Vac Power brakes soft

[gsjimmy1]

Working on the Stage 1 conversion and have run into a strange issue. I've replaced the braking systen, except for the power booster. Bled out the brakes and got out the air in the lines.

Have a hard pedel without the engine running, but if I start the car, goes to the floor with limited braking power. The original engine was a hot air 231. The car did this with both the 454 and with the Stage 1 455. Since everything has been tried I'm suspecting that the booster is incorrect and/or defective due to the stronger vac. signal of a larger engine.

Any ideas floating around? I am getting discouraged on this but will keep trying til its fixed.

 

[1quick6]

What master cylinder do you have on the car?

 

[gsjimmy1]

Master cyl

It is the original size master for a 231 hot air turbo (new replacement with the BBC).

 

[1quick6]

This 231 hot air car had hydroboost before, correct? Is your vacuum booster off of a normally aspirated G-body?

 

[gsjimmy1]

brakes

Was always vac assist. With a small booster. The GS has a bigger booster (1969) But my old MC SS was set up the same as this car.

 

[278cikiller]

Brakes

I have the same problem, I have a 82 N/A car did the switch to stage motor andi have a soft padel, Change both power booster and same deal soft, Iam wonding now if its the proportioning vavle that doing it.

 

[gsjimmy1]

Hmmm, there's an idea

Not sure on the prop valve, but I have not changed it out either. I have access to several N/A Malibu's & Regals. I'm starting to think about going to manual brakes.

 

[Red Regal T]

I have the same problem, I have a 82 N/A car did the switch to stage motor andi have a soft padel, Change both power booster and same deal soft, Iam wonding now if its the proportioning vavle that doing it.

Perhaps your engine vacuum is on the low side in your Stage Motor, and that's what's causing the soft pedal.

 

[Red Regal T]

Working on the Stage 1 conversion and have run into a strange issue. I've replaced the braking systen, except for the power booster. Bled out the brakes and got out the air in the lines.

Have a hard pedel without the engine running, but if I start the car, goes to the floor with limited braking power. The original engine was a hot air 231. The car did this with both the 454 and with the Stage 1 455. Since everything has been tried I'm suspecting that the booster is incorrect and/or defective due to the stronger vac. signal of a larger engine.

Any ideas floating around? I am getting discouraged on this but will keep trying til its fixed.

Sounds more like a master cylinder issue than a booster issue. Bad boosters cause hard pedals, not an easy push to the floor. Change the master cylinder.

 

[278cikiller]

Brake

Perhaps your engine vacuum is on the low side in your Stage Motor, and that's what's causing the soft pedal.

I had the same set in a 87 N/A regal and it was fine.

 

[Red Regal T]

I had the same set in a 87 N/A regal and it was fine.

Well, sure. 87 NA Regals may not get out of their own way, but they have killer vacuum. How about your stage motor?

 

[gsjimmy1]

Brakes....

OK, the motor is not the issue here. The car did this with both a 454 & 455, also simular with a 350. The master is new, hoses are new. Tonight I'll start at the line I just changed (dr front) and get out the air there first. Then bleed the car out normally.

THe 455 Stage 1 came out of my 1969 GS California. No braking problems with that car (disc/drum set-up). Everyone is saying a failing booster gives a hard pedel, which is not what I have. So must be pulling air somewhere.

I have not found any wet lines/hoses that would indicate this is leaking. Is it possible that the prop valve is at issue? I did add 224 more cubic inches which would have a different signal (12-14 lb range with stock stage 1 cam).

I know that I'll get some air up front as that was opened, but there should be little air in the rear of the system. I'll let everyone know what I find.

 

[1quick6]

You say you are getting plenty of assist, so it doesn't seem to be vacuum related. Assuming you bench bled the master, I would have to agree that you are introducing air into the system somewhere. When you attempt to re-bleed the brakes, are you seeing additional air bubbles that seemingly weren't there before in previous bleeding attempts? Air compresses quite well, so if your pedal is going to the floor with plenty of assist available, it would be a large amt of air in the system or an internal leak in the master cylinder. Just because it is new doesn't mean it's good.