Master cylinder issue

[86 chevy silverado]

My master was replaced recently along with most of my brake components. I noticed it was leaking along the back of the reservoir cover (and dripping down my freshly painted inner fenders). The first time I checked it the front chamber of the reservoir was very low and the rear was filled. I thought that it was fairly odd since I usually dont overlook topping it off after servicing and wouldn't of filled the rear so much. So I adjusted my levels and searched the lines to the back to be sure no leaks, none were found. This weekend I check again, the same, front almost empty and the rear filled to the top again. I recheck for leaks, again non found.
I believe what is happening is the fluid from the front is leaking through the seals internally to the rear, it is a reman master and I am going to assume that is what is happening and replace it.
Has anyone ever run across this problem before? I have never seen this myself.

[VileZambonie]

Are you sure you don't have a leaky wheel cylinder?

[86 chevy silverado]

Everything is new, even the lines. Even knowing what I have replaced, I still inspected everything thoroughly in case something new was not up to par, everything is dry. The question is not only where did the fluid from the front chamber go but how is the rear chamber filling up to the point of leaking. Thats why it seems that it would have to have leaked internally, but again I have never seen this. I would have to question the rebuild of the master.

[VileZambonie]

I've had new leaky wheel cylinders. If you are positive they aren't leaking I'd replace the master.

[86 chevy silverado]

I am getting new parking brake cables with the replacement master and I'm aiming for a brand new (oppose to rebuilt) master, which I will replace because of the leak alone and will check everything more thoroughly when the drums are off (I have a full float). Either way the master should not gain fluid in one chamber unless its going over the top during acceleration or something and I'm not launching this thing. The rears have been touchy since everything went together as mentioned in a previous post, so there are a few questions to clear up. Maybe I have a moody wheel cylinder. With the amount of fluid disappearing I would think I would see signs of a leak around the drum area as you usually would. (Between the backing plate and drum area)

[86 chevy silverado]

Vile, would you recommen an adjustable prop valve, I'm dying to install one just for the adjustability and I guess I need a good excuse. Have you used these in the past?

[VileZambonie]

That really depends on what you mean? There was a factory one installed near the rear axle but these usually failed and I've always bypassed them when they did. The combination valve is not a common failure either on these trucks but I've had to replace a few.

Now if your base brakes are all working correctly and you are having problems with brake bias due to huge tires or because of payloads then yeah it'll definitely help but if it's fairly close to stock then I don't see the need.

Are you having a problem besides losing brake fluid?

[86 chevy silverado]

Just the catchy rears at times, I'm sure I can get that fixed after new cables and doing a once over and adjust hopefully
I eliminated that rear height adjust valve as well.
I thought it might be worth being able to adjust the brakes for my particular height, tire, load etc.
Does it deserve thought?

[VileZambonie]

I think I made a couple of posts on the importance of the shoes sitting on the anchor pin. Not sure if you read that but I can't tell you how many drums I've pulled and found someone cranked up the parking brake adjuster without checking the adjustment first. So make sure your rear brake cables aren't moving the shoes off of the anchor pin. Make sure the backing plate is straight and that you lube the lands where the shoes sit. Make sure the primary and secondary shoes are installed correctly. Check your hardware and replace if it looks old. one method that works well is to take a spring and drop it on the floor. It should make a nice ting sound instead of a thud. True drums and proper adjustment is equally important. From there if you are still having problems then I would replace the combination valve before attempting to install an adjustable proportioning valve. The combination valve also consists of a metering and a pressure differential valve. So that's my thoughts on that but like I said unless you are over 35" tires or carrying lots of weight I don't think it's necessary.

[86 chevy silverado]

Gotcha, know when to say when. If you don't need it then you don't need it.
From years at dealerships I'm pretty particular with things, The drums are freshly turned, all new hardware, shoes, cylinders, all contact points cleaned and lubed. The only thing overlooked was the a parking brake cable hanging up slightly on one side and is possibly my rear brake problem.
Thanks for the advice. God I hate taking these drums off.

[VileZambonie]

LOL I just did them on my Soon to be green truck. But at least I know they'll work good when everything is hooked up.....

[86 chevy silverado]

Them big drums!
Talked to my parts guy today concerning the weird master problem I'm having. He had a car way back when that pushed the fluid from the rear chamber of the master to the front chamber, opposite of my problem and he deduced an internal leak as well. Anyway I have a replacement waiting for me. I'm taking it apart as soon as it comes off, I'm going to figure it out. A seal tore or folded or something during rebuild I would guess.
I got two bad calipers in a row for my little Nissan, one leaked at the banjo bolt, the other around the piston. Gotta love Napa! Bad parts have cost me endless labor in the past. I trust no one, I even take apart my heads when I get them back from the machine shop to insure everything was done correctly.

[VileZambonie]

That's why I do as much as possible myself. Work quality in all trades has degraded so much over the years and high schools are dropping hands on technical programs like they're poisonous. You should see how many people that don't know the difference between a claw hammer and a ball peen. Or I ask what's bigger 3/8" or 5/16" and 20 people haven't a clue.... Just building my garage I nearly assasinated home depot! lol /end rant....

Let us know if the master takes care of the problem.

[86 chevy silverado]

Its been a while since last post, I know. Since the ground thawed I have been overwhelmed with work.
I finally did a once over on the rear brakes, I replaced the parking brake cables and the master cylinder, bled and adjusted the brakes and my problem with lock up seems to be gone.
The new master is not leaking at the cover and fluid level stays stable. I did take apart the other master looking for a clue of any problems but nothing conclusive was noted with the seals. So I guess I'll never know for sure why the fluid from the front chamber gets to the rear. Maybe they over honed the inside of the master during rebuild.(?) I'm happy its fixed.