bleeding 87 GXL single piston rear calipers
 

So I replaced all my brake systems. calipers in the rear, single type, have two bleeder screws. according to my manual, since I opened up everything (replaced disc, pads, lines, calipers et al.) one is suppose to bleed any air out using the lower of the 2 bleeder screws. so all was okay, (did front complete as well, weekend before) but when I Test drove it, I felt the brakes were a bit mushy. so my assistant (son) and I bleed the both rears again. and low and behold, now nothing! pedal goes all the way to floor. I should have stuck with mushy. anyone out there experience this before perhaps has some pointers?

Well, there are a few things that could be going on..

My first question is, did you put something on the floor behind the brake pedal to prevent the pedal from travelling all the way to the floor? The thing about it is that under normal operation, the piston inside the cylinder on the brake master does not travel the length of the cylinder. Over many years, corrosion can happen in the unused portion, so when you bleed the brakes via pedal pumping you end up chewing the seal in this area...ruining the master. By preventing the pedal from hitting the floor, you help to avoid this. I usually use a brake pad box or small bit of wood.

That being said, I prefer motive power bleeders.. or vacuum bleeding with a mitivac.

Additionally, air can get trapped in places and be difficult to get out. But it sounds to me like the master is blown. Luckily it is a very inexpensive part that is very easy to replace. A tip I can give you is to 'bench bleed' the replacement part.. Which is really just kind of priming it with brake fluid before you install it to speed up the bleeding process.

If you can't achieve a solid pedal after bleeding the brakes correctly, you have a leak somewhere.

If you find no leaks, re-bleed the brakes using the upper bleeder screws on the rear calipers. I've never used the lower ones because air normally collects at the top of the caliper. When bleeding, be sure to keep the resevior full, and the parking brake off.
I've met so many people who claim to know how to bleed a brake system using the old fashioned two-person method, but infact have no idea how to do it correctly.

Ensure you are using proper bleeding procedures:

- Always start with the caliper furthest from the master cylinder, and end with the one closest to the master cylinder.
- Don't pump the pedal too fast when bleeding. This can cause problems with air not completely escaping the system through the resevior when the pedal is released between pumps. (The fluid can aerate.)
- Completely release the pedal between pumps. With your helper holding the pedal after three or so pumps, open the bleeder screw to release pressure.
- Close the bleeder screw while the other person is still pushing on the pedal. If the pedal goes to the floor, tell them to hold it there while you tighten the bleeder screw.
- If the person operating the pedal releases the pedal before the bleeder is tight, you have just introduced air back into the system.

This advice was applicable back when we had single circuit systems but makes no difference now to the dual circuit MCs we use as there is no connection between the front and rear calipers.
Bleed the fronts first if you like, it doesn't matter.

I'd hope that the OP knows at least the basics of how to bleed brakes.. I suppose I assume a lot.

Maybe his son isn't getting the bleeder tight when he has the pedal down?

A leak as bad as to cause a dead pedal would be extremely noticeable.

I meant while bleeding. If you let off the pedal without the valve shut good, it will suck air in.

redeaux -- rear caliper brake bleeding
 

thank you all for the input and responding to my call for help. we figured it out,
no leaks

the brakes are fine now, I did not resort to a power bleeder.

So, what did you "figure out"?

'Resort' to a power bleeder ? You make it sound like it's a bad thing.. it's a wonderful tool to have. One man bleeding, no pedal pumping.. quick and easy.

I am cheap and I like the one man bleeder from the help section at Autozone. Has a magnet, the inlet tube goes to the bottom of the catch reservoir, works great! I recommend a slow pumping action (waiting for "That's what she said"). Next is the vac pump and identical catch can.

Cheap, works.

I've used those before and like them alright, but they're not large enough for a thorough brake flush.

A nice thing about the motive bleeder is that you can attach hoses to all four calipers with bottles, then just open up the bleeders. It's great for those annual flushes.. super fast.