Correct Brake Fluid?

[OUTFXD]

I asked before and seem to remember dot 4 Being ok to use. 

 

When My breaks Where low I switched to Dot4.  In short order my Breaks Failed, I rebuilt the master cylinder with a NOS kit and filled it with the Remaining Dot4.  The breaks failed nearly immediately,  The Fluid in the master cylinder was a murky black.  I rebuild again with a "modern" rebuild kit.  Being out of fluid I bought some DoT3/  Breaks worked great,  But I had a slow leak somewhere.  fast forward till last week.  Breaks where again low,  I swung by a stab-n-shop.  All they had was Dot3/4m0.  Potato Tomato. I topped up with dot3/4 and my breaks again failed nearly immediately leaving the fluid in the master cylinder murky black.   

 

This time I ordered a NOS master Cylinder.  While I am waiting on it to arrive I decided to check the sight.  I see references to Dot3 and Dot5,  but nothing on Dot4.   Should I be avoiding Dot4?  What is the Proper Fluid for our cars?  (Driving a 1946 Plymouth P-15 with manual breaks)

 

Thanks in advance!

[Sniper]

I would not trust NOS rubber parts for anything much less my brakes.  Dot 4 should not be a problem

[Митя]

I use Dot 4 in all my cars
I always put on new cuffs. all machines are working.
The only car I specifically bought brake fluid for was a Rolls Royce.

[BobDeSoto]

I've always used Dot 3.

You can use Dot 4.

You can mix Dot 3 and Dot 4.

Don't use or mix Dot 5.

[DonaldSmith]

The Previous Owner put in DOT 5 when he redid the brakes, many yeers ago.  I figure I'll keep wtih it unless and until the brakes get ccmpletely redone.  

 

A few years ago. our 2008 Ford was recalled because there was reason to believe that the the DOT 3 had allowed some sensor to corrode.  The dealer checked the sensor, replaced it if necessary, flushed the system, and put in DOT 4.  Like the man said, DOT 3 and DOT 4 are compatible.  But DOT 4 must be better for some reason. 

[FarmerJon]

15 hours ago, BobDeSoto said:

I've always used Dot 3.

You can use Dot 4.

You can mix Dot 3 and Dot 4.

Don't use or mix Dot 5.

All that, but also

 

*you can mix and use DOT 5.1 woth DOT 3 &4

But dont mix Dot 5 with Dot 5.1

 

Who made this system !?

[Sniper]

1 hour ago, DonaldSmith said:

The Previous Owner put in DOT 5 when he redid the brakes, many yeers ago.  I figure I'll keep wtih it unless and until the brakes get ccmpletely redone.  

 

A few years ago. our 2008 Ford was recalled because there was reason to believe that the the DOT 3 had allowed some sensor to corrode.  The dealer checked the sensor, replaced it if necessary, flushed the system, and put in DOT 4.  Like the man said, DOT 3 and DOT 4 are compatible.  But DOT 4 must be better for some reason. 

 DOT 4 has a higher dry and wet boiling point.  Important on more modern brakes that are undersized, from a thermal mass perspective, compared to older brakes.  The BMW I have requires DOT 4 and a flush every two years.  Time to do that, so to keep is semi related to the forum, I will be using the same Motive Power Bleeder I used on the Cambridge, just gotta get the right adapter.

 

Eerily enough, I was just talking about this very thing with my son just before Christmas.  We were at the parts store looking over brake fluid in prep for the work on the BMW.  That devolved into the various fluids in general and we were squatting down looking at power steering fluid.  When I tried to stand up my right knee gave me the finger and I had to use my son as a crutch to get to my feet.  He asked me if I wanted to sit down till my knee got better and I told him I'd walk it off.  He responded "It's your knee, how's that going to help?" to which I told him it wasn't going to get better sitting around and I didn't have any dirt to rub on it.  He got the GenX reply, lol.  Anyway, I survived.

[Dan Hiebert]

I don't recall off hand what the designation for what is currently DOT3 brake fluid was when these cars were new.  But the brakes in these cars are/were engineered to use what is now designated DOT3 brake fluid, so the "proper" brake fluid to use would be DOT3.  There is no added performance benefit for these cars to use anything but DOT3.

 

As an aside, I put DOT5 in our D24 when I rebuilt the brakes about 20 years ago because it does not draw in moisture like DOT3 does and we were not driving the car much in a humid climate, and it does not damage paint.  I check the brakes at least annually, the internal components are still pristine as of last spring, and I have had no leaks at all.   That said, I would now only recommend using DOT5 in these cars if it is a show car and not driven regularly.  I would best describe braking performance with DOT5 as mushy.   

[Sniper]

34 minutes ago, Dan Hiebert said:

There is no added performance benefit for these cars to use anything but DOT3.

 

I would generally agree with this statement, but add that DOT4 and DOT 5.1 have improved wet and dry boiling points, lessening the likelihood of brake fade in hard use.  But as Dan said, for our cars that's not really ever going to come into play, is it?  Now if someone out there wants to play Mario Kart with their car, well maybe then it'll matter, lol.

[Veemoney]

Another aspect of these brake fluids is water absorption rates.

 

To achieve the higher boiling points the percentage of Borate Ester in the base Glycol Ether DOT3 fluid is increased in DOT4 and DOT5.1 Glycol brake fluid. The higher the DOT rating the higher the water absorption rate and the increased fluid maintenance. Dot 5 is not a Glycol based fluid so water absorption is not a trait of DOT5. The link provided details of % and boiling points if interested.

 

DOT 3 vs. DOT 4 Brake Fluid: What's the Difference? - AutoZone