Brake booster
11-24-2016, 07:33 PM
#21
Race Director
I read this entire thread...and I will add this.
YES...many members are correct.
1.) Bad or old dirty brake fluid DOES effect the crispness of your brakes. And what might amaze people that even if they pressure bleed there system ( or whatever method they choose)..it is still possible that the brakes may still be a bit spongy. And this is because if anyone has ever removed the valve/piston of the master cylinder and see how much sludge can build up in that circuit...there is no wonder why the brakes may still feel spongy.
2.) Brake hoses being bad.
3.) Air still in the system.
4.) The power booster having an internal leak that caused the idle to drop when you press on the pedal. YES...it is normal to hear a 'whoosh' when you press the brake pedal with a factory booster.
What I am more concerned with is IF when you press the brake pedal it is hard as a rock and takes everything you got to try to stop the car. That for me is either an instant indication that the booster is BAD....OR...as I have seen...the check valve in the front of the booster is BAD.and does not want o flow freely.
5.) A bad master cylinder can cause this due to possibly attaching pressure a pressure gauge at the caliper ares and checking that the master cylinder is able to apply the correct pressure. I have found this in many Corvette and think goodness I have the gauge to test this.
Lastly...I can say that there is no comparison in a hydra-boost and a factory booster. Just like manual brakes to a power brake system. They are two completely different systems. And I am only commenting from two systems I installed that when done would amaze you. Literally 'day and night'.
DUB
YES...many members are correct.
1.) Bad or old dirty brake fluid DOES effect the crispness of your brakes. And what might amaze people that even if they pressure bleed there system ( or whatever method they choose)..it is still possible that the brakes may still be a bit spongy. And this is because if anyone has ever removed the valve/piston of the master cylinder and see how much sludge can build up in that circuit...there is no wonder why the brakes may still feel spongy.
2.) Brake hoses being bad.
3.) Air still in the system.
4.) The power booster having an internal leak that caused the idle to drop when you press on the pedal. YES...it is normal to hear a 'whoosh' when you press the brake pedal with a factory booster.
What I am more concerned with is IF when you press the brake pedal it is hard as a rock and takes everything you got to try to stop the car. That for me is either an instant indication that the booster is BAD....OR...as I have seen...the check valve in the front of the booster is BAD.and does not want o flow freely.
5.) A bad master cylinder can cause this due to possibly attaching pressure a pressure gauge at the caliper ares and checking that the master cylinder is able to apply the correct pressure. I have found this in many Corvette and think goodness I have the gauge to test this.
Lastly...I can say that there is no comparison in a hydra-boost and a factory booster. Just like manual brakes to a power brake system. They are two completely different systems. And I am only commenting from two systems I installed that when done would amaze you. Literally 'day and night'.
DUB
11-24-2016, 08:53 PM
#22
Had a 1976 L-82, 4-sp
Member Since: Mar 2011
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Educate me. Does the hydro boost lock the wheels with less pedal pressure or decrease the stopping distance? My oem brakes lock up just fine when pressed hard enough.
11-24-2016, 09:06 PM
#23
Everybody has some really good ideas. You just need to put them in order, and diagnose each individual part of your brake system.
Check the master cylinder, it would be very favorable to check brake pressures, if at all possible. That will put any myths about your master to bed once and for all.
Check the booster, there are plenty of place for instructions, SSBC is a good source.
Check the length of the brake pedal rod for proper length. This is important. If the rod is too long, you may have a damaged diaphragm in the booster.
Check each wheel for leaks in the brake lines/calipers, etc.
You asked about stainless hoses on the rear. Yes, even though the rear brakes are 30% of your stopping power, I want all 30%, not 2 or 10 of 10%, I want all 30%. Rubber hoses will expand.
Just for giggles, I'd check each steel factory line also. Probably good, but I'd check for my piece of mind.
You should have a good handle on your brake problem by now.
I'm in the middle of this right now, 4 new loaded calipers, new cross drilled rotors on all 4 corners, stainless lines on all 4 also, new booster and master, all the steel factory lines have been checked. With my son's help today after eating, we have come to the conclusion that that "new" booster is bad. And, to be 100% honest, it may have been my fault. We'll tear into it Sat and see.
Good luck, brakes are a big thing out on the roads
Check the master cylinder, it would be very favorable to check brake pressures, if at all possible. That will put any myths about your master to bed once and for all.
Check the booster, there are plenty of place for instructions, SSBC is a good source.
Check the length of the brake pedal rod for proper length. This is important. If the rod is too long, you may have a damaged diaphragm in the booster.
Check each wheel for leaks in the brake lines/calipers, etc.
You asked about stainless hoses on the rear. Yes, even though the rear brakes are 30% of your stopping power, I want all 30%, not 2 or 10 of 10%, I want all 30%. Rubber hoses will expand.
Just for giggles, I'd check each steel factory line also. Probably good, but I'd check for my piece of mind.
You should have a good handle on your brake problem by now.
I'm in the middle of this right now, 4 new loaded calipers, new cross drilled rotors on all 4 corners, stainless lines on all 4 also, new booster and master, all the steel factory lines have been checked. With my son's help today after eating, we have come to the conclusion that that "new" booster is bad. And, to be 100% honest, it may have been my fault. We'll tear into it Sat and see.
Good luck, brakes are a big thing out on the roads
11-24-2016, 09:08 PM
#24
They lock up easier, due to using the power steering pump for the pressure. I had thought about it, but too much money for me, and too much work to make it fit on my big block 69....
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resdoggie (11-25-2016)
11-24-2016, 10:17 PM
#26
Tech Contributor
Member Since: Jun 2004
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The only things that will stop your car quicker are stickier tires or reduced vehicle weight. The boost/assist system just reduces the needed pedal pressure so your wife doesn't break a heel when she borrows your car.
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resdoggie (11-25-2016)
11-25-2016, 10:50 AM
#27
Instructor
Thread Starter
I read this entire thread...and I will add this.
YES...many members are correct.
1.) Bad or old dirty brake fluid DOES effect the crispness of your brakes. And what might amaze people that even if they pressure bleed there system ( or whatever method they choose)..it is still possible that the brakes may still be a bit spongy. And this is because if anyone has ever removed the valve/piston of the master cylinder and see how much sludge can build up in that circuit...there is no wonder why the brakes may still feel spongy.
2.) Brake hoses being bad.
3.) Air still in the system.
4.) The power booster having an internal leak that caused the idle to drop when you press on the pedal. YES...it is normal to hear a 'whoosh' when you press the brake pedal with a factory booster.
What I am more concerned with is IF when you press the brake pedal it is hard as a rock and takes everything you got to try to stop the car. That for me is either an instant indication that the booster is BAD....OR...as I have seen...the check valve in the front of the booster is BAD.and does not want o flow freely.
5.) A bad master cylinder can cause this due to possibly attaching pressure a pressure gauge at the caliper ares and checking that the master cylinder is able to apply the correct pressure. I have found this in many Corvette and think goodness I have the gauge to test this.
Lastly...I can say that there is no comparison in a hydra-boost and a factory booster. Just like manual brakes to a power brake system. They are two completely different systems. And I am only commenting from two systems I installed that when done would amaze you. Literally 'day and night'.
DUB
YES...many members are correct.
1.) Bad or old dirty brake fluid DOES effect the crispness of your brakes. And what might amaze people that even if they pressure bleed there system ( or whatever method they choose)..it is still possible that the brakes may still be a bit spongy. And this is because if anyone has ever removed the valve/piston of the master cylinder and see how much sludge can build up in that circuit...there is no wonder why the brakes may still feel spongy.
2.) Brake hoses being bad.
3.) Air still in the system.
4.) The power booster having an internal leak that caused the idle to drop when you press on the pedal. YES...it is normal to hear a 'whoosh' when you press the brake pedal with a factory booster.
What I am more concerned with is IF when you press the brake pedal it is hard as a rock and takes everything you got to try to stop the car. That for me is either an instant indication that the booster is BAD....OR...as I have seen...the check valve in the front of the booster is BAD.and does not want o flow freely.
5.) A bad master cylinder can cause this due to possibly attaching pressure a pressure gauge at the caliper ares and checking that the master cylinder is able to apply the correct pressure. I have found this in many Corvette and think goodness I have the gauge to test this.
Lastly...I can say that there is no comparison in a hydra-boost and a factory booster. Just like manual brakes to a power brake system. They are two completely different systems. And I am only commenting from two systems I installed that when done would amaze you. Literally 'day and night'.
DUB
DUB,
let me try and reply to each of your statements.
1.) Bad or old dirty brake fluid DOES effect the crispness of your brakes. And what might amaze people that even if they pressure bleed there system ( or whatever method they choose)..it is still possible that the brakes may still be a bit spongy. And this is because if anyone has ever removed the valve/piston of the master cylinder and see how much sludge can build up in that circuit...there is no wonder why the brakes may still feel spongy.
At this point I'm almost certain more than a gallon of DOT 3 brake fluid has been flushed through the lines.
2.) Brake hoses being bad.
The front are new stainless hoses and I have new ones on order for the rear. The plan is to install new rear hoses next week and bleed the brakes -- again.
3.) Air still in the system.
This is always a possibility but I've done just about everything I know to flush all the air out -- speed bleeders included.
What I am more concerned with is IF when you press the brake pedal it is hard as a rock and takes everything you got to try to stop the car. That for me is either an instant indication that the booster is BAD....OR...as I have seen...the check valve in the front of the booster is BAD.and does not want o flow freely.
The brake pedal is not hard it's soft and travels excessively before solid braking occurs. I understand this can be subjective, but it just seems excessive to me.
5.) A bad master cylinder can cause this due to possibly attaching pressure a pressure gauge at the caliper ares and checking that the master cylinder is able to apply the correct pressure. I have found this in many Corvette and think goodness I have the gauge to test this.
I agree. This was the first item I replaced. I bought a new master cylinder from NAPA. I've seen others online that claim to be better but I went with a new version of the OEM type.
What would be considered good brake caliper pressure at the front and rear?
Last edited by ONeill202; 11-25-2016 at 10:54 AM.
11-25-2016, 12:12 PM
#29
Had a 1976 L-82, 4-sp
Member Since: Mar 2011
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Royal Canadian Navy
Not sure how many pumps of the MV you need but a quicker way may be to "T" in a vacuum gauge before the check valve, start engine, clamp hose between "T" and intake manifold port to seal the hose with the engine still running and see if the vacuum holds.
11-25-2016, 01:02 PM
#30
Team Owner
All of these ideas are valid. But, doing all this 'stuff' when the OP has disintengrating rubber hoses on his rear calipers is a total waste of time. Let the guy replace those hoses...THEN see how it operates.
P.S. Any 'properly' operating C3 brake system will lock up the wheels with no problem. Generally speaking, putting hydroboost on a street car is just overkill, unless it is installed to counteract another undiscovered problem. Manual brakes on a C3 will lock up the brakes just as well as power brakes. The only thing power brakes do is reduce the pedal effort used to apply them. THERE IS NO DIFFERENCE IN BRAKING EFFECTIVENESS. Same would be true of installing hydroboost. Once you are able to lock the brakes up, improving that process is just making it easier to do so.
Save your money and find the problem[s] in your system.
P.S. Any 'properly' operating C3 brake system will lock up the wheels with no problem. Generally speaking, putting hydroboost on a street car is just overkill, unless it is installed to counteract another undiscovered problem. Manual brakes on a C3 will lock up the brakes just as well as power brakes. The only thing power brakes do is reduce the pedal effort used to apply them. THERE IS NO DIFFERENCE IN BRAKING EFFECTIVENESS. Same would be true of installing hydroboost. Once you are able to lock the brakes up, improving that process is just making it easier to do so.
Save your money and find the problem[s] in your system.
Last edited by 7T1vette; 11-25-2016 at 01:06 PM.
11-25-2016, 08:01 PM
#31
All of these ideas are valid. But, doing all this 'stuff' when the OP has disintengrating rubber hoses on his rear calipers is a total waste of time. Let the guy replace those hoses...THEN see how it operates.
P.S. Any 'properly' operating C3 brake system will lock up the wheels with no problem. Generally speaking, putting hydroboost on a street car is just overkill, unless it is installed to counteract another undiscovered problem. Manual brakes on a C3 will lock up the brakes just as well as power brakes. The only thing power brakes do is reduce the pedal effort used to apply them. THERE IS NO DIFFERENCE IN BRAKING EFFECTIVENESS. Same would be true of installing hydroboost. Once you are able to lock the brakes up, improving that process is just making it easier to do so.
Save your money and find the problem[s] in your system.
P.S. Any 'properly' operating C3 brake system will lock up the wheels with no problem. Generally speaking, putting hydroboost on a street car is just overkill, unless it is installed to counteract another undiscovered problem. Manual brakes on a C3 will lock up the brakes just as well as power brakes. The only thing power brakes do is reduce the pedal effort used to apply them. THERE IS NO DIFFERENCE IN BRAKING EFFECTIVENESS. Same would be true of installing hydroboost. Once you are able to lock the brakes up, improving that process is just making it easier to do so.
Save your money and find the problem[s] in your system.
12-03-2016, 02:09 PM
#32
Instructor
Thread Starter
Well here's the update...
I replaced the rear brake lines and unfortunately I saw no improvement in braking performance. I've noticed that they seem to get better the longer I drive the car? I have not tested the booster yet, I'm still waiting for the Mityvac I ordered.
I replaced the rear brake lines and unfortunately I saw no improvement in braking performance. I've noticed that they seem to get better the longer I drive the car? I have not tested the booster yet, I'm still waiting for the Mityvac I ordered.
Last edited by ONeill202; 12-03-2016 at 02:10 PM.
12-08-2016, 05:40 PM
#33
Instructor
Thread Starter
"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.
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.
I did a vacuum test and the needle never moved. I guess we can say the brake booster is bad?
12-08-2016, 08:59 PM
#34
Melting Slicks
More often than not these Threads of soft and spongy brakes always start out with somebody replacing the Master Cylinder with an auto parts supplied replacement. Was the replacement intended for a Manual or Power Brake car ? Was it for an early or late C3 ? Or was it some sort of universal GM replacement. There is some sort of washer that goes in between the brake rod and the master cylinder piston did it get moved from the old one to the new one ? I assume the Parts guy asked all of these same questions.
When You move the brake peddle how much of its travel is used up before anything starts to happen ? Did You bleed the master before You installed it in the Car ? If your Booster is completely blown out and You stand on the brakes You will still lock them up with a properly working system. Its not like GM sold a non power brake car that couldn't stop. If Your Peddle is functioning correctly then I would re bleed the master. You will need to run some short lines right back into the reservoirs and watch for bubbles. Once done put some caps on the end of the short lines and you will of Hydraulically locked the system. Now press the Brake Peddle, if its not hard and firm then the problem lies between the brake peddle and Caps. Nothing to do with lines, hoses or calipers.
When You move the brake peddle how much of its travel is used up before anything starts to happen ? Did You bleed the master before You installed it in the Car ? If your Booster is completely blown out and You stand on the brakes You will still lock them up with a properly working system. Its not like GM sold a non power brake car that couldn't stop. If Your Peddle is functioning correctly then I would re bleed the master. You will need to run some short lines right back into the reservoirs and watch for bubbles. Once done put some caps on the end of the short lines and you will of Hydraulically locked the system. Now press the Brake Peddle, if its not hard and firm then the problem lies between the brake peddle and Caps. Nothing to do with lines, hoses or calipers.
12-09-2016, 02:01 PM
#35
Instructor
Thread Starter
More often than not these Threads of soft and spongy brakes always start out with somebody replacing the Master Cylinder with an auto parts supplied replacement. Was the replacement intended for a Manual or Power Brake car ? Was it for an early or late C3 ? Or was it some sort of universal GM replacement. There is some sort of washer that goes in between the brake rod and the master cylinder piston did it get moved from the old one to the new one ? I assume the Parts guy asked all of these same questions.
When You move the brake peddle how much of its travel is used up before anything starts to happen ? Did You bleed the master before You installed it in the Car ? If your Booster is completely blown out and You stand on the brakes You will still lock them up with a properly working system. Its not like GM sold a non power brake car that couldn't stop. If Your Peddle is functioning correctly then I would re bleed the master. You will need to run some short lines right back into the reservoirs and watch for bubbles. Once done put some caps on the end of the short lines and you will of Hydraulically locked the system. Now press the Brake Peddle, if its not hard and firm then the problem lies between the brake peddle and Caps. Nothing to do with lines, hoses or calipers.
When You move the brake peddle how much of its travel is used up before anything starts to happen ? Did You bleed the master before You installed it in the Car ? If your Booster is completely blown out and You stand on the brakes You will still lock them up with a properly working system. Its not like GM sold a non power brake car that couldn't stop. If Your Peddle is functioning correctly then I would re bleed the master. You will need to run some short lines right back into the reservoirs and watch for bubbles. Once done put some caps on the end of the short lines and you will of Hydraulically locked the system. Now press the Brake Peddle, if its not hard and firm then the problem lies between the brake peddle and Caps. Nothing to do with lines, hoses or calipers.
Was the replacement intended for a Manual or Power Brake car ?
Power Brake
Was it for an early or late C3 ? Or was it some sort of universal GM replacement.
Early C3
There is some sort of washer that goes in between the brake rod and the master cylinder piston did it get moved from the old one to the new one ?
I don't recall seeing a washer but it has been some time since I replaced the master cylinder
I assume the Parts guy asked all of these same questions.
The parts guy didn't ask any questions other than the year, make, and model.
When You move the brake peddle how much of its travel is used up before anything starts to happen ?
About half way
Did You bleed the master before You installed it in the Car ?
I had someone install it so I'm not sure what they did. However, to eliminate the possibility of having air in the master cylinder I have since bleed it.
Once done put some caps on the end of the short lines and you will of Hydraulically locked the system
I like this idea. Where can I find these locks?
12-09-2016, 07:33 PM
#36
The is the same result I got from my bad brake booster. Now the new booster required many many pumps to get to 15 inches of vacuum. But showed a few inches within 100 pumps. Also check the check valve to make sure it works as well. Check valve should allow air movement only 1 way.
12-09-2016, 07:56 PM
#37
Race Director
Did you replace the steel braided lines leading to the brake calipers or add steel braided lines to anywhere else in the system? Steel braided lines can expand under pressure and can cause a brake system to feel like there is air in the lines and give the spongy feel.
Last edited by OldCarBum; 12-09-2016 at 07:56 PM.
12-09-2016, 08:03 PM
#38
Instructor
Thread Starter
12-09-2016, 10:58 PM
#39
Race Director
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.
12-10-2016, 12:26 AM
#40
Drifting
Pu**ies...LOL.