vacuum reserve system

[chevy55210]

Hi! Just wondering, if I have a dial 8" master brake booster on my 11" disc brakes
would a vacuum reserve tank help my stopping? I'm not running a big cam or anything.
Thanks for any input.

[chevynut]

A reserve tank won't "boost" vacuum so I doubt it will help. Do you know how much vacuum you're getting now? The problem may be something else, like too large of a master cylinder or improper pedal ratio. What is the MC bore, what calipers are you using, and what is the problem you're having?

[55 Tony]

It can help but can also be intermittent. An extreme example would be if you wind it out in 1st then let off the throttle. You will get a higher vacuum than your idle vacuum, and the check valve will hold that higher vac. But that is only good for 1 or 2 pumps of the brakes.

I opted to use a generic nova 1" master and on the brake pedal welded the clevis pin hole closed and drilled a new hole up a little higher. Yes you will get a little less pedal, and yes locking up the brakes is easier than with the clevis in the stock location. I think it's a damn fine compromise compared to trying to stuff a vacuum booster in next to a BB.

[chevynut]

Every setup can be different. Depending on caliper piston size you might get away with a smaller bore master cylinder, but pedal travel will increase. A smaller bore pushes less volume per inch of travel, so filling up the calipers takes more pedal travel. Also, increasing pedal ratio by moving the pushrod pivot upwards increases travel too. So there's a balancing act you need to play to optimize a non-optimal system. If you're comfortable increasing pedal travel on a particular setup that might work. Personally I like a "tall" pedal with lower travel.

ECI has this product that may solve some of the pedal travel issues. It's a step-bore hydraulic "booster" that fills the calipers with a large bore piston with less pedal travel, then the smaller piston applies the pressure. Pretty ingenious, but I don't know how well it works. I think it's similar to the floor jacks that go up a lot with one pump but apply more pressure once resistance is met. It may help in some cases.

http://www.ecihotrodbrakes.com/brake_pressure_multiplier.html

"The ECI brake pressure multiplier (BPM) utilizes a unique step piston configuration to increase brake system pressures 50-60% where it’s needed most- at higher pedal forces. The BPM uses the excess fluid capacity available in the master cylinder bore to provide increased line pressure for the low volume requirements of a small piston caliper brake system, such as Ford Explorer, Corvette and GM rear disc brake calipers, and is ideal for use with rear drum brake systems. Due to it’s step piston multiplication system, the BPM continues to provide 150% to 160% of inlet pressure as pedal effort increases, unlike a vacuum booster’s assist, which remains constant after maximum boost is reached with line pressure only increasing linearly with increased pedal force."

[55 Tony]

The BPM is the most interesting thing in brakes I've seen. I'll have to see if it can work with large gm calipers. I unsuccessfully tried using a "step bore" master cylinder, which is supposed to seat the brakes with little pedal travel, then the step bore comes in which is smaller and gives more powerful stroke for the second half of pedal travel. I tried 3 of them. The very first one worked WELL, but it went out on me. The next two replacements were made differently and worked about the same as a standard master cylinder. Hold on, I had to call the BPM manufacturer and here is what I just found out. It *WAS* basically the same as a step bore master, but they started getting crappy parts and didn't want to put out the money to tool up and build it in the US, so it is no longer available. So much for that.

[Custer55]

MPBrakes sells an electric vacuum pump and remote brake boosters. https://www.mpbrakes.com/
Not sure how well either of these actually work though. The electric pump is supposed to maintain the proper vacuum level in the booster when the engine is not able to.

[Bihili]

Vacuum pump works for me..