Brake System Help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

CCCC · 10-19-2007, 01:59 AM

The brakes on this 1972 C30 work, and pedal is quite firm, but it feels as though the power assist is not what it should be. Braking feels more like regular (non-power) effect with no real "grab" even with a quick/hard pedal application.

There is good vacuum to the booster and the grommet/check valve seem to be functioning fine - 5 minutes after engine shutdown I get a significant sucking effect when the valve is pulled from the booster - so it is holding vacuum.

Fluid levels good on both sides of the master cylinder and no apparent leaks.

Questions:
Can the booster drum be holding vacuum and yet still not do its proper assist work? How does one check the function of the booster action itself?

Might it be that only one side of the master cylinder is working - giving only 2 wheel brakes - and causing the weak effect even with what may be good booster function? Other than the visible test for turbulence with the lid off the reservoir, or removing a line connection and looking for the "squirt", how to check the MC function on both sides?

What else?

Any insights will be much appreciated.

CCCC

10-19-2007, 01:59 AM	#1
CCCC Registered User Join Date: Mar 2007 Location: San Pedro River, SE Arizona Posts: 734	Brake System Help The brakes on this 1972 C30 work, and pedal is quite firm, but it feels as though the power assist is not what it should be. Braking feels more like regular (non-power) effect with no real "grab" even with a quick/hard pedal application. There is good vacuum to the booster and the grommet/check valve seem to be functioning fine - 5 minutes after engine shutdown I get a significant sucking effect when the valve is pulled from the booster - so it is holding vacuum. Fluid levels good on both sides of the master cylinder and no apparent leaks. Questions: Can the booster drum be holding vacuum and yet still not do its proper assist work? How does one check the function of the booster action itself? Might it be that only one side of the master cylinder is working - giving only 2 wheel brakes - and causing the weak effect even with what may be good booster function? Other than the visible test for turbulence with the lid off the reservoir, or removing a line connection and looking for the "squirt", how to check the MC function on both sides? What else? Any insights will be much appreciated. CCCC __________________ CCCC 67 Sting Ray Coupe 327 4sp; 68 K10 Suburban 327 4sp; 69 K20 Lifted 383 4sp; 69 C80 Fire Truck 478 V6 5sp/2sp; 69 C20 Longhorn 327 4sp; 70 C30 Wrecker 350 4sp; 70 C30 Flat Bed 350 4sp; 71 C20 LWB 350 4sp; 72 K5 Blazer 350 4sp; 72 C30 Flat Bed Gooseneck Hauler with sleeper 350/TH400; 72 C20 Longhorn 402 4sp; 52 Mack LTL Supercharged Cummins 5sp x 3sp; 01 Dodge 5.9 HO Cummins 6spd; 02 Safari Trek 2430 8.1 Vortec on Workhorse Chassis; 03 Silverado 2500 HD 4wd Duramax/Allison Moved but still in the family 70 C20 Custom Camper 350/TH350; 72 K5 Blazer CST Highlander 350/TH350 Recently sent to new homes 72 C30 MoHome 402 4sp; 72 K5 Blazer Conv 350 4sp; 75 GMC 6000 Aerial 350 w Allison; 72 GMC 3500 Utility 350 4sp; 70 GMC 3500, 350 4sp



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