Brake booster
Drifting
Joined: Jul 2009
Posts: 1,534
Likes: 14
From: Dallas-Fort Worth TX
Recently replaced my booster. Did the mity vac test and it would not even hold a single inch of vacuum.
New booster works much better. I feel the assist, but I have that spongy feeling as well. I used a power bleeder, and ran 2 quarts of new brake fluid thru all 4 corners.
Still a bit spongy but I can lock up the fronts. Not sure if backs are locking.
I do not have a stock cam and it noticebly stops better when I have higher vacuum per my vac gauge in car.
My issue is now that the front left caliper I have had to replace 4 times in last 2 months because it starts to leak after about 10-20 miles. They are all rebuilds. The other 3 are 7 years old no issues, yet...
I will be replacing the caliper again soon. #5.
yes, upgrade to braided steel caliper hose lines. Makes a difference.
New booster works much better. I feel the assist, but I have that spongy feeling as well. I used a power bleeder, and ran 2 quarts of new brake fluid thru all 4 corners.
Still a bit spongy but I can lock up the fronts. Not sure if backs are locking.
I do not have a stock cam and it noticebly stops better when I have higher vacuum per my vac gauge in car.
My issue is now that the front left caliper I have had to replace 4 times in last 2 months because it starts to leak after about 10-20 miles. They are all rebuilds. The other 3 are 7 years old no issues, yet...
I will be replacing the caliper again soon. #5.
yes, upgrade to braided steel caliper hose lines. Makes a difference.
Thread Starter
Instructor
Joined: Jul 2012
Posts: 174
Likes: 6
From: McDonough Georgia
The easy to test a brake booster is : with the engine off put your foot on the brake and push down. while pushing down start the engine the pedal should go down further.
If not the booster is bad.
You can also put vacuum to the booster and see if it holds - use a Mity Mite vacuum pump - I have an electric vacuum pump and test that way. If the pressure drops when the pump is off the booster is bad.
Both my 71 and 72 stop correctly, I can lock up the wheels. . I had to replace the check valve on my 71 when I got it as the PO said the brakes faded. I do pull vacuum from the base of the carb.
Be sure you have the correct master cylinder for the application, as power and non power can be different.
I found that Pressure bleeding from the master works best.
If not the booster is bad.
You can also put vacuum to the booster and see if it holds - use a Mity Mite vacuum pump - I have an electric vacuum pump and test that way. If the pressure drops when the pump is off the booster is bad.
Both my 71 and 72 stop correctly, I can lock up the wheels. . I had to replace the check valve on my 71 when I got it as the PO said the brakes faded. I do pull vacuum from the base of the carb.
Be sure you have the correct master cylinder for the application, as power and non power can be different.
I found that Pressure bleeding from the master works best.
Any recommendations on which brake booster to get? I was thinking of ordering one from Rock-auto they seem to have the best price.
Last edited by ONeill202; Dec 10, 2016 at 02:43 PM.
Le Mans Master
Joined: Jul 2000
Posts: 6,664
Likes: 162
From: columbia city in
I tried your test and nothing happened. As you said, I pressed firmly on the brake and started the engine. I got zero movement on the pedal. I think it's safe to say that the booster is bad. I was hoping this wasn't the case because pulling this baby is going to be a bear.
Any recommendations on which brake booster to get? I was thinking of ordering one from Rock-auto they seem to have the best price.
Any recommendations on which brake booster to get? I was thinking of ordering one from Rock-auto they seem to have the best price.
Race Director
Joined: Oct 2008
Posts: 19,295
Likes: 1,681
From: Long Island
Rock Auto or Auto Zone are good sources, unless you are NCRS.
I chose Auto Zone for the lifetime warrantee.
The C3 is easier, if you remove the seat. - spray the nuts before you start ( Freeze Off / Rust Buster) and use a long extension, 6 point sockets. . The wobble extension may help. The old Craftsman magnets in the socket help hold things.
Make sure the booster is oriented correctly - vacuum port location.
Assemble everything ( Never Seize the threads ) before you tighten it all up.
I did my 85 last month, it makes my 71 C3 appear it was so easy. At 65, the 85 left a mark
.
The front brakes do most of the stopping. As a note if the rear locks up the vehicle will tend to have the rear come around to the front.
I chose Auto Zone for the lifetime warrantee.
The C3 is easier, if you remove the seat. - spray the nuts before you start ( Freeze Off / Rust Buster) and use a long extension, 6 point sockets. . The wobble extension may help. The old Craftsman magnets in the socket help hold things.
Make sure the booster is oriented correctly - vacuum port location.
Assemble everything ( Never Seize the threads ) before you tighten it all up.
I did my 85 last month, it makes my 71 C3 appear it was so easy. At 65, the 85 left a mark
.The front brakes do most of the stopping. As a note if the rear locks up the vehicle will tend to have the rear come around to the front.
Last edited by BLUE1972; Dec 10, 2016 at 06:34 PM.
Thread Starter
Instructor
Joined: Jul 2012
Posts: 174
Likes: 6
From: McDonough Georgia
Just to let everyone know what ended up happening... I replaced the brake booster with one that actually did hold pressure and the improvement in brake performance was like night and day. I'm really happy with the results. Unfortunately, this was one of the worst jobs I've had to do on this car. Pulling the brake booster was a nightmare!
Anyway, thanks for all the input!
Anyway, thanks for all the input!
Last edited by ONeill202; Feb 12, 2017 at 07:07 PM.
Thread Starter
Instructor
Joined: Jul 2012
Posts: 174
Likes: 6
From: McDonough Georgia
All,
Since replacing the brake booster I haven't driven the car much. I was busy pulling the engine for paint and a few upgrades. I know have everything back together and after a short drive I noticed that my brakes are locking up. The only way for me to get moving again is to open the bleeder valve on the master cylinder.
Does anyone have any suggestion on what might be the cause of the problem?
Thanks!
Since replacing the brake booster I haven't driven the car much. I was busy pulling the engine for paint and a few upgrades. I know have everything back together and after a short drive I noticed that my brakes are locking up. The only way for me to get moving again is to open the bleeder valve on the master cylinder.
Does anyone have any suggestion on what might be the cause of the problem?
Thanks!
Instructor
Joined: Jan 2016
Posts: 148
Likes: 16
From: Verona KY
Late entry to this thread as I'm having a bit of the same issue. BTW my car is a '86 coupe w/ manual trans.
My stopping and pedal feel is fine. However, I'm hearing the dreaded hiss under the dash as I apply the brake pedal. It's quiet if the pedal isn't pressed and appears only on brake application. Most likely, the foam silencer is not available separately from the booster.
Idle does not seem to change when the hiss occurs but I haven't hooked up the scan tool to watch IAC steps to see if the idle air valve is closing to compensate for the added air flow of a vacuum leak.
Jonathan.....
My stopping and pedal feel is fine. However, I'm hearing the dreaded hiss under the dash as I apply the brake pedal. It's quiet if the pedal isn't pressed and appears only on brake application. Most likely, the foam silencer is not available separately from the booster.
Idle does not seem to change when the hiss occurs but I haven't hooked up the scan tool to watch IAC steps to see if the idle air valve is closing to compensate for the added air flow of a vacuum leak.
Jonathan.....
Melting Slicks
Joined: Jun 2011
Posts: 3,123
Likes: 605
All,
Since replacing the brake booster I haven't driven the car much. I was busy pulling the engine for paint and a few upgrades. I know have everything back together and after a short drive I noticed that my brakes are locking up. The only way for me to get moving again is to open the bleeder valve on the master cylinder.
Does anyone have any suggestion on what might be the cause of the problem?
Thanks!
Since replacing the brake booster I haven't driven the car much. I was busy pulling the engine for paint and a few upgrades. I know have everything back together and after a short drive I noticed that my brakes are locking up. The only way for me to get moving again is to open the bleeder valve on the master cylinder.
Does anyone have any suggestion on what might be the cause of the problem?
Thanks!
Try this simple test start the car and press the brakes in park. Lift 1 front wheel and confirm the brakes are locked.
Then loosen the MC from the brake booster and pull it forward to confirm there is no pressure being applied from the booster.
Now confirm if the wheel stays the same or if brakes released an additional amount. If it does release, then confirm when you slide the MC to the booster that the booster pin isn't apply brakes as you tighten down the MC.
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Thread Starter
Instructor
Joined: Jul 2012
Posts: 174
Likes: 6
From: McDonough Georgia
When you install the Master cylinder to the brake booster did you find the booster pin was applying pressure to the master cylinder, like the booster pin was to long.
Try this simple test start the car and press the brakes in park. Lift 1 front wheel and confirm the brakes are locked.
Then loosen the MC from the brake booster and pull it forward to confirm there is no pressure being applied from the booster.
Now confirm if the wheel stays the same or if brakes released an additional amount. If it does release, then confirm when you slide the MC to the booster that the booster pin isn't apply brakes as you tighten down the MC.
Try this simple test start the car and press the brakes in park. Lift 1 front wheel and confirm the brakes are locked.
Then loosen the MC from the brake booster and pull it forward to confirm there is no pressure being applied from the booster.
Now confirm if the wheel stays the same or if brakes released an additional amount. If it does release, then confirm when you slide the MC to the booster that the booster pin isn't apply brakes as you tighten down the MC.
Racer
Joined: Dec 2014
Posts: 374
Likes: 42
From: Coldwater Mi
I disagree with changing to the hydroboost setup, as it IS very expensive...and like some have said, IF you get your brake system dialed in correctly, there's no need to convert....I had to totally replace my rear brake lines, calipers, pads & park. brake parts, and had a rock hard pedal ever since....I gravity bled them....all by MYSELF!!
Thread Starter
Instructor
Joined: Jul 2012
Posts: 174
Likes: 6
From: McDonough Georgia
I disagree with changing to the hydroboost setup, as it IS very expensive...and like some have said, IF you get your brake system dialed in correctly, there's no need to convert....I had to totally replace my rear brake lines, calipers, pads & park. brake parts, and had a rock hard pedal ever since....I gravity bled them....all by MYSELF!!
Replacing the brake booster made a huge difference for me.
Last edited by ONeill202; Jul 10, 2017 at 08:09 AM.
Thread Starter
Instructor
Joined: Jul 2012
Posts: 174
Likes: 6
From: McDonough Georgia
Late entry to this thread as I'm having a bit of the same issue. BTW my car is a '86 coupe w/ manual trans.
My stopping and pedal feel is fine. However, I'm hearing the dreaded hiss under the dash as I apply the brake pedal. It's quiet if the pedal isn't pressed and appears only on brake application. Most likely, the foam silencer is not available separately from the booster.
Idle does not seem to change when the hiss occurs but I haven't hooked up the scan tool to watch IAC steps to see if the idle air valve is closing to compensate for the added air flow of a vacuum leak.
Jonathan.....
My stopping and pedal feel is fine. However, I'm hearing the dreaded hiss under the dash as I apply the brake pedal. It's quiet if the pedal isn't pressed and appears only on brake application. Most likely, the foam silencer is not available separately from the booster.
Idle does not seem to change when the hiss occurs but I haven't hooked up the scan tool to watch IAC steps to see if the idle air valve is closing to compensate for the added air flow of a vacuum leak.
Jonathan.....
Well, mine is a 70 and I'm sure the brake booster is different, but I was hearing the hissing sound on my old booster as well. The best advise I got was to test it using a mityvac to see if it would hold pressure. If you look earlier in the thread I believe there is a reference to using one.
Last edited by ONeill202; Jul 10, 2017 at 08:22 AM.