Power brake question

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Mar 6, 2010 | 09:41 AM

pwsusi

Thread Starter

Burning Brakes

Joined: Aug 2006

Posts: 793

Likes: 11

From: Grafton MA

Power brake question

on my '71 (with power brakes), when you press the brake in to the floor the 'brake' light on the tach comes on (similar to when you put the parking brake on). is this correct? my other car does not have power brakes and this brake light only come on with the parking brake, never the foot brake.

thanks,
Paul

Mar 6, 2010 | 10:03 AM

Grumpy 427

Melting Slicks

Joined: Oct 2008

Posts: 2,154

Likes: 69

From: Regina Sk Canada

You might be low on fluid. Or the proportioning valve has an issue.

Mar 6, 2010 | 10:10 AM

Duke94

Le Mans Master

Joined: Mar 2001

Posts: 6,640

Likes: 287

From: Ann Arbor Michigan

Air in the system is the most common cause. It should NOT come on during normanl brake apply. The brake warning valve (no proportioning valve in 71') is working correctly since one of its functions is to light the red dash light in the event of a partial system failure (air in one system or leak). Check first to be sure the master cylinder is full of brake fluid. If not you have a leak that must be fixed.

Gary

Mar 6, 2010 | 10:54 AM

jae1971

Instructor

Joined: Mar 2010

Posts: 136

Likes: 0

From: Grayson Louisiana

bled the brake system on mine and cured the problem with the light

Mar 6, 2010 | 11:01 AM

70 LS1

Melting Slicks

Joined: May 2001

Posts: 2,812

Likes: 4

From: Gig Harbor Wa

Quote:

Originally Posted by Duke94

Yup

If you lose pressure in one side of your system, then the valve shifts to that side, turning on the light.

I had the same problem and it turned out to be a leaky caliper.

Mar 7, 2010 | 08:28 AM

pwsusi

Thread Starter

Burning Brakes

Joined: Aug 2006

Posts: 793

Likes: 11

From: Grafton MA

Quote:

Check first to be sure the master cylinder is full of brake fluid. If not you have a leak that must be fixed

here's a simple question - how does one go about checking the MC to see if it's full of brake fluid? if not, how does one go about adding it?

Thanks.

Mar 7, 2010 | 09:37 AM

7T1vette

Team Owner

Joined: Jan 2006

Posts: 37,637

Likes: 3,118

From: Crossville TN

You just use a flat bladed screwdriver to pry each of the retaining bales out of their detent, then swing them off the top of the M/C and lift the lid. Lift it straight up and slowly, as the rubber bladders will be sitting in the brake fluid and you don't want to sling that stuff all over the engine compartment. Have a clean towel or rag with you to put under the lid...DO NOT get brake fluid on your paint!!!

If the fluid is low [but not too low], just add more brake fluid up to 1/4" of the top (at closest point on fluid bowls), push the rubber bladders back into the cap [they just 'accordion' in], then reinstall the cap and bales. Use the screwdriver again to pop the bales back into their detents.

If the level of the brake fluid is at or below the fluid port going to the brake lines, the system has been sucking in some air and you will need to bleed the brake lines. That's the penalty for not checking the fluid level on some regular schedule. Nasty job...takes 2 people, or 1 person and a power bleeder device. Check the archives for detailed instructions and sequence of wheels for best results.

Mar 8, 2010 | 08:22 AM

muskegonbrake

Supporting Vendor

Joined: Mar 2008

Posts: 576

Likes: 3

From: Muskegon MI

Most likely either a leaky caliper or one that is about to leak and is sucking air. Could also be cause by out-of-round rotor that is causing the caliper to suck air. Let me know if you have any questions or need another caliper.

Andrew
800-442-0335