I've been having a helluva time trying to get my brakes working again on my 70 after the body off resto. Before the resto, everything was working perfect. All the lines are new along with a new prop valve and distribution block.

I ended up replacing the stock master cyl because the rear seal was leaking. Went with a BRAND NEW master cyl for a replacement. I had trouble getting fluid to the rear brakes, but I eventually solved that. I also had a bad wheel cylinder on the right rear (which was brand new, but was letting air in) so I replaced that as well. I then found out my line lock solenoid was letting air in the system where the to halves are piece together, so I removed that competely for the time being. I'm getting plenty of fluid to the fronts for bleeding, but still have very poor stopping power.

So I bought a reman. master cylinder to replace the new one to see if that was the problem. This one is even worse. I'm getting NO fluid to the rears at all, but plenty to the fronts. I pulled it out of the garage for a test drive and couldn't even stop going down my driveway. I'm at a complete loss here guys!!!! I bench bled both masters for a good 10 minutes, and even bench bled the new one I took off again and it came up fine. What does this problem sound like? Could it be I don't have enough pedal travel? The thing that gets me is everything was fine before the body off. What else could be wrong??

Anyone?? This is really racking my brain and I have no idea where to go next!

Well, flame me if you want to, but I NEVER, NEVER, bench bleed.

Number one, I'm lazy, number two, I didn't get paid to do a job twice. I was a flat rate mechanic and couldn't see why I should bleed the m/c in a vise, then do it on the car. I have seen too many cylinders ruined when they are stroked so far that the piston bottoms out. That doesn't happen when the cylinder is mounted on the car. Mount the cylinder on the car, jack the rear up until the cylinder is level (so that's a lot of jacking, do it). If the cylinder is level air won't be trapped in the end of the m/c. Then do your "bench bleed" with the cylinder on the car if you feel you must. Personally, I just fill the cylinder with fluid and push the pedal (tiny strokes) with one finger till the air bubbles stop coming up in the bowls. Then have somone else push the pedal down once and bleed the air at the line connection.

Since your car was completely apart and needs everything bled, do the gravity bleed thing (with master cylinder level). Fill the master cylinder and open all the bleeders. When the fluid starts coming out, close bleeders one at a time as they start to drip. Then bleed as usual.

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Jon N.

"Those who grant sympathy to guilt grant none to innocence" Ayn Rand, Atlas Shrugged, 1957

Did you replace the brake line going over the top of the rear end? Sounds like it might be bad.

It was new when I bought the car, and I blew it all our with air and its fine. I also blew the whole rear line out last night starting at the master cyl and ending and the right rear wheel cyl and it flows fine...no clogs or anything. I went and bought a new master today (again) so I'm going to try that once more.

Any other ideas are welcome!!

I've used the aforementioned "open all the bleeders until they drip" method before, works well to get things going, while you're doing other jobs. Nowadays, I use a Mityvac pump with the bleeder attachment. Uses vacuum to pull the fluid all the way back. Don't know if you're doing it, but you need to start at the passenger side rear, and get fluid there first. Don't do any other corners until this one is done, or you'll be sucking an air bubble around in your system. Then driver's rear, shouldn't take near as long. Passenger front, driver's front last. On some newer cars and trucks, the proportioning valve has a valve on it that must be depressed with a special tool to be able to bleed the rears. Did you change this valve? Just a thought. The ultimate bleeder is supposed to be the Phoenix Injector. I've seen them, haven't used one yet, but I can see one in my future, especially since I work on my own bikes, and trying to bleed the front brakes on a bike properly is almost impossible. This one injects fluid from the caliper or wheel cylinder all the way back up into your master cylinder. Great idea, but they are kinda pricey. The cheap plastic ones are close to $100, nice ones are about $300, from what I've seen advertised.

UPDATE: on the new master cyl (second one).

I bench bled it by running the tubes from the brake line holes back into the resevoir. Got all the air out. Put it on the car and rigged up my own Mityvac pump with a bottle and my vac pump (did not use this previously). Started at the right rear and sucked about a whole resevoir of fluid through the line, and the same for the left rear. Got in, pressed the pedal and got GREAT pedal with no bottoming out. So I'm very excited now. Proceded to bleed the left rear again by the old fashioned method (pump, hold, open bleeder) and then did the two fronts. By the time I got to the front I had lost ALL pedal...very spongy and it just bottoms out!

So now theres only a couple of things I can think of thats happening. Since I got great pedal on the first few strokes, and none after numerous strokes, could I have too much pedal travel and just be blowing out the seals on the master cyl? Also I noticed my prop valve is leaking a little by the button you push in, so maybe thats letting air back into the system?

You ARE opening the bleeder valve and then having someone SLOWLY depress the pedal, closing the bleeder before the pedal completely reaches the floor...THEN closing the valve before the pedal is let up, correct? I ask this only because of your statement "Proceded to bleed the left rear again by the old fashioned method (pump, hold, open bleeder)...." The word "PUMP" is what stood out. At NO time should the pedal be "pumped" while bleeding. Unless the bleeder is closed, the pedal should not be released. I still use the time honored method of "short piece of hose submersed in brake fluid in a jar". This way I can SEE the air bubbles escaping. I own a pressure bleeder as well, but still wind up doing the job the old fashioned way, with a helper in the vehicle "working" the pedal (too lazy to drag out the equipment). Also, the proportioning valve should not have any fluid leaking...a source for air entering the system, for sure.

The way I've been bleeding is by pumping the pedal about 3 times with the bleeder closed, then on the 3rd time holding the pedal down while someone opens the bleeder screw. Then have them close the bleeder screw while the pedal is still down and only let up once its closed.

I think instead of spending $140 on a new prop/metering vlave I'm going to bypass it to see if that solves the problem. Spent awhile searching the site and it seems theres not much trouble without running a metering valve.

DON'T pump the pedal at all. Open the bleeder and have someone SLOWLY depress the pedal, closing the bleeder right before the pedal reaches the floor. Start with the right rear, left rear, right front, left front. Use the "hose in the fluid" technique. This way you can actually see the fluid stream and if there are any air bubbles present. I've doing it this way for about 40 years now, and have never had a problem, even when I converted the drum brakes to discs on the Chevelle.

Sounds good...I'll give your bleeding method a whirl. I hope bypassing the metering vlave works, because after that I'm lost.

Also, how much travel does the piston in the master cyl actually have? How easy is it to over extend it and blow out the seals?

I went through many many bad M/C's on my disc brake swap. The key was to get a GOOD M/C from carquest (raybestos) all the others were wrong for my car but autozone kept selling them to me.

Do you have a pic of what your raybestos master looks like? I've only got one that has been wierd looking, but my two new ones (from different parts stores) are the same.

You can kind of see it here

http://f1.pg.photos.yahoo.com/ph/silky20gumball/detail?.dir=/1968+Chevelle&.dnm=Engine+Shot+Chevelle.jpg

if that doesn't work goto http://photos.yahoo.com/silky20gumball and look in the 2nd album.

The ones i got from the zone were a lot more square then the raybestos one. The rabestos one looked TOTALLY wierd but it works great, it looks very similar to my buddy's 71 camaro.

ALSO the ones from the zone had only one metal ring to hold it down while this one had 2.

That makes me feel better because that is exactly what the new one I have looks like. Thanks for the pics...I really hope I can track this problem down before gas gets up to $3 a gallon!

No problem, yep gas is $2.35 today and i don't see it going down anytime soon. I wish now i didn't put such high compression in my motor but it sure is fun.

Anyway good luck, i have come to hate brakes because anything we touch them something goes to crap TOTALLY unreleated to what we just worked on.