ONeill202

Hey Guys,

I started noticing a vacuum sound every time I press on my brake peddle is this normal? I've learned to live with a spongy brake peddle, but I don't want to add to an already crummy braking system with a bad booster.

Thanks,

Al

resdoggie

If you have a spongy brake pedal then you may have air in the lines resulting in a crummy brake system.

ONeill202

I have been bleeding, and bleeding these brakes with no success. I upgraded the front calipers to Wilwood calipers mistakenly thinking that it would help and it didn't. The brakes will work but I am not able to lock the wheels when I stand on them.

mrvette

I bought my '72 in '95 and in all them years early on, I have tried all sorts of solutions for that soft pillow we call brakes.....hit the pedal and it goes ehhhh, squisssssh to the firewall, and sharkey MAY feel like stopping.....I went to over bore sized truck m/cyl, took out that silly brake fail switch, commonly called a proportioning valve, which it is NOT and put in a simple splitter to the front brakes, and the line to the forward port on the m/cyl......rear brakes of course already had a T splitter so nothing done there.....

and still the brakes sucked, along with vacuum......

SO many years ago I picked up on the Hydroboost brake booster that runs off the power steering pump, installed it, and hit the brakes, sharkey stood on her nose and MY nose went into the wheel.....

takes a bit getting used to.....only 2-3 inches to lockup which is hard as a rock......not that soft feeling that goes to the firewall like a limp sister......

69427

I welcome any correction here, but it's my understanding that if you hear a hissing sound when applying the brakes, it's generally due to the disintegration of the foam filter/silencer at the brake pedal rod going into the booster.

mrvette

I can't really say anything as to your comment, but aside from the sound, on MY car it was the pedal travel that got to me, and the soft feel of it at bottom of the stroke.....I took the old booster apart, and found nothing obvious to be rong with it.....

ONeill202

Where can I acquire one of these amazing devices?

sunflower 1972

Have you considered stainless steel braided brake hoses? Hella of a lot cheaper and less
labor intensive than installing a hydro boost system.

ONeill202

I have them installed on the front calipers. Do you think installing them on the rear calipers will make a difference?

cagotzmann

"live with spongy brake"

Test the brake booster. Connect a hand vacuum pump and see if it holds. Similar to this thread. ( I tested the unit outside of the car ) but you can do a similar test while on the car.

https://www.corvetteforum.com/forums...f-the-car.html

After this tests ok. Did you replace the pads when you where bleeding the brakes. If the pads have wear then it is very possible to trap air in the caliper pistons and the only way to remove this air is by pushing the piston in. I usually shim the pads to force them to completely push the pistons into the caliper. I also use my air compressor connected to the master cylinder and set to 10-15 PSI to pressurize the brake lines to bleed.

ONeill202

How did you manage to connect the handheld vacuum pump to the brake booster?

resdoggie

I knew when my brake booster went bad. After I turned off the engine, I pulled the check valve from the front of the booster and didn't hear a hiss of rushing air into the booster. When I replaced the booster, I could pull the check valve a day after shutting down the car and would hear a hiss.

ONeill202

That sounds like an easy test...I'll give that a try.

ONeill202

I ran it for a few minutes and pulled the check valve. I heard a slight hiss but nothing very spectacular.

7T1vette

Bad booster. Seals are old/dried/shrunk and not sealing well.

Now, that will improve the power-assist function of the brakes...but it will NOT tighten-up the brake pedal problem. That is due to air in the system or very old brake fluid which as ingested some water into it over the years. Also, if you have any OLD rubber brake hoses on ANY of your calipers, you NEED to replace them. The rubber on the inside of those hoses deteriorates and tends to block off fluid flow. They can cause continuous partial apply of that brake set [and constantly build heat!] or cause spongy feel in the pedal because they tend to 'bulge' under pressure.

ONeill202

The front calipers are new and have stainless steel hoses. I have not replaced the rear but that is about to change. I ordered new rear hoses today. I've had this car for about four years and the brakes have always been a disappointment. I have never owned a C3 before so I don't have a point of reference for what I should expect but they seem very spongy to me. Like I said in my previous post, I have tried standing on the brakes at about 30 MPH and they don't lock, it continues to roll for about 10 feet or so.

I'll followup with an updated post as I continue to swap out parts.

mrvette

My '72 passed that test several times, just says the booster is good, basically......not that it's good enough.....

Get some advice from a junkyard as to what vehicles a HydroBoost comes off of......or if it's a U pullit yard....bring your tool set and start lookin'.....

'75

Years ago, my brake pedal was spongy, I bled it till there was no air, I eventually determined the reaction disc in the booster was soft and causing it. Instead of replacing the booster, which would have fixed it, I changed over to the hydro boost without opening a brake line, I instantly had a good hard pedal. I don't see ever needing better brakes than what it has now, I can lock them up anytime I want.

resdoggie

Correct and I also agree with 7T1vette. But if you have a bad booster with the symptons I described, there's a good chance you have a vacuum leak also i.e. booster can't maintain a vacuum. So when you hit the brakes hard at speed, your idle drops and maybe your vacuum. Not good. As for hydroboost, it's an option that's just as effective as a properly functioning oem brake system. That's why I haven't converted - no need.

mrvette

Depends on your definition of proper function......GM brakes are notorious for soft pedals, and in these old vettes with 8 pistons per end that are basically a take off from some aircraft brake designs....the vacuum boosters just not up to the job.....

believe me, you will be FAR happier for the conversion....