What brake fluid to run

[03BlkZ]

I am restoring my 70 C10 and wanted to know what brake fluid I should run. I installed a new CPP disc brake setup up front and kept drum in the rear but installed new brake cylinders. Also have all new lines, master cylinder and booster. The entire system is new. So with that said what should I run?

[Grumpy old man]

I've got a total 100 % new system front to back and using dot 4 .

CPP booster / calipers/ disc -drum all new inline tube stainless lines .

Info from Duntov Corvette page - http://www.duntovmotors.com/tech-brake-fluid.php


Brake Fluid School

There is a lot of misinformation out there, so here is some information I have put together about brake fluid as it applies to your Corvette!

Brake Fluid Ratings, with BP (Boiling Point Standard) in degrees Fahrenheit:

DOT 2 - Forget about it, it is obsolete.
DOT 3 - Glycol based, Dry 401, Wet 284
DOT 4 - Glycol based, Dry 446, Wet 311
DOT 5 - Silicone Based, Dry 500, Wet 356

Dry refers to virgin fluid; wet to fluid that has been in use for a while.

For owners of 63-82 Corvettes, we can eliminate DOT 5 silicone fluid. First of all, it is non hydroscopic, meaning it doesn't mix with moisture. But in the course of normal driving, moisture is going to get into your brake system and cause havoc. By not mixing with the brake fluid, this trapped and highly compressible moisture becomes highly corrosive. Corrosion is one of the reasons every brake caliper on 65-82 Corvettes has either already been sleeved, or probably should be.

Unless you flush and bleed your fluid a couple of times a year, silicone fluid is not the answer. Even dry virgin silicone fluid is more compressible than glycol fluid, so it doesn't work for me, even right out of the box. You can't mix Dot 5 fluid with even a trace of glycol fluid, whereas you don't have to worry about compatibility when switching between glycol-based fluids.

So now we are down to deciding between DOT 3 and DOT 4 fluid. The key number is the wet boiling point, as that is where your car lives. Dry boiling point is only relevant for road racecars, as their fluid is normally changed before every event. The higher the wet boiling point, the longer the fluid will perform well in your car. DOT 3 fluid should be flushed and replaced every year. DOT 4 fluid might give you an extra year. Our Type 200 fluid has a wet boiling point of 396 degrees, the highest of any glycol-based fluid I considered. I concur with the manufacturer's recommendation of a three-year interval between changes.

One last consideration on brake fluid is packaging. The smaller the container the better, and a steel can is much better than a plastic bottle. Moisture penetrates plastic containers, so it is 'wet' by the time you open it.

[Bigdav160]

You forgot DOT 5.1

The glycol brake fluid with the performance of DOT 5

[Steeveedee]

If moisture penetrated plastic containers then brake fluid would leak out. Other than that, I generally agree with that guy's assessment. I used DoT 5 "fluid" many years ago in my '56 Chevy 210 wagon. The system got corroded. That was with all new parts. Just because it doesn't draw water like glycol brake fluid doesn't mean the system won't get moisture in it. Flushed, rebuilt and back to glycol it went. DoT 5 "fluid" is really made of teeny tiny spheres, so it's easy to get air in the system, and it's why it doesn't give the hard hydraulic feel like glycol gives- it's not an "incompressible" fluid.

[Accelo]

I am going to post another (manufactures) opinion below.
It isn't my opinion. Just theirs. I suggest you use which every fluid suits you best.
I for one am still looking for a long term study of the best fluid for old cars.
I do know Corvette owners do not like the Dot5 fluids as it will acquire air through the caliper seals if the rotor run-out is much less than perfect.
I did notice the caveat "which non-petroleum based fluid is specified"
For what it's worth;


DOT 5 silicone brake fluid
DOT 5 silicone brake fluid is a very high specification fluid based on polydimethylsiloxanes (silicones) and offers many advantages over conventional glycol based fluids. Silicone fluid does not absorb water from the surrounding atmosphere while in service and therefore offers greatly extended service life whilst improving corrosion resistance of the main components of the braking system.

Recommended for use in the hydraulic brake and clutch systems of all cars, commercial vehicles and motorcycles for which non-petroleum based fluid is specified. Particularly recommended for classic cars or vehicles that are garaged for much of their life but must be usable at short notice.

This fluid must only ever be mixed with DOT 5 fluid which has the same silicone base. Never mix DOT 5 with regular glycol based fluids.