Settle a brake argument

Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
6,626
113
Queens, NY
Manual brakes VS power brakes. Manual brakes, or power brakes with NO boost assisting, which are basically manual brakes then, can be adjusted up where the pedal travel is minimal. You can get good hard pedal almost immediately. As soon as booster assist is applied the pedal travel increases. Sometimes dramatically so. Yes or no and why? EDIT: The question is do boosters cause more pedal travel?
 
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Clone TIE Pilot

Clone TIE Pilot

Royal Smart Person
Aug 14, 2011
2,140
113
Galaxy far far away
Power brakes get my vote. This is a tricky question as there are more than one type of booster available in G bodies. Single diaphraghm vacuum bosters, small dual diaphraghm vacuum boosters, large B body dual diaphraghm boosters, and GN hydraulic boosters. My Regal originally had a small dually booster but after it failed I replaced with a larger B body dual booster which reduced braking effort.
 
Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
6,626
113
Queens, NY
I am talking stock boosters as came from the factory. The question is do boosters affect pedal travel? I apologize if that was not clear.
 
69hurstolds

69hurstolds

Comic Book Super Hero
Supporting Member
Jan 2, 2006
3,390
113
More pedal travel with boost? Yes and no. The "hard" pedal you get with the brake booster without vacuum is only closing the diaphragm valve, sometimes called the balance valve and opens the filtered inlet valve from the cabin. Problem is, there's spring pressure and NO vacuum assist available, thus the pedal stops short of actually applying the brakes when you hit that "hard spot". You have to press the dog pee out of the pedal some more to get the brakes to actuate with no boost. The brake pedal itself doesn't actually push on the master cylinder in a typical power brake set up. There's an extension pin that actually does that. It relies heavily on vacuum to apply the brakes. But yes, you can manually operate them in an emergency without vacuum, but it's a stiff pedal for sure.

When vacuum is applied to the front of the diaphragm, and the pedal is at rest, the balance valve is open allowing vacuum to be on each side of the diaphragm, effectively balancing out the diaphragm where it has no pressure on either side of it, except the spring in the front to keep it from actuating the master cylinder. The filtered air inlet (brake pedal shaft inside the car) valve is closed. So vacuum builds up in the booster on both sides of the diaphragm. As you press the brake pedal, it closes the balance valve on the back side of the diaphragm, and now the vacuum is only felt on the front side. The valve also opens allowing atmospheric (higher pressure) air on the back side of the diaphragm. This easily overcomes the spring pressure on the front of the diaphragm, which pushes the diaphragm forward, and full pedal travel can occur. This in turn, actuates the master cylinder. Some cars come with an adjustable master cylinder actuator pin that goes in the front section of the diaphragm balance valve, which can be adjusted to actuate the master cylinder sooner or later depending on the need which in turn will affect pedal travel.

I could be off a bit on this, as I'm only going by memory. If I was looking at some pictures, I could probably explain it better. I know how it works, but sometimes my "explain mode" doesn't work so good.
 
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Clone TIE Pilot

Clone TIE Pilot

Royal Smart Person
Aug 14, 2011
2,140
113
Galaxy far far away
I am talking stock boosters as came from the factory. The question is do boosters affect pedal travel? I apologize if that was not clear.
Stock boosters vary by make, model, sub model, and year for G bodies. Most stockers are either 11 inch dia singles or 9 inch dia duals, except for turbo Buicks which used hydraulic boosters.
 
TURNA

TURNA

Rocket Powered Basset Hound
Jul 24, 2009
10,062
113
Socialist NY
Pedal travel is the same

The pressure or resistance you feel is different, tricking you to believe its more or less

The fluid/caliper piston still has to move the same distance to do the same job
 
69hurstolds

69hurstolds

Comic Book Super Hero
Supporting Member
Jan 2, 2006
3,390
113
It's still a yes/no answer when you're comparing to two different systems, though. Pedal travel can vary from car to car to get it to stop and to press the m/c enough to stop the car. Variables abound on this such as if there is air in the lines, mal-adjusted brakes, leaky m/c or other issues, requiring more or less pedal pressure, and whether the actuator pin or push rod is adjusted correctly (there's a tool for that). IIRC, the G-body boosters came with a non-adjustable push rod to the m/c which you use the go/no-go tool to see if it's at the right position. If it's not, there was supposedly a service kit with an adjustable push rod that could be installed to correct it.

All things being equal, I like the power brakes myself. But as TURNA points out, it will always take that certain pedal travel to push the m/c pistons the amount necessary to stop the car. But they still can be different from car to car. The pedal is direct to the m/c in the non-power brake setup obviously, so you can't simply take the booster off and think you can bolt the m/c to the firewall to get manual brakes. You would need an adapter plate and a new push rod setup for a G-body anyway. In the power systems, that hard pedal is a fakeout because if you're on a hill, see how far you roll when you hit that hard pedal when you put it in neutral with E-brake disengaged and the engine off. You'll then be standing on that joker trying to stop the car. It takes a more pressure than manual brakes to override the booster without vacuum similar to losing power steering. It just takes more effort.

Luckily, if the valving is sound, the booster has enough vacuum reserve for maybe one or two more vacuum-assisted pumps of the brakes if the engine shuts off.

No idea about quality here, but they do make kits to put manual brakes on a G-body (shown for example only) if you prefer.
https://www.amazon.com/dp/B072MK6BFY/?tag=gbody-20

For most of our 82-88 G-body power brake cars without hydroboost, they used the "FB" coded p/n 18010120 dual diaphragm booster. Supersession number is 18060040. The factory ones were cadmium plated through 1984, and then painted black from 85-up. Same unit other than paint/plating.

The rebuild kits have been discontinued, and even the latest ACDelco remanufactured service replacement booster p/n 19286983 has been recently discontinued as well. There's some other brand rebuilt units out there, but again, no idea of quality. There may be booster rebuild kits out there, but they're not sold by GM and I'm not sure where to get them. Boosters are a bit complex to rebuild and if you don't know what you're doing in there, don't go there. It's all simple until you get to the valve guts/seals. This is major safety you're talking about. No hacks allowed in there.

Then again, I could be talking out of my arse.
 
pontiacgp

pontiacgp

Canadian Prime Minister
Mar 31, 2006
26,804
113
Kitchener, Ontario
with the manual brake I get a consistant pedal that is higher than than the power brake set up and the pedal does not travel like it did with the power brake set up
 

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