I give up with brake bleeding

[vstol]

YES, booster came today

[Hydratech®]

Have you attempted to install your vacuum booster yet? If not, be warned that the C3 Vette steering column support bracket is different than the power brake support. I have no earthly idea why Chevrolet did that. Besides having to cut a different hole lower down in the fiberglass firewall for the vacuum brake booster location, you will also find that the bolt pattern isn't anywhere near what you need for the bottom two mounting points. The top two MC mounting studs can be extracted, which then at least places the top two vacuum booster mounting points in the correct location, but then you find that the lower two mounting points will not correlate properly with the manual brake spec steering column support structure (which is what the C3 Vette vacuum boosters essentially bolt to) (besides the fiberglass). I checked out a bit of your build thread and see that you are a competent fabricator. I recommend you pull the manual brake steering support structure out and weld in some further material at the bottom of the bolt pattern to properly support the bottom two fastener points of your vacuum booster, OR swap in a factory C3 power brake spec steering column support bracket.

This why we developed a special direct bolt in C3 manual brake spec conversion system that accommodates the different manual brake firewall and the different manual brake spec steering column support bracket:

http://www.hydratechbraking.com/C3Co...920161312A1BD0

Rest assured that I am not sales pitching you on a hydraulic brake assist system, just covering the bases on converting a factory manual brake C3 Vette to a power brake (bizarre why Chevrolet did that)...

[Hydratech®]

As another interesting and pertinent side note, (that some do not know or consider in their builds), be aware that the Wilwood MC's are specifically designed to provide a 75/25 output (75% to the front, but only 25% to the rear). By direct comparison, the factory C3 MC's are designed to provide approximately a 65/35 (65% to the front and a larger output of 35%+ to the rear). You have been mentioning that your front brakes are behaving, but can't quite get your rear brakes to bite down properly. Soooo.... The output difference between the Wilwood MC and the C3 Vette MC's are indeed different - the C3 MC's put out more volume to the rear brakes by design (it's the location of the comp ports inside the fluid wells of the MC fluid bowls that makes the difference).

[vstol]

Thanks for the info. Wilwood told me their manual setup put equal pressure front and back. Anyhow I am going to put the booster in today, I hope then mock up the MC so I can see how to a new fuel line into the rails and hopefully not have to move the clutch reservoir as well.

[Hydratech®]

Here it is in Wilwood spec sheet in the link below:

"The stroke is set at 1.10” with a volume ratio of 2:1 between the primary and secondary chambers"

http://www.wilwood.com/mastercylinde...temno=260-9439

Semper Fi !

[Hydratech®]

If you still can't find your happiness after this next wave of mods, give us a call as we can make that bad boy stop like a fighter jet being snatched up by a tail hook coming in for a landing on an aircraft carrier. (Interestingly mentioned to us by a few actual fighter pilot customers running our systems in their muscle cars over the years).

Study all of the firewall and steering column support structure mods, and also your clutch MC positioning. If it's going to be the surgery I believe it will be to install the vacuum booster, you may as well strongly consider our bolt in special manual to power brake conversion package to save you all of the hassle. It is as slender as the master cylinder is on the engine side, clears all known clutch combinations, and in your application would bolt down from the engine side of the firewall as a true plug n play without any mods at all what so ever.

As a general rule, manual brakes will typically provide 700-1000 PSI of line pressure. A factory C3 vacuum booster will typically add a couple / three hundred PSI to that (given high levels of engine vacuum feeding it). If you have chosen to obtain and install a "mini booster" you will find exactly that: "mini boost" output. By comparison, our hydraulic assist system will *****cat around at normal stock type levels during regular driving maneuvers, but is capable of easily punching out 1600 - 1800 PSI on demand when called upon, "stopping you on a dime and giving you two nickels change"!

[vstol]

Originally Posted by Hydratech

If you still can't find your happiness after this next wave of mods, give us a call as we can make that bad boy stop like a fighter jet being snatched up by a tail hook coming in for a landing on an aircraft carrier. (Interestingly mentioned to us by a few actual fighter pilot customers running our systems in their muscle cars over the years).

Study all of the firewall and steering column support structure mods, and also your clutch MC positioning. If it's going to be the surgery I believe it will be to install the vacuum booster, you may as well strongly consider our bolt in special manual to power brake conversion package to save you all of the hassle. It is as slender as the master cylinder is on the engine side, clears all known clutch combinations, and in your application would bolt down from the engine side of the firewall as a true plug n play without any mods at all what so ever.

As a general rule, manual brakes will typically provide 700-1000 PSI of line pressure. A factory C3 vacuum booster will typically add a couple / three hundred PSI to that (given high levels of engine vacuum feeding it). If you have chosen to obtain and install a "mini booster" you will find exactly that: "mini boost" output. By comparison, our hydraulic assist system will *****cat around at normal stock type levels during regular driving maneuvers, but is capable of easily punching out 1600 - 1800 PSI on demand when called upon, "stopping you on a dime and giving you two nickels change"!

As a tail hooker myself I understand the I hope I locked my harness before the cable stops me on the carrier. Thankfully flying harriers on the ship it was better to stop and land. I might give you a tomorrow as the booster is not going to fit as nicely as I thought it might. I am running the LS3 with the C4 rack and pinion.

[carbuff]

Wouldn't a 2:1 ratio be 66.6% / 33.3% instead of 72/25? Thus closer to the original ratio you quoted?

Regardless, that is interesting information. Do you know if other aftermarket MC's are also built this way? I use a GM unit, but it's good knowledge to have for the future...

Thanx!

[Hydratech®]

I have found that most all aftermarket MC's are typically C3 Vette MC's in disguise (once torn down and carefully scrutinized). My math? Ok, it is my kryptonite, and good lord it looks like I'm wrong. Many many years ago (about twenty or so), I burette tested the CC outputs of various MC's x 1" of exact input stroke and got into all kinds of math... Over the next further years I actually didn't particularly chuck the math, but instead went into real world testing (less some of the math) Tobin at Kore3 is my go to guy for math these days LOL (caliper piston sizes x MC bore size x mechanical pedal leverage) The variable output of the hydroboost unit's can't seem to be exactly calculated though due to other variables such as PS pump max relief pressures and such. I have found that an installation with a Wilwood MC of exact same bore size (Wil-260-8856 with 1.125" bore) versus a C3 Vette MC (with the same 1.125" bore size)(as a back to back swap out) required considerably different inline adjustable proportioning valve settings. With the Wilwood in place, we could run the adjustable prop valve just about wide open (knob screwed all the way in), while swapping in the C3 Vette MC required considerable pressure reduction adjustments to the rear brakes = my type of real world "math" indicating a higher rear port / rear brake output with the C3 Vette MC as compared to the Wilwood. Hmmm...