V1 Super soft brakes

[Kenny123]

Hey guys I bled my brakes and they bled great. Have solid pressure when the car is off. As soon as I turn the car on however and the power brakes are active it is so soft and squishy. Pedal travel is far too however the brakes work super well at the top of the pedal throw. Anyone else have super soft squishy brakes? Is that the nature of the beast?

 

[Ross]

I noticed that I was only using the first half of the brake pedal too.
I added a
249 Brake booster vacuum regulator to control wheel lockup
and now I can use the whole brake pedal.

Basically this light Goblin doesn't need as big and powerful of a brake booster.

 

[Kenny123]

I noticed that I was only using the first half of the brake pedal too.
I added a
249 Brake booster vacuum regulator to control wheel lockup
and now I can use the whole brake pedal.

Basically this light Goblin doesn't need as big and powerful of a brake booster.

Is your pedal super soft with the car running too?

 

[Ross]

No, I haven't noticed that. I did vacuum bleed and then pressure bled (by pumping the brake pedal) the system to get all the air out.
Sounds like you still have some air in it.

 

[ctuinstra]

Yep, you still have air in the lines or something. Stupid question, do you have all of the bleeders facing up? I have to ask, the calipers have been installed backwards and they end up facing down and you'll never get all the air out.

Also, do you have stainless steel lines or the old factory hoses?

Without the booster assist, the pedal may feel solid with air still in the lines. The booster just makes it more noticeable.

 

[Kenny123]

No, I haven't noticed that. I did vacuum bleed and then pressure bled (by pumping the brake pedal) the system to get all the air out.
Sounds like you still have some air in it.

Yah I vacuum bled too but maybe just need to do more of that. Thanks for the help

 

[Kenny123]

Yep, you still have air in the lines or something. Stupid question, do you have all of the bleeders facing up? I have to ask, the calipers have been installed backwards and they end up facing down and you'll never get all the air out.

Also, do you have stainless steel lines or the old factory hoses?

Without the booster assist, the pedal may feel solid with air still in the lines. The booster just makes it more noticeable.

Yah I did do the bleeder facing up thank you!!

 

[Desert Sasqwatch]

There are a few different ways to improve the brakes, most of which reduce the power assist and or the line pressure to the calipers. As Ross stated, the easiest is to reduce the vacuum on the brake booster with the vacuum regulator. It must be a vacuum regulator and not a pressure regulator - which will not work for vacuum. I have one to install to fine tune my system in conjunction with other modifications (below).
Another way is to reduce the size and assist pressure by using a smaller brake booster. I've replaced the 10 inch dual diaphragm Cobalt booster with a 7 inch single diaphragm booster, shorter in length and diameter, and almost 2 pounds lighter. It's a 'universal' fit so the Goblin mounting bracket requires modification.

Desert Sasqwatch #155 Track (mods) - 08 SS/TC crate LNF F40

Well I did it, I pulled the trigger and have placed my order. I had to renegotiate with the accountant/wife and rehash the benefit of building a Goblin - versus building something else like a '69 Camaro (big $$$). I got the thumbs up and hit the purchase button. So I will be getting the TC...

dfkitcar.com

Additionally the brake master cylinder can be increased in diameter to reduce the line pressure at the caliper. The Cobalt master cylinder has a metric piston about 3/4 inch diameter. Replacing with a master cylinder of 1 1/8 inches will reduce the line pressure by about 25%. I purchased a Chevy Astro master cylinder that bolts directly to the 7 inch booster.

Desert Sasqwatch #155 Track (mods) - 08 SS/TC crate LNF F40

220 new holes. Added ..... hummm #40. Removed #20. Love the classic Batman and Robin, wasn't laughing at your guesses. ;)

dfkitcar.com

My mods are being done to prove out they will work as an alternative to the stock donor parts.

 

[Mayor West]

I've gone through 2 big bottles of DOT fluid and my brakes are still squishy.... feel super solid with the car off, but goes almost to the floor with it on. As far as I can tell, there's still air in the lines.... all my brake nibs are pointing up and synched down very tight... I have an air compressed vacuum bleeder and as I'm using it I see a consistent dribble of air bubbles through the line, that's almost never ending... I am probably doing this wrong, I haven't used this tool in years.

 

[Waterdriver]

Might check for any brake fluid weeping from the back side if the master cylinder, where the pedal pushrod enters.
If theres any fluid there, replace the master cylinder.

 

[Anks329]

I've gone through 2 big bottles of DOT fluid and my brakes are still squishy.... feel super solid with the car off, but goes almost to the floor with it on. As far as I can tell, there's still air in the lines.... all my brake nibs are pointing up and synched down very tight... I have an air compressed vacuum bleeder and as I'm using it I see a consistent dribble of air bubbles through the line, that's almost never ending... I am probably doing this wrong, I haven't used this tool in years.

Check to make sure all the connections are tight between the hard lines and the Ts. I thought I had tightened them down, but was having problems with the brakes. I loosened the connections slightly and then really cranked down on them and got it tighter. Bleeding the brakes after doing this fixed the problem entirely.

 

[Ross]

Adding a brake booster will always make your pedal feel more squishy, as it amplifies your power... Drive it a while, and see if it gets worse, or if it is working normally.

 

[Lonny]

Ross is correct, when all of the brake pads are new there is going to be a lot of deflection until everything gets worn flat. If the brakes feel like they are stopping safely, it is best to give the brakes some time to wear in.
While parked with the engine running the brakes will feel spongy but while driving they should feel reliable.

 

[Gtstorey]

I've gone through 2 big bottles of DOT fluid and my brakes are still squishy.... feel super solid with the car off, but goes almost to the floor with it on. As far as I can tell, there's still air in the lines.... all my brake nibs are pointing up and synched down very tight... I have an air compressed vacuum bleeder and as I'm using it I see a consistent dribble of air bubbles through the line, that's almost never ending... I am probably doing this wrong, I haven't used this tool in years.

The problem with the vacuum style bleeders is that they can pull air from around the bleeder threads or at the hose connection to the bleeder. You might try a little teflon tape around the bleeder threads and safety wire at the hose connection to make sure the air bubbles are coming from within the system.

 

[ctuinstra]

Ross is correct, when all of the brake pads are new there is going to be a lot of deflection until everything gets worn flat. If the brakes feel like they are stopping safely, it is best to give the brakes some time to wear in.
While parked with the engine running the brakes will feel spongy but while driving they should feel reliable.

Technically there is bedding process that should be followed the first time using the brakes but it’s kind of hard to get the brakes up to a good temp (on public roads) to effectively to bed them properly.

 

[ctuinstra]

The manual brakes on my ‘68 Vette are rock hard all the time. There’s like a half inch of pedal. Of course, it takes a heck of a lot of pressure on the pedal to stop that car. But with the racing pads, once the get warmed up, it’s almost like having power brakes.

 

[Mayor West]

The problem with the vacuum style bleeders is that they can pull air from around the bleeder threads or at the hose connection to the bleeder. You might try a little teflon tape around the bleeder threads and safety wire at the hose connection to make sure the air bubbles are coming from within the system.

Yeah I'm pretty sure this is my problem (in addition to seepage at almost every port)... I'm going to have to just bleed them manually.

 

[Goblin Graber]

I have used a Phoenix Systems RFI For over a decade. Best brake bleeder I ever bought. You fill the brakes from the bleeder. I do a lot of motorcycle work and that has made it so I can swap brake lines and a set of dual disc front calipers in 15 minutes total.

 

[Kenny123]

I think I'm just being too picky. I think I may be bled. I can touch the pedal and the brake are strong. Just feels so easy to push.

 

[Goblin Graber]

I think I'm just being too picky. I think I may be bled. I can touch the pedal and the brake are strong. Just feels so easy to push.

Did you reuse the front rotors in the back? If so Lonny could be right and you just need to get the pads worn into the old rotor. New pads on old rotors feels soft for a hot minute.