73 Soft Pedal Learning Process

[Cav73]

I have a 73 Challenger with power brakes and soft pedal. I am reviewing the information about this issue on the forum.

* Restoration of body and mechanical completed 3 years ago; I have been working on the interior. This included removing the complete dash unit and steering column. Those are now back in and the car runs again, so I can finally get to the brakes.

* The car had a 340 originally and came with front disk brakes and rear drums, and a limited slip differential.

* My restorer reused the front calipers, put in all new brake lines, a new power master cylinder and booster from Classic Industries, a rear brake adjustable proportioning valve, and cleaned and rebuilt the rear drums.

* On delivery the car had a soft pedal. The pedal went nearly to the floor before it would stop (which was quite interesting given that the first time stopping it was on a significant downslope into the woods - just barely stopped). It has been in the garage ever since.

* I cannot see any leaks in the braking system but I have not pulled the wheels to check more carefully yet.

* When I started the car the other day, I pressed the brake pedal and it still went nearly to the floor. I think I only put pressure on it once or twice.

* Last night, with the engine off, I depressed the pedal 3 times. The first time it went to the floor, the second time it went half way down, and the third time it was pretty firm.

* Today, with the engine off, the pedal was pretty firm. I could depress it maybe an inch or so.

I just lifted the car and tried rotating the rear wheels in both directions, engine off and e-brake released, clutch in neutral. The wheels do not spin freely, they do rotate with significant resistance. I had to pull and push with some force, but they do move. Researching, more to follow.

 

[pschlosser]

Regarding pedal going to floor:

If there is no brake fluid leak, and the hydraulic system is intact, a pedal going to the floor is typically a worn Master Cylinder (MC).

Air in the system can make the pedal spongy, but going to the floor, even when the car is NOT running, sounds like a worn MC.

If your MC is OEM, and you hope to retain it's aged (and possibly surface-rusted) appearance, you'll need a rebuild kit to set it right, otherwise, a replacement MC may be in order.

All that said, I would bleed the brake system, just to make sure there is no air, and the system is full. I would do this and retest before buying parts.

A worn MC may allow you to "pump" the pedal to get more function. But that's a warning sign the MC needs a rebuild.

 

[Steve340]

With the engine off the pedal should be firm and move to around the same freeplay distance each time you apply the brakes.
Engine on the booster will make the pedal "softer" and move somewhat further.
Sounds a bit like trapped air - and readjust the rear shoes.
All wheels front and rear should move easily.

 

[Cav73]

Pschlosser, Steve340, thanks for the input.

I took some photos today to show the MC, Wilwood adjustable proportioning valve, and the plumbing underneath. I also uploaded the data sheet from the Wilwood site for the adj prop valve that most closely matches mine, as a pdf.

Please note that the MC and booster came together from Classic Industries just a few years ago - apparently the MC was not painted and flash rusted. I plan to paint it with an anti-rust product asap. My restorer assembled the brake system as part of the resto.

I know I have to adjust the rear brakes but I have been looking into whether the adj prop valve might have something to do with the low pedal. I at least want to eliminate the possibility. It is not clear to me what setting the knob on the adj prop valve needs to be at when the brake system is first assembled. However, the data sheet does seem to indicate it should be fully open (full pressure).

Also, the data sheet calls for the hard line for the rear brakes to go from the MC direct to the input port on the adj prop valve. It may not be fully clear in the pics, but the rear brake line actually goes from the bottom of the metering valve, under the MC, up to the adj prop valve. I believe the metering valve in this car is a combo metering/proportioning valve. It looks like the one in the 73 chassis service manual, page 5-17, Fig 3. Hopefully this is not an issue; I plan to call the Wilwood tech line to be sure. My restorer has well over 30 years in auto resto and much racing experience, but I want to make sure I did not ask him to do something that does not make sense by putting in this adj prop valve. I don't see how the rear brake line could come out of the MC separately anyway, but I did not look closely at the MC to see if there is some other port.

I depressed the brake pedal several times today with the engine off. It was pretty firm, but it sits below the clutch pedal about 1.5 to 2 inches - I think I read that they should be about a 1/4 inch apart? I didn't start the car again to test it with power on yet. It is sitting cross-wise in the back of my garage and the fumes become incredible even with both doors open - I really need to swing it around which means moving a lot of stuff!

 

[Cav73]

I found this via google:

https://www.bing.com/ck/a?!&&p=847a...hbHZlK29uK215K21vcGFyJmZvcm09Q1NCUkFORA&ntb=1

Installing a Wilwood Adjustable Proportioning Valve After the Metering Valve on a Mopar​

On a Mopar with a manual 1" master cylinder (e.g., 69 Super Bee, 67 300), the distribution block (also called the metering valve) is part of the factory brake system. It’s mounted on the frame rail and controls the split between front and rear brakes. The residual pressure valve is built into the master cylinder and keeps a small pressure in the rear line for initial brake feel www.forbbodiesonly.com.

Wilwood’s adjustable proportioning valve (e.g., 260‑11179) is designed to replace the factory block and allow you to fine‑tune the front/rear pressure split. It has front inlet/outlets and rear inlet/outlets, and can be plumbed to match your setup Wilwood.

Placement — After the Metering Valve?​

If you’re keeping the factory metering valve (distribution block) and want to add the Wilwood valve, it should be plumbed into the rear brake line after the metering valve. This is because:

• The metering valve already controls the front/rear split and has its own function for the brake warning light.
• Placing the Wilwood valve after the metering valve in the rear line allows it to modulate rear brake pressure without interfering with the front brake circuit www.forbbodiesonly.com.
• If you install it between the master and the metering valve, it could affect the warning light circuit or cause unintended pressure changes www.forbbodiesonly.com.

 

[Challenger RTA]

You need to focus. Pull the drums. I had the same problem just about a year ago. Your are going to find it's a frozen wheel cylinder.
Make sure paring brake is adjusted.

Just had some bake problem on an other car of mine. Did the same thing as yours. Right a way I was going to change the booster and master cylinder. Diagnose first. Is the booster holding vacuum? When at idle can you pull the vacuum hose off the booster and is there vac? Check the check valve see it it is working. Has vac and holding vac. Master cylinder working Does it pump up and can you bleed any fluid out? I could bleed mine but it was only a 50% stream as usual. Is the fluid clean? Even with fresh fluid it was the same. Mine was a little dark. Ended up the line where flushed from the constant bleeding. When moving car very slowly will it stop when using the brakes. Yes mine did but it was not full pedal. Pedal would kind of pump up but when done only about half way up when done.
Ended up finding a rear wheel cylinder was not working. Replaced it and all is good.

 

[pschlosser]

A worn MC will leak fluid around the piston seal, and when (for example) stopped at a stop light, the pedal will slowly go to the floor. If one does not pump the pedal back up, the car can begin to roll forward into the intersection.

The brake hydraulic system is a closed system. If the system is bled, and free of air, then when the brake pedal is depressed, the pressure builds in the system and stops the pedal travel.

The seals on the piston, inside the MC can wear, and when they do, this is the system people find - the pedal going top the floor without providing full brake function.

Having said that, you indicated these brake parts are only a few years old. I am dubious the MC is worn and needs a rebuild. If it's not the MC, I'm not sure what the issue is.

Challenger RTA nails it, though. It may be time to start pulling the wheels and drums, and looking for a smoking gun. Or, take it to a brake and tire shop. This problem doesn't seem unique to Mopars, or vintage muscle cars, so it may be hard for a shop to screw it up.

 

[Cav73]

Thanks guys; I am going step by step (and yes trying to focus LOL).

The calipers and drums on this car are original to it, but all the other brake hardware, hoses and lines are new (the booster is new and the MC should be also). The car was just driven (not by me) a half mile to my garage from the truck that dropped it off, so it never received a proper test before I started into the dash, column and other parts of the interior. The pedal was low and braking ineffective until practically hitting the floor the only time I moved the car (before delivery).

First thing I found checking the brakes this week is that the fluid level is not 1/4 in from the rim, it is closer to 1 in below. So it is low.

Second is that the passenger side front brake caliper has a leak at the brake hose - caliper fitting. The fitting and washers are still shiny new. My manual says the fitting should be tightened to the caliper at 25 ft lbs. I have to see if my torque wrench will fit, doing that shortly. I have never seen any brake fluid leak under this car until now, with a slight amount on the floor under this caliper. I have been depressing the brake pedal recently and that may be why I have fluid appearing where I can see it.

Does leaked brake fluid evaporate?

Proceeding to checking the rear brakes. It may be a day or more before I post again.

 

[Cav73]

In retrospect I should have nailed the brakes down first.

 

[pschlosser]

My manual says the fitting should be tightened to the caliper at 25 ft lbs.
Does leaked brake fluid evaporate?

25-ft pounds is not super tight, just... tight. You can guess, if needed, as to the torque. If the fitting is already pretty tight, and it leaks, my instinct is tightening it further will not correct the leak.

no. brake fluid doesn't evaporate like...water. it's an oil, so if it drips onto the garage floor, it may seep into the concrete, so there is no puddle, but there should be a stain.

I recommend you bleed the brake system, and make sure it's full.

Reminder, the pedal going to the floor suggests hydraulic pressure is being LOST when the pedal is depressed.

If there is a leak, then there is your source of pressure loss. each pump of the pedal can squeeze out an ounce or so of brake fluid. If you can pump it to the floor 25 times, you should find pretty good sized leak, spill, puddle and stain.

However, if the MC is worn, then pressure can squeeze by the piston seal.

As always, during your testing, it is essential you keep checking the brake fluid reservoir in the MC to make sure it doesn't run dry. If it does, you gotta bleed the whole system, again.

Loss of pressure. I can think of no other cause for the pedal going to the floor.

 

[Challenger RTA]

The calipers and drums on this car are original to it,

They might all be froze?

About that. My son had car trouble. Had to use one of his other cars. It wasn't used much through the year. There was a brake caliper froze. Looked to get an other caliper. None no where close for the day. I had him unbolt the caliper put a C clamp in the cup. Losing to get what need exposed. Pushed on the brake until the rusted area was exposed. Rolled the dust boot back. He scrapped and sanded with 120 grit emery cloth. Put it together and he was on his way.

I didn't get one of my other cars.

Second is that the passenger side front brake caliper has a leak at the brake hose - caliper fitting.

That is more than likely your problem. Fix that and bleed.

25 ft lbs

If you have put spark plugs in. That's about the same. Run them in and give that little snug 1/8 to a 1/4 turn more.

 

[pschlosser]

Some of you seem to suggest a frozen caliper or drum cylinder may also be the cause of the pedal going to the floor.

Are you guys sure? Can anyone clarify how a frozen caliper (that doesn't leak) and that won't take on any more brake fluid, causes the pedal to go to the floor?

 

[Challenger RTA]

Some of you seem to suggest a frozen caliper or drum cylinder may also be the cause of the pedal going to the floor.

Are you guys sure? Can anyone clarify how a frozen caliper (that doesn't leak) and that won't take on any more brake fluid, causes the pedal to go to the floor?

It happen to me on a wheel cylinder. I went through it the hard way. Changed master cylinder, booster, proportion valve. Changed a few brake lines while I'm at it. No! All of them! OH YEAH! I swapped the parts out to an other car to check if the parts worked.

WAIT! . OK now I get it. Two days later. I could bleed at all points. Still the same. Wait a minute not going to do that again.

Pushed pedal and placed a stick to hold in place. Went and turn what tires that could be turned. 3 didn't moved and one did.

The only thing about what you ask that comes to mind. The portioning valve reroutes or bypass the pressure.

I'm not a fluid engineer fluid mechanics
EXCUDAME!

---

 

[Cav73]

Wow, thanks guys for the rapid response.

I did what I could today before the heat beat me back into the house - major heat wave on the East coast.

Responses:

5-ft pounds is not super tight, just... tight. You can guess, if needed, as to the torque. If the fitting is already pretty tight, and it leaks, my instinct is tightening it further will not correct the leak.

* I had a lot of trouble tightening the connection any further. It was not until I moved from the rear of the caliper to the front, and looped my thumb around the sway bar, that I was able to rotate the nut about 1/8 in. I posted a photo of the caliper and hose connection below. I am very concerned about trying to get it any tighter (I do not want to strip the threads) and yes, I would not be surprised if it still leaks.

* I got back in the car before trying to tighten the connection and pumped the pedal several times. This did not produce any fluid from the connection. Same after I tightened it. I expected to push out more fluid. But I did not run the engine and the fluid in the MC is low anyway.

no. brake fluid doesn't evaporate like...water. it's an oil, so if it drips onto the garage floor, it may seep into the concrete, so there is no puddle, but there should be a stain.

* That is what I thought, but there was only a small, fresh stain on the floor, dime size. There was not a lot on the caliper either, but enough to see and wipe off. This was before I tried tightening the hose connection.

I recommend you bleed the brake system, and make sure it's full.

* Yes, I am resigned to that now but it would be my first attempt at doing this. I suppose I have to bench bleed the MC. I have a neighbor who may be able to help.

Reminder, the pedal going to the floor suggests hydraulic pressure is being LOST when the pedal is depressed.

If there is a leak, then there is your source of pressure loss. each pump of the pedal can squeeze out an ounce or so of brake fluid. If you can pump it to the floor 25 times, you should find pretty good sized leak, spill, puddle and stain.

However, if the MC is worn, then pressure can squeeze by the piston seal.

* It is amazing so much fluid is gone with nothing on the floor, despite a pretty tight hose connection to the caliper. My thought is that once the resto shop installed the brakes, they may have not tested the system thoroughly for leaks. The car pretty much went straight to my garage. But I did move it myself while there, on a sharply sloping lot, and I barely got it stopped before getting into the trees. Maybe in the process I pushed out a good amount of fluid. I never got to checking until now.

They might all be froze?

About that. My son had car trouble. Had to use one of his other cars. It wasn't used much through the year. There was a brake caliper froze. Looked to get an other caliper. None no where close for the day. I had him unbolt the caliper put a C clamp in the cup. Losing to get what need exposed. Pushed on the brake until the rusted area was exposed. Rolled the dust boot back. He scrapped and sanded with 120 grit emery cloth. Put it together and he was on his way.

* I am glad this worked out for your son's car. The resto shop completely cleaned the original calipers and they look really good. But I can't be sure how they actually function until I stop the one leak I found and any others, and refill/bleed the system. I will try the C-clamp depending on how this goes.


The next part of this process is to back off the parking brake adjustor and then adjust the rear brakes. Right now they are pretty tight. I am not sure if the parking brake is doing that or if they adjusted that way. My understanding is that they should rotate at least a full turn or more by just giving them a spin, with minimum hand effort. I have to physically turn the rear wheels now, pretty much a two hand deal. Once I relax the parking brake adjustment, I will test this again before adjusting the drum. Of course I will also check for leaks back there and inspect the wheel cylinders.

It looks like the adjustor for the parking brake is along the centerline so it will be a bear to reach. Hopefully it isn't rusted as it is just a few years old.

 

[pschlosser]

"bench bleeding" calls for the MC to be removed, and bled on the bench. I think this is really unnecessary.

I have a tendency to overthink and complicate things. I encourage you to keep it simple and to seek out some youtube videos on the topic. Bleeding the brakes is easy, but it's still a chore, unless you're young and agile.

Before this is through, you may be bleeding the brakes more than once. So you're gonna git good at this, whether you want to or not

with the youtube videos, there may be more than one bleeding method presented. the gravity method is lame, and I don't recommend it. That one, you more or less let gravity drain fluid at each wheel, and it can take several hours.

i recommend the method where a helper presses the pedal (on command) and you are at the wheel, tightening and loosening the bleed fitting. You will need a helper to bleed the brakes, unless you buy special tools. Harbor Freight makes a tool so one can bleed the brakes solo using vacuum (at each wheel).

 

[pschlosser]

if you had to really torque on that hose fitting to get it to seal, the sealing may not last. But once this is all resolved, and you're driving the car, keep an eye on that fitting, and if it doesn't leak after miles of city driving, you're good to go.

 

[Cav73]

Thanks Pschlosser. You Tube University is great - I have learned a great deal hitting videos, from rebuilding the carb on my 30 year old snow blower to hanging a door. The carb was far easier LOL.

But this forum is great and you get feedback - essentially instantly - which I very much appreciate. I have learned a lot, some of it obvious, but not if you doing the task for the first time.

I am 65 but still in pretty good shape so running around the 4 corners of the car to bleed the brakes won't be that bad... except doing it in 98 degree heat will be no fun. I may wait for a relatively cool day before making the attempt. I actually have a brake bleed kit I have never used, so I need to pull it out.

Bleeding the system without removing the MC sounds far more appealing. If it turns out that the MC itself is bad, or if the rod is somehow out of adjustment or incorrect, maybe then I will have to pull it. I hope not as I bought the MC and booster together but I understand some of them come bad.

Meanwhile I will see what I can do with the rear brake adjustment. Hopefully no leaks...

Thanks for all the help!

 

[pschlosser]

I cannot say I have ever heard of anyone or a shop, removing a MC just so they can bench bleed it.
that is normally reserved for a new MC already on the bench.
it's a handy process to get the air out of the MC, so once installed, further brake system bleeding goes smoothly.
that said, there are some that do not bother to bench bleed at all.
they install the MC dry, fill it, and bleed it all from there.

 

[Cav73]

Ha! I am all for less work LOL!

 

[Challenger RTA]

I did what I could today before the heat beat me back into the house - major heat wave on the East coast.

I just finish my shingling my roof at 9 PM. It was only 90. The roof was a bit more warmer. I did take a break from 1-3 Pm. The warmer time of the day.