Extremely touchy brakes - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ohmsc10 · 03-26-2010, 08:32 PM

Just bought a 71. Truck has been converted to power brakes sometime in the past. I can tell by the new hole in the pedal arm. The brakes are so touchy I think I am going to fly thru the windshield if I don't just barely touch the pedal. Anyone have a solution?

beautimus · 03-26-2010, 09:06 PM

my guess is that you still have the non power brake calipers on it.
i think, there may be a difference in the calipers from power and non power disks. you could check with a parts store and see if there is a different part number for power and non power assist, just to be certain.

OhOneWS6 · 03-26-2010, 09:18 PM

Check for contaminated pads and shoes. Grease on brake shoes = touchy breaks.

ERASER5 · 03-26-2010, 09:36 PM

A bad poppet valve in the vacuum booster will cause extremely touchy brakes too.

I am pretty sure that the calipers are the same for power and non power brakes. The MC has different bore sizes to obtain the needed pressure for the calipers to work. A manual MC bolted to a vacuum booster would result in to much pressure too fast. As will having the rod attached to the wrong point on the pedal arm.

There should have only been 1 hole on the pedal arm. The 71 vacuum booster assembly should have leaver assembly on the rod and not a rod that goes straight through the firewall. That leaver assemble has a reducing effect on the pedal instead of a different attachment point.

A picture of what you have would be nice. Something has been changed. Also, in my limited experience, I have never seen a 71 disc brake without a power booster from the factory. It is possible I suppose. Maybe LMH can tell us for sure.

crushermechanic · 03-26-2010, 10:25 PM

my 71 was non power discs when i bought it. i converted it to power with a new booster and master cylinder. the calipers are the same. mine works great.

ERASER5 · 03-27-2010, 12:15 AM

OK then. Does your MC/booster have the linkage setup?

crushermechanic · 03-27-2010, 08:26 AM

yea i put the linkage i pulled off a parts truck.

Shyguy · 03-27-2010, 09:21 AM

My '71 is also a non power disc brake setup from the factory and it works so well I see no need for power brakes.

Of course I am an old guy that grew up with vehicles that did not have power brakes, lol.

Heck when I was just young boy we had an old F*rd car that you had to run the slack out of it, as my mom says to stop it. What she was saying was you better anticipate when you needed to stop and let off the gas and let it coast to a stop, it had a manual,lol.

Danny

JRBECK64 · 03-27-2010, 09:28 AM

Have you thought about installing an adjustable proportioning valve? When I bought my 69 Short Step the back end of the truck kept locking up on me and I was about to install one and decide to waite until I figured out if I were going to install Disc Brakes on the back or not. Its an Idea.

JRBECK64

03-26-2010, 08:32 PM	#1
ohmsc10 Registered User Join Date: Feb 2006 Location: Hanover PA Posts: 24	Extremely touchy brakes Just bought a 71. Truck has been converted to power brakes sometime in the past. I can tell by the new hole in the pedal arm. The brakes are so touchy I think I am going to fly thru the windshield if I don't just barely touch the pedal. Anyone have a solution? __________________ 71 Bagged Longbed

03-26-2010, 09:06 PM	#2
beautimus Registered User Join Date: Mar 2002 Location: woodstock, alabama, usa Posts: 938	Re: Extremely touchy brakes my guess is that you still have the non power brake calipers on it. i think, there may be a difference in the calipers from power and non power disks. you could check with a parts store and see if there is a different part number for power and non power assist, just to be certain. __________________ i survived cancer and kidney stones, but my kids are killing me.

03-26-2010, 09:18 PM	#3
OhOneWS6 Registered User Join Date: Dec 2009 Location: DFW, TX Posts: 764	Re: Extremely touchy brakes Check for contaminated pads and shoes. Grease on brake shoes = touchy breaks. __________________ 72 Cheyenne Super 1/2 LWB White/Dark Yellow 07 Avalanche 2LT 74 Sleek Craft Rebel Jet Boat W/Pontiac 400

03-26-2010, 09:36 PM	#4
ERASER5 Registered User Join Date: Jun 2006 Location: Indiana Posts: 4,859	Re: Extremely touchy brakes A bad poppet valve in the vacuum booster will cause extremely touchy brakes too. I am pretty sure that the calipers are the same for power and non power brakes. The MC has different bore sizes to obtain the needed pressure for the calipers to work. A manual MC bolted to a vacuum booster would result in to much pressure too fast. As will having the rod attached to the wrong point on the pedal arm. There should have only been 1 hole on the pedal arm. The 71 vacuum booster assembly should have leaver assembly on the rod and not a rod that goes straight through the firewall. That leaver assemble has a reducing effect on the pedal instead of a different attachment point. A picture of what you have would be nice. Something has been changed. Also, in my limited experience, I have never seen a 71 disc brake without a power booster from the factory. It is possible I suppose. Maybe LMH can tell us for sure. __________________ '70 GMC C1500 LWB Power disc brakes. WooHoo! Posi 6 Lug Dana 60

03-26-2010, 10:25 PM	#5
crushermechanic Registered User Join Date: Dec 2009 Location: Fort Walton Beach, Fl Posts: 357	Re: Extremely touchy brakes my 71 was non power discs when i bought it. i converted it to power with a new booster and master cylinder. the calipers are the same. mine works great.

03-27-2010, 12:15 AM	#6
ERASER5 Registered User Join Date: Jun 2006 Location: Indiana Posts: 4,859	Re: Extremely touchy brakes OK then. Does your MC/booster have the linkage setup? __________________ '70 GMC C1500 LWB Power disc brakes. WooHoo! Posi 6 Lug Dana 60

03-27-2010, 08:26 AM	#7
crushermechanic Registered User Join Date: Dec 2009 Location: Fort Walton Beach, Fl Posts: 357	Re: Extremely touchy brakes yea i put the linkage i pulled off a parts truck.

03-27-2010, 09:21 AM	#8
Shyguy Junior Member Join Date: Dec 2006 Location: Southeast Missouri Posts: 2,436	Re: Extremely touchy brakes My '71 is also a non power disc brake setup from the factory and it works so well I see no need for power brakes. Of course I am an old guy that grew up with vehicles that did not have power brakes, lol. Heck when I was just young boy we had an old F*rd car that you had to run the slack out of it, as my mom says to stop it. What she was saying was you better anticipate when you needed to stop and let off the gas and let it coast to a stop, it had a manual,lol. Danny __________________ '67 Chevy C-20 short stepper - build complete, 454/SM-465. '75 C-30 Single Cab DRW-350 small block/NP-435. '77 GMC-6500 Dump Truck, 427 Tall Deck. '92 GMC K-3500 Duallie, 454/4L80E.

03-27-2010, 09:28 AM	#9
JRBECK64 Registered User Join Date: Sep 2008 Location: Cornelius Oregon Posts: 1,073	Re: Extremely touchy brakes Have you thought about installing an adjustable proportioning valve? When I bought my 69 Short Step the back end of the truck kept locking up on me and I was about to install one and decide to waite until I figured out if I were going to install Disc Brakes on the back or not. Its an Idea. JRBECK64



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