Same car, problem with master has me baffled. tried another new 50$ new master, bled correctly.....same thing, low pedal. Put original one on, same thing. Now I'm thinking that perhaps the plunger is the wrong one, and am wondering if different years had different length plungers. First, let me tell you this...this car is a made up car, was in pieces when purchased, and assembled by the seller in a big hurry, if you know what I mean. 427-390 rag, with PB. Would and improper booster or any other part be a possible reason.....?

P.S. no fluid leaks evident any where on system, but having a hard time clearing air from drivers rear caliper. thanks in advance.

 

Getting air out once its in the system can be tough. There are different lengths of pushrods between power brakes and standard and sometimes between different booster manufacturers. New problems are created when suppliers mix and match boosters and masters.
Do you have power brake master cyl. ,its 1 1/8" bore ?
Have you checked the pushrod clearance ?

 

The ones the owner picked up are for power brakes, and seem to be the same as the original one, but the pedal goes down about 4 inches before you can feel the brakes start to work, which made me think it is the wrong rod. Anyone know the right length?
Pushrod clearance where and to what....? Pushrod sticks out and engages the master when mounting.
I'll check the bore tomorrow.....thanks again.

 

You can measure the depth of the hole in the master cyl piston and then measure how far the pushrod sticks out past the booster.
That will get you close.

 

One of the masters I tried to buy last week was in a 1 1/8" part number box and I measured it to be a 1 incher. Wrong box. The wizard at Advance started to argue with me about it.
Almost as bad as Homey Depot, got to openn boxes in the store before you leave.

 

The fun thing about the brake systems on these cars is that you can do ten in a row as easy as pie and the eleventh one will make you pull your hair out for no apparent reason.

First thing is to adjust the rod on the booster. Take the new master and hold it against the booster to see if it seats tight on the flange. If it does, adjust the rod out a little bit. Retest, and keep adjusting until there is just a hairline space 1/64", just enough to know you are snug.



This is the way I bleed the master off the car. Using clear line you can see when all the bubbles are gone. I rotate it in all positions under pressure to make sure there are no air pockets. Release the pressure in the pressure bleeder and install plugs in the master ports in the 12 o'clock position.
Then install the master with the pressure bleeder attached.



After it is installed, test the brake pedal, engine off. It should not go down more than 1/4", then engine running, it should go down about 3/4". This also tests the brake booster at the same time. If the master leaks internally, it will slowly go toward the floor.
I press as hard a I can, in fact this time I broke the adjustment spot welded nut for the seat back, now I have to take the seat out to reweld it.



Then you can connect the lines and bleed the calipers as usual.
If you have problems with them, you cann always use plugs and caps ahead of each suspected caliper to isolate the problem one.
You can make these out of old brake hard line and female caps out of old brake flex hose. The caps must be brazed shut after the hose is cut off.
Over the years, I've accumulated a box full of different sizes etc, really useful even if just replacing one caliper.



It's really important not to aerate the fluid, I even pour it in the pressure bleeder slowly. The very tiny bubbles take forever to disappear.

This the best way I have found to do these, and not have to backtrack and waste a lot of time and fluid.

 

mine does the samething. air in the system in my case. power bled it and everything. still pedal goes to floor and barely holds. these brakes are a **** to get the air out of. even professional mechanics cringe at working on them. been putting mine off since i have been redoing the interior but now that it is done, gotta get back on them

 

great write up noonie. i will use that info when i tackle mine again. just gotta round up the plugs to start from the master cylinder and work my way back.

 

Don't use the plastic plugs, you'll blow fluid all over the place.
Go to a U pick um yard with some side cutters and a few sockets a load up on some sizes.
If you can't, short line adapter lengths with the proper master tube nuts are available at Pepboys under the part number PAA-G360 and PAA-B410. Napa carries them also under their own part numbers. Cheaper than ordering just the nuts online. Most parts stores no longer have them, can be tough to find.

 

Thats pretty dang interesting ,never thought of doing it that way !
I use hardlines to bleed but I'll have to find some clear ones and give that a shot.

 

i use the clear lines and they work great. i use a phillips screw driver to manually pump the master cylinder instead of a power bleeder. only because i don't have one. u can usually buy a cheap brake bleeder kit from autozone that has all the plastic fittings and clear lines. i am going to pull my master cylinder back off and check the rod length. then plug the brake lines and see if the master cylinder is leaking internally. i bought a new one, not rebuilt, but i don.t think it matters these days. my 67 camaro has always had soft brakes, going to get on it next. thanks again for the advice.

 

Roger, here is something for you to ponder. A possible solution to your bubbles.

Originally those red bleeder adapters came with good new masters with a very thin black rubber hose attached, in fact I think Autozone still has them available for sale separately. They worked well.
After sitting around for 20 or so years, the rubber deteriorated, would slit at the fittings and leak. I replaced them with thicker harder plastic tubing.
It was then that I found that the thin, seemingly cheap rubber hoses had a designed purpose, when attached to the tapered plastic adapters with the 2 holes in the side of the taper, in effect acted like a check valve. You could force the fluid out, but the thin hose tightened on the holes and prevented the fluid and bubbles from returning into the master when the piston returned. It wasn't until I used the plastic lines and pushed in the piston by hand that I discovered that bubbles would just move back and forth out and back into the master, . I probably cycled the piston 50 times and no matter how much fluid went out the hoses into the master reservoir, some of the tiny bubbles were still returning into the master ports. Has to do the same thing with hard line bleeders, you just can't see it.
The hard line bleeders were in use back when I was a kid, and they worked well, but back then most systems were drum/drum and all masters had tiny "residual valves" (check valves) under the port cones to prevent return of the fluid. No disk brakes use residual valves.
So ever since I ran into this little discovery, I have used the pressure method with great results, since replacing a master, I flush the system anyway, so it's no more work or fluid.

 

Noonie, thanks for the great pics and info. I believe the pushrod is all the way in, which might explain the problem. No thread was visable on the rod. As I said, I will check this stuff out next time around and perhaps isolate the rear drivers caliper. I just figured since there wasn't any leaks, it couldn't suck air, but I'll check. The inside bleeders are frozen and obviously haven't been open in recent history, and I don't feel like breaking them off. Do you need to bleed both sides of the caliper or just the farthest one (outside)?
I also failed to rotate the master when bleeding, and will do that as well. Do you mean to bleed it at 10 and 2? Only hand power, no pressure setup.
Awesome help gents....!

 

Hit those inside bleeders with some WD or kroil and get em open. You'll never get all the air out if you don't bleed both sides.

 

I agree completely. I remember those those bleeders with holes in the side of the taper,you had to push the piston pretty hard to get the fluid to move,I popped one once and sent fluid flying.
That's when I made some hard lines with rubber tips that are buried in the bottom of the reservoir to create resistance for the return fluid (thought about a speed bleeder on each tube but decided it wasn't necessary).
I'm convinced the tiny bubbles I'm referring to are coming in around the first seal , once I lube the bore they go away.

I'm still liking your way of using the Motive type on the bench bleeding, I see it reducing the mess and maybe save some time.
Hard lines or plastic might be a thing of the past.

 

YOu can buy those little rubber hose clamping 'pliars' at NAPA and do the same thing while the MC is under pressure. Just clamp the hoses before releasing the pressure. Small vise grips would work too, but a little clumsy I think.

This is a 4-star thread.

 

Is it possible your booster came from a later year? My '72 power brake master cylinder has a deep hole for the pushrod coming out of the booster. I think they changed the hole to a shallow one (looks more like a dimple) in '77. If your car was thrown together with parts from a couple of cars, this mismatch could be the cause of a really long pedal stroke before you get any brake action. Here's a deep-hole master:

 

thanks Bob, I'll check that tomorrow. I think it's gotta be something like this, and the air from the rear caliper is probably because of the inside bleeder not being used, maybe ever, WD40 on it now.
So I'm going to check the master for bore width, depth of indentation, and proper rod adjustment. I'll let you know the results.

 

What does the pedal do if the booster is bad.....?? on this car the pedal seems to go down even farther when you start up the car.

 

The brake pedal will require a great deal of foot pressure to stop the car.
You can disconnect the vacuum line and try it for yourself.