dot 3,4 or 5 for brakes?

ok guys im plumbing in new brake system for the the shoebox. question is should i use dot 3 or 5? all new steel lines, braided front and over the rear. new disc in the front, proportioning valve for the rear, residual valves for the master in mounted on the frame. so what fluid should i run???
ive been told so many different things i might just stick to 3? thanks in advance!

 

If I were you, living where you live, I would use DOT 3 or 4.

 

DOT 5 silicone should only ever be used with synthetic seals that are compatible with it. It is primarily a racing fluid and using it on street cars is pure BS IMO. Usually by people who hang on to a catch phrase or a marketing gimmick. When they first started using it in the 1980s after multiple brake failures because it is incompatible with rubber seals and can lead to instant total brake failure, without warning, major car manufacturers started putting out warnings about not using it. If you find a can, check out the warning label. There are really good high temp non silicone brake fluids out there Motul and Wilwood 570 spring to mind - if you feel your ride will be subject to severe and extraordinary braking extremes. Otherwise DOT 3 or DOT 4 should be fine.

I do however await the 'I used it for years and never had a problem' brigade to chime in....

 

What weasel says 2x.

 

thanks guys! i had a funny feeling about dot 5! just wanted to run here on the board and get a second opinion.

 

Let me add to Weasel's EXCELLENT response. You also have the option of DOT 5.1. This fluid is NOT silicone based, nor does it have anything to do with DOT 5. It has a higher boiling point than both DOT 3 and DOT 4, in simple terms a racing type fluid- BACKWARDS compatable with DOT 3 or DOT 4. A good application would be in a very heavy hot rod that will be driven very aggresively. BDM.

 

DON'T DON'T DON'T DON'T USE DOT 5. I did and regret it to this day. Can never get all the air out and once you use Dot 5 you can never change to 3 or 4 without changing the entire brake system

 

Two issues that have kept Dot 5 (silicon) brake fluid out of the assembly plant: 1) while it does not absorb water - a good thing - it does entrap air, making it VERY difficult to bleed. 2) silicon is murder to paint and paint systems - even the vapor can contaminate paint. Same goes for a finished car - any spillage can give you headaches. There are other more minor issues, such as decreased lubricity, etc.

I agree with the above posts - don't use DOT 5 !! I usually use 4, since you get higher boiling point with not a lot of cost. I don't think a properly set up road car will ever need the expensive, higher boiling point racing fluids - although I do use in road race cars.

 

Frankly, for the average vehicle 3 is fine; if you plan to drive it hard, you might step up to the 4 or 5.1. I mean, I've run 3 in all my vehicles and my one Suburban I used to tow lots of other vehicles, sometimes way beyond the rated stopping ability of the brakes on it, and I never had any issues there.

 

That's good to know. Thanks.

 

yea i think 5.1 in my work truck, but i think 4 in my shoebox.

 

good info--a friend of mine put dot 5 in his car--brakes seem to work fine but after reading this, it sounds like a mistake--can it be flushed, I know it can't be mixed--it is in a 40 with drum rear and disc front and an underfloor MC
THX

 

The one thing I can think to add to this that doesn't necessarily include your situation is this - some rubber products are not compatible with D.O.T. 3. The best example I can think of off the top of my head is English rubber products. Back when I was peddling Brit parts years ago, I personally screwed up and dumped 3 into a Girling system, and within days, everything rubber turned to jello... Don't know if that has changed over the years, but if you buy a part that says "D.O.t. 4 only" heed it well. For that reason to this day I still pop an extra buck or so for Casterol D.O.T.4 in all of my stuff.

 

my buddy got a rolls royce from his father in law, the brake system on that thing was over kill stupid!!!!!!!!! and only one kind of fluid can be in it! MINERAL OIL CASTROL! thats shit is expensive!!!!!

 

For those British cars, the problem is the rubber used and DOT 3 eats it. The best fluid for those is Castrol GT-LMA