I am rebuilding my entire brake system on my 74 and wanted to know if I should go with silicone brake fluid? I've read many things about it, but am not sure if it's the best way to go. Should I use Silicone brake fluid or DOT4?

 

Dot4

 

On a complete rebuild I'd definitely go silicone. I've had the silicone in mine for 15 years without a bit o' trouble. You can't mix the silicone with any old glycol based fluid. The proportioning valve and any other areas that could trap the old fluid should be flushed/cleaned to avoid contamination of the silicone fluid. The silicone is not hygroscopic and will not absorb water like the glycol based fluids do. Another nice feature is the silicone won't damage the paint should there be a spill.....

 

You will find this is the source of much debate. Obviously you don't have ABS in a C3, so silicone is fine provided you thoroughly flush the old stuff. The primary difference between DOT5 and DOT3/4 is the latter is hygroscopic (absorbs water) and the prior is hydrophobic (doesn't). Now the knee jerk reaction from many is that silicone (DOT 5) is better because it doesn't absorb water, but is that really better? Because if the water doesn't go into solution with the fluid, then it's going to collect in spots and potentially form corrosion pockets. Whereas a glycol based fluid is going to spread the moisture throughout the system. Soooo ... decide for yourself which you think is better. And don't kid yourself. ALL brake systems take on water to some degree or another.

I think what's much more important than your choice of fluid is simply keeping the fluid clean and the entire brake system in good working order.

 

Correct, and while at it, blast carb cleaner through the metal lines, and replace every rubber hose without fail.....use the Oring kits from VBP and a new master cylinder....

not to use the springs behind caliper pistons...not needed with Oring pistons.....

check runout so as on the rear, engine running on stands under the T-arms...you can feel the pads against the rotors.....and see how much if any lateral runout you have, it has to be nearly zero....1/32 at most....but with Orings, that's fine....

AFTER that, you know the brake hydraulics are fine....and IF you not happy with the 'feel' of the pedal.....

we get into more modifications.....

another thread....

 

Another vote for silicone here. I've been running silicone for almost 30 years without any problems. For the street it's great, track time you might want to go with glycol.

 

Or... go with a standard DOT 4 performance fluid like the:

ATE Super Blue Racing Brake Fluid


BTW... How many quarts does a C3 need for a complete fluid change? Anyone?

 

Do you guys think I should buy new proportioning valve and new rear blocks, or can I just clean them up real good? What's the best way to clean them out, if so?

 

Silicon fluid is expensive compared to Dot 4 and IMHO not worth the cost. I have tried it and found the break pedal feels softer then using Dot 4.

 

You can flush them out with alcohol then blow dry. I'd go with Silicone since it won't take paint off and won't absorb water. I've used it for 20 years with no problems.

Gary

 

same here, alcohol flush and blow dry. Let the silicone sit on the shelf for several days in the warm garage or in the sun, that will get rid of the bubbles in the jug. Don't chake it like a can of tomato juice. 1 quart will be plenty, but get 2. Sometimes its hard to get all the air out of the system. Push the pistons all the way in the calipers and gravity bleed the system+

 

I went with silicone.

 

OK, I'm gonna make sure I clean the blocks up real good and get the silicone brake fluid, is there any particular brand you guys recommend? I was flipping through the pages on the Jegs catolog and saw the Wilwood Performance Brake Fluid, has anybody tried it?
http://www.jegs.com/p/Wilwood/Wilwoo...53141/10002/-1

 

Other than the fact that it is not a Silicone product, it appears to be a high quality performance brake fluid designed for racing applications where the fluid sees extreme temperatures. If you are going for a high performance fluid, I would just use ATE Blue. It is an excellent performance brake fluid I have used with great results. For a street car that sees limited performance use, there is really no advantage over a good quality DOT 3 or 4 fluid. If you will be doing HPDE's or road racing, by all means use a good high temp performance brake fluid.

On my street cars without ABS, I do use Silicone and have for many years without any problems. I even used it on my '73 that I autocrossed for a number of years with no problems. VB&P sells an excellent Silicone brake fluid at a very competitive price. One quart should be all you need.

Good luck with your decision... GUSTO

 

The biggest issue I have with glycol is the hygroscopic properties.... the trapped moisture collects behind the pistons against the cast iron caliper despite having stainless steel sleeves.

The silicone has a higher boiling point than DOT 3 & 4 and should be suitable even in racing applications. Don't confuse silicone DOT 5 with DOT 5.1 which is glycol based. Also, good point made about ABS and silicone incompatibility.

"Minimal boiling points for these specifications are as follows (wet boiling point defined as 3.7% water by volume):
Boiling point ranges
Dry boiling point Wet boiling point
DOT 3 205°C (401°F) 140°C (284°F) GLYCOL
DOT 4 230°C (446°F) 155°C (311°F) GLYCOL
DOT 5 260°C (500°F) 180°C (356°F) SILICONE
DOT 5.1 270°C (518°F) 191°C ( 376°F) GLYCOL

DOT 4, like DOT 3 and DOT 5.1, is a polyethylene glycol-based fluid (contrasted with DOT 5 which is silicone-based). Fluids such as DOT 4 are hygroscopic and will absorb water from the atmosphere. This degrades the fluid's performance, and if allowed to accumulate over a period of time, can drastically reduce its boiling point. In a passenger car this is not much of an issue, but can be of serious concerns in race cars or motorcycles.

As of 2006[update], most cars produced in the U.S. use DOT 3 brake fluid." <<< because of ABS and expense I presume.

I good pressure bleeder is very useful in accomplishing a good brake bleed....http://www.automedia.com/Power-Bleed...cr20050501pb/1 Summit sells them. As far as silicone fluid... I find it easy to acquire at the local auto parts store such as Advance Auto Parts

Here's a link to a post about bleeding sequence FWIW
http://forums.corvetteforum.com/c3-t...ing-order.html

 

My only cautionary comments on the use of Silicone fluids would be:

1. Silicone is compressible; meaning pedal feel will be effected in what some consider a bad way. Certainly not what the enthusiast track user would consider ideal.
2. Silicone may be harder to source should you find yourself in need of some at an odd location and time.
3. Once in the system it will be very difficult to purge it from the system fully and replace with conventional fluid. Even small amounts of it can become compressed and will act as bubbles in the regular fluid.

Ideal for show cars where potential paint damage and a long life with little or no attention is the goal...but for most street applications I'd probably not go this way.

 

100% OTM

 

That's a lot of great information, and great links. Thank you guys for all of your help. I am going to think it over very hard.

 

I have used silicone in mine since 1982. No problems, and have only had to rebuild two of the calipers in all that time, and replaced the rubber lines only once. When I did I went with DOT Goodridge braided SS lines.

 

I don't think it's worth the cost or the trouble on a street-use car. If you raced it, maybe....