New Master cylinder weeping in back around piston

T

Tim Ayers

Well-known member
Finished the brakes on my AV8 project. Bleeding went really well and took under an hour to get a really firm pedal. No real leaks and just a two fittings needed to be wrenched tighter to stop weeping.

Today, I noticed a small drop under the US made Wagner master cylinder. I pull the plunger boot back and I can see fluid in the boot and wetness around the back of the piston. Cleaned it off, pumped the brakes a few times and it seemed it stop. An hour later it is weeping again.

I know that brake fluid swells seals, so it is concerning me that its weeping a day after bleeding the brakes. At this point, I don't think it's going to stop on it's own.

I have a few options: I have M/C rebuild kits. I could bleed out the fluid, change the piston and plunger from the back side without breaking open the lines. Refill and bleed and see if that fixes it.

Or, I also have a Chinese made Wagner that seems like a newer design. I could put that one in, but I'd rather keep the US made if possible.

I'm using Dot 3 fluid.

Thoughts?

Thanks,

Tim
 
Can you replace the seal. It may have a small crack or imperfection.
Manufacturing standards aren't what they used to be.
 
Yeah, it's not going to stop leaking on its own. That's a shame...shouldn't be this way. I suppose I'd pull the master back off to do the work if possible,but if you can swap seal cup/piston in place that should be fine as long as you can inspect the bore for defects. May be the cup has an imperfection on the lip that leaks when pressure is absent. Good news is, bleeding the line at the master should get the air.



Terry
 
Checked this AM and the weeping stopped. Now it's bugging me. I feel like I should replace that seal now before it becomes a problem later. Crud.
 
cadillac512 said:
It quit weeping and now you are! LOL. Natural perversity of mechanical things. :mad:


Terry
Click to expand...

Right, Terry?

I'm going to move forward. The body is off so I have time to keep an eye on it. If it shows even the slightest weep, I''ll fix it. I don't want any brake issues.
 
Tim keep us up to date on your project, I'm reminded every so often of the words "shelf life". This winter it would not hurt to get a fresh rubber seal kit if the weeping shows up again. Who know how long that MC sat waiting to be had.

It just might have seated and now sealed properly after operating the cylinder, we sometimes have slight seal weeps after a pump impeller seal kit replacement and after thing heat up and flowing all things are dry.
 
39portlander said:
Tim keep us up to date on your project, I'm reminded every so often of the words "shelf life". This winter it would not hurt to get a fresh rubber seal kit if the weeping shows up again. Who know how long that MC sat waiting to be had.

It just might have seated and now sealed properly after operating the cylinder, we sometimes have slight seal weeps after a pump impeller seal kit replacement and after thing heat up and flowing all things are dry.
Click to expand...

Will do. Good point about the kits/shelf life. The rebuild kits I have are all 20+ years old. Picked them up along the way.

Motor & trans going in next.
 
Wheel cylinders and master cylinders that have sat on the shelf for years the cups will stick and when you put pressure on them will tear the cup causing a leak. I put NOS wheel cylinders on my 40 and had to put cups in them because they leaked. When I disassembled them they had a ring of rubber stuck to the cylinder bore. No rust or anything just the cups had stuck.
 
I recently used a NOS USA master cylinder and wheel cylinders. I disassembled all of them, checked and cleaned them and re-assembled them using McKay Brake Cylinder Assembly Lube with rust inhibitor. I replaced several of the wheel cylinder cups I didn't like the looks of. Mckay recommended by someone here on the barn. $10, incl. free shipping on Ebay. Good investment, no leaks with DOT 5.
 
russcc said:
I recently used a NOS USA master cylinder and wheel cylinders. I disassembled all of them, checked and cleaned them and re-assembled them using McKay Brake Cylinder Assembly Lube with rust inhibitor. I replaced several of the wheel cylinder cups I didn't like the looks of. Mckay recommended by someone here on the barn. $10, incl. free shipping on Ebay. Good investment, no leaks with DOT 5.
Click to expand...

Thanks, Russ. I'm going to do that. Did you just search Mckay rebuild kit for Ford master cylinder? Could you forward me the auction you bid on?
 
I would consider returning the master cylinder to the store it was purchased from.
I always buy my brake cylinders from C&G. They are a large enough store to have a good turn over.
I got all five cylinders for my F1 from C&G in the year 2000.
After installing new shoes too I used DOT 5. No leaks.
Now when I do brakes I use dot4. Less chance of a leak.
 
I got the Mckay from ebay, JSerry post. It was recommended by Aarongriffey here on the barn. Take a good look at the MC bore, it may have some residue in it you probably can clean off with acetone and or a fine scotch brite pad on a slotted stick. I would use the hone very lightly as a last resort.
 
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