C3 Calipers / brakes
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From: New England
69 LT1, I believe the fluid must be leaking onto the rotors that would be the only explanation. That was exactly the type of smoke I saw. Like oil on the exhaust manifold.
Didnt see the glowing rotor like on a frozen calp
Wouldnt need the whole master to empty. Looks a little low.
Didnt see the glowing rotor like on a frozen calp
Wouldnt need the whole master to empty. Looks a little low.
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From: Virginia
...
Question: what would cause no fluid to come out of the brake lines when I pulled the calipers? Is that normal? I thought when you disconnect the calipers then the brake lines they drip brake fluid. Always had as far as I remember. Still have fluid in the master cylinder.
Question: what would cause no fluid to come out of the brake lines when I pulled the calipers? Is that normal? I thought when you disconnect the calipers then the brake lines they drip brake fluid. Always had as far as I remember. Still have fluid in the master cylinder.
1. Ignition switch: You should see the light illuminate when you crank the engine.
2. Parking brake: You should see the light illuminate when you pull the handle up.
3. Combination Valve switch: If either half of the brakes have failed, a piston will slide to one side or the other inside the combination valve, blocking fluid flow to that half of the circuit (front or rear), as well as grounding the brake light in your dash, causing it to illuminate.
If your brake light doesn't come on in the previous two scenarios, it's a good chance it was disabled. You can test continuity in the switch on the combination valve, and make sure it is still connected.
Here's the description from the 79 Shop Manual. Do you have a copy for your car?
Last edited by Bikespace; Jun 29, 2020 at 07:35 AM.
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From: New England
Yes- the check engine light stays on. I definitely have a brake system failure. Are you saying I may have a combination valve issue too? Or that is just a result of a failure at the calipers?
I have the 74 manual but it doesn't have a diagram of the combo valve. I'm googling it now.
I have the 74 manual but it doesn't have a diagram of the combo valve. I'm googling it now.
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it does have the diagram- diff page. "Combination valve". Funny over the years the name changed to "proportioning". You cant find a combo valve under a web search. I matched the diagrams with retail sites and its the exact same thing
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From: New England
So that explains the lack of fluid coming out of the lines. So since the combo valve was triggered do I need a new one?
Also can i simply hook the whole system back up and do a basic bleed process or are C3s more complicated.
Can I simply do this?
1. re-assemble
2. fill liquid
3. open 1 bleeder / someone pump brakes till full stream / close bleeder
4. Repeat on all 6 bleeders.
Also can i simply hook the whole system back up and do a basic bleed process or are C3s more complicated.
Can I simply do this?
1. re-assemble
2. fill liquid
3. open 1 bleeder / someone pump brakes till full stream / close bleeder
4. Repeat on all 6 bleeders.
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Well, "Combination Valve" is what GM called it when they wrote my shop manual. Proportioning valve is what the vendors call it. I didn't mean to confuse you.
Even if your calipers don't leak, if you have lines/hoses filled with air instead of brake fluid, and you press the brakes, the "proportioning section of the combination valve" will detect this pressure imbalance, skew to one side to prevent further leaks, and allow braking with only the other two calipers (front or rear, opposite of where the problem is). If your brake light is illuminated, and you are not cranking the car, and the parking brake lever switch is not engaged (lever up), then, yes, you have a problem.
I'm not 100% sure how you reset the combination valve at this point. There is a tool that keeps it centered, but I don't know how to get it centered without bleeding the brakes and solving the problem, and I don't know how to bleed the brakes with the combination valve off center.
BTW, your 1974 does not have a "check engine" light, but it should have a "brake" light on the dash.
Even if your calipers don't leak, if you have lines/hoses filled with air instead of brake fluid, and you press the brakes, the "proportioning section of the combination valve" will detect this pressure imbalance, skew to one side to prevent further leaks, and allow braking with only the other two calipers (front or rear, opposite of where the problem is). If your brake light is illuminated, and you are not cranking the car, and the parking brake lever switch is not engaged (lever up), then, yes, you have a problem.
I'm not 100% sure how you reset the combination valve at this point. There is a tool that keeps it centered, but I don't know how to get it centered without bleeding the brakes and solving the problem, and I don't know how to bleed the brakes with the combination valve off center.
BTW, your 1974 does not have a "check engine" light, but it should have a "brake" light on the dash.
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confusion is a part of learning. I know a ton more now then I did last night. So right meant- "brake" light. I found a good video that has a short intro then jumps right into it. 6 minutes with all good info.
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The method poo-pooed in the video (opening up the working brake circuit, then hitting the brakes hard), may work. I haven't tried, but I'd search the Forum for additional tips.
Here's the tool that will keep it centered, once you center it.
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well not sure what i did but i was under the car and messing around with the combination valve. Just feeling around it / spraying with PBuster. Then fluid started drippng out of the brake lines: both front. I had them pointed up and taped. Didnt tape them well since they werent leaking at the time. Now I wrapped them tight.
I may have opened the MC cover and that caused it? I def didnt touch the brake pedal. I poured enough fluid in to make sure air doesnt get it. It never fully emptied.
I got the pistons out- nasty looking. Emptied 2 cans of brake cleaner on them. The pistons look OK. Noticed one of the piston rubber seals was installed backwards.
I may have opened the MC cover and that caused it? I def didnt touch the brake pedal. I poured enough fluid in to make sure air doesnt get it. It never fully emptied.
I got the pistons out- nasty looking. Emptied 2 cans of brake cleaner on them. The pistons look OK. Noticed one of the piston rubber seals was installed backwards.
Le Mans Master
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Some of my brakes require at least a half an hour to get a fair amount out for bleeding when I use the drip method. On my brake light goes off after I got everything hooked up and bled I stab the brake pedal several times hard it may take two or three times but for me it always resets
that assumes that the parking brake light is adjusted correctly and not triggering the light as well
that assumes that the parking brake light is adjusted correctly and not triggering the light as well
Last edited by interpon; Jun 30, 2020 at 08:31 AM.
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There were some holes in the rubber brake lines so I used some scotch tape...that should work right? Its the wife's car so...
No, when I removed the calipers i just taped off the end of the SS brake lines so they wouldnt leak all the fluid out while I rebuild the pistons.
No, when I removed the calipers i just taped off the end of the SS brake lines so they wouldnt leak all the fluid out while I rebuild the pistons.
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finished the piston seal rebuild. They dont all feel the same. On a few the outer seal (which i believe is really just a dust seal) sometimes expands a little spits out some air when compressing the pistons. Is that normal?
Melting Slicks
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From: PHX AZ
don't pump it without calipers! Depress the pedal!
If you depress the pedal to the floor your will push the pistons and cups in the M/C PAST the normal 'swept volume area' and probably kill the M/C.
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Thanks Mel. I didnt pump them.
I actually plan on just re-assembling the whole system and see what happens. I'm missing 1 seal set and the new bleeders. Waiting for it to arrive from the retailer. Once I get it I'll install all and start from the back. See If i can get fluid to the rears. If not then I'll have to screw around with the comb valve and see if I can get it to center.
I actually plan on just re-assembling the whole system and see what happens. I'm missing 1 seal set and the new bleeders. Waiting for it to arrive from the retailer. Once I get it I'll install all and start from the back. See If i can get fluid to the rears. If not then I'll have to screw around with the comb valve and see if I can get it to center.