Dot 4?

[a-5 freak]

I went to autozone today and saw DOT 4 fluid/ Synthetic DOT 3 brake fluid. Can i run this in my 1991 ranger XLT? If so, what are the bennefits?

 

[fastpakr]

Dot 4 is interchangeable with Dot 3 fluid, no problem. Dot 5 is a whole different situation.

 

[ItsA5Spd]

what's DOT 5 used in?

 

[exbass94]

what's DOT 5 used in?

Mostly motorcycles.

 

[a-5 freak]

are there any advantages though for using DOT 4? and what is so different with DOT 5?

 

[Toms01PSD]

are there any advantages though for using DOT 4? and what is so different with DOT 5?

I'd have to look in my book, I don't remember exactly the difference but I BELIEVE DOT 5 is a silicone based fluid? Feel free to correct me, and the difference between DOT 3 and DOT 4 is boiling point...feel free to correct me again!

 

[AllanD]

Correct on all counts

I personally run Dot5 Silicone fluid, but getting the stuff to work right requires a completely different approach to bleeding.

Conventional brake fluid absorbs water from the air
It does so the salt absorbs air... this water reduces the boiling point.

What silicone fluid does is absorb AIR particularly if you bleed the
sytem incorrectly and when heated the air comes
out of suspension and produces nearly the same effect as boiling fluid
there are special bleeding proceedures that prevent this
including a slow "low fluid velocity" bleeding proceedure
followed by getting the brakes hot (I mean REALLY HOT)
then bleeding them before they can cool

It is a tedious proceedure, but if you are used to doing it
it is well worth the effort.

AD

 

[Toms01PSD]

Thank you Allan! I suppose I learned something

 

[JoshT]

IIRC one of the major differences in the fluids isn't how they act but how the react. A dot 5 brake system and a dot 3/4 brake system will operate exactly the same, but if you put one fluid in the other system you can run into problems with the seals, and lines in the system. Lets say dot 5 requires one type of seal where as do 3/4 requires a different. Not in a system designed for it the dot 5 will work fine and never have problems (only in a perfect world, right?). Put the dot 5 in the dot 4 system and it can, and most likely will, cause the seals in the system to prematurely wear out and fail, right when you need them most. Same goes for the dot 4 in a dot 5 system.

EDIT: Guess I must have been wrong about this. But I could have swore I read it in a reputable source, can remember what it was now though.

Did just find this though seems to be a pretty good read, Different types of brake fluid. Yeah I know it's a Chevy site, but hey it looks like a good read.

 

[AllanD]

The idea that dot 5 needs special seals is myth.

The only problem with Silicone is the special, for most people
"Royal Pain In The Ass", bleeding proceedure to get ALL the
air out without aerating the fluid and dissolving air in it.

Once that problem is dealt with Silicone filled systems rarely need
any kind of special attention, or for that matter any attention at all.

Some military vehicles and most Post Office vehicles run the stuff
because of it's non-hygroscopic nature.

You've gotta understand that normal brake fluid is chemically an alcohol
Like all ?-Glycol chemicals and all of them "LOVE" water, they soak it up
like a sponge and since many brake parts are made of iron that is a receipe
for internal corrosion.

I run silicone in my truck but I started off with a completely disassembled system
(including the master cylinder) and EVERYTHING was washed free of conventional
brake fluid with ethanol before reassembly and coated with silicone fluid as assembly "lube" while I put it back together.

I have all the air out of my system...


AD