72 K-10 Brake System Problems - The 1947 - Present Chevrolet & GMC Truck Message Board Network

azsmokey · 10-09-2011, 02:58 PM

I would appreciate any ideas, feedback or suggestions on this matter. A little about the build and setup before I get into the specifics.

The truck is a 1972 Chevy K-10.
-2003 Silverado SS drivetrain
-6.0L LQ9 motor with Vortech supercharger
-4L65E trans
-NP205 T-case
-4 wheel disc brakes
-All new stainless brake lines
-8inch Dual Diaphragm Booster/Master/Combination valve setup from Right Stuff detailing via Summit http://www.summitracing.com/parts/RSD-J85315672/
-

Our problem is with brake pressure. After setup and brake bleeding, there was barely enough brake to hold the vehicle in place while idling in drive. Initially, we did not bench bleed the master cylinder. I completed that yesterday, re-bled the system and the problem persists. I checked the vacuum and we are reading between 17 and 20 vacuum, both via the dash vac/boost gauge and a separate vacuum gauge. What am I missing?

azsmokey · 10-09-2011, 11:51 PM

Any ideas?...

dhaymaker · 10-10-2011, 12:01 AM

Try searching through the forums (particularly the '67 - '72) for a previous thread on this same issue. IIRC there was a reference to the rod running from the pedal to the booster/master cylinder relating to the reach, or travel. It's possible you actually are not seeing enough pedal travel, by virtue of the rod not having sufficient length.

I'll also look and see if I can locate it, or perhaps someone with experience with the issue can further advise you.

don

dhaymaker · 10-10-2011, 12:04 AM

azsmokey - Here's one of the threads...just don't stop reading when you hit the part about the vacuum, as you've indicated you're pulling a fair amount of vacuum...http://67-72chevytrucks.com/vboard/s...d.php?t=439261 Edit: Adding another URL to check... http://67-72chevytrucks.com/vboard/s...d.php?t=412779

stsalvage · 10-10-2011, 03:27 AM

the portioning valve could be stuck you might of got a master cylinder that was for drum brakes all the way around.But how now is the booster i went throw 3 boosters before i found one that worked.dose your fluid come out normal is there a blockage. in the line isone of the rubber lines culapsing

10-09-2011, 02:58 PM	#1
azsmokey Registered User Join Date: Dec 2007 Location: Glendale, AZ Posts: 156	72 K-10 Brake System Problems I would appreciate any ideas, feedback or suggestions on this matter. A little about the build and setup before I get into the specifics. The truck is a 1972 Chevy K-10. -2003 Silverado SS drivetrain -6.0L LQ9 motor with Vortech supercharger -4L65E trans -NP205 T-case -4 wheel disc brakes -All new stainless brake lines -8inch Dual Diaphragm Booster/Master/Combination valve setup from Right Stuff detailing via Summit http://www.summitracing.com/parts/RSD-J85315672/ - Our problem is with brake pressure. After setup and brake bleeding, there was barely enough brake to hold the vehicle in place while idling in drive. Initially, we did not bench bleed the master cylinder. I completed that yesterday, re-bled the system and the problem persists. I checked the vacuum and we are reading between 17 and 20 vacuum, both via the dash vac/boost gauge and a separate vacuum gauge. What am I missing?

10-09-2011, 11:51 PM	#2
azsmokey Registered User Join Date: Dec 2007 Location: Glendale, AZ Posts: 156	Re: 72 K-10 Brake System Problems Any ideas?...

10-10-2011, 12:01 AM	#3
dhaymaker Registered User Join Date: Jan 2006 Location: Peyton, CO Posts: 448	Re: 72 K-10 Brake System Problems Try searching through the forums (particularly the '67 - '72) for a previous thread on this same issue. IIRC there was a reference to the rod running from the pedal to the booster/master cylinder relating to the reach, or travel. It's possible you actually are not seeing enough pedal travel, by virtue of the rod not having sufficient length. I'll also look and see if I can locate it, or perhaps someone with experience with the issue can further advise you. don __________________ don "The DRBMan" 2014 Audi A4 (The Wife's Daily Driver) 2017 HD Ultra (The Cruiser) 2003 HD Fatboy (The Ride) 2001 Chevy Suburban (Another back up!!) For the first time in forever, not a single 67-72 Chevy truck, Blazer, or Suburban on the property! Basically retired and getting the new Motorhome ready for some traveling. Doing a bit of work on the house getting it ready to sell! LOL!!

10-10-2011, 12:04 AM	#4
dhaymaker Registered User Join Date: Jan 2006 Location: Peyton, CO Posts: 448	Re: 72 K-10 Brake System Problems azsmokey - Here's one of the threads...just don't stop reading when you hit the part about the vacuum, as you've indicated you're pulling a fair amount of vacuum...http://67-72chevytrucks.com/vboard/s...d.php?t=439261 Edit: Adding another URL to check... http://67-72chevytrucks.com/vboard/s...d.php?t=412779 __________________ don "The DRBMan" 2014 Audi A4 (The Wife's Daily Driver) 2017 HD Ultra (The Cruiser) 2003 HD Fatboy (The Ride) 2001 Chevy Suburban (Another back up!!) For the first time in forever, not a single 67-72 Chevy truck, Blazer, or Suburban on the property! Basically retired and getting the new Motorhome ready for some traveling. Doing a bit of work on the house getting it ready to sell! LOL!!

10-10-2011, 03:27 AM	#5
stsalvage Scrapper 1 Join Date: Jan 2007 Location: Riverside Calif Posts: 1,649	Re: 72 K-10 Brake System Problems the portioning valve could be stuck you might of got a master cylinder that was for drum brakes all the way around.But how now is the booster i went throw 3 boosters before i found one that worked.dose your fluid come out normal is there a blockage. in the line isone of the rubber lines culapsing



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.