just trying to figure out what is wrong with my brakes. my dad is the original owner and i remember driving this car years ago and you could not floor the brake pedal.

for the past few years however, i've noticed that at a stop light i basically have to floor the pedal (or very close) to keep the car from lurching forward. the brake action feels fine for the most part, havent really had the need to slam on the brakes to try to lock them up or get the ABS to kick in, though i may have just got used to driving it like this...

is this a brake booster problem? maybe a vacuum leak in the booster?

all thoughts and suggestions would be appreciated!

kyle

 

ttt

really need suggestions on this issue!

 

It may be the booster, but you didn't say it was a hard pedal throughout the pedal movement.
sort of sounds like an internally bypassing master cylinder in the first movement of travel just before the internal valve "cracks".
The secondary piston has a little valve that limits the rear caliper pressure, and that might be weeping.
Also, try flushing the old fluid out and putting in new brake fluid. Sometimes you get suspended contamination that floats in the fluid and causes transient problems.

Unfortunately, these master cylinders aren't cheap, and the repair kits cost more than rebuilt units.
When was the last time the calipers were bled? water in the fluid will go to the calipers.
I rebuilt my 86 calipers a while back, and the insides looked like I had picked them up off a beach somewhere. all corroded. I ended up changing them.

 

Sounds like the Master Cylinder to me. See if one side is empty and the other full which would be the piston seal. Eventually, the cap pops off the side that's getting liquid and you end up with brake fluid eating the paint off the frame rails (and anything else it gets on). New at NAPA is a $150 or so.

 

Start small. Flush the old brake fluid from the master cylinder and replace with fresh new fluid. Then, bleed all 4 wheels at the calipers to flush as much of the old fluid out as possible. Be sure to bleed in the right sequence per the FSM (C4's with ABS have a different sequence from C4's w/o ABS). You may have to do this twice. After you've done this, let us know if anything changes with the pedal feel.

 

okey dokey, a month later.... just replaced the master cylinder today and bled the brakes... manual bleeding sucks btw, glad my dad was here to press the pedal... got fluid to run "clear" (new brake fluid color) at the master cylinder and at each caliper, used a whole bottle of fluid basically.

pedal still doesnt feel right... might be slightly worse than before, but probably not by much...

did a little test drive, if i slam the pedal it will engage the ABS/chirp the tires, just feels off, at least compared to other cars (unfortunately i cant remember what the vette felt like long ago, im only 26)

any ideas? i dont want to throw more money at the problem (probably shouldnt have done the master swap but that eliminates the possible piston seal problem)

 

ttt

 

Remove vacuum line from booster. With engine running do you have any vacuum?

Remove the inline vacuum check valve. You should have air flow in only one direction. Towards the engine.

If you have vacuum then plug the vacuum to engine line.

Test drive, does it brake the same. If same then the booster has a leak and is bad.

Good luck.

 

Hi just to clear this up and describe some symptoms of various problems that can happen.

Does your pedal feel firm (not spongy) it should only have a very small amount of travel and feel fairly hard but not much effort required to stop the vehicle from speed or to keep it stopped even when revving the engine.

The power booster is designed to lessen your input to stop the vehicle, if the booster is faulty leaking air the pedal will feel hard and required a lot of effort to stop the vehicle but no further movement. Note some brake pads with little friction compound can make it hard to stop the car like the booster is not working ..

If you have air in the brake fluid the pedal will feel spongy, however old rubber brake hoses can go soft and give a similar symptom.

If you can feel the brakes start to work with a lot pedal travel and requiring more pedal travel to really start working that may be a power booster pin adjustment to the master cylinder and or a bit of air in the system.

Usually a new master cylinder is bled before fitting to the car.
You can always bleed the brakes with gravity, undo the bleeders and let the fluid drip while topping up the reservoir.

If you feel the pedal slowly go down while waiting at the lights that is usually a symptom of the rubber master cylinder piston not sealing correctly allowing brake fluid to push past it and having the pedal to travel further to the floor to keep the car stopped.

Hope this helps you

 

no, the pedal doesnt feel hard, its spongy, the pedal travels much farther than i feel it should (or used to a number of years ago)

im pretty sure i got all of the air out of the brake lines and the master, i spent a few hours bleeding it with my dad according to the FSM manual bleed directions... bled the master first, then bled the lines (calipers) til the fluid ran clear

honestly never thought of the booster pin adjustment, how do i go about adjusting that, or is it simple to figure out, im at work (and its dark out ) so i cant go check it out prior to my posting


i thought this was the original problem so i purchased and put on a new master cylinder yesterday...

thanks a bunch!

 

Hi if you are 100% sure that all the air is out the brake lines then it must be the rubber brake hoses, they can get soft with age and swell when applying the brakes. It should be a gradual thing over years.

Perhaps gravity bleed the brakes to be sure, just remove the brake bleeders let around half the master cylinder reservoir go thru the brakes and replace the bleeders do the front first then back.

If the pedal is still soft then it must be your brake hoses.

Good luck

 

what about the booster pin adjustment though?

 

The booster pin will determine the clearance between master cylinder and booster. If it is not adjusted correctly/ too loose that can affect where the master cylinder takes effect, would have more pedal travel travel but no spongy feeling. The pedal will travel further than normal before the brakes work.

Spongy feeling is nearly always air in the system or old rubber brake hoses and swelling when pressure is applied.

 

maybe i dont know what a spongy brake pedal means... i just assumed it meant a farther throw, and didnt feel right, but i honestly dont remember what it SHOULD feel like anymore... the pedal definitely travels way too far though

(and yes i know someone is going to say its going to feel like stepping on a sponge )

 

Yes that is what it feels to have air in the system, the brakes will grab but you need to apply more pressure to stop the car and the pedal travels further while doing this. That does kind of feel like stepping on a wet sponge.

More travel before the brakes work but a hard pedal will be the pin between booster and master cylinder

 

sweet, thx for the help, i will test this during halftime of the NFL games this afternoon... need some sleep first

 

i've replaced my booster,looking at the front face,you can see a pin that pull inside the bottom of the master cylinder,you have to adjust that pin simply screwing/unscrewing it .If you simply unscrew your master cilinder,without bending the lines attached to it,you can set the pin for a less traveling brake pedal.