I give up with brake bleeding

[Hydratech®]

"It's only about a 1 inch difference and the angle of the pushrod is hardly an issue."

The 1st gen F car factory vacuum booster is angled upward at whopping 17 degrees. Go crawl under the dash of a 1st gen F body and try to force the manual brake rod into the lower power brake pedal hole and see how that goes for you - it flat out isn't going to happen. If you somehow do actually manage to force it to happen, you are definitely going to get into linkage bind and extreme MC piston side loading leading to direct failure. Sooooo..... unless you angle your manual brake MC upwards by whatever means imaginable (to accommodate a 17 degree angle as bolted to the firewall), you are causing trouble talking about moving the brake pedal rod connection point from the upper manual brake pedal point to the lower power brake point in a manual brake equipped 1st gen F car.

[vstol]

Originally Posted by Hydratech

Note that the brake pedal rod MUST enter the master cylinder dead on straight in a manual brake scenario. Discussions of drilling different holes in the brake pedal in efforts to alter brake pedal ratios are not valid because the brake pedal rod will then enter the backside of the MC at an inappropriate angle causing linkage bind, MC failure from extreme side loading of the pistons, and even possible complete failure of the brake pedal rod linkage entirely.

Summary? You MUST keep your brake rod connection in the factory manual brake top hole - no if's, and's, or but's about it.

Thanks it is in the manual position now but switching to power and like Greg said the power location is about an inch lower. Thanks for the comments to both of you.

[GregWeld]

Originally Posted by Hydratech

Note that the brake pedal rod MUST enter the master cylinder dead on straight in a manual brake scenario. Discussions of drilling different holes in the brake pedal in efforts to alter brake pedal ratios are not valid because the brake pedal rod will then enter the backside of the MC at an inappropriate angle causing linkage bind, MC failure from extreme side loading of the pistons, and even possible complete failure of the brake pedal rod linkage entirely.

Summary? You MUST keep your brake rod connection in the factory manual brake top hole - no if's, and's, or but's about it.

I'm not sure you're tracking here. There are two holes in the pedal -- changing ratio - depending on if you have power or manual....

If the cars pedal only has the power brake hole -- but is being used as a manual car... then of course the ratio is messed up (4:1 vs 6:1) and the pushrod position and angle would be in the wrong location.

What I stated is that the MANUAL hole - if missing - needs to be added to the pedal to correct the ratio. When corrected - the pushrod would then be in the proper position for the manual master cylinder - and the ratio would also be corrected.

You're trying to inject a different issue -- which is to try to use the wrong position. The lower hole (closer to the floor) is there for POWER brakes - and the booster is at an angle so the rod and arc etc work correctly. The Manual brake position is about 1 inch higher -- making it a straighter "angle" -- and the factory manual master is mounted as such -- flat to the firewall.

[vstol]

I will use the lower hole in the 71 corvette pedal for the power brake setup thanks

[Hydratech®]

You're trying to inject a different issue -- which is to try to use the wrong position. The lower hole (closer to the floor) is there for POWER brakes - and the booster is at an angle so the rod and arc etc work correctly. The Manual brake position is about 1 inch higher -- making it a straighter "angle" -- and the factory manual master is mounted as such -- flat to the firewall.

Rest assured that I am certainly not trying to cause any trouble. In fact, I'm only making it certain that "under discussed" issues are crystal clear for some of our members / readers.

[vstol]

No issues here thanks for all your help guys. Once it is set up I will get back and close this out.

[dontlifttoshift]

So you are going to power brakes?

[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).