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Brake Fluid Filling Problem help


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I need a bit of help deciphering what I'm doing wrong with filling an empty system with brake fluid.
 
I started filling the system with fluid at the farthest wheel cylinder from the master.  It took quite some time, with the help of another pumping the brake with me opening and closing the bleeder, until I noticed a leak at the front junction 'T'.  Ok, had to tighten a few connections to fix that.  But when fluid started appearing in the bleeder hose the pumping stopped moving fluid.  The system started with new brake lines, new hoses, honed master cylinder, honed wheel cylinders and I've double checked to make sure I had installed the new master cylinder kit in the correct order (it's so simple, only one cup to check is installed it the correct direction, a sixth grader to figure it out) but I can still pump the brake pedal and the fluid doesn't appear to move.  All connections and bleeders are closed and I can still pump the brake pedal up and down.

 

I've never filled an empty system before but I've bleed cars plenty of times and when the line is filled and you close the bleeder you can no longer depress the brake pedal.  I assumed when each line is full I'd notice the strong resistance to pedal pressure.  So what am I missing?  I feel a bit stupid I can't determine  the cause of the problem.

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Suggest you fill the master cylinder and crack the closest bleed valve to start with then work towards the next closest bleed valve.  Finally do the back wheel cylinders last as they are the  longest run of pipe to displace of air.

If you have overhauled the master cylinder, suggest you fill /  bleed it on the bench first before you install it onto the chassis, that will considerably speed the removal of air  from the system. If you are doing the bleed operation on your own, suggest you purchase a check valve type bleeder that will make the bleeding operation a success. 

Lastly if you have troubles with getting the last of the air out of the system piping and the pedal gets spongy overnight after sitting, utilise a tyre lever or such to hold the pedal down hard overnight and hold the fluid under pressure for quite a few hours. Then open the furthest bleed valve . Or use a hand operated vacuum pump from the bleeders.
I have had success with all of the above methods in various times and older models in the past. Good luck

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Well ,JFranklin, I suspect my explanation wasn't very clear as to what I did. But no, I didn't fill the system from a wheel cylinder.  I've never heard of, nor think it's possible, to fill a system from a wheel cylinder.

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Thanks for the suggestions, Russ.  I've always bleed from the farthest wheel cylinder first working back to the closest.  Come to think of it I hadn't even given it a thought to do the front wheels first.  My first thought was maybe I had honed the master cylinder too much but then ruled out that thought remembering how much I had to squeeze the rubber cup to get it in.  I'll give a few of your suggestion a go when I get another bottle of brake fluid.

 

Grampa's 37 Pontiac 6 has given me a few sleepless nights but with the help of fellow 'real' mechanics I may finally get this puppy back on the road.

 

Thanks again for taking your time to respond!

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Funny, I was always told to bleed the farthest cylinder first just like you did. I once was working on a truck that after bleeding the brakes I could never get a good pedal or good stop. I got my wife to work the pedal while I went under to see if I could see anything at all and I did. Someone in the past had turned the drums so thin that they were deforming as if they were plastic. I had never thought that would be what I would see!

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Always the farthest first.  Make sure to pump the pedal slowly.

Good Luck.

 

I am so glad to have mechanically actuated brakes on my daily driver of the last 59 years.

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Kookie1 et al:

 

Coincidentally, I just completed replacing all brake lines, master cylinder, wheel cylinders, etc on my 1937 6-cylinder two-door touring sedan last evening.  This is also a "family heirloom".  My former wife's mother had owned this car since 1941, and it last ran in 1968.  When she passed away 15+ years ago, my former wife gave the car to me ... but not much happened to it.

 

Regarding the brakes, while I would have started at the furthest wheel just like you did .... and would have likely encountered the same problems you did ... a careful reading of the brake bleed ing procedure from the 1937 Pontiac Shop Manual indeed says to start at the closest wheel cylinder.  As you can see, they also suggest using a glass jar partially filled with clean brake fluid ... rather than shutting the bleed valve .... as a means of keeping additional air from getting drawn back in on the "return stroke".  Of course, it does not state that this applies to a complete fill situation.

 

In any event, I have attached a copy of those two pages from the shop manual.

BrakeBleeding_Page78.JPG

BrakeBleeding_Page79.jpg

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I am in the verge of filling and then bleeding my 1937 brake system.  Earlier in this thread, Russ mentioned bench bleeding the master cylinder which is nothing that I have done before.  I gather that fills the actual cylinder from the reservoir, but it is not clear whether I will need some sort of plugs on the front and rear connections at the MC to prevent creating a big mess ... or do I misunderstand what bench bleeding is?  Alternatively, without bench bleeding, how does one insure that the master cylinder gets filled?  Finally, and this may all be related: there is a hole approximately 1/4" in diameter between the reservoir and the master cylinder.  When the brake pedal is fully released, is the primary master cylinder seal pushed back towards the firewall, so that this hole is open from master cylinder to reservoir so that the master cylinder is always full ... but then get quickly closed off by the primary seal as the brake is applied so that pressure builds in the master cylinder?  Is the pedal play adjustment part of what insures that this hole is open between master cylinder and reservoir, or do I misunderstand what that does?

 

Sorry for these neophyte questions ... I suddenly realize that bleeding a largely functional brake system is far easier that a completely dry start.

 

Kookie1, did you get your system fully bled to your satisfaction?

 

Thanks for your consideration.

 

John

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Bench bleeding, on more modern cars, is done on the bench with a little hose kit to run fluid back into the reservoir and get as much air out of the cylinder as possible. It saves a lot of time bleeding on such more modern cars with firewall mounted master cylinders, especially if the cylinder isn't level. It does not save you from the final bleeding routine, and possibly even tipping the car in some cases

 

None of that is likely to apply to your 37. On a more modern car you are scrambling to mount it and get the lines closed before too much fluid leaks out. With the cylinder under the floor, it is probably a waste of time due to the longer process of mounting it and hooking it up. The good news is those under the floor systems are easier to bleed, and an empty master cylinder will almost bleed itself overnight if it is the only thing empty.

 

I would do the following. Get a vacuum bleeder with the hand held "Mityvac" clone and a bleeding jar (the harbor freight one will do). FIll the master cylinder with FRESH fluid. It spoils. Buy the brand your FLAPS sells the most of. Get the big jar.

 

Suck the furthest bleeder first (longest line). Thats probably the right rear, but look at the line routing to be sure. Do not allow the master cylinder to get empty. If you do, start over. Suck until you get clean fluid. Don't worry about bubbles too much. Even when the air is gone, you will still be sucking air from the bleeder threads. Close the bleeder. Then do the second farthest, and so on until all four corners are done and have spit out nice clean fluid. The system is full of FRESH fluid now, only a quick final bleeding needed to get any remaining air out.

 

Now carefully pump the pedal up. It is probably best not to stomp it all the way to the floor. With a friend's help, have a friend crack the furthest bleeder then quickly shut it while you hold pressure on the pedal. The idea is to do it quick before the pedal goes to the floor. When the bleeder is closed, let pedal back up, then push back down again, Do another quick squirt.

 

Do all 4 corners like this, 2 or 3 quick squirts each. You can use the hose and jar from your bleeder kit to help keep the mess under control. You may want to do this part yourself instead of having the friend do it because the jar and hose seems to have a mind of it's own. Brake fluid eats paint. Be careful.

 

Once you have done all that, quick bleed the master cylinder using the same method you used at the corners. Crack its fitting like a bleeder using a tubing wrench or wrenches. You will need a rag or something to keep the brake fluid under control (it squirts out under high pressure, and there is no place to hook a hose).

 

All done! Good luck. :)

 

Edited by Bloo (see edit history)
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Once you have the system bled and working, adjust your brakes. Instructions are in the manual. I am pretty sure 37 is too old to have any self adjusters (my 36 doesn't have any), so they probably need adjusting. You will be rewarded with a higher pedal.

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Bloo:

 

Thank you for your quick response.  I seem to be massing something pretty basic:  I have filled the master cylinder reservoir ... but nothing I have done has reduced the level.  I DO have one of the Harbor Freight MightyVac clones.   If I am pumping on the closed bleed screw, I can easily achieve 25" of vacuum.  However, when I crack the bleed screw and keep pumping to hold it at about 10" of vacuum, I get no fluid and the level in the reservoir has not gone down.

 

They are the "funky" bleed screws that have the internal 8-24 thread.  However, I happen to have some 8-24 stainless cap screws that are designed for vacuum work and have a hole drilled axially along the length of the screw as shown in the first attached photo.

 

So, my setup includes that speciatly screw and some vinyl tubing to connect to my vacuum pump as shown in the second photo.  Note: when I crack the bleed valve, I AM opening the 3/8" bleed screw (rather than loosening the vacuum cap screw).

 

The other thing that seems a little curious in this brake system (I don't know if this is true on your '36), but at the end of the master cylinder is a "3-way" banjo bolt setup where the bottom connection goes to the rear brakes, the forward-pointing one goes to the front brakes, ,and the top one goes to the brake light switch.  However, to the best of my knowledge,, these are the original cleaned parts.

 

So, at this point, I can't quite figure out why I don't seem to be gettting any fluid movement out of the reservoir.

 

 

Thank you for your help and consideration.

 

John

 

VacuumScrew.thumb.jpg.617958baa175fce17e4d830e9245c411.jpg

 

WheelCylinderVacuumSetup.thumb.jpg.1e36d2fd7a229cadc39091903f64cf7f.jpg

 

MasterCylinderBanjoBolt.thumb.jpg.2a27d9be01234a42f4ff84812789444d.jpg

 

 

 

 

 

 

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I like your bolts. I forgot about the weird bleeders. Most cars no longer have them, but mine has them too. I forced one of the HF boots over it. Not great because you cannot get a wrench on at the same time. I like your way better. I wonder if your bleeders or the hole underneath could be plugged? You may not notice the fluid going down (until its too late and you sucked air), but you should be getting fluid sucking out into the cup that goes with the mityvac.

 

My brake light switch is where yours is. I am not sure if the fittings are the same. You could crack anything there to bleed, preferably the front fitting, but only do that last after everything else is bled.

 

My bleeders have a screw capping off the threads that you have to take out. I think their purpose is to keep dirt out. If yours have no screws in there, maybe they are full of dirt? I would take one off and make sure its not plugged, and maybe stick a piece of wire in the hole in the cylinder where you took the bleeder out.

 

Another possibility is a bad brake hose. It is common for them to block the line when they break down internally.

 

Come to think of it, I had a couple of plugged bleeders the first time I bled mine. Are screws like that readily available somewhere?

 

 

Edited by Bloo (see edit history)
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Bloo:

 

Thanks for your quick response.  Yes, my wheel cylinders had screws in them to keep out dust and dirt as well.  I'm pretty certain that all of my special vacuum screws are not plugged and I took out the bleed screws before installing all of the wheel cylinders to inspect them and they were not plugged.  If I remember correctly, the four wheel cylinders are NOS and the master cylinder was either NOS or was rebuilt by someone else.  The three brake hoses and all brake lines are new.

 

Thus far, I've seen no liquid in the vacuum cup with the Mityvac.

 

I think tomorrow, I will double check all my connections, may go get a couple of "modern" non-threaded bleed screws, and see if I can get fluid flowing.

 

Thanks for your quick responses ... you have been a great help thus far.

 

Have a good evening,

 

John

 

p.s. I have a spare 8-24 screw through-drilled for vacuum.  If you want it, PM me your address and it is yours.

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Agree with Charles.

You may wish to try the bench bleed method to confirm the master cylinder operation.
If you are concerned as to the brake fluid making a mess, just use fresh water when you have it on the bench,  this will confirm that the internal components are configured correctly and it will displace fluid again when you have it installed and full of brake fluid. Drain the reservoir of water and displace it with brake fluid when you have confirmed the master cylinder operation. It will soon displace when you bleed the rest of the system to the lines.

its one of the advantages of displacing to the shortest line first also.

I bench bleed all of the master cylinders I overhaul / fit as I did on the 51 and the 53 to ensure it will work before its fitted to the vehicle. just confirms the functionality of the component before its fitted .
On the discharge port I used a tapered adapter plug that you find in the handvac pump systems to plug into the port and then run a short hose back up to the reservoir so effectively you are just recycling the fluid internally and using the reservoir as a separator to allow the air to migrate out of the fluid. These small single acting master cylinder's usually only take 5-10 strokes to fill and bleed the air from the internal bore. See how you go :)

 

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Pontiac1953, Russ, and Bloo:

 

Thanks for your input and suggestions.

 

This evening I began to pull out the master cylinder.  The first thing that I noticed was that there was no brake fluid in either the front or real line where it connects to the master cylinder ... so, clearly, something is wrong with my master cylinder.

 

I have a spare.  While it is not the original Delco casting, just from looking into it, I can see that the aluminum "plunger" is in a different position than it is in mine.  I suspect that means that something is jammed in mine.  Tomorrow, I will hope to bench bleed the replacement and, if that goes well, install that one to hopefully get a set of functional brakes and then, at a later date, explore what is amiss in the original Delco master cylinder.

 

Thank you all for suggesting that my master cylinder was likely the culprit ... you collectively saved me time in trying to bleed a brake system that was likely never going to fill ...

 

Have a good evening all.

 

John

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  • 2 months later...
On 6/21/2020 at 3:59 PM, jdshott said:

I am in the verge of filling and then bleeding my 1937 brake system.  Earlier in this thread, Russ mentioned bench bleeding the master cylinder which is nothing that I have done before.  I gather that fills the actual cylinder from the reservoir, but it is not clear whether I will need some sort of plugs on the front and rear connections at the MC to prevent creating a big mess ... or do I misunderstand what bench bleeding is?  Alternatively, without bench bleeding, how does one insure that the master cylinder gets filled?  Finally, and this may all be related: there is a hole approximately 1/4" in diameter between the reservoir and the master cylinder.  When the brake pedal is fully released, is the primary master cylinder seal pushed back towards the firewall, so that this hole is open from master cylinder to reservoir so that the master cylinder is always full ... but then get quickly closed off by the primary seal as the brake is applied so that pressure builds in the master cylinder?  Is the pedal play adjustment part of what insures that this hole is open between master cylinder and reservoir, or do I misunderstand what that does?

 

Sorry for these neophyte questions ... I suddenly realize that bleeding a largely functional brake system is far easier that a completely dry start.

 

Kookie1, did you get your system fully bled to your satisfaction?

 

Thanks for your consideration.

 

John

 

Yes, the rubber is visible in the big hole. there should be a second "pinhole" just ahead of it. This pinhole is important as it prevents pressure building in the system. If it is plugged it may contribute to your problem. Also... make sure the pedal is not holding the piston down slightly as that will prevent it refilling. 

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@Oldtech:

 

Thank you for your post. I ended up putting a replacement master cylinder in … and that one did allow me to fill and bleed my lines and wheel cylinders. However, I would like to replace it with the original (but problematic) Delco. 
 

While I don’t have it in front of me (I’m in a different state …) I remember seeing the smaller pinhole that you describe but did not check whether it was open and clear. 
 

Thank you for helping me to understand how the master cylinder should work. 
 

John

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