Bad master cylinder?

Attempting to bench bleed the master cylinder, I just can't get the air out. Fittings and tubes are tight, but it continues to blow huge air bubbles through the lines. Took around two or three dozen pumps just to get fluid through the line. Also, there is almost no pressure at all on the rear line. At the end of my brake pedal travel, the front line pushes fluid but the rear barely moves. I'm starting to think this is just a bad cylinder. I did this once before on my CJ7 years ago, but don't remember it being this hard, seems like it only took a few pumps to bleed.

 

Are you doing this in the jeep? Or on a bench? I used a vice to hold mine and had no issues

 

In the Jeep.

 

My neighbor went through 3 rebuilt ones (on his chev pickup with the same results as you. I told him to go buy a new (not rebuilt) and he had no more problems. YMMV

 

You need to do it on the bench out of the jeep.. I mount mine in the vice and use a screw driver to push the piston in. You can get bleeder kits at NAPA..

http://www.napaonline.com/Catalog/C...stalling-On-Vehicle/_/R-NDP7001795_0412991268

http://www.youtube.com/watch?v=kEPXgDGU6_0

 

I have a pretty nice bleeding kit, I'll give it a try tomorrow outside of the Jeep.

 

I bought one for my 72 CJ5 from Quadratec (Crown, I think, the one with the bolt on the top instead of the flip clasp) and bled it on the Jeep. The installed cylinder sits almost completely level on mine, so I figured this would be OK. It seemed to bleed fine. Once I got it all hooked up and drove on it though, it never seemed quite right. When I pumped it, the brake pedal would sit up at the top. If I pressed the brake and held it, the brake pedal would very slowly move down toward the floor, until I pumped some more. I replaced it with a Napa cylinder, again bled it on the Jeep, and it's still rock solid. I was told by others that master cylinders in general have a fairly high leak rate out of the box.

 

I just spent 30 minutes trying to bleed the cylinder in the vice, I'm pretty sure it is bad. I still get no fluid moving in the rear port until almost full stroke, and the front is constantly spitting out huge bubbles. Also getting a ton of tiny bubbles coming from inside the front section. I'm going to pick up a new one tomorrow from the store and exchange this heap.

 

Problem fixed. My lovely wife purchased a new NAPA cylinder while I was at work. I just finished bleeding it, took less than 5 minutes. Cheap re-manufactured piece of junk...at least I have spare master cylinder cap.

 

One of the issues in the automotive world is the (lack of) quality of replacement parts now being supplied. Had this same conversation with a co worker who just sold his thriving Automotive Repair shop to retire and move on to other endeavors.
Sounds like you have an keeper in that woman!

 

I've had to return a few MCs at times. 2nd was as bad as the 1st. On the 3rd trip to the FLAPS they figured out they had a half dozen poorly rebuilt MCs on the shelf. I got a screaming good deal on a new MC. It didn't pay for my time involved but I got a good MC out of it.
Like you did, sometimes you just need to go to another parts store.

 

Probably have an internal leak on it but who knows.
A Dodge minivan came in last week with the same problem and they brought a rebuilt mc from advance and it had the same problems as yours.

 

QC is the issue, well, the lack of it. I've rebuilt many wheel or MCs over the years, the problem is getting the parts anymore.
I imagine there is a lawer involved somewhere. Sorry, didn't want another trash can.
Old saying, "You get what you pay for" So if you pay the lowest price, You'll probably get a part that reflects that.

 

I heard it is just cheaper to buy another mc instead of rebuilding it. Am I wrong? As in having a shop do it not you. Yea you do get what you pay for..........

 

The origional theme was not being able to get a good rebuilt unit. The other thing I've found is that I can't get parts anymore, at least not around here. In the '70s we had a suitcase sized cabinet with about any sized part you would need in it to rebuild any brake system, I haven't seen one of those in many years. Well you are right, I could buy China made wheel Cyls in the '70s for less than the cost to rebuild mine.
I'm a grumpy old fart so unless it involves an AC or a modern computer, I'd rather do it myself. Just the way I am.
I am trying to learn...

 

The price for a master cylinder complete was about 60 bucks. the price for the rebuild kit was between 25 and 35. I went with the wagner branded one. It works alright and I had to spend some time getting it to bleed correctly. I had some installation errors that i needed to address, but in the end it seems to work alright. We are just talking about some orings on a piston. Either the Oring has a nick in it or the cylinder has a score. I would have rebuilt mine, but after I bought some new stones for my hone and the kit, I would have spent more than just having amazon prime or rock auto send me one, not to mention the time.

 

In my experience, rebuilt master cylinders have always had quality issues. I sold a bunch of them working parts counter back in school, and a lot came back. I speculate that the main problem is with the quality of the cores. Any water in the cylinder will put pits into the bore that will not hone out. If you go with a restoration-level reman where they sleeve the core, then you may get the same level of reliability as a new part. But I predict that is only makes economic sense when you are rebuilding the master cylinder of your Duesenberg, and the only core that exists is the one in the car.

JMO - skip right to the new, brand-name master cylinder when you need a replacement. Maybe Wagner, EIS, Delco, Bendix, Raybestos. Dorman or Centric if you can't get the better brands.

Same for wheel cylinders.

 

Many modern replacement master cylinders and wheel cylinders cannot be honed. They have "bearingized" bores. Basically they are machined and then a precise diameter ball bearing is forced through the bore to bring them to the desired diameter. This gets them to the correct size, more concentric, and makes for a smoother bore. The problem is if you hone them then you ruin the finish. Now you have a piece of scrap metal.

 

Just aluminum or cast iron too? Aluminum MCs seem common now.

 

Both.