proportioning valve 77
09-09-2013, 08:45 AM
#1
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proportioning valve 77
77 vette with new calipers ,hoses new master cyl new proportioning valve. brakes work fine but when you press on pedal hard the brake light comes on. there are no leaks and no air in system. brakes have been bled several times. tried another master cylinder with no change. drove vette and then bled again no air in system. I blocked off all four calipers and pressed on pedal and I still get the light. I confermed with meter that it is the valve causing the light. So did I get a bad proportioning valve or am I missing something. dave
09-09-2013, 11:36 AM
#3
Team Owner
IDK if that valve/block in a '77 is the same as in earlier C3's, but my '71 has just a shuttle valve that is supposed to trip over to either front or back, depending on which end of the system has sprung a fluid leak.
Thus, if you are bleeding the brakes and depress the brake pedal too quickly, that block will interpret it as a fluid leak and the shuttle valve will trip. And when it does, only half of the braking system will be functional and the "BRAKE" light will be on.
The Chev. Chassis Service Manual shows how to 'lock' that shuttle valve in place when bleeding the brakes, then release it when done. Not sure how to re-center it when it has been tripped.
Thus, if you are bleeding the brakes and depress the brake pedal too quickly, that block will interpret it as a fluid leak and the shuttle valve will trip. And when it does, only half of the braking system will be functional and the "BRAKE" light will be on.
The Chev. Chassis Service Manual shows how to 'lock' that shuttle valve in place when bleeding the brakes, then release it when done. Not sure how to re-center it when it has been tripped.
09-12-2013, 04:34 PM
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Ok after exhausting all other options I installed another proportioning valve from a different vender and problem is solved. The first valve was no good. dave
09-12-2013, 05:08 PM
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First valve MAY have just needed to be reset.
If the shuttle valve is over to one side it can cause said issue.
reset procedure is something like open bleeders on the side that was good, and stomp on the brakes or sumthin.
See the repair manual for the actual procedure
If the shuttle valve is over to one side it can cause said issue.
reset procedure is something like open bleeders on the side that was good, and stomp on the brakes or sumthin.
See the repair manual for the actual procedure
09-12-2013, 11:11 PM
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The first valve reset fine and the brakes felt great. But when you got on the brakes a little hard the light would come on. I bled the system again with no change. All worked fine after second valve install. I am going to take the first valve apart and see if it was assembled wrong. dave