I've been having an issue with my '92 Camaro's brakes ever since I replaced all four calipers and rubber lines. It has a '96 10 bolt rear end with disks, otherwise it's all stock. Drove just fine like that for years prior.

Is the next logical step a master cylinder replacement?

Essentially, my brakes will sometimes be soft, and sometimes be completely fine. I can drive the car for hours and not have any issues, then I'll put my foot almost to the floor before they really start to slow the car down. However, if they are soft, I can release then push the pedal again and they will be firm. Or, at least, firmer. However, the very next time I brake it's a 50/50 chance whether or not they will be soft again. Sometimes it'll happen once then never again for that particular drive, sometimes it happens every time I brake, and sometimes it won't happen at all. It'll happen hot, it'll happen cold. I can't find any pattern to it.

I've bled the brakes numerous times, both with a vacuum bleeder and the two-man game of "open," *push,* "closed," *release,* repeat. and never a bubble comes out. I've also looked the car over several times and found no leaks anywhere. Fluid is clean and clear.

I don't want to just throw money at it, so if the master cylinder the next logical step, or is there something else I should be looking at? I'd try taking the MC out and bleeding it, but if I'm going through that trouble, why not just replace it? It's 30 years old at this point, anyhow...

 

Air is really the only thing that acts like that. Either didn't bleed it all out, or there is a leak letting it in. Hardly takes any air to feel funky.

 

You could try what I did recently - let gravity do the work.
Connect a hose to the bleeder screw and run the other end to a container.
Just crack the bleeder screw open about a quarter turn. Now wait.
Fluid will start flowing and you can tighten the bleeder when you are convinced that there is no air remaining.
Repeat for the other 3 calipers. Don't let the master cylinder run dry!

 

If there was a leak, wouldn't they slowly lose pressure as I held the brakes, though? They stay firm no matter how long I sit there with them applied. Even when they're squishy, the pedal will never go all the way to the floor. It always firms up and stops the car before then. I was running a diagnostic test with a Tech 1 scanner and I sat there in drive with the brakes applied for 15min and they didn't give at all.

At this point, I've blead the system about six times, and besides the initial blead we've not seen a single bubble come out. I always pump the brakes slow and steady, mostly to keep the fluid from squirting all over the place, but also to keep it from emulsifying. I've pumped about an entire large O'Reilly's DOT3 bottle of fluid out of that system since putting it all back together.

Yeah, I pretty much did that. Hooked a long-ish tube to the bleeder, then ran it into a cup part-filled with fluid so that as I slowly pumped the brakes it would push the air out and suck the fluid in. But no air ever came out, and I almost pumped an entire bottle of DOT3 out by the time I was done with all four corners.

 

The 30-year-old master cylinder is probably leaking internally. Time to replace it along with all the other brake components you've already replaced.

 

If the master is leaking you should be able to detect that in the reservoir.

This may be a stupid question but one I have made in the past (on a different car) when replacing calipers. Are you sure that the left and right calipers are on the correct axle? If you do this by accident the bleeder screws will be in the wrong position (usually pointing down) and prevent them from fully bleeding (air will be trapped at the top of caliper).

Either way I bet your missing something obvious. Maybe get a second set of eyes to look at your brake system.

 

Yeah. I've done that before, too. Bleeder screws all point up.

The issue has been going on since late last summer when I replaced everything. Since then there hasn't been any change in the fluid reservoir level. My dad has helped me bleed the brakes twice in that time, on top of the three or four times I've done it on my own. He gave it a good look over both of those times as well. None of the fittings are wet, the bleeders and where the rubber lines connect on the calipers are dry. I've even looked at all the hard lines under the car to make sure nothing is cracked. For the life of me I can't find anything wrong or out of the ordinary.

I plan on giving it a really, really thorough lookover (again) this weekend. If worse comes to worst, I can put the old calipers back on one-by-one to see if the problem goes away. Really hoping I don't have to go that far.

 

Do think it could be vacuum related? Maybe a brake booster issue?

 

I've thought about that, too. But wouldn't that give the opposite effect? The booster is what gives you power brakes, so I would think if it was going out the brakes would be getting super stiff instead of soft. I could be wrong about that, though...

Is there a way to test the booster?

 

Sure there is. Run the engine, pinch off the vacuum line going to the booster.
Stop engine and wait a while. Unseat the white 90* check valve and see if the booster held the vacuum.
Or you could check it with a handheld vacuum pump.