1973 Dart brake failiure

[SputnikOne]

Hey all, It's me yet again.

After I drove my dart back home from its storage location and sat overnight, the brake pedal felt alittle too easy to press, and the brake pressure got worse and worse until now it won't even hold the car in idle while in drive. The brake warning light comes on Intermittently aswell.

I checked for fluid but I dont see anything around any of the brake components, and my next logical step is to check the MC for brake fluid, but I've never touched this system before.

I looked at the service manual and either I just don't understand it or it doesn't describe it very well but after reading the brake section I am still confused as to how to go about doing this.

 

[Dana67Dart]

Look under the dash and under the carpet all on the driver's side. If you see or feel fluid your master cyl is leaking. If it's power it might be leaking into the booster.

Google " Chrysler master tech video" and the subject at hand "brakes"

 

[SputnikOne]

Under the dash? My car doesn't have carpet, it has the plastic style floor, but I dont see or smell anything around there.

 

[missing linc]

Pop the top off of the master cylinder and visually inspect for fluid, or lack of.
Slip the spring clip off to on side or the other, the lift the lid.
If there is fluid in the reservoir, and no leak visible anywhere from any of the wheels, steel lines, or rubber hoses, the seals inside the master are probably worn out and no longer holding pressure.
It's possible that your master cylinder has a single bolt holding the lid down as well, I'm not positive when the change was made, if so it will be a 1/2 inch or 7/16 bolt head.

 

[missing linc]

Also check the bottom of the master for signs of leakage.
Does your car have 4 wheel drum brakes or front disc/rear drum, and power or manual brakes?

 

[SputnikOne]

It's four drums

 

[SputnikOne]

Popped the cover off, there is still brake fluid in the two ports but the back one is significantly lower, is this normal?

 

[RustyRatRod]

No. That's the reservoir for the front brakes. Look for leaks on the bottom of the back sides of the backing plates and also inspect the brake hoses to see if one or the other or both are ruptured. Also inspect the hard lines for rust through as it does happen. If you see leaking from the back sides at the bottom of the backing plates, the front wheel cylinder(s) have probably failed. They should be repaired or replaced in pairs.

 

[1WildRT]

Under the dash? My car doesn't have carpet, it has the plastic style floor, but I dont see or smell anything around there.

Look again.... If there's a rubber boot pull it away from the back of the master cylinder...

 

[SputnikOne]

There's definitely some fluid there, but could that cause the aforementioned front only fluid loss?

 

[Dana67Dart]

Under the dash? My car doesn't have carpet, it has the plastic style floor, but I dont see or smell anything around there

I see you found your issue but for the record...

My dart sat for 4 years and seeped for 4 years. Looked just like your photo when I found it and I pulled the carpet up there was pools of fluid in the recesses of the floor and the paint was goo. In my case the carpet was saturated with it as well.

But no smell, no feel, no nothing but fluid loss. It never got to low so no air in the lines. The reason I looked for it was the rear most reservoir was really low while the front was ok. I would add fluid and in a fairly short time it would do it again.

 

[SputnikOne]

So you think this leak caused just slowly drained my reservoir probably during my trip and now me pressing the brakes caused them to pull air into the lines? What's the reccomended fix for this type of leak? It's alittle hard to see what component here is actually causing the leak.

 

[Mattax]

Look under the dash and under the carpet all on the driver's side. If you see or feel fluid your master cyl is leaking. If it's power it might be leaking into the booster.

Google " Chrysler master tech video" and the subject at hand "brakes"

The pamphlet that goes with the filmstrip is here. However it focuses on the drum system

Browse MTSC by Model Year – 1967 – MyMopar

mymopar.com

You will also want to be familiar with the disk brake system, which is also covered in the 1967 MTSC.

 

[Desoto291hemi]

That happened last year when I purchased my Dart

It had sat for years inside and was in excellent condition when I brought it home

After I drove it for several miles on several occasions I noticed the pedal felt weak

After checking the fluid it was very low
I topped it off and drove a few more times
It stopped leaking after topping it a couple of times

My car has 4 wheel factory drums and has never been apart
It was full when I purchased because I checked it first hand
I’m guessing it developed a leak after I started using it some and I was getting ready to replace some seals or the master

But it has stopped leaking now but I still check it every time before I take it out to drive

Tommy

 

[SputnikOne]

Yeah, unfortunately I have no clue if it was leaking since I got it and just got low enough coincidentally or if it's just recently leaking and is not worth just refilling temporarily

 

[Desoto291hemi]

You have no choice really
Put sone fluid in it and see what it does
If if keeps leaking repair it

You will know fairly quickly what’s happening

Tommy

 

[Mattax]

Popped the cover off, there is still brake fluid in the two ports but the back one is significantly lower, is this normal?

View attachment 1716541642

This actually is a regular maint. check, especially with disk brakes.

Assuming the back seals of the master are leaking the master needs to be removed. If the bore is good, then it needs new seals. If the bore is damaged then it can be sleeved by a shop.

Start soaking the flare nuts with a penetrating oil. Its going to take a lot of patiance to free the nuts and not twist the tubing. After soaking for several days or more, break them free a fraction of turn, then tighten, then loosen a fraction. Eventually it will turn without the tube turning with the nut.

My mechanic says heat can be used, carefully, but I haven't done it.

Remove fluid from the resevior first and bleed the brakes.
It needs fresh brake fluid anyway.

 

[Mattax]

There's definitely some fluid there, but could that cause the aforementioned front only fluid loss?

View attachment 1716541645

Looks like its wet.
Clean that up as soon as possible. Pull the vinyl flooring up and get all of it dry. Then use some brake cleaner on a cloth to try to ge tthe residue. Brake fluid (except silicone DOT 5) will damage or remove paint. Rubber isn't bothered by it.

Before concluding this is the problem, look at the brake hoses for both calipers. Make sure neither is leaking.

 

[dr dodge]

my dart did the same sitting for 10 years.
added fluid, short stroked (1/2 - 1" max) pedal, and quick release (toe under pedal) to fill the MC,
1-2 pumps, had tight brakes, no leakage
seems they (MC's ) often drain the rear but if you fill and short stroke the pedal they often come right back

 

[SputnikOne]

If the brakes are already non existent is it safe to assume there's air in the lines that I need to bleed out? I'll refill it and keep watching it over a few days while I wait for parts to arrive, but I'll probably end up replacing the MC anyways with the deplorable state it's in.

 

[Dana67Dart]

Yeah, unfortunately I have no clue if it was leaking since I got it and just got low enough coincidentally or if it's just recently leaking and is not worth just refilling temporarily

No one not there can say if a temporary fix will last for any amount of time.

I would plan on replacing or rebuilding or haven't the master cylinder rebuilt.

It will not magically fix itself.

When mine leaked under the carpet it removed all the paint it contacted to bare metal.


Luckily I have never had a catastrophic brake failure but I know someone who has.

I'm pretty sure he had to change his shorts and was an hour from home.



For the short term, you could add fresh fluid and bleed your brakes front and rear

Then have someone observed the back of the master cyl where it's leaking. You press on the pedal hard and see if fluid seeps out.

That will tell you if you can squeeze out a week or two.

Monitor the level very carefully.

But you may be taking your and a strangers life in your hands

 

[340six]

When you change parts like wheel cylinders, master cylinder, calipers.
Rent or buy a Mity-Vac. Hook farthest wheel to it and pull fluid until clean and bubble free. Move onto the next further one.
Even buying a cheap plastic knock off HF one will do. That's if the local auto parts place can't loan or rent you one.

 

[Mattax]

That looks like the correct master cylinder. Fix it. Correct replacements are almost only available as new old replacement stock (NORS) and last I checked were going for over $200. You can throw a 'cheap' replacement on temporarily if you are short of cash or in a rush. These are made by removing the residual valve from the outlet for front brakes of a drum brake master cylinder. Several threads about this.

 

[slantsixdan]

That looks like the correct master cylinder.

I don't agree. OP said the car has 4-wheel drum brakes. In their pic is a master cylinder for a disc/drum system. The correct master cylinder for the 4-wheel drum system has equal-size reservoirs, like this:

You can throw a 'cheap' replacement on temporarily if you are short of cash or in a rush. These are made by removing the residual valve from the outlet for front brakes of a drum brake master cylinder. Several threads about this.

The residual pressure valve was discontinued after the 1972 model year; drum brake wheel cylinder seals were redesigned to make the RP valve unnecessary.

 

[Mattax]

I don't agree. OP said the car has 4-wheel drum brakes.

You're right he did say that but the photo shows a disk brake master. So I could be wrong or I could be right. LOL
I think we agree its best to use the correct master cylinder for the brake system, which ever it is.
Yes his car is a '73 - for some reason I was thinking it was a '70 in spite of the subject line. the brain is weird thing.