swap because of lack of time, but I will find out pretty soon if any moisture got in and did anything funky.

Oh, yeah, one more thing, is I had a hell of a time bleeding the system when I made the swtich. Not sure why, and I'm not all that experienced, but I grabbed a piece of steel stock I had lying around, drilled a hole in the center, and welded an air fitting on it. I clamped that down with a quick hand cut rubber seal and put a little pressure to it. That did the trick for me. I thought what a cool little product if I wanted to market something. A few months later, I saw that very device listed under new products in a car magazine. Oh well, you snooze, you lose.

[sinned]

You had a hard time bleeding because DOT 5 is very difficult to bleed.



Believe the hype, DOT WILL cause system rust if not flushed regularly.



DOT 5 does contain more absorbed air so consequently it is more susceptible to aeration when the fluid reaches boiling point. Track cars DO NOT run DOT 5 for this reason. If you intend to run a track...even once, I would suggest not running it. A little streaked paint on a sub frame is far better than hitting a tire wall because you lost the brakes.

[Joe_Rocket]

Sounds like good advice, Dennis. I'll keep that in mind.


Anyone interested in the full article on Brake Fluids can see here:

http://www.roddingroundtable.com/tech/articles/brakefluid.html


Also, below all the product info on this page has some info on brake fluids:

http://www.raceshopper.com/brake_fluid.shtml

[inSANe DIEGO]

I plan on running Performance Friction's "Z" rated fluid. Baer highly recommends it on their website and Grass Roots Motorsports Mag mentioned it in a brake article in last month's issue.

If anyone's heard anything bad about the stuff please correct me...

John