Woosh sound and variable braking effort.

[Rodney Gold]

all of a sardine I have a "woosh" when braking or holding the brake pedal down , and sometimes the pedal is easy and sometimes hard and high. Revs rise as well on braking indicating a vac leak.
Braking is all there and I have ruled out any vacuum leaks in hosing etc right to the brake booster - IE no vac leak elsewhere.
I have sucked on the booster hose and it seems the booster doesnt hold high vacuum and I think its boggered...It doesnt suck your tongue at the end of the hose , you can feel resistance but can continue sucking without increasing vacuum.
Braking effort much better when the car is cold , as soon as I drive it a few mins the braking effort rises a lot.

1) How would I know for certain its the booster (grommet and check valve seem 100%)

2) I'm in South Africa , so parts not that easy to get , what booster do i need to replace it with?
1980 Vette....

3) Should I get it repaired here by one of local brake shops? whats the chance they can fix it ok?

Ta for any responses

 

[gmjunkie]

all of a sardine I have a "woosh" when braking or holding the brake pedal down , and sometimes the pedal is easy and sometimes hard and high. Revs rise as well on braking indicating a vac leak.
Braking is all there and I have ruled out any vacuum leaks in hosing etc right to the brake booster - IE no vac leak elsewhere.
I have sucked on the booster hose and it seems the booster doesnt hold high vacuum and I think its boggered...It doesnt suck your tongue at the end of the hose , you can feel resistance but can continue sucking without increasing vacuum.
Braking effort much better when the car is cold , as soon as I drive it a few mins the braking effort rises a lot.

1) How would I know for certain its the booster (grommet and check valve seem 100%)

2) I'm in South Africa , so parts not that easy to get , what booster do i need to replace it with?
1980 Vette....

3) Should I get it repaired here by one of local brake shops? whats the chance they can fix it ok?

Ta for any responses

You have leaking Brake Booster internal Seals or Diaphragm!!

I don't know about where your at,but here locally we have a company that rebuild mine in about 3 hours!! They also build High Performance Brake Kits for Street Rods,Corvettes,All Sports Cars and the Braking Systems for the NASCAR boys!!

 

[TimAT]

If there are many GM cars in South Africa then getting a booster should be no problem. The booster is your problem BTW.
The intermittent peadl is the giveaway- one time it's normal and next time it's not- internal seals in the booster will do that.
It might be a good time to check into hydroboost if you've ever thought about that too. it may be that because of the shipping one may be more cost effective than the other,

 

[Adams' Apple]

Also check the seal between the booster and the master cylinder. They deteriorate over time, and create the same problems. The seal isn't available separately, but I have found that the seals for the headlight actuators fit perfectly with a little modification, and work like a champ.
If this seal is leaking, the booster will not hold a vacuum sometimes, but other times it may, depending on the position of the brake pedal. It's worth taking a look at before shelling out the cash for a new booster. If it's only the one seal leaking, it's a quick fix, and much cheaper. If the seal looks ok, and fits tightly around the booster rod, then the booster is probably shot.
hth

 

[Rodney Gold]

Thanks for all the advice.......my problem is Im drag racing the car on Saturday , it does high 12's and goes over the line at some high speeds , I disconected the vac hose from the brake booster and tried 140km/h to 0 and the brakes are all there , but requires a huge effort.
The booster still holds "some" vacuum and does give a little assist , so I dunno what to do , chance it with all vacuum off and the car running correctly without vac leaks or keep the vac connected?
PS when the brakes are NOT applied , there is no vacuum issue at all. Our track has a very short stopping distance , I'm a little worried.

Im caught between the devil and the deep blue sea , I have another race vehicle , a street going 454 El Camino (also mid 12's) , brakes work ok cept one of the discs or drums is warped and hard braking makes the car judder.
This drag event is one of the highlights of our drag calendar and i really dont want to miss competing.
What to do.....??
Too late to do any repairs , everything including the motor and v8 supply houses and brake repair centres all closed or not inclined to tackle any work prior to xmas and new year... arrrghh....