roger3

76 Corvette with Power Brakes

Replaced brake switch (proportioning valve) with new unit from Zip this weekend, now my brake light stays on. When I press the brake pedal about 1/2" it goes out. Any ideas on how to correct this?

I assume the piston is not centered in the unit. I read that to center it you should mash the brake pedal with a lot of force and hold it down for a few seconds and it will "pop" into place. I've tried it several times but no luck yet.

Right now I am in the process of gravity bleeding it, thinking maybe there's more pressure on one side of the piston, than the other.

Just about everything on the brake system is new, except the metal brake lines. The brake light was not on with the previous proportioning valve. I was replacing it since its all that's left (in my mind) that might cause the pedal to still be soft.

Thanks,

Roger

damoroso

Assuming you've bled the brakes and that hasn't done it, try stabbing the brake pedal, very quick and hard, a couple times with a second or two between "stabs". It's worked for me in the past.

oldalaskaman

if that doesnt work, with another person pushing slowly and steadily on the brake pedal, loosen the rear line on the mc, if the pedal gets all the way to the floor without the light going out, tighten the line back up and do the same with the front line. As soon as the light goes out, tighten the line back up. Should be good to go

roger3

Damaroso,]

Bled the brakes several times, confident there is no air in the system.

I tried mashing the pedal with a lot of force, and holding it. Didn't try the quick stab method. Will give it a try right now.

Oldalaskaman,

If stabbing the pedal doesn't work, i'll try releasing a bleeder as you layed out.

thanks,

Roger

0Willcox Corvette

Roger... stabbing it should solve your problem. If the brakes are find just drive it a few blocks it should go out.

7T1vette

To bleed the brakes and not have the P-valve shift, you have to depress the pedal very slowly. But, the valve being off-center does sound like your problem.

roger3

Just tried stabbing pedal - light is still on

Tried slowly depressing left rear with bleeder open, close bleeder, release pedal - brake light stayed on

Moved to left front - light stayed on

Tried right front, then right rear, brake light still on.

Only difference, prior to this excercise I could mash pedal real hard and light would go off. Now no matter how hard I press pedal, light stays on.



Brake pedal is pretty firm. Yesterday I drove the car about 25 miles around town. Light was on at all times.

oldalaskaman

not bleeders grasshopper, lines at the master cylinder, you're trying to jiggle the valve back and forth and center it. if all else fails, sometimes a gentle tap to loosen it. also sounds like you still have some air in the system



a good thread
http://forums.corvetteforum.com/c3-t...fo-please.html

Peterbuilt

Is the parking brake lever down all the way?

oldalaskaman

excellent

roger3

Aaaah, grasshopper have lot to learn. Will try master cylinder fittings shortly and report back.

Yes, emergency brake is all the way down.

Thanks

roger

roger3

Tried loosening lines at mc one at a time. Light still on.

Did find that when I loosen line to front brakes, light goes out while pedal is all the way down. When I tighten the line connection, and release brake pedal, light comes back on.

I tried same thing loosening connections at proportioning valve. No luck, light still on.

I'll sleep on it and try some more tomorrow evening.

Thanks

Roger

oldalaskaman

those symptoms usually mean air, may need to pressure bleed.

roger3

I have pressure bled it twice. I have ran about 16 to 20 ounces through each calliper.

I also tried gravity bleeding. Right rear didn't flow as well as other lines but it did flow.

Also had my daughter pump brakes so I could manually bleed each caliper.

I'm out of brake fluid. I'll pick up another gallon and do it again tomorrow night.

Roger

dannyman

As stated above; by releasing the pressure on the front and having the light extinguish means that the rear system is at fault.

You still have air in the rear system. Possibility that air is still in the master cylinder? Did the level drop enough to allow air in the system while bleeding; if so then start over beginning by bench bleeding the master. Fully bleed the rears and ensure free of any air.

You need to have all the air out of the front and rear systems before you will be able to stab the light "off". Any air at all allows one system to keep the valve off centre.

Dan

roger3

master cylinder never went dry, but I'm game to try anything. Will the air bubbles be big enough to see? I have a clear hose hooked to a small plastic cup and aftEr making one round with pressure bleeder I never saw any more bubbles.

Thanks

Roger

dannyman

When you replaced the proportioning valve was it dry or full of fluid?

If dry then you need to pump through enough fluid to rid all the air from the system. Air bubbles hanging on to the inside of a caliper is enough to give you problems. A tapping of a rubber mallet to calipers as you bleed; will help. You should see the bubbles as they are pumped out if the clear tubing has an inverted u-shape at the bleeder.

roger3

I put the valve in dry.

I'll do more bleeding tomorrow after work and will be glad to hit with mallet. My wife is hiding the matches.

I'll be watching for bubbles.

Right now when I mash the pedal really hard, then release it I don't see any fluid shoot back into the master cylinder. I thought this meant no air is in the system. Is this true for corvette systems?

dannyman

Not sure about fluid shooting; just know from your explanation that you still have air somewhere in the rear system.

Try to visualize the distance that the air pocket has to travel from the proportioning valve to the rear bleeders.

Keep bleeding, you'll get it!

Dan

roger3

More bleeding tomorrow.

Thanks

Roger