I had a discussion with a guy about synethic brake fluid. I said I felt it didn't compress the same as reg. fluid,and I felt a small loss of pedal pressure! What do you guys think?

 

I think you are mistaken. It is a basic law of physics..... you cannot compress as liquid......

 

I'm not sure why but my GM Shop Manual is very specific about not using anything except DOT 3 fluid.

If you changed to synthetic fluid and felt a difference it's likely that the old fluid had some air or moisture.

 

Synthetic fluids will not compress any more than water will. Whether or not the use of synthetic brake fluid (DOT 5.1) is any better than a DOT 3 or DOT 4 fluid is up for lots of discussion.

Brake fluid is hydroscopic; it will absorb moisture out of the air which in turn causes rust and corrosion in the brake system and that moisture (water) will boil when the fluid gets hot resulting in reduced braking power even to the point where the pedal feels "mushy" or even a loss of braking.

The moisture effectively turns to steam with heavy braking and that creates pockets in the system and the pedal feels soft or could even go right to the floor

I use a DOT4 fluid in my 87. DOT 4 fluids typically have a higher wet boiling point and for extreme braking use like track days, you need a fluid that will resist boiling due to the heat generated by this type of braking. For steet use, a DOT3 fluid is fine.

DOT 5 fluid, which is a silicone base fluid is not recommended at all for ABS braking systems. Silicone fluid will cause cavitation in ABS systems from the rapid pulsating of the ABS pump and that can result in loss of braking power.

 

Wow; We just got a science lesson!....... Thanks for taKing the time to explain everything,......as I always tell my friends,"I don't know the answer,but I'll bet someone on the FORUM does"! Thanks again guys

 

i do know that the net recommended fluid is the ford type. it is (i think) the high grade castrol or something like it in a cheaper bottle since ford buys it in bulk.

 

I've been using Valvoline supersyn for about two nears. Great results and clear as water. Give it a try.

 

i use Castrol LMA for both brake and clutch fluid. zeros problemos.

 

The Ford Motorsports Heavy Duty fluid is rated as a DOT3 but is is a very good fluid for street use along with autocross and the occasional track day if you are not real hard on brakes.

The Castrol LMA is also a great fluid to use and that is available at most parts stores.

This list of fluids and their wet/dry boiling points was posted some time ago:

BRAND................... Wet Boiling Point.......Dry Boiling Point
Castrol SRF....................518.............. ..........590
MOTUL 600....................421.............. ..........585
AP-600.........................410......... ................572
ATE Super Blue...............392.................. ......536
ATE TYP 200..................392................ ........536
Valvoline........................333.... ....................513
Castrol LMA....................311.............. ..........446
Ford HD.........................290.......... ..............550
Wildwood 570.................284................. .......570
PFC Z-Rated...................284............. ...........550
AP-550..........................284........ ................550

DOT3 rated fluids are the Castrol LMA and below, above that is DOT4 fluids.

The wet boiling point is the value to be concerned with for choosing a fluid where you are concerned with the possibility of boiling the fluids on a track.

(The ATE Super Blue and the TYP 200 fluids are the same except for the color; the TYP200 is a gold color so if you flush fluids frequenty, you can simply change betweent he two and when the different color comes out, you have flushed all the old fluids)

 

I have had great success using Valvoline SYNPOWER in my 88 with a C5 brake upgrade

It doesn't turn black after a couple of days on the dragon

seeya

 

When you water is absorbed into the brake lines, not only do you get the boiling problems mentioned above but you get more pedal travel as water compresses easier than brake fluid.

Wet boiling point tends to be the most imporant number for most of us as we do not change fluid for every race. The wet BP is the temp the fluid will boil after it has absorbed water from the atmosphere.

Dry boiling point is the BP right out of the can. As you can see from the list above, high dry BP does not always mean high wet BP.

 

Where in the world did you hear that from?

 

Apparently I made it up...here's what I meant to say:

This leads one to contemplate the type of liquid that is used as brake fluid. In theory, even simple water would work – since, being a liquid, water cannot be compressed. However, it is important to remember that the fundamental function of the braking system is to convert kinetic energy into heat energy through friction. And the reality of this process is that certain parts of the braking system will be exposed to very high temperatures. In fact, it is not uncommon to see rotor temperatures during a race as high as 1200 degrees Fahrenheit – which can raise the temperature of the brake fluid to well over 300 degrees Fahrenheit. Since the boiling point of water is 212 degrees Fahrenheit, it is easy to see that water within the brake system could boil easily – and therefore release gases into the brake pipes – which would reduce the efficiency of the system. (Water would also present a big problem in cold weather if it froze to ice!)

 

You are right,and that goes for tranny fluid also,I was told Ford has better fluids,especially trans. I am going to change mine anyway,I still think the synthic is not as responsive as reg. fluid,will let you know when I do it! thanks

 

All liquids are compressible. It's called bulk modulus, read up on it.

 

The information in these posts are just great. This is the kind of information one might think about but here is it, so much info all together. Being an engineer I am appreciative of this kind of information although I am mainly electrical, my interests are broad when it comes to neet information like this. Here it is in the Forum, questions and answers all in one place, a wealth of information for a unit of time. Been involved with cars many many years but never knew this much about brake fluid.

It’s great to find posts like this from people who have done the research and have the knowledge. There are many areas to get smart about, this is just one. Thanks

 

This is excellent info. The only point of clarification I would add to this is that DOT5 silicone fluid is not hygroscopic -- a major advantage for non-ABS vehicles -- while DOT3 and DOT4 are hygroscopic.

Regular flushing of the (DOT3 or DOT4) brake system with fresh fluid from a freshly-opened container helps to keep the moisture gremlins at bay, minimizing the damage (corrosion) to hydraulic system components that this moisture can cause, and helping to maintain the high boiling point of the fluid. Don't neglect this routine maintenance procedure.

Be well,

SJW

 

Could it be that when your car was manufactured, DOT 3 was the very latest spec in brake fluid??

Larry
code5coupe

 

Oh come on already! I'll bet you lunch on it.

Water is more compressible than seawater, and less compressible than oil. If you want some killer brake fluid, use some quicksilver.

 

Okay, I looked up bulk modulus, and...
I owe CC lunch at Rubio's on a technicality.

Liquids are considered "relatively incompressible". At the pressures attainable in a car's braking system, we can, for all practical purposes, consider brake fluid, water, etc. incompressible, but..in reality...they will compress a certain amount.

I was wrong.

Larry
code5coupe