Replaced power booster and MC. Pedal soft now - The 1947 - Present Chevrolet & GMC Truck Message Board Network

CST10 · 04-29-2019, 09:37 PM

Well ol Samson got a new brake booster (stock) and master cylinder. Stock 4 drum brake system. Bench bled till no bubbles. Installed and hooked up lines. Bled from the farthest to the closest ran about 2 quarts through the system until clear fluid at each point.

Brake pedal still seems soft and sinks further to the floor than before. Way softer than before and goes almost to the floor before it stops. Also brakes don’t lock up like they use too.

Old MC leaking out the back end seal and old booster leaking was the reason for replacement.

Checked booster for leakage, nope. Checked vacuum, at 18hg, nope. Checked all bleeder points, no leakage, nope.

Guess I’ll try to bleed the system again.........any ideas?

**AussieinNC** · 04-29-2019, 09:42 PM

Is the bore diameter of the new master the same as the old?

Is the size of the power booster unit the same as old?

Is the pivot point the same as the old?

Are the brakes adjusted correctly?

Can you pump up the pedal?

Does the pedal drop when pumped up and then the engine is started?

External · 04-29-2019, 10:20 PM

Subscribed

enduroride · 04-30-2019, 07:40 AM

Quote:

Originally Posted by CST10

Well ol Samson got a new brake booster (stock) and master cylinder. Stock 4 drum brake system. Bench bled till no bubbles. Installed and hooked up lines. Bled from the farthest to the closest ran about 2 quarts through the system until clear fluid at each point.

Brake pedal still seems soft and sinks further to the floor than before. Way softer than before and goes almost to the floor before it stops. Also brakes don’t lock up like they use too.

Old MC leaking out the back end seal and old booster leaking was the reason for replacement.

Checked booster for leakage, nope. Checked vacuum, at 18hg, nope. Checked all bleeder points, no leakage, nope.

Guess I’ll try to bleed the system again.........any ideas?

Neil, try that bleeder system that Stevens dad posted on the club website.
Wade

CST10 · 05-02-2019, 11:01 PM

Yeah, I’m try that system out. Hopefully it’s just trapped air in the master. Had this issue quite a few years back one time. Took me two times bench bleeding it.

CST10 · 05-02-2019, 11:03 PM

Quote:

Originally Posted by AussieinNC

Is the bore diameter of the new master the same as the old?

Is the size of the power booster unit the same as old?
Yes it is.

Is the pivot point the same as the old?
No change

Are the brakes adjusted correctly?
Yes

Can you pump up the pedal?
Yes

Does the pedal drop when pumped up and then the engine is started?
Yes, so the booster is good.

See above

Mbeef61 · 05-02-2019, 11:15 PM

Are the pushrod depths the same in both master cylinders? I know there is a deep and a shallow one. A deep one where there should be a shallow would make it so it doesn’t brake until the pedal is to the floor

CST10 · 05-02-2019, 11:26 PM

Quote:

Originally Posted by Mbeef61

Are the pushrod depths the same in both master cylinders? I know there is a deep and a shallow one. A deep one where there should be a shallow would make it so it doesn’t brake until the pedal is to the floor

That is an excellent point. I will compare them tomorrow when I pull the new one back off to try a second d bench bleed. Still got the old one on the table.

Thanks. Had not even thought of this as a potential issue.

Mbeef61 · 05-03-2019, 01:13 AM

I think one is for power brakes and one is for manual but when at the parts counter there is so specification on it. Seems like it’s luck of the draw

volksworld · 05-03-2019, 04:06 PM

i believe the manual is a one inch bore and the power is larger...i just dont remember if its 1 1/16 or 1 1/8

04-29-2019, 09:37 PM	#1
CST10 Registered User Join Date: Sep 2013 Location: Gonzales, La Posts: 1,441	Replaced power booster and MC. Pedal soft now Well ol Samson got a new brake booster (stock) and master cylinder. Stock 4 drum brake system. Bench bled till no bubbles. Installed and hooked up lines. Bled from the farthest to the closest ran about 2 quarts through the system until clear fluid at each point. Brake pedal still seems soft and sinks further to the floor than before. Way softer than before and goes almost to the floor before it stops. Also brakes don’t lock up like they use too. Old MC leaking out the back end seal and old booster leaking was the reason for replacement. Checked booster for leakage, nope. Checked vacuum, at 18hg, nope. Checked all bleeder points, no leakage, nope. Guess I’ll try to bleed the system again.........any ideas? __________________ MyToys: Goldilocks the "Ol School Survivor" 1968 C10, SWB Stepside, 08/15 TOTM, 250 CI 6 cylinder, 3 on the tree, 3.73 rear, 3/5 static drop, 23,500 original miles. Samson the 1970 CST10, LWB, 462Ci, Turbo 350 tranny, 3.08 rear gear, PB, PS, A/C, AM/FM, 2/4 Drop. Brutus the 1998 Camaro Z28, 33,500 original miles, LS1, 519 RWHP/497 RWTQ. Member of the Louisiana Classic Truck Club, LCTC Member of the Louisiana C10 Club Member of the Baton Rouge Drifters Car Club

04-29-2019, 09:42 PM	#2
AussieinNC Moderator Join Date: Jun 2017 Location: Cherryville, NC Posts: 2,204	Re: Replaced power booster and MC. Pedal soft now Is the bore diameter of the new master the same as the old? Is the size of the power booster unit the same as old? Is the pivot point the same as the old? Are the brakes adjusted correctly? Can you pump up the pedal? Does the pedal drop when pumped up and then the engine is started? __________________ Family and country before all others... 2006 Chevy Silverado (Daily Driver) 2012 Chevy Equinox

04-29-2019, 10:20 PM	#3
External Registered User Join Date: Jun 2018 Location: Louisiana Posts: 185	Re: Replaced power booster and MC. Pedal soft now Subscribed __________________ '72 Chevy Custom Deluxe Highlander. Med Olive/White 350/200 ps,pb and Air Conditioning!

05-02-2019, 11:01 PM	#5
CST10 Registered User Join Date: Sep 2013 Location: Gonzales, La Posts: 1,441	Re: Replaced power booster and MC. Pedal soft now Yeah, I’m try that system out. Hopefully it’s just trapped air in the master. Had this issue quite a few years back one time. Took me two times bench bleeding it. __________________ MyToys: Goldilocks the "Ol School Survivor" 1968 C10, SWB Stepside, 08/15 TOTM, 250 CI 6 cylinder, 3 on the tree, 3.73 rear, 3/5 static drop, 23,500 original miles. Samson the 1970 CST10, LWB, 462Ci, Turbo 350 tranny, 3.08 rear gear, PB, PS, A/C, AM/FM, 2/4 Drop. Brutus the 1998 Camaro Z28, 33,500 original miles, LS1, 519 RWHP/497 RWTQ. Member of the Louisiana Classic Truck Club, LCTC Member of the Louisiana C10 Club Member of the Baton Rouge Drifters Car Club

05-02-2019, 11:15 PM	#7
Mbeef61 Registered User Join Date: Jun 2009 Location: Portland - OR Posts: 243	Re: Replaced power booster and MC. Pedal soft now Are the pushrod depths the same in both master cylinders? I know there is a deep and a shallow one. A deep one where there should be a shallow would make it so it doesn’t brake until the pedal is to the floor Attached Images

05-03-2019, 01:13 AM	#9
Mbeef61 Registered User Join Date: Jun 2009 Location: Portland - OR Posts: 243	Re: Replaced power booster and MC. Pedal soft now I think one is for power brakes and one is for manual but when at the parts counter there is so specification on it. Seems like it’s luck of the draw

05-03-2019, 04:06 PM	#10
volksworld Registered User Join Date: Apr 2011 Location: formerly NY currentlyNC Posts: 390	Re: Replaced power booster and MC. Pedal soft now i believe the manual is a one inch bore and the power is larger...i just dont remember if its 1 1/16 or 1 1/8 __________________ 1970 short step c10 leaf spring 454



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