Synthetic Brake Fluid

As long as it is a liquid, it is considered incompressible. It may have components that will vaporize at lower temperatures, but without knowing anything about it, it's impossible to say.

No, I can't imagine a difference, but why are you bothering to replace brake fluid in your truck with something designed for high performance sports cars?

The last brake system in the truck lasted 61 years before you had to replace the hydraulics, just how long do you plan to keep it - another 70 years?

that old truck DID NOT have the original brake fluid in it!!!!

no I doubt that but the master cylinder is original.

not to worry, I am in the process of ordering everything to completely replace all equipment the comes in contact with brake fluid.

If the replacements are rebuilds and the seals are to the 48 model spec they may not be compatible with the newer fluids. I would check that first before use of the newer fluids.

If it isn't compressible then it would give you a hard petal.

I agree with the other guys, just use the regular stuff that they'd use in the local brake garage/shop. That way you won't have any weird compatibility issues later on.
If you really want to pay extra for a fancy name I can sell you some synthetic virtual extra high gullability KrisDel^TM specially blended cat and squirrel piss hydaulic fluid.
Del
_{(No offense intended, the KrisDel thing is a running joke in these parts)}

Are you asking about 'synthetic DOT4? or silicone DOT5?

All DOT4 brake fluids are cross compatible. 'Synthetic' in this case (DOT4)means the raw ingredients used to make the glycol-ether are 'synthesized' from natural gas or other simple hydrocarbons. It is a meaningless marketing term in my opinion.

DOT5 is a totally different brake fluid and NOT compatible with other classes (Dot 2,3,4) DOT5 is a poly-silicone based material used for static displays and very high performance braking systems such as racing cars--in which service it is replaced after EVERY race. It does not absorb moisture and then decompose into sludge and corrosive acids like the glycol stuff, and has very high boiling point, giving it much higher temperature limits in service.

IF you are going to have the vehicle sitting in an air conditioned display, DOT 5 will last forever and will not cause corrosion and never need replacing.

If you are driving it daily, I recommend using a premium quality DOT3 or DOT 4 fluid with changes every other year--and you will never have any corrosion or sludge deposits. (DOT 3 vs DOT 4 is a boiling point difference) In daily driving service, silicone brake fluid should be flushed and changed at least every other year to remove any moisture ingress and thermal decomposition products. Moisture in silicone fluid DRASTICALLY lowers the boiling point of the system at the point where the water droplet is. While glycol will dissolve water, silicone fluid will not--and that drop of water WILL BOIL at the boiling point of water, while the 'wet glycol' will have a much higher boiling point than 'wet' silicone fluid (though lower than dry glycol.)

Note that many people say you never have to change silicone brake fluid in daily driver service. It is much better practice to flush out the fluid that has been subjected to high heat because some of the silicone does decay into low boiling components.

What they said!

As ozzb indicated, NOT being compressible is desirable; the less compressible the fluid, the harder the pedal will be (all other factors being constant).

Being a member of a large antique car club, some of our members have converted to DOT 5 silicone fluid. The DOT 3, DOT 4 fluids do absorb moisture which has a tendancy to settle at the lower points. Wheel cylinders lower halve, master cylinder again bottom halve. The Silicone fluid appears to not absorb water as readily so there is less problems with corrosion. These cars generally are not driven too much 500-2000 miles/year in better weather conditions.

The only problems have been the DOT 5 leaks easier than the others. Tight fittings and connections are needed. Note the extra "spring back" of stainless steel brake lines makes this even harder but not impossible.

All fluids degrade over time, temperature, contamination etc. so change outs are still recommended but the corrosion problem appears to be eliminated.

No compatibility problems with seals have been reported. A complete flush of other fluid is needed.