Invisible brake leak?

[OUTFXD]

Lately,  I noticed Jacquilines Brake pedal doesnt want to come up from where I push it to brake.  I would use my toe to bring the pedal back up,  and it was quite stiff.  The Zirk fitting for the brake pedal was filled with 70 year old grease and wouldnt accept new grease.   I took it off and soaked it in solvent,  the cleaned it out with a drill bit (No drill attached  just a drill bit).  I got it cleaned out and put it back on.  Put fresh grease in the pedal pivot.   It loosened up the pedal,  but it was still staying on the floor.  I opened up the master cylinder and found it empty even though I filled it last weekend.   I checked all four corners and found no traces of leaky bake fluid.

 

I have a leaky front main bearing seal so the master cylinder is soaked in oil so I cant see any obvious  signs of a leak.

 

I filled the brake master cylinder and drove to the corner store (four point four miles each way).  On the way down the breaks worked properly most of the way,  getting squishy near the end of the run.   On the drive home it was back to the pedal near the floor and not wanting to return.

 

I havent checked but I feel it is safe to assume the master cylinder is empty again.

 

So one of two things is happening.  1) the master cylinder is leaking and it being soaked in oil is hiding the evidence.  or b) the wheel cylinders are leaking inside the brake drum.

 

My question is this.  If the wheel cylinders where leaking,  wouldnt there be tell tale signs of the leak at the bottom of the break drum and on the wheel/ tire.  Or would it hold the fluid until someone pulled the drum off?  Ive never heard of such a thing,  but it has been decades since I worked on drum breaks.

[Plymouthy Adams]

usually with that much loss of fluid as you suspect in such a short run, yes you should have trace evidence of this fluid...put some fluid back with a helper holding a firm pedal with lots of pressure and inspect the rear of the master for bypassing, then all the external lines and fittings and see if dripping from inside any drum before you result to pulling the drums themselves.  Coud be master, could be lines or various fittings.

[Jerry Roberts]

Also , master cylinders usually have a rubber boot that can be pulled back for inspection of leaked fluid . 

[Veemoney]

As PA suggested wipe it all down and fill the MC again. Get someone to push the pedal while you check for fluid leaks. Not sure when your last R&R of the system was but don't rule out a bad line leaking under pressure when checking the MC underneath the car.  

[Dan Hiebert]

A master cylinder's amount of brake fluid leaking from a wheel cylinder in four miles would be readily visible from outside the drum.  Once stopped, you would see fluid coming from the bottom between the drum and backing plate.  The drum would not hold the fluid once stopped.  The wheel cylinder boots can't hold that much fluid without leaking, either.  So, you probably have a leak somewhere else.  If there is a pin hole in one of the lines, it may not be readily apparent if the leak is pointing away from any surface where it would show.  Before disassembling anything, I would echo cleaning off the brake system, filling the master, and having a helper push the pedal while you observe all the lines and connections.  If it is a small leak, it may be helpful to hold a light from behind what you are looking at so you can see any fine mist.  Holding a sheet of paper near connections and suspected leaks may help reveal leaks, too.

[kencombs]

Good advice already given.  I only offer this:   Please don't drive it until fixed a sudden loss of brakes is not fun, BTDT.   And, add a return spring so you aren't relying on the masters internal spring to return the pedal.

[desoto1939]

It might be the presure relief valve inthe MC. I had a similar situation inwhich the pedal was working and then it would go to the floor, but no loss of brake fluid. It was off and on situation.  Pull all four drums to determine no leakage. Took the MC out of the which is under the floor on a 39 Desoto took the MC apart and did a rebuild on the internal parts.

 

Left the pressure relief value the old one onthe table. The next day looked at it very closely and then found a very small slit in the rubber gasket. This was allowing the fluid to not build up pressure so the pedal woud go to the floor. After replacing the vale the issue was corrected.

 

Also check the wheel cylinder belled screws to make sure they are not leaking any fluid at the threads where they screw into the wheel cylinder.

 

Rich Hartung

[OUTFXD]

Does anyone have a parts number for a master cylinder rebuild kit from a reputable company?   Like Standard or Raybestos?

[Sniper]

You know, when I worked the parts store I always disliked it when customers didn't give me the vehicle info. 

 

I mean I could assume it's the 46 in your profile.  Or I could assume it's a 67 F100,

 

https://www.oldmoparts.com/parts/g_service_brakes/master-cylinder-kit-3/

[Hickory]

Come on sniper, post one clearly stated 70 yrs old. Can't be a 67. Lol. Yes info helps.

[Sniper]

51 minutes ago, Hickory said:

Come on sniper, post one clearly stated 70 yrs old. Can't be a 67. Lol. Yes info helps.

 

Look, I can't count past 20 without getting arrested, lol

[OUTFXD]

2 hours ago, Sniper said:

You know, when I worked the parts store I always disliked it when customers didn't give me the vehicle info. 

Sorry.  I just assumed at this point everyone knows what my car is LOL.   I promise to do better

 

[OUTFXD]

Finally got everything appart.  Clean up the parts and what do I have?

 

Looks like it has been recently rebuilt.  The Piston is alluminum interestingly, stamped "Built in USA" and "Wagner".  My "new" one (a NOS piece) has Brass color but not quite that heavy,  Coated steal?

 

Edited July 14, 2023 by OUTFXD

[OUTFXD]

(sorry for the blurry photos,  my camera didnt want to focus on the piston)

 

Everything LOOKED alright,  seals where soft with no tears,  Looked new...ish.

 

On closer inspection of the piston,  the leading edge had a chip out of it and it (the chip) was lodged in the seal. 

[OUTFXD]

The Cylinder bore looked okay,  Felt around with my finger and it was absolutely smooth,  No scoring or pitting.

Edited July 14, 2023 by OUTFXD

[Los_Control]

Just now, OUTFXD said:

On closer inspection of the piston,  the leading edge had a chip out of it and it (the chip) was lodged in the seal. 

IMHO, it is the thin leading edge of the seal that does 90% of the work.

 

Good job on finding it, sure a new seal will make a difference.

[OUTFXD]

okay.  new problem.  I put all the new parts in the master cylinder,  ran new brake lines.  Pressure built emediately  and I had a firm brake petal.   Took her out for a test run.  I made it 2 or so miles and suddenly the brake petal went to the floor.  Total loss of all brake petal pressure.  

 

I figured I had failed to tighten one of the new brake lines.

 

Went out this morning. took a look and the master cylinder was low on brake fluid, but didnt appear to be leaking at any of the lines. 

 

I refilled and pumped up the brakes.  It took some doing, but it built pressure.  ass soon as I let off the petal all the pressure went away.  Scratching my head I went to top up the master cylinder again and I noticed the whole top of the brake cylinder was wet with brake fluid.   I pumped up the brakes.  Held them. and nothing happened.

 

But when I released the brake petal,  a stream of brake fluid appeared out from under the master cylinder cap.  Quite a feat for a not-topped-up master cylinder.  I did some observations and it appears to be building pressure INSIDE The brake fluid reservoir,  then releasing it out the cylinder cap when I release the petal.

 

What in the world is going on here?  HELP!!!

Edited July 16, 2023 by OUTFXD

[desoto1939]

did you put the release value in backwards?  Something is wrong inside the MC make sure you assembled it correctly.

 

Rich Hartung

[kencombs]

Sounds to me like you have air in the lines still.  Pumping up the brakes compresses that air, it then pushes fluid back into the reservoir when the pumping stops.   At least we're sure your return port is open!

[OUTFXD]

Pulled the master cylinder,  tried turning the return valve over but it wouldnt lay flat, returned it to its previous position and it fit perfectly, 

 

The brake fluid is full of little black particles and the seal on the piston is WAAAAAY more pliable than it was when I started.  is this normal?

 

Using dot3 brake fluid FYI

[kencombs]

Little black particles is not normal.   I think a brake flush is in order.   Since I can't feel the seal from here I can't offer an opinion, except to say that dot3 shouldn't attack any parts for a car that age.

The black stuff commonly appears when brake flex lines start to fail internally. 

Edited July 16, 2023 by kencombs

[Dave72dt]

Did you by chance use oil to lube the parts when installing?  Oil softens and destroys rubber brake parts.

[JBNeal]

On 7/16/2023 at 4:34 PM, OUTFXD said:

Pulled the master cylinder,  tried turning the return valve over but it wouldnt lay flat, returned it to its previous position and it fit perfectly, 

 

The brake fluid is full of little black particles and the seal on the piston is WAAAAAY more pliable than it was when I started.  is this normal?

 

Using dot3 brake fluid FYI

Black particles in your brake fluid is very bad and a sure sign that every rubber part in your brake system will need to be replaced with all contaminated brake fluid removed and flushed out...I ran into this issue with the QuadCab and it took years to get corrected...

 

additional information - brake fluid contamination cautionary tale

[OUTFXD]

so... Took the Master cylinder apart for the third time. 

 

Please remember that this is a NOS item,  with less than 10 miles  on it.  and honestly,  it failed in about 2. 

 

This is the seal that goes around the outside edge of the piston.

Edited July 23, 2023 by OUTFXD

[OUTFXD]

Trying to figure out the "why" of it all.   the brakes started going soft so I added some DoT3 brake fluid.  Then They failed.  I rebuilt the master cylinder, with NoS components, cleaned it out with Brakeclean and added fresh DoT3,  the new components failed nearly immediately .

 

I wouldnt think brakeclean would dissolve  components.  is it possible this was caused by a "pool" of brakeclean  in the master cylinder?  Also... DoT3?  Not interested in repeating this issue again.