Bleeding Brakes

[Furyus67]

I recently had everything out of the engine bay, so prior to reinstalling the Master Cylinder I bench bled it with full piston travel, dumping the fluid back into the reservoirs.

Now I just tried to bleed the brakes on the car. The rears seem fine. When I got to the fronts, I topped off the fluid, had my wife mash the pedal (everything seemed fine) and then I loosened the bleeder to release the fluid. I tightened it back up and began repeating the process. Wife stated the pedal did not feel the same (she said no resistance), but I could also hear that the brakes themselves were not expanding. When releasing the bleeder the flow was not as strong, with a couple spits of air here and there. I then went and topped off the MC before it got dry. I tightened up the MC and went back to the wheel. Immediately after topping off the MC my wife began pumping the brakes and stated it felt good again and I could hear the brakes expanding. So I release the bleeder and got a nice strong flow of fluid. So we did it a second time and immediately after that good bleed, wife stated the pedal didn't feel good and I could hear the brakes were not expanding, we did this a few times and the pedal never felt good and the brakes didn't expand. So I go top off the MC again and immediately after topping off the MC the brakes felt good again.

This repeated multiple times on the front passenger, so I moved to the front driver. Same exact sequence of events.

It's almost like taking the top off the MC is letting the air out and making things better.

Any ideas?!

67 Fury
Manual brakes.
New brake lines all the way around.
New MC.

 

[MONC440]

I recently had everything out of the engine bay, so prior to reinstalling the Master Cylinder I bench bled it with full piston travel, dumping the fluid back into the reservoir

Everything you describe sounds like master cylinder to me. When you bench bled it did you fill the reservoir and put the ends of the bleeder lines in the fluid and pump it until all the bubbles stopped?

 

[Furyus67]

Everything you describe sounds like master cylinder to me. When you bench bled it did you fill the reservoir and put the ends of the bleeder lines in the fluid and pump it until all the bubbles stopped?

Yes, that is how I bench bled it.

 

[MONC440]

Yes, that is how I bench bled it.

Does that system have any type of metering valve between the front and rear brakes? Also, I’m sure you did, but did you replace all the rubber lines?

 

[Trace 300 Hurst]

If I recall correctly from a long time ago, it's possible when bleeding an empty system for the piston in this valve to be forced all the way to "front" or "rear", thus closing off that port, as it's supposed to do. This is part of the "dual master cylinder safety brake system" that came along in the mid-60's. If a hydraulic failure occurs in the rear system the fronts still work, and vice-versa.

The last paragraph says you need a new switch, but I seem to recall that the switch can be reset. Remove plug and center the piston, maybe?

 

[volksworld]

when you topped off the master was it still at least half full? or was it empty? if you let the level of the master get too low it will suck in air and put you back to square one...I'm assuming the brakes were fine before you started this? cause if the pedal was low you'll need to adjust them otherwise most of your pedal travel will just be expanding the wheel cylinder and not moving enough fluid to push the air out...i'm not a fan of pumping brakes, that can make the air in the system harder to remove...my method...open bleeder, push pedal to floor and hold it there, close bleeder, slowly let pedal back up (like 3 to 5 seconds), repeat...this way you're pushing straight fluid through the lines rather than foam and less likely to suck in air from the resevoir

 

[Big_John]

If I recall correctly from a long time ago, it's possible when bleeding an empty system for the piston in this valve to be forced all the way to "front" or "rear", thus closing off that port, as it's supposed to do. This is part of the "dual master cylinder safety brake system" that came along in the mid-60's. If a hydraulic failure occurs in the rear system the fronts still work, and vice-versa.

The last paragraph says you need a new switch, but I seem to recall that the switch can be reset. Remove plug and center the piston, maybe?


View attachment 681731
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I don't believe that the safety switch does anything more than light the e-brake light. It's a simple hydraulic switch. Lack of pressure on front or rear lets the shuttle valve make electrical contact, but it does nothing to close a set of ports. Even the illustration (if it's to scale) shows there's not enough travel in the shuttle to do this.

 

[Big_John]

I recently had everything out of the engine bay, so prior to reinstalling the Master Cylinder I bench bled it with full piston travel, dumping the fluid back into the reservoirs.

Now I just tried to bleed the brakes on the car. The rears seem fine. When I got to the fronts, I topped off the fluid, had my wife mash the pedal (everything seemed fine) and then I loosened the bleeder to release the fluid. I tightened it back up and began repeating the process. Wife stated the pedal did not feel the same (she said no resistance), but I could also hear that the brakes themselves were not expanding. When releasing the bleeder the flow was not as strong, with a couple spits of air here and there. I then went and topped off the MC before it got dry. I tightened up the MC and went back to the wheel. Immediately after topping off the MC my wife began pumping the brakes and stated it felt good again and I could hear the brakes expanding. So I release the bleeder and got a nice strong flow of fluid. So we did it a second time and immediately after that good bleed, wife stated the pedal didn't feel good and I could hear the brakes were not expanding, we did this a few times and the pedal never felt good and the brakes didn't expand. So I go top off the MC again and immediately after topping off the MC the brakes felt good again.

This repeated multiple times on the front passenger, so I moved to the front driver. Same exact sequence of events.

It's almost like taking the top off the MC is letting the air out and making things better.

Any ideas?!

67 Fury
Manual brakes.
New brake lines all the way around.
New MC.

Question... Are you using conventional brake fluid? I had similar experience with silicone fluid where I couldn't get a firm pedal by conventional bleeding and in a conversation with another guy that is familiar with silicone fluid, he said that was typical.

I had a similar issue with another car (conventional fluid) that had a minute leak in a bleeder. Not enough to let fluid out, but would let air back in. Drove me nuts (short drive) and I only found it by junking the Chinese wheel cylinders that came with the car and using some NORS wheel cylinders I got on eBay.

If nothing else, I'll suggest spending a little cash on a power bleeder. I have this one. Amazon.com Hint: use a c-clamp rather than the chains. When trying to figure this out, it's a little easier for you and a whole lot better than having to ask the bride to try bleeding the brakes one more time.

 

[Trace 300 Hurst]

I don't believe that the safety switch does anything more than light the e-brake light. It's a simple hydraulic switch. Lack of pressure on front or rear lets the shuttle valve make electrical contact, but it does nothing to close a set of ports. Even the illustration (if it's to scale) shows there's not enough travel in the shuttle to do this.

I see what you're saying....the shuttle contacts (and grounds-out) the electrical post long before it could close-off a port.

But how did I have that brainfart about this? I know I've heard of something like this before, a long time ago. Am I thinking of a proportioning valve doing the same thing?

 

[Big_John]

Am I thinking of a proportioning valve doing the same thing?

Possibly. I don't know if that could go into a mode where it shuts off one side completely, but then again, I've never really looked at them in depth.

 

[Trace 300 Hurst]

Possibly. I don't know if that could go into a mode where it shuts off one side completely, but then again, I've never really looked at them in depth.

Well, we've all given @Furyus67 a few things to think about.

 

[Furyus67]

Thank you all for the suggestions.

Yes I'm using conventional brake fluid, not silicone based.

I tried using the gravity bleed method, leaving the cap off the MC and the bleeder open for a while. They still feel like there is way too much pedal travel before the brakes engage.

I'll probably use that Motive bleeder and report back.

I'm going to read the brake section of the service manual. I may need to adjust the brakes. Got the motor back in and exhaust on and everything running. Now just dialing in all this other stuff.

Thanks for the tips

 

[MONC440]

Great. Keep us posted. Love to see another one get on the road!