New Master cylinder weeping in back around piston
 

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

Re: New Master cylinder weeping in back around piston
 

Can you replace the seal. It may have a small crack or imperfection.
Manufacturing standards aren't what they used to be.

Re: New Master cylinder weeping in back around piston
 

Yes. I have a replacement. It would mean draining the system I guess.

Re: New Master cylinder weeping in back around piston
 

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

Re: New Master cylinder weeping in back around piston
 

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.

Re: New Master cylinder weeping in back around piston
 

It quit weeping and now you are! LOL. Natural perversity of mechanical things. :mad:


Terry

Re: New Master cylinder weeping in back around piston
 

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.

Re: New Master cylinder weeping in back around piston
 

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.

Re: New Master cylinder weeping in back around piston
 

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.

Re: New Master cylinder weeping in back around piston
 

are you using dot 5 . dot 5 will find a leak in a bull frogs ass

Re: New Master cylinder weeping in back around piston
 

Haha. No, Dot 3.

Richard, Did you get my DM?

Re: New Master cylinder weeping in back around piston
 

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.

Re: New Master cylinder weeping in back around piston
 

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.

Re: New Master cylinder weeping in back around piston
 

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?

Re: New Master cylinder weeping in back around piston
 

This is just the lube, I was taking a look at it.

https://www.ebay.com/itm/McKay-Brake...-/282935241245

Re: New Master cylinder weeping in back around piston
 

OK, thanks. I'll get a kit from 3rd Gen since I need to order a few others things from him.

Re: New Master cylinder weeping in back around piston
 

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.

Re: New Master cylinder weeping in back around piston
 

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.

Re: New Master cylinder weeping in back around piston
 

Perhaps the seal just took time to "swell up".

Re: New Master cylinder weeping in back around piston
 

We'll keep an eye on it and I'll report back.