[STEELCITYFIREBIRD]

Brake pedal to the floor is not a low vacuum problem. You would have a hard pedal, high effort to stop with low vacuum. More likely is air in the hydraulic system,or high travel of the pads/shoes to the rotors/drums.

Good news but a different approach to the brake repair.

It will all come together, and I don't think it will be expensive.

[TedRamAirII]

For sure on a low pedal, check rear brake adjustment. Also check for any free play in the pedal. The pedal should only have minimal free play before in engages the Master Cylinder, but it HAS to have some. If you can pump,the pedal a few times and it slowly sinks down, you could have a MC problem. If you have low vacuum, usually a high hard pedal.

[STEELCITYFIREBIRD]

"I'm told that you turn the distributor to get the highest vacuum reading, then back it off 2 inches. Does that sound feasible??"

Try it and see what you timing is.

Probably best to get your brakes working well firstly, then move on.

[dmac]

I always start with adjusting the idle screws to achieve best vacuum.Then readjust rpm, check timing. And back and forth. Adjustment of any one parameter requires adjustment of the others, until all are optimized. And you need to check the mechanical advance. If the springs are too loose, you may have mechanical coming in at idle. That's easy to check with a 'normal' old fashioned timing light.

And since your set-up doesn't seem to have a ported vacuum source, perhaps the prior owner installed an adjustable vacuum can to stop all the vacuum advance from coming in at idle. I recall needing to do that on one motor. Maybe he wasn't screwing it up- he may have been doing what he needed based on the carb he was using.

My thinking has always been that if your vacuum advance is coming in, or already all or mostly in at idle, then you leave nothing extra to come in after mechanical is in for efficiency at higher cruising RPM.

If your vacuum advance is all or mostly in at idle, you may as well disconnect it and just set your idle higher strictly by turning the distributor. That's the idea behind using a ported vacuum source for advance.

[1968GTO421]

Originally Posted by Carmine

Well guys and gals, the verdict is in. No matter where I tested for vacuum, I only had 10 inches. Disappointed yes. Surprised no. But, as the motor goes up in rpm's so does the vacuum. So, I do believe it is decision making time. It's either change the cam shaft or a vacuum pump. The power brakes are going to work one way or the other. That cam shaft has to be fairly radical. You don't see the engine shake much, but siting in the car, you certainly feel it. Standing behind the exhaust, definitely can tell it's not stock. Almost sounds like a little miss in it, but it's not. The engine seems to rev short and quick if that's the way to explain it. I bought this car to enjoy driving it asap. So, a cam removal is out of the question; at least for now. Perhaps over the Winter I might see it happening. That leaves me with a vacuum pump. I previously did some research on them just in case. Just in case has arrived. I can't recite the brand or name, but Summit sells one for about $250.00. It got real good reviews. Users remarked on how quiet it was. So, I have to ask, any members ever use one of these?? Which brand did you buy?? Were you happy with it?? Many thanks, Carmine.

I think the tuning recommendations members have given you will probably solve your low vacuum problem and concern for your PB. If you still have a problem after the tuning with vacuum for the PB, I suggest you can save $$ on a vacuum pump by using a vacuum canister.

https://www.summitracing.com/parts/mrg-3701

My brother had a long duration solid lifter Isky cam in his Chevelle that affected his PDB and 7" booster negatively. He installed one of these canisters and, voila, he had power brakes again. An effective solution for less then $50. Hope this is of some help.

[Squidward]

Originally Posted by dmac

I always start with adjusting the idle screws to achieve best vacuum.Then readjust rpm, check timing. And back and forth. Adjustment of any one parameter requires adjustment of the others, until all are optimized. And you need to check the mechanical advance. If the springs are too loose, you may have mechanical coming in at idle. That's easy to check with a 'normal' old fashioned timing light.

And since your set-up doesn't seem to have a ported vacuum source, perhaps the prior owner installed an adjustable vacuum can to stop all the vacuum advance from coming in at idle. I recall needing to do that on one motor. Maybe he wasn't screwing it up- he may have been doing what he needed based on the carb he was using.

My thinking has always been that if your vacuum advance is coming in, or already all or mostly in at idle, then you leave nothing extra to come in after mechanical is in for efficiency at higher cruising RPM.

If your vacuum advance is all or mostly in at idle, you may as well disconnect it and just set your idle higher strictly by turning the distributor. That's the idea behind using a ported vacuum source for advance.

I see no downside to running manifold vac advance. Here is an interesting read I came across some time ago. Manifold vacuum and ported vacuum become effectively the same with just a small throttle opening off idle. You never lose the extra timing for cruise efficiency. The only difference is at idle. Do you want fat timing at idle, or don't you? I like the extra timing at idle.
http://www.gofastforless.com/ignition/advance.htm

[Carmine]

Originally Posted by 1968GTO421

I think the tuning recommendations members have given you will probably solve your low vacuum problem and concern for your PB. If you still have a problem after the tuning with vacuum for the PB, I suggest you can save $$ on a vacuum pump by using a vacuum canister.

https://www.summitracing.com/parts/mrg-3701

My brother had a long duration solid lifter Isky cam in his Chevelle that affected his PDB and 7" booster negatively. He installed one of these canisters and, voila, he had power brakes again. An effective solution for less then $50. Hope this is of some help.

Back in the late 80's-early 90's-I put a high performance cam in my '67 GTO. Unbeknownst to me, I would lose vacuum for my power brakes. I tried one of these vacuum reserve canisters I believe made by Crane. I honestly don't think it worked very well. Not sure why. Maybe I didn't have it installed properly. Removed it and that camshaft. Think I still might have it but no desire to use that particular one again. But, I would consider the one in your link which I already looked at. Maybe it's a new improved version. I have 12-13 inches of vacuum at idle and it increases as my rpm's do. Knowing that, do some members think this might work in my application?? I don't want to compare it to a vacuum pump. I know they are 2 different appliances. Thank you, Carmine.

BTW, that above canister got very good reviews for what it was intended for. I think it was 4.5 out of 5. That always encouraging.

[Formulajones]

Originally Posted by Squidward

I see no downside to running manifold vac advance. Here is an interesting read I came across some time ago. Manifold vacuum and ported vacuum become effectively the same with just a small throttle opening off idle. You never lose the extra timing for cruise efficiency. The only difference is at idle. Do you want fat timing at idle, or don't you? I like the extra timing at idle.
http://www.gofastforless.com/ignition/advance.htm

Yep. Lots of discussion over this for a long time but in a nut shell, just as you said, they both act virtually the same once the throttle is cracked open, with the only difference being ported doesn't work at idle (throttle closed)
I think what it comes down to with most people here is whether they can maintain a stable consistent idle that doesn't vary much in and out of gear, and some struggle with manifold vacuum in that scenario. Usually because they have a can that is too sensitive.
What people forget or don't realize, is that older cars originally were built with vacuum advance at manifold vacuum. The ported idea came along for emissions reasons (less hydrocarbons), and then that was taken a step further with TCS solenoids that wouldn't give any vacuum advance unless in high gear.
We are on the same page Squidward.