I have read every thread I can find on bleeding brakes but none found with my problem.
I recently rebuilt my rear suspension, part of which required taking off the 2 rear calipers. After I finished bushings, bearings, shocks etc. I reinstalled the two calipers.
When trying to bleed the air out of the system I could not get the pedal to come up off the floor. I was using a helper to pump the pedal while I was doing the bleeding.
So, I dug out my vacuum tool and tried using it. Lots and lots of small air bubbles coming out. Same result on the pedal.
I also tried gravity bleeding which seemed to work fine. Lots of fluid came through. Still no pedal.
I bought a combo unit with master cylinder and booster from Speedway already assembled. Bled it per instructions on the bench, seemed to work as expected.
Installed it and same results. I again tried all 3 methods of bleeding and none got all the air out and none gave me a decent pedal when it was pressed.
Just out of curiosity I took the cap off the MC and very slowly pushed the brake pedal. Both front and rear sections pumped fluid with no air bubbles.
I took the new MC off the new booster and measured the distances on the rod tip in the booster to the flat mounting surface and the MC from the piston to the flat section of the mounting tabs of the MC.
I did the same on my old MC and booster. The rod in my old booster seems to be about 1/16th of an inch longer but distance on MC piston is the same.That is the only thing I can find that is different in the whole system.
I am open for suggestions and would appreciate any help.

 

Did you bench bleed the new master?
Did you bleed all 4 rear bleeders that are on the top end of the calipers?

 

C3Lover1978
Stopped farting around and get a pressure bleeder.....or just make one.
I don't even try to do my 68s brakes w/o a pressure bleeder...not that i've really had to do anything in a dozen years....but whenever I do my other vehicles brakes I use the pressure bleeder on those also.

 

Can you tells which pressure bleeder you have?

 

I made mine from a garden sprayer, a flat piece of 1/4" aluminum (notched underside to connect the fore & aft reservoirs), tygon tybing, a pressure gauge (to pump it up between 10 psig and 20 psig). and some air tool fittings. I made it because I did not want to wait for a manufactured one to be shipped and I figured I'd order one later.....BUT it has worked so well that I never saw need to order the motive pressure bleeder.
The only thing that I replace is the tygon tubing since it gets hard after a few years. Cheap at the local hardware store.

PS- I also made a rubber gasket out of an inner tube scrap. Seal well tighten it down with a c-clamp. No leaks

 

Did you bench bleed the MC in a nose down position to get all the trapped air out?
Pat

 

Any chance you installed the rear calipers upside down? If you reversed them the bleeders end up on the bottom and you will never get the air out.

 

Did you get this resolved?

I had the exact same issue on my '69.

The fix was to simply do a good pressure bleed of the brakes. Turns out there was a decent amount of air in the right rear line. You'd be surprised at how just a little air will make the pedal go to the floor. I'm not talking about it just being soft, I'm talking right to the floor and no pumping up.

 

Where did you get the adapter?

 

What I'm using there is an Orion Motor Tech bleeder from Amazon:



It's basically a half-price copy of the Motive bleeder. It comes with the adaptor you see there. The only thing I supplied was that big C-clamp. It works better than the chains and J-bolts that come with the kit. I just wrapped the other end of it with a towel so it wouldn't slide off the bottom of the MC and it held the adaptor just fine.

It's less than half the price of the Motive kit and includes a nice catch bottle with a hanger to use at the caliper end.

 

Update: I am finally making progress on my brake issue.
I leveled the master cylinder by jacking the rear of the car. When I slowly pressed the brake pedal a LOT of small air bubbles came out . Apparently my attempt at bench bleeding the master cylinder did not do a complete job.
Next I discovered that the new bleeder screws I bought from a local auto parts store are junk. I had one caliper that was leaking air into the line if I turned it 1/8 of a turn. I still had 1 of the original bleeder screws so I swapped it out with the new one I had put in.
Stopped the leak. Just out of curiosity I put several of the new screws in and tested. They all leaked.
I have ordered new ones from Eckler's. Hopefully that will fix that problem. I believe that once that is done I will have a good pedal.
I appreciate all of the helpful suggestions I received.

 

I took a flat bit of aluminum plate and drilled and threaded a hole in it over one compartment and used a master cylinder gasket and a C clamp to hold it to the master cylinder. Then I used a bicycle pump with the tapered adapter to pressure the master cylinder. Just don't let the master cylinder run empty. Worked very fast, right rear might need to refill the master cylinder once before all the air bubbles are out.

JT

 

Another update: I got involved in other projects and let this slide for a while.
To summarize -
1. Bleeding brakes with a pressure bleeder - I pumped the bleeder up to about 15 PSI and bled the system. Seemed to work OK.
Did all four wheels in proper order and everything seemed ok with no leaking. I let the car sit for a week with pressure on it. No leaks.
Got into car and pushed the brake pedal - ALL 4 WHEELS LEAKED AROUND THE BLEEDER SCREWS!
Tried many different bleeder screws and they all leak.
One thing I found out talking to a professional mechanic - when you mash the brake pedal you can be applying several hundred PSI.
Does ANYONE know of someone who sells bleeder screws that won't leak!

 

Did you completely remove the screws and checked for rust on the screws or damaged seats in the calipers.

 

These are new bleeder screws and 2 of the (rear) calipers are remanufactured and the 2 front were originally on the car from a previous brake job..
Not sure how I can check the seats.
I have tried bleeder screws from several sources. All leak on all four calipers.

 

Then you need copper crush washers or different calipers. If you tried other bleed screws the caliper seats are bad.

 

Automotive hydraulic brake systems typically operate between 300 to 1,500 psi (pounds per square inch). During light to normal driving, you generally use 300 to 500 psi, while aggressive braking or "panic stops" can spike the pressure to 2,000 psi or higher.

I would question if you have the correct bleeder screws for your calipers.

JT

 

I've never been faced with this.
Perhaps the precision tapered seats in calipers are badly worn/scored/corroded ? Perhaps those seats could be touched-up with a specialized cutter ?