Hyd assist unit? - Impala Tech
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post #1 of 7 (permalink) Old 09-24-2015, 10:43 AM Thread Starter
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Hyd assist unit?

Anyone ever install a hyd assist for their brakes? Just wondering how it worked.

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post #2 of 7 (permalink) Old 09-24-2015, 03:40 PM
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Power boosters are supplied as a factory option from GM. It consists of an eleven inch rubber diaphragm that has engine vacuum pull on one side (or atmospheric pressure minus engine vacuum push on the other) which is controlled by a spool valve cut in the booster mechanism that opens as you put your foot on the brake pedal. It is the difference in pressure spread out over the area of the diaphragm that assists you in pressurizing the hydraulic fluid in the master cylinder. Additionally they change the size of the master cylinder piston from a little less than an inch to a little over an inch to move more fluid since power assist was normally only ordered with disc brakes that has larger volume single front wheel cylinder requiring more brake fluid to move the piston.

Power assist doesn't improve the ability of the car to stop. It doesn't even reduce the effort needed to apply the brake as there are two holes in the brake pedal to gain mechanical leverage on non-power assist brakes. The only thing power assist does is allow your mom to hold her foot on the brake with the car in gear effortlessly as she applies her make up at the stop light.

That is why Power Assist brakes are an option. It is for the weaker sex to operate a two ton battering ram without having to think of the physics involved. Power Assisted Steering allows her to parallel park her land yacht using just her pinky. And an automatic took away that troublesome clutch thing so that any one can cause a two ton object to careen down any public road without any physical requirements as to dexterity or strength.

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post #3 of 7 (permalink) Old 09-24-2015, 09:42 PM
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I've heard of folks adaptingi the Astrovan hydro brakes to older cars, personally, I bought a kit from the old Hydroboost company for my old 'non-Impala'.
https://www.hydratechbraking.com

HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
http://www.impalas.net/forums/blog.php?u=1432
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post #4 of 7 (permalink) Old 09-24-2015, 10:48 PM Thread Starter
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I think Big Dave just gave me a biotch slap! Lol,

Thank You
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post #5 of 7 (permalink) Old 09-25-2015, 08:23 AM
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Nah. I apologize if you read it that way. I just was wondering why you would want to go to the hassle?

Manual transmission, brakes, and steering is the preferred performance option. Fewer things to go wrong, and you have a little bit better feel for how the car is behaving (though up until the mid eighties steering was vague at best as the engineers had been building marshmallow ride and steering intentionally as that is what the marketing guys told them how to build them). Wasn't until the marketing guys asked why they were loosing market share to German imports such as BMW and Mercedes that they discovered that people liked to actually drive cars, not just be transported from A to B.

If you ever install a rumpitty rump cam in your motor it takes away from the vacuum needed to make power brakes work. You can actually loose the ability to stop the car safely with a big cam and power assist brakes using engine vacuum.

Then you have to spend even more money on power assist brakes out of a diesel powered pick up truck (diesels do not use a throttle body having an intake manifold that is open to the atmosphere so that the engine can draw in as much air as possible). You must then add a power steering pump (if you don't already have power steering) and a all new hydraulic lines to use hydraulic pressure to assist the braking. This system is sold by Delco-Moraine and is called a Hydro-Boost.

I have the opposite problem of finding manual steering gear boxes and clutch linkage to convert my project cars into street bruisers from an economy car with powered everything except the motor. Loosing power assist brakes is the opposite of your procedure of bolting on a booster diaphragm changing the push rod and its position on the brake pedal (it goes into the top hole), and then buying and bleeding a replacement power assist master cylinder (to get the correct size piston in the master cylinder though this step isn't absolutely required).


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post #6 of 7 (permalink) Old 09-25-2015, 10:14 AM Thread Starter
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I was just kidding with ya Big Dave! My Impala has a 540 in it. It seems as though my pedal pressure seems to be excessive to me. I have discs in front and a 9" Ford rear with drums and a 69 Corvette master cyl. I think I read somewhere that there might be another hole in my brake pedal to change the pedal ratio, (I could drill one if not). I had to do this on my Nova drag car and it made a significant improvement. So maybe that is the route I'll try. The car is a lot heavier than my drag car and the feel of manual brakes is different from power found on new the vehicles of today so I might just be over thinking the issue, which I tend to do.

Thanks for the suggestions and info, that's why I asked.

popper
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post #7 of 7 (permalink) Old 09-25-2015, 12:37 PM
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Try going to a seven eighths inch (7/8") diameter manual brake master cylinder. That will build more line pressure with less pedal effort.

There is a chance that the master cylinder in your car was replaced with a one and one eighth inch (1-1/8") diameter or even a one and three sixteenths (1-3/16") inch master cylinder in the past (since you stated it came out of a Corvette that had four wheel disc brakes) as every counter parts jockey automatically assumes an Impala is going to have power assist brakes installed. That would increase your pedal effort substantially. The lower hole increases your leverage but it also increases brake pedal travel (which is a plus if you like to feather the brakes application instead of a sixty foot panic stop every time, the way my wife drives).

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