Staff member
Snoopysvet said:
Issue -

The brake pedal goes to the floor but the car stops.

If I plug the vacuum hose to the booster the pedal is firm and does not go to the floor, I can drive the car around the block with no issue other than the pedal being very firm.

Background -

I successfully swapped the Master Cylinder about 8 months ago with no issue and I am familiar with odd sequence of bleeding the brakes in C3s.

Assumptions -

I assume the booster is bad however I thought if it was not working the pedal would be very stiff
If the master cylinder was bad would the pedal go to the floor if the vacuum hose to the booster was disconnected?

yes reading links and sub links may be a P.I.T.A. but it leads to ANSWERS
your question basically contains two separate but interacting systems, the vacuum booster which allows you to apply minimal brake pressure but have it amplified at the master cylinder significantly, and the master cylinder which actually applies hydraulic pressure to the fluid.
look thru these links, AND DIAGRAMS CAREFULLY

if the booster is not working the petal in most cases will be down near the floor but not on it, , as the movement in the booster assembly is already taken up,the brakes will still work but probably require a great deal of effort to be applied as in both feet and putting all your weight on the petal.
the info you posted earlier makes me think the booster is leaking or its connection to the brake master cylinder is loose but the master cylinder is functional


There is a Huge Coil Return spring inside of the GM Power Brake Booster.
Made of Steel & Can corrode severe. Rust & Snap in 2 one day.
So master cylinder does not return fully to uncover & replenish the Compensating port with brake fluid.
The Result is brake pedal stays near the floor board.
No Brakes.
Ultra hard both feet on brake pedal to barely slow down from road speeds.
It happened to me 2 summers ago driving my '63 Pontiac G.P.
Scary.....2 tons moving 65mph & bang....Power brake booster internal spring snapped apart.
Spent 6 months finding another brake booster.
Not remanufactured no longer.
1963-64. only Pontiac part.


Staff member
yes as pointed out above ,theres a return spring in the booster that may be defective or busted,and on the c4 corvette the boosters frequently made from PLASTIC, not metal, and subject to cracking and leaking




c4booster1.png ... vi=1041219 ... -1996.html ... cc=1041398

now I recently found these little clear canisters deals with taps for clear plastic hose that when used with a vacuum pump gun make bleeding the air,out of a hydraulic clutch or brake lines far easier and far less messy, and it allows you to do it effectively by your self if you have enough plastic hose, you simply crack the bleed valve, on the brake caliper or clutch slave cylinder, then slip a clear plastic hose that fits tightly on the bleed valve nipple
(usually 1/4" or 5/16" plastic hose)between the brake slave cylinder or calipers and route one end to the canister, route a second plastic tube to your vacuum gun and pour brake fluid into the master cylinder while pumping the gun, the old fluid collects in the canister.
the great thing here is that its use it makes it a one man job and you can use longer plastic hose so you can stand next too the master cylinder to make sure its never going low on fluid, as you keep it topped off, while you pump out the old brake or hydraulic fluid

NOTICE THEY COME 12 too a carton and cost about $40 a dozen so get two buddies to split the cost, and youll each get 3-4
vacbra.jpg ... 39522.html


read this ... 13448.html



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