Thread: Power brake booster modification

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I have heard of being able to recallibrate a booster so that it will operate at lower vacuum levels, like in a case where
you'd get only 8-10" vacuum the booster can be set up to assist at that level.
Do any of you guys know who does this?
I am also interested is the hydratech system useing hydraulic pressure from the power steering to assist in brakeing, if any of you guys have experience with that i would appreciate your input on that too.
Thanks, oj

that system works super--on some trucks and also Mustangs---mustang units are reasonably sized and priced---wrecked stangs every where in junk yards

GM used the hydraulic boosters on several models, including some Pontiacs, Olds, Buicks... Worked great, but expensive to replace if they quit.

I have hydroboost on my 39 and it works wonderful.....it will put you thru the windshield if you stomp it. Hydroboost is great for cars with big cams and low vacuum. It is also a smaller diameter unit that will fit under the floor if desired. Chevy pickups with diesels have hydroboost

Not sure it is possible to change the operating range on booster, this is the first time I have heard of that. There is a third option for low vac pressure and radical cams. That would be an electric vacuum pump, you would want one that cuts off at pressure. One more tip you will want to mount it under the car, they are about as noisy as an electric fuel pump.

How about a vacuum canister with a check valve? Builds vacuum at above idle, then feeds when needed? Not sure if it would work or not, but the OEM's used a lot of tomato juice cans painted black back in the 70's.

Originally Posted by pepi

Not sure it is possible to change the operating range on booster, this is the first time I have heard of that. There is a third option for low vac pressure and radical cams. That would be an electric vacuum pump, you would want one that cuts off at pressure. One more tip you will want to mount it under the car, they are about as noisy as an electric fuel pump.

I have a couple projects that i need to replace those electric vacuum pump systems i have tinked and dinked on those things from the day i installed them. They are poorly engineered, overrated, noisy, cumbersome - you name it. A poor solution to a problem and the sooner i get them into the trash the safer the car will be.
I'll continue looking into the operating range change of the booster and will let you guys know what i find.
Thanks for all the replies, it looks like the hydrosystem is the way to go.

Originally Posted by ojh

I have a couple projects that i need to replace those electric vacuum pump systems i have tinked and dinked on those things from the day i installed them. They are poorly engineered, overrated, noisy, cumbersome - you name it. A poor solution to a problem and the sooner i get them into the trash the safer the car will be.
I'll continue looking into the operating range change of the booster and will let you guys know what i find.
Thanks for all the replies, it looks like the hydrosystem is the way to go.

I just added a system from "ABS' brake in So.Cal and it's a little pain to install but it works great!!
Now My ride stops quick and that's just what I was looking for.
Yes they are a little noisy when you start the engine,{powers up],but I very happy with the set-up.

I have used Gm and ford Hydroboost systems on several cars. They work excellant, but take up alot of room. I have had the best luck with the mid 70's Lincoln systems. They are readily available in the junk yards here in California cheap. They work real well on fat fendered cars and trucks, and fifties/sixities, but are a little much for the smaller cars.

"I have a couple projects that i need to replace those electric vacuum pump systems i have tinked and dinked on those things from the day i installed them. They are poorly engineered, overrated, noisy, cumbersome - you name it. A poor solution to a problem and the sooner i get them into the trash the safer the car will be.
I'll continue looking into the operating range change of the booster and will let you guys know what i find.
Thanks for all the replies, it looks like the hydrosystem is the way to go."


I disagree, I have run one for 12 years without so much as a hick cup and the car is on the road every weekend, is not a garage queen. You do get what you pay for I will say that. For my application a hydrosystem with all the hoses, the size of the power steering pump would look out of place and junky. The electric pump in out of the way and hidden, my motor is exposed to the world not buried under a hood and fenders. I will bet my next paycheck you will not find a way to adjust the operating range of the booster . Will not be holding my breath waiting for that answer.

Originally Posted by pepi

"I have a couple projects that i need to replace those electric vacuum pump systems i have tinked and dinked on those things from the day i installed them. They are poorly engineered, overrated, noisy, cumbersome - you name it. A poor solution to a problem and the sooner i get them into the trash the safer the car will be.
I'll continue looking into the operating range change of the booster and will let you guys know what i find.
Thanks for all the replies, it looks like the hydrosystem is the way to go."


I disagree, I have run one for 12 years without so much as a hick cup and the car is on the road every weekend, is not a garage queen. You do get what you pay for I will say that. For my application a hydrosystem with all the hoses, the size of the power steering pump would look out of place and junky. The electric pump in out of the way and hidden, my motor is exposed to the world not buried under a hood and fenders. I will bet my next paycheck you will not find a way to adjust the operating range of the booster . Will not be holding my breath waiting for that answer.

You're right, i have spoken with a couple booster rebuilding shops and you can't change the vacuum requirements, it is a 'per square inch' kind of thing.
As far as the electric vacuum pump, similiar to what stainless steel brakes sells, i have installed several. To date three have failed for different reasons and i now keep spare parts in stock - esp the vacuum switch. I believe the oldest unit is 4years old? maybe. I am trying to find a better system. As far as i am concerned with properly designed 4wheel disc brakes you don't need power assist, it is a drivers preferance kind of thing unless you have a physical problem with your hips for example.
It would be nice if we had a ton of space and could have about a 8:1 pedal ratio and do away with all the 'add-on' stuff to reduce pedal effort. I have even made toggle cams Between the pedal and the booster) to change the ratio in cases where i could get only 5ish:1 pedal ratio.
Here is the level of effort difference (in case you are wondering), for an aggressive stop - not panic - it takes about 75lbs of leg effort for mechanical and 50lbs for power assist. They both equal the same amount of force at the caliper/drum. The caliper/drum works at about 1200psi because of the hydraulic seals, so that power assist can't stop quicker it is just easier to get there.
I didn't mean to get into engineering gobbeldygook but maybe somebody will find it interesting.

Originally Posted by ojh

I have even made toggle cams Between the pedal and the booster) to change the ratio in cases where i could get only 5ish:1 pedal ratio.
Here is the level of effort difference (in case you are wondering), for an aggressive stop - not panic - it takes about 75lbs of leg effort for mechanical and 50lbs for power assist. They both equal the same amount of force at the caliper/drum. The caliper/drum works at about 1200psi because of the hydraulic seals, so that power assist can't stop quicker it is just easier to get there.
I didn't mean to get into engineering gobbeldygook but maybe somebody will find it interesting.

I'm finding it very interesting! I am curious if you have any pics or drawings of these toggle cams? Thanks for the gobbeldygook (spelling lesson!) and thanks for sharing the info.

Originally Posted by 34_40

I'm finding it very interesting! I am curious if you have any pics or drawings of these toggle cams? Thanks for the gobbeldygook (spelling lesson!) and thanks for sharing the info.

I'll see what i can do. I made and tested the entire system on my bench befor installing it into the car, whether i can find pics of it is the question.

Thanks Again.

Couldn't find shop pics but heres a couple views underneath. The toggle is in the middle, the brake pedal attachment is the outside stainless heim and you can see the pedal protrude thru the floor the irride heim and stainless shaft are going into the booster (out of view)