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Have I F'd my dual circuit M/C? - No Brakes!
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MrGoodtunes
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PostPosted: Thu Jun 28, 2018 8:11 pm    Post subject: Have I F'd my dual circuit M/C? - No Brakes! Reply with quote

Found a leak in front left flex hose. Replaced it along with the short metal tube from master cylinder to bracket. Bled and bled and bled the front left wheel cylinder, but air bubbles were never ending and pedal went all the way to the floor. Then I realized that I should've started with front right. Better late than never, began bleeding it, with same result.

Question: Should I need to bleed rears too?

Brakes were working when I began this, but felt like rears only. Now I don't have any! (Brake lights don't light up.)

Doing the job myself, using a piece of PVC tube; one end pressing down brake pedal, other end prop'd behind steering wheel, while I open bleeder valve. Brake shoes barely scrape from having pedal all the way in before opening bleeder. I install'd new drums and linings a couple months ago. The master cylinder has been in since 1986, when I replaced the original 1965 single circuit M/C while moving pedal cluster ~5" forward to make driving less cramp'd in such a short vehicle (70" wheelbase Mini-Camaro body).

Can the M/C introduce air into circuit(s)?

I kept reservior top'd up during entire job and have bled ~12oz of brake fluid, having bled fronts only.

Any thoughts, hints, suggestions greatly appreciated. Thanks in advance.
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jspbtown
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PostPosted: Thu Jun 28, 2018 8:41 pm    Post subject: Re: Have I F'd my dual circuit M/C? - No Brakes! Reply with quote

Adjust shoes until they are tight against drums on ll 4 wheels

Bleed starting from the wheel farthest from the MC and end up with the left front (RR, LR, RF, LF)

Get a friend to help....pump pump pump, release bleeder, press to floor, hold, tighten bleeder

Back off shoes evenly.

Enjoy your ride
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Letterman7
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PostPosted: Fri Jun 29, 2018 4:47 am    Post subject: Re: Have I F'd my dual circuit M/C? - No Brakes! Reply with quote

^ That. A way to do it without help is to put a piece of flexible clear tubing on the bleeder (like a power bleeder uses), and put the other end in a clear soda bottle or something similar. Fill the bottle 1/3 the way or until the end of the tube is covered with brake fluid. Crack the bleeder and pump. Right rear is hardest to see (you can generally pump by hand out of the car with the door open and watch the others) so you might want a friend there to monitor.
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EVfun
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PostPosted: Fri Jun 29, 2018 8:35 am    Post subject: Re: Have I F'd my dual circuit M/C? - No Brakes! Reply with quote

You should not have to bleed the rear too, since you have a dual circuit master cylinder. I usually bleed the front first with a dual circuit system. I have been known to do wheel cylinder replacements and only bleed the half of the system I opened up.

My guess is that you previously only had front brakes and the rear had failed (either leaking into the frame or just internally failed.) Now you have opened up the front and haven't got the air out so it falls flat too. If you have one circuit working in a dual circuit system the brake pedal should not hit the floor. You where low before and now you hit the floor. So my guess is the simplest way to get that result.
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MrGoodtunes
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PostPosted: Fri Jun 29, 2018 8:54 am    Post subject: Re: Have I F'd my dual circuit M/C? - No Brakes! Reply with quote

Thanks for reminding me of the textbook procedure. And the clear tube from bleeder to recepticle bottle trick is how I've done it forever. Interesting theory about rears having fail'd before I discover'd the pin hole leak (thin squirt) in front left. Fluid level was almost at max when leak was found. At that time brakes began to slow buggy with just a nice slightly depress'd pedal, but to get a full stop required pressing alot further, which caused me to look for trouble and find the leak.

My situation now is that brake pedal will not "pump up." It just goes to the firewall and back with only the return springs's tention. It's as if the master cylinder lost its prime and pumps only air.
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GS guy
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PostPosted: Fri Jun 29, 2018 10:17 am    Post subject: Re: Have I F'd my dual circuit M/C? - No Brakes! Reply with quote

One "trick" I've used to help get rid of frustrating air bubbles in the system (especially if suspected being near the MC) is one I learned from my motorcycling days. When you get tired of pumping the brakes, or just can't seem to get that last little bit of air out, depress the pedal as far as it will go and secure it there. Leave minimum overnight, or longer. It works better on cycles as the vertical drop from reservoir to caliper is more straight up and down, but it's helped on autos too. Keeping the pedal down, as I understand it, keeps the fluid circuit "open" from reservoir to caliper/wheel cylinder. This allows pesky small air bubbles to gradually make their way to the "top" of the system - up into the reservoir. Obviously any air in the rear lines could take a looong time to make that journey (if ever), but it's minimal effort and might help.
I picked up a power bleeder to hopefully alleviate the frustration from the brake bleeding process.
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MrGoodtunes
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PostPosted: Fri Jun 29, 2018 4:10 pm    Post subject: Re: Have I F'd my dual circuit M/C? - No Brakes! Reply with quote

Success! After taking all 4 wheels off and adjusting brakes as tight as possible (neither of which have I ever had to do during the 43 years I've own'd this project) and doing alot of pumping, a tiny bit of resistance began to build way down at the bottom of pedal strokes. Then with some help from the Mrs, my master cylinder now seems ready for another 32 years of service.
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jspbtown
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PostPosted: Fri Jun 29, 2018 5:10 pm    Post subject: Re: Have I F'd my dual circuit M/C? - No Brakes! Reply with quote

Awesome!
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MrGoodtunes
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PostPosted: Sat Jun 30, 2018 2:14 pm    Post subject: Re: Have I F'd my dual circuit M/C? - No Brakes! Reply with quote

Uggh. Before I could finish getting air out of front circuit, pedal went back to going all the way down without resistance. So I inspected every inch of the rear circuit line, and found this:

Image may have been reduced in size. Click image to view fullscreen.


The dark grungy sludge under the "T" is thick and wet. Incoming line (right) looks okay.
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jspbtown
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PostPosted: Sat Jun 30, 2018 9:22 pm    Post subject: Re: Have I F'd my dual circuit M/C? - No Brakes! Reply with quote

That be a leak.....Smile
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