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

LuckyHenriksen · 08-14-2008, 05:19 PM

I have a '68 LWB, and it came with manual drum brakes all around. I converted the front to disc and rebuilt the rear drums. I am using the original master cylinder, and want to know if I need to change that or do something different. I have bled the brake system several times, but the pedal is still soft or gives way. What am I doing wrong?
Thanks, Steven

PanelDeland · 08-14-2008, 05:50 PM

Disc brakes require a disc brake MC.You probably want to go to a power booster also.You also need to use a proportioning valve for a disc/drum set-up.There will be lots of info in the FAQ's section that will help you pinpoint the problem.
I think you will find that you still need the same pedal pressure to stop without the booster.The residual valves for drums are (IIRC) 10 # and disc use a 2 #.
All that said I know some members claim to be running drum MC's on disc equipted trucks but I doubt they have as much improvement in braking as they could have.
Just some random thoughts about what may be causing your problem.

LuckyHenriksen · 08-14-2008, 06:05 PM

Thanks for the reply, I have heard from different people that you can use the same MC, but I don't know what to believe. I guess if it's not working then its time to change something

Longhorn Man · 08-14-2008, 09:11 PM

"mine worked like that" is NOT the same as "was designed to work"
The fluid amount delivered, the pressure delivered, the front to rear differance, all of it is crutial to proper brake operation.

08-14-2008, 05:19 PM	#1
LuckyHenriksen Registered User Join Date: Oct 2007 Location: Sherwood Oregon Posts: 1,908	Brake Troubles I have a '68 LWB, and it came with manual drum brakes all around. I converted the front to disc and rebuilt the rear drums. I am using the original master cylinder, and want to know if I need to change that or do something different. I have bled the brake system several times, but the pedal is still soft or gives way. What am I doing wrong? Thanks, Steven __________________ 1968 Yenko Chevy LWB 6.0L/TH400 3/4 Drop Senior Project Build Thread Here

08-14-2008, 05:50 PM	#2
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,992	Re: Brake Troubles Disc brakes require a disc brake MC.You probably want to go to a power booster also.You also need to use a proportioning valve for a disc/drum set-up.There will be lots of info in the FAQ's section that will help you pinpoint the problem. I think you will find that you still need the same pedal pressure to stop without the booster.The residual valves for drums are (IIRC) 10 # and disc use a 2 #. All that said I know some members claim to be running drum MC's on disc equipted trucks but I doubt they have as much improvement in braking as they could have. Just some random thoughts about what may be causing your problem. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"

08-14-2008, 06:05 PM	#3
LuckyHenriksen Registered User Join Date: Oct 2007 Location: Sherwood Oregon Posts: 1,908	Re: Brake Troubles Thanks for the reply, I have heard from different people that you can use the same MC, but I don't know what to believe. I guess if it's not working then its time to change something __________________ 1968 Yenko Chevy LWB 6.0L/TH400 3/4 Drop Senior Project Build Thread Here

08-14-2008, 09:11 PM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Brake Troubles "mine worked like that" is NOT the same as "was designed to work" The fluid amount delivered, the pressure delivered, the front to rear differance, all of it is crutial to proper brake operation.



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