Bleeding master cylinder

[chris norman]

Right let me start from the beginning, I've recently noticed brake fluid running down the outside of my master cylinder body dripping onto the floor etc and after several attempts at straightening the lid and adjusting clip tension etc I am no further forward. The cylinder was new 2 years ago and was fine for most of that time so I wasn't convinced the lid has been the problem anyway. I recently overhauled the rear brakes and during the bleeding process with the lid off I noticed upon the first press of the pedal I get a pretty high geyser/fountain ejecting from the rear brake portion of the reservoir, nothing at all from the front section. It appears to be shooting out of the forward most hole in the base of the reservoir, leading me to think I've got a big bubble of air stuck in the front most section of the cylinder. Does anyone agree with this and if so any good suggestions on how to shift it as I've tried bleeding from the line fitting but struggling on my own to do it using a pry bar ( wrapped in cloth between firewall and pedal link) . The new cylinder did not have a bench bleed kit with it and I can't seem to find one in the uk so unless anyone has a clever trick I'll have to order one and wait a few weeks to get it! The amount of splash produced by this fountain is no surprise it finds its way out past the lid seal! It hit the hood first time I saw it!
May thanks for anyone's help on this.
'74 360 duster disk/drum by the way

 

[slantflat]

If you have some old brake line hanging around disconnect the lines to the cylinders and cut two pieces of brake line, and attach them where the other lines go. Bend the cut ends into the reservoirs and fill it up. Just like bleeding anything else keep pumping away until you don't see any bubbles.

 

[375inStroke]

Sleazeball way is to have the lines disconnected, cover the outlet ports with your fingers, and have someone pump the brakes. Put the lid on this time, though, when you do it. Pump until just fluid comes out. You don't have to press with your fingers very hard, and don't have the pumper go too fast. Use rags and whatnot to deal with the mess. It'll work, though, and brake fluid is water soluble, so just hit the area with a garden hose when you're done.

 

[TrailBeast]

None of what I have read so far takes into account that the air might not be in or close to the master.
Sounds to me like you have a good handle on what the issue is, and I have used a squirt bottle with a hose on it to force the fluid up to the master from the wheel cylinder end.
It works well when you are doing the bleeding by yourself.
FYI, it's ok to only fill the master half to 2/3 of the way also because it helps keep the fluid away from the cap a little better.

 

[BillGrissom]

I like using bent steel brake lines when "bench bleeding" the master, with a short clear section so you can see bubbles. The plastic tubes can come free and spray brake fluid everywhere. Some MC's come w/ a really cheesy bleed kit that doesn't screw in, but you just push in the port holes and hope friction holds them. You may have to pump the pedal 50 times to get all the air bubbles out. I always do it on the car, not on a bench. I can push the pedal w/ my foot and crane my neck to see, but I am 6'1". Otherwise, I would pay my daughter $1 to push, or tell her it is a competition called "push the pedal".

I know a geyser can spray fluid past the reservoir lid seal, but still seems bad since if fluid can get out, moisture can get in. I have a newer MC w/ plastic reservoir on all my old Mopars. They seal better.

 

[chris norman]

If you have some old brake line hanging around disconnect the lines to the cylinders and cut two pieces of brake line, and attach them where the other lines go. Bend the cut ends into the reservoirs and fill it up. Just like bleeding anything else keep pumping away until you don't see any bubbles.

I was hoping do do just this as I have plenty of brake line about but I cant locate the right thread unions to fit the master cyl over here as European ones are much smaller, I think I need 9/16.

 

[chris norman]

None of what I have read so far takes into account that the air might not be in or close to the master.
Sounds to me like you have a good handle on what the issue is, and I have used a squirt bottle with a hose on it to force the fluid up to the master from the wheel cylinder end.
It works well when you are doing the bleeding by yourself.
FYI, it's ok to only fill the master half to 2/3 of the way also because it helps keep the fluid away from the cap a little better.

that's a very good point you make about the air could be elsewhere, I was assuming as I`d bled the system several times that it was where I couldn`t get at (in the cyl), maybe a big syringe full of fluid from the wheel pushing back is the way to go

 

[TrailBeast]

that's a very good point you make about the air could be elsewhere, I was assuming as I`d bled the system several times that it was where I couldn`t get at (in the cyl), maybe a big syringe full of fluid from the wheel pushing back is the way to go

However you feel you can do it without introducing more air.
The pressure bleeders are great, but not many regular people have one.
That's why I use the squeeze bottle.

 

[AJ/FormS]

Hang on a sec.
Geysers are normal.
Especially from the rear system,which is usually the frontmost reservoir,closest to the rad.. And it may not have anything to do with air. The rears are drums. Which have huge return springs on the shoes. When you push down on the pedal, you push fluid out to the rear. And when you lift, the fluid is returned by those springs. If you pump too fast,not all the fluid has time to return. If the rear shoe adjustment is loose, it can take many pumps before the shoes finally hit the drums. Then the pedal gets hard. So then you lift off the pedal, and all that fluid is returned rather violently by the return springs, and you get the huge hit-the-hood geyser. That would be a normal consequence of a loose rear shoe adjustment. To prevent this I always crank the rear adjusters until the shoes are jammed up pretty hard; then I slack them off about 3 tool strokes or maybe 10 clicks,just until the drums can be turned with some difficulty. After the system is bled, I redo the rear adjustment. If you crank the adjusters hard and leave them there, it may be difficult to bleed the fronts.
>Yes the geyser may indicate air, but then the pedal will never get hard.
>Once everything is adjusted right and bled, then the geyser thing will be minimized to just a roiling of the fluid.
>Bleeding the master using your fingertips as one-way valves is the fastest way to get the job done. I do it on the bench, with the M/C in a vise. I don't want brake fluid clean up under a customers hood.
>There should never be brakefluid on top of the lid seal,often called a diaphragm. If there is, then it is perforated somewhere. If you are not careful, or if the reservoir is too full or if the reservoir is severely angled n the fore and aft direction, then it is possible to have the fluid forced over the edge during the diaphragm install.Then when you secure the lid,the bailing wire will put the clamp on and the fluid will be weeping for a while. But it should eventually stop. You must make it stop, cuz if fluid is escaping, it probably means air is going in. And air contains moisture. And moisture is the one thing that kills a brake system. So it has to be eliminated.

 

[chris norman]

Hang on a sec.
Geysers are normal.
Especially from the rear system,which is usually the frontmost reservoir,closest to the rad.. And it may not have anything to do with air. The rears are drums. Which have huge return springs on the shoes. When you push down on the pedal, you push fluid out to the rear. And when you lift, the fluid is returned by those springs. If you pump too fast,not all the fluid has time to return. If the rear shoe adjustment is loose, it can take many pumps before the shoes finally hit the drums. Then the pedal gets hard. So then you lift off the pedal, and all that fluid is returned rather violently by the return springs, and you get the huge hit-the-hood geyser. That would be a normal consequence of a loose rear shoe adjustment. To prevent this I always crank the rear adjusters until the shoes are jammed up pretty hard; then I slack them off about 3 tool strokes or maybe 10 clicks,just until the drums can be turned with some difficulty. After the system is bled, I redo the rear adjustment. If you crank the adjusters hard and leave them there, it may be difficult to bleed the fronts.
>Yes the geyser may indicate air, but then the pedal will never get hard.
>Once everything is adjusted right and bled, then the geyser thing will be minimized to just a roiling of the fluid.
>Bleeding the master using your fingertips as one-way valves is the fastest way to get the job done. I do it on the bench, with the M/C in a vise. I don't want brake fluid clean up under a customers hood.
>There should never be brakefluid on top of the lid seal,often called a diaphragm. If there is, then it is perforated somewhere. If you are not careful, or if the reservoir is too full or if the reservoir is severely angled n the fore and aft direction, then it is possible to have the fluid forced over the edge during the diaphragm install.Then when you secure the lid,the bailing wire will put the clamp on and the fluid will be weeping for a while. But it should eventually stop. You must make it stop, cuz if fluid is escaping, it probably means air is going in. And air contains moisture. And moisture is the one thing that kills a brake system. So it has to be eliminated.

The fluid geyser I have is on the 1st downwards stroke of the pedal not the return release stroke which is what led me to "air in the master cyl", the pedal does feel good and I have adusted the brakes further than I normally would. Maybe its normal and I just need to find a good quality lid and seal! It might just be me but I don't think "modern" rubber repop seals seem to be as good as the older oe type rubber ones. Any thought on where to buy a decent one?
thanks for your reply

 

[AJ/FormS]

The fluid geyser I have is on the 1st downwards stroke of the pedal not the return release stroke which is what led me to "air in the master cyl", the pedal does feel good and I have adusted the brakes further than I normally would. Maybe its normal and I just need to find a good quality lid and seal! It might just be me but I don't think "modern" rubber repop seals seem to be as good as the older oe type rubber ones. Any thought on where to buy a decent one?
thanks for your reply

On the down stroke is also normal
That is how the compensating port works. Whenever the pedal parks, it allows the piston in there to return to it's parked position. Fluid pressure in the line relaxes. the cylinder remains full of fluid. When yo press down on the pedal, some of the fluid is forced back out into the reservoir, before the piston passes by the hole and closes the port. In this way that little hole adjusts the fluid volume in the system in "compensation" for the pads and shoes wearing. And it also ensures that in a good working system there is no pressure in the lines when the pedal parks, and thus the brakes cannot remain on.
However,
There may be more here than meets the eye. The geyser on the downstroke, in your case seems excessive. I might suspect that the hole is too large. It does not need to be any larger than 1/32 or .030. If the hole is too small it can rust shut over time.It doesn't hurt to be larger, but larger creates the issue you have, in as much as the geyser is constantly flooding the diaphragm. Also, if the pushrod that depresses the piston is too short, then this also aggravates the situation, as it then has a pretty good speed when it hits the piston, and Wham! the fluid is blasted up out thru the port.
So,IMO, the hole may be too large or the pushrod adjustment is too short, or the pedal is parking too high.
If the mechanicals are 100% ok, then,The most simple solution is to install a deflector over the hole. I have used any old piece of thick plastic that cannot be sucked tight to the hole;problem solved.

 

[chris norman]

On the down stroke is also normal
That is how the compensating port works. Whenever the pedal parks, it allows the piston in there to return to it's parked position. Fluid pressure in the line relaxes. the cylinder remains full of fluid. When yo press down on the pedal, some of the fluid is forced back out into the reservoir, before the piston passes by the hole and closes the port. In this way that little hole adjusts the fluid volume in the system in "compensation" for the pads and shoes wearing. And it also ensures that in a good working system there is no pressure in the lines when the pedal parks, and thus the brakes cannot remain on.
However,
There may be more here than meets the eye. The geyser on the downstroke, in your case seems excessive. I might suspect that the hole is too large. It does not need to be any larger than 1/32 or .030. If the hole is too small it can rust shut over time.It doesn't hurt to be larger, but larger creates the issue you have, in as much as the geyser is constantly flooding the diaphragm. Also, if the pushrod that depresses the piston is too short, then this also aggravates the situation, as it then has a pretty good speed when it hits the piston, and Wham! the fluid is blasted up out thru the port.
So,IMO, the hole may be too large or the pushrod adjustment is too short, or the pedal is parking too high.
If the mechanicals are 100% ok, then,The most simple solution is to install a deflector over the hole. I have used any old piece of thick plastic that cannot be sucked tight to the hole;problem solved.

Thanks, that actually makes a lot of sense! Do you have a miracle cure for a leaky axle tube where it meets the centre section too without stripping the whole rear end, as that's next on my leak list lol

 

[AJ/FormS]

Thanks, that actually makes a lot of sense! Do you have a miracle cure for a leaky axle tube where it meets the centre section too without stripping the whole rear end, as that's next on my leak list lol

No, sorry
but you could try a wicking agent from permatex, and of course clean it out with some type of degreaser first..Also make sure the vent is open and the fluid level is not too high.
If you can't find what you need at the jobber you frequent over there, You can probably try Super Glue; that stuff wicks into anything, and drys rock-hard. There is no way to get it out of there if you ever want to tho.
Super Glue is a generic term for cyanoacrylate glue or some such a word. You can find large tubes of it in the hobby shops over here for way cheaper than an equivalent amount at the grocery stores.