Thanks all! It shouldn’t be a clog because brake fluid comes out of the rear lines when the pedal is pressed and the bleeder screw is opened. This is the case on both sides.

regarding adjusting the shoes after replacing the wheel cylinders - I thought the brakes auto adjust. I watched it do that when I pulled the e-brake a few times.

EDIT: Out of curiosity, once he bleeds the front calipers, will the pedal feel solid despite the rears not working? I'm concerned that will happen and they will tell me the brakes are fixed when in reality, only the fronts are working.

Edited January 17Jan 17 by chaseincats
e-brake written as belle-brake due to auto correct

Both front and back have to be bled and rear shows adjusted correctly in order to get a firm high pedal.

You can get a good idea on if the rears are adjusted correctly by how high the parking brake pedal rises. It should come up about a quarter to a third of the available travel.

Since you were using the rears with the parking brake theyr'e probably adjusted correctly. Your brake guy should know all of this, the way they function is common across many brands of car.

1 minute ago, Zed Head said:

Both front and back have to be bled and rear shows adjusted correctly in order to get a firm high pedal.

You can get a good idea on if the rears are adjusted correctly by how high the parking brake pedal rises. It should come up about a quarter to a third of the available travel.

Since you were using the rears with the parking brake theyr'e probably adjusted correctly. Your brake guy should know all of this, the way they function is common across many brands of car.

That makes me feel better. His guess yesterday was the proportioning valve needing to be replaced but that wouldn't make sense since the car stopped perfectly before I changed the rear wheel cylinders/the front leak. Would the pedal not be firm if the proportioning valve needs to be replaced? My concern is the pedal feeling good once the fronts are bled despite the rears in-actuality not working.

The parking brake handle did come up about halfway - definitely more than it was before I took the drums apart, but it did still stop the car/hold it. By half I mean from the center console to all the way up being 90 degrees - the handle stopped at around 45 degrees. When I was stopping the car with it, it definitely went up to two thirds of the way (60 degrees?), but never to 90.

Regarding the brake pedal - I did notice when pressing the brake pedal at the VERY end of its travel, the brakes did BARELY seem to be barely slowing the car. I'm not sure if that helps, but slowing in that if I held the brake pedal, it would stop the car in a quarter mile or so. So basically when pressing the brake pedal all the way, the shoes moved enough to barely touch the drum, but that's it. Definitely not usable unlike stopping the car with the parking brake.

Edited January 17Jan 17 by chaseincats

When one circuit in the master is empty (doesn't matter which, front or rear), the master cylinder travel will be very large compared to normal. That's because you have to completely compress the spring in the dead circuit before the system builds any significant pressure.

Normally, neither spring inside the master is compressed much because both chambers in the master are full of fluid (which is not compressible). But with an empty circuit, that is not the case. One circuit has to compress completely before the other one does much of anything.

So.... What does that mean to you? It means that when you push the pedal, nothing happens until you get waaaaaay down to the floor. And even then, you also have to shuffle the little warning switch plunger and the proportioning valve movable bits. Both of those things take up some fluid volume, and In the end, you might not have enough pedal travel to ever build enough pressure to get a firm pedal, even near the floor. Sometimes a couple quick pumps of the pedal will help because the drain back valves built into the master may slow the flow back to the reservoirs enough to build some master pressure.

Bottom line, I think your proportioning valve is fine. I think this is all related to your empty front circuit.

3 hours ago, Captain Obvious said:

When one circuit in the master is empty (doesn't matter which, front or rear), the master cylinder travel will be very large compared to normal. That's because you have to completely compress the spring in the dead circuit before the system builds any significant pressure.

Normally, neither spring inside the master is compressed much because both chambers in the master are full of fluid (which is not compressible). But with an empty circuit, that is not the case. One circuit has to compress completely before the other one does much of anything.

So.... What does that mean to you? It means that when you push the pedal, nothing happens until you get waaaaaay down to the floor. And even then, you also have to shuffle the little warning switch plunger and the proportioning valve movable bits. Both of those things take up some fluid volume, and In the end, you might not have enough pedal travel to ever build enough pressure to get a firm pedal, even near the floor. Sometimes a couple quick pumps of the pedal will help because the drain back valves built into the master may slow the flow back to the reservoirs enough to build some master pressure.

Bottom line, I think your proportioning valve is fine. I think this is all related to your empty front circuit.

Gotcha. It doesn't make sense though because the drum's brake cylinder (the cylindrical one closer to the front of the car) is full and bled. I thought the point of a dual cylinder master cylinder is that if one reservoir (in this case the disk's one - the rectangular reservoir closer to the driver's cabin) is empty, the other one should still let the drums work to stop the car. In this case, I had no brakes to any wheel.

Does your brake guy still have the car? What's he doing?

7 hours ago, chaseincats said:

Gotcha. It doesn't make sense though because the drum's brake cylinder (the cylindrical one closer to the front of the car) is full and bled. I thought the point of a dual cylinder master cylinder is that if one reservoir (in this case the disk's one - the rectangular reservoir closer to the driver's cabin) is empty, the other one should still let the drums work to stop the car. In this case, I had no brakes to any wheel.

So... You're asking "Why does the description of how it is SUPPOSED to work differ from the way it ACTUALLY works?"

I'm not sure. I'm thinking you'd need to check with the guys who designed the thing. 🙂

1 hour ago, Captain Obvious said:

So... You're asking "Why does the description of how it is SUPPOSED to work differ from the way it ACTUALLY works?"

I'm not sure. I'm thinking you'd need to check with the guys who designed the thing. 🙂

Right, but I thought the point of moving from master cylinders with 1 reservoir like cars of the 50s to master cylinders with dual reservoirs like we have today/in the Z is a safety thing where if one cylinder fails, the other will still work/help the car to stop. No? That's why I'm confused why even though one was not holding pressure/leaking, the reservoir for the rears held pressure but didn't stop the car.

Edited January 21Jan 21 by chaseincats

8 hours ago, Zed Head said:

Does your brake guy still have the car? What's he doing?

Coincidentally I heard from him today.

They made a replacement hard line which should take care of the fronts. Regarding the rear, he thinks the shoes aren't making enough contact with the drums because the drums are fairly worn. I noticed when I took them off that if you drag your finger from the inside of the drum outwards, there are very noticeable wear grooves on them and he thinks the brake shoes aren't making enough contact with the drums to properly stop the car.

They want to replace the drums, but that shouldn't be the issue since I can stop the car with the emergency brake, right?

Edited January 21Jan 21 by chaseincats

10 hours ago, chaseincats said:

Right, but I thought the point of moving from master cylinders with 1 reservoir like cars of the 50s to master cylinders with dual reservoirs like we have today/in the Z is a safety thing where if one cylinder fails, the other will still work/help the car to stop. No? That's why I'm confused why even though one was not holding pressure/leaking, the reservoir for the rears held pressure but didn't stop the car.

Well without being there and looking things over in person, I can only theorize. And the theory is that the rear circuit WOULD work if you could get enough pedal travel to actually build pressure. But all the other forces at work (having to fully compress the front circuit spring, having to shuttle the brake warning switch piston, having to move the guts of the proportioning valve, having to take up the play in the rear wheel cylinders before the shoes contact the drums......... all that) are making it such that you just don't have enough pedal travel available to build pressure before the pedal hits the floor.

That's why I was suggesting that a couple rapid pumps might get the rears to work enough to stop the car.

My suggestion at this point would be to tell the mechanic to fix the front circuit... Make a new hard line, bleed the master, bleed the fronts thoroughly, bleed the backs thoroughly, make sure there are no leaks anywhere, and then see how the brakes feel. If they feel good, you're done. If they still don't work, then lets go from there.

12 hours ago, chaseincats said:

They want to replace the drums,

When I rebuilt my rear brakes I found that the shoes that I had bought didn't fit the drums well. Their curvature was a fit for a larger drum. They only contacted the drum at the ends. If your guy thinks the drums are too worn he'd only see contact in the middle or edges. Beside that, doesn't he have drum-turning equipment?

But, as CO suggests, it's best to get the hydraulics working correctly before worrying about the hardware.

I literally woke up at 3am last night with the answer. Before I swapped the new master cylinder in, the rear brakes worked, driving it to the brake shop after that, the rear brakes did not grab using the pedal (but do with the hand brake). That means that the drums and shoes are fine, and its the hydraulics that are at issue.

Years ago, I changed the master cylinder out and the one I changed it to had a shorter cavity for the pushrod to travel through. When I pressed the brake once, they car would stop, and the brakes would permanently lock until opened the bleeder screw on the master and let the pressure out. Since the rears worked with the old master, and now don't with the new, my theory is the new master I received has a cavity that is too long for the pushrod in the booster. I told the brake shop to install the old master (which still worked if you guys remember at the beginning of this saga) because that was the perfect length for the push-rod to actuate fully. The drums aren't the reason the brake hydraulics in the rear are no longer working essentially overnight - its the new master cylinder.

I will report back when I hear from them.