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1970 Cuda Soft Brakes

70340Cuda

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I have a 1970 Cuda with disc fronts and drums on the rear. It does have power brakes. Ever since I’ve owned it, the brakes always felt pretty soft. They feel soft for the first bit of travel and get firm towards the end of travel, but they are nearly touching the floor by that point. If I let off the brakes and then get back on them (effectively pumping the brakes) they feel more firm on the second press.

I’ve recently put in all new fluid and flushed the lines. Then I made sure to bleed them. The drums on the rear Are not self adjusting, so I made sure to adjust them too. Adjusting the rears helped, but it still feels soft. Originally I started working on the brakes because they would squeal after driving for about 30 minutes. I noticed the front right brake wasn’t releasing fully, so I took off the calipers on the front and cleaned them both. That issue has been fixed. I did notice on the rears that only the bottom or top edge of the shoes looks like it is catching when braking. The car was fully restored relatively recently to factory specs, so everything is new/refurbished.

At this point I’m not sure what else to check. I’ve heard people talk about bleeding the master cylinder or adjusting the pushrod. I wanted to wait on those until I new for sure that was an issue/potential fix. I also don’t know if that’s just how these cars were back in the day. I’m still learning about these cars specifically. Any suggestions or wisdom would be greatly appreciated! If there is anymore info needed, please let me know.
 

moparleo

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Are these the factory brakes or is it a conversion ? Are the rear brake drums new ?
Can you pull all of the wheels and rear drums and take a few good, closeup pictures of what you have?
Helps to see what you see.
Are you using the Factory Service Manual ?
 

Chryco Psycho

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Disc brakes will not rise pumping them so I bet the rear drum can be adjusted better .
The low pedal can also be an adjustment between the power brake booster & the master cylinder , there is a 2 piece rod in there you can lengthen , it should almost touch without pushing the rear piston in , often this is overlooked when replacing a master cylinder .
Are the shoes the correct size , if they only touch top & bottom possibly they are for a different diameter drum .
 

70340Cuda

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Thank you both moparleo and Chryco Psycho For your responses. I’m not fully sure if they are factory or a conversion. If there is a way to check, I’d be more than happy to look into that. Not fully sure if the drums are new, they are in pretty good condition from what I can tell.

I took several photos of the front left disc and the both rears. I also got a couple of pictures of the master cylinder. The car did come with power brakes from the factory if that means anything to y’all.

I believe I am using the factory service manual. I included a pic of the page where they start discussing the brakes since I only printed out a small section of it temporarily.

The drums appear to be 11”. I did notice when I pulled off the drums that the rear right had shoes that looked different than the ones on the rear left. I’ll be putting another reply to show more pics.
 

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70340Cuda

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I have more pics beyond what is posted so far. If any more are needed, I’ll be more than happy to get them.
 

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70340Cuda

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Are these the factory brakes or is it a conversion ? Are the rear brake drums new ?
Can you pull all of the wheels and rear drums and take a few good, closeup pictures of what you have?
Helps to see what you see.

Are you using the Factory Service Manual ?
Let me know if there is any trouble viewing the photos. I uploaded them from my phone and not sure if it will be an issue. Still new to posting on forums.
 

dadeo1852

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On the dash, does the red brake light come on when you're braking hard? (same light as emergency brake)
Andy
 

70340Cuda

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On the dash, does the red brake light come on when you're braking hard? (same light as emergency brake)
Andy
It does not. I went ahead and checked it again cause I needed to get the car inspected and I didn’t see anything come on while braking hard.
 

moparleo

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If you look at the brake illustration in your service manual you should notice right away that the shoes are not installed in the correct place. The short shoe goes to the front of the car and the longer shoe goes on the rear.
1970 Plymouth Factory Service Manual,
Section 5-5 to 5-10. Read all of it and take notice of the pictures showing the brake parts orientation.
 
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Chryco Psycho

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the right side is incorrect , the left looks correct with the longer brake pad on the rear shoe .
 

70340Cuda

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If you look at the brake illustration in your service manual you should notice right away that the shoes are not installed in the correct place. The short shoe goes to the front of the car and the longer shoe goes on the rear.
1970 Plymouth Factory Service Manual,
Section 5-5 to 5-10. Read all of it and take notice of the pictures showing the brake parts orientation.
After looking at the diagram and what was on the car. It looked like the original owner who restored the car had put both short shoes on the rear right and both long shoes on the rear left. I went ahead and swapped one of the long and short shoes to where the short shoe is now on the front of both drums and the long shoe is on the rear.

I’m not sure how long it will take for them to seat but the pedal still feels the same. Is there a chance the rod that comes out from the booster is out of adjustment?
 

70chall440

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So I have read through this several times and I am going to say that despite having bled the brakes you still have air trapped in the lines some place.
 

70chall440

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Its either air in the system or something going on with the PB/rod. The brakes are a hydraulic system, when done right it is a solid connection (via the brake fluid). Now I suppose its possible that you have something restricting the fluid motion (metering valve, distribution valve, etc.) or perhaps even the wrong or a bad MC. But what you are describing sounds like air in the system.
 

70340Cuda

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Its either air in the system or something going on with the PB/rod. The brakes are a hydraulic system, when done right it is a solid connection (via the brake fluid). Now I suppose its possible that you have something restricting the fluid motion (metering valve, distribution valve, etc.) or perhaps even the wrong or a bad MC. But what you are describing sounds like air in the system.
I just finished separating the MC from the booster to look at the push rod. I checked it’s length and it appears to be correct after measuring. I’m going to bleed the system again this weekend and see if I can maybe find some trapped air somewhere in the system. I really appreciate the help!
 

moparleo

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Bench bleed your aster cylinder before you reinstall it on the booster.
Decoding your fender tag, B51 is for power front disc brakes. So it came with disc brakes. But not the HD option according to your fender tag. Rear should be 10"
Like I have said before, never assume that parts are good or in spec. Especially if someone else installed them. Look at how the previous owner didn't install the shoes correctly. Measure the drums inner diameter. If they are 11" The max spec would be 11.030 . If it is larger than that, the shoes will not extend with the correct amount of contact pressure.
When you reinstalled the shoes did you lube the backing plate contact pads that the shoes rub on ? Did you take some emery cloth and buff/clean the shoes surface so that they will make better contact with the drums. ?
To back up a bit, does the car stop ok and just has a "soft" pedal or is it hard to stop ?
Make sure that the wheel cylinder pistons are moving freely. A stuck piston can cause pedal problems.
Always use a fresh, sealed bottle of D.O.T 3 fluid. A bottle that has been open starts to immediately absorb moisture/water.
 
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dadeo1852

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I have to agree to bleeding master assuming check valve on booster is good.
Andy
 

70340Cuda

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Bench bleed your aster cylinder before you reinstall it on the booster.
Decoding your fender tag, B51 is for power front disc brakes. So it came with disc brakes. But not the HD option according to your fender tag. Rear should be 10"
Like I have said before, never assume that parts are good or in spec. Especially if someone else installed them. Look at how the previous owner didn't install the shoes correctly. Measure the drums inner diameter. If they are 11" The max spec would be 11.030 . If it is larger than that, the shoes will not extend with the correct amount of contact pressure.
When you reinstalled the shoes did you lube the backing plate contact pads that the shoes rub on ? Did you take some emery cloth and buff/clean the shoes surface so that they will make better contact with the drums. ?
To back up a bit, does the car stop ok and just has a "soft" pedal or is it hard to stop ?
Make sure that the wheel cylinder pistons are moving freely. A stuck piston can cause pedal problems.
Always use a fresh, sealed bottle of D.O.T 3 fluid. A bottle that has been open starts to immediately absorb moisture/water.
I checked the drums, and they appear to be within tolerance. I did put lube on the backing plate, but I did not use emery cloth to clean the surface.

The car does stop okay, it just has a soft pedal. I will go ahead and double check the pistons to be sure they are operating properly.

I will also go ahead and bench bleed the master cylinder. I won’t be able to get to that until this weekend, so once I complete that, I’ll let you know what the results are.

Again, I greatly appreciate everyone’s advice and patience. It’s helped me out a lot and I’m gaining a much better understanding of the system.
 
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