bleeding brakes help

rjm428 · 09-15-2005, 07:03 PM

just rebuilt the calipers on a 77 911 s
started the bleeding process and couldn't get any fluid to bleed out of the back bleeders. the front is fine and it streams out of the bleeders. also disconnected the lines in the rear and only got a few drops of fluid.
could the lines going to the rear be clogged? or am i doing something wrong?

VincentVega · 09-16-2005, 06:03 AM

I would disconnt the rubber lines completely, so you can verify fluid coming through the hard lines. If you dont have fluid before the rubber line you might have some junk in the lines, or a pinch somewhere.

Odds are the rubber lines are shot, but might not be your only problem. Does 77 have a proportioning valve? Might be clogged.

sammyg2 · 09-16-2005, 06:22 AM

It could be a few things, like cologged lines (unlikely) or a bad master cylinder (also unlikely but still possible) or it could just be that the lines are completely full of air and the master cylinder isn't displacing enough to get the air out.
That's when a presurized bleeder works wonders. You can still get it with conventional bleeding procedures, it just takes longer and is a PITA.

shillier · 09-16-2005, 07:18 AM

I had a similar problem where I could bleed the fronts but not the backs after rebuilding my calipers. It ended up being the Master Cylinder. Here's the thread that explains what had happened.

Newbie - Frustrated with my 911's brakes... Do I need a new Master Cylinder?

Hope this helps. Good luck.

Shayne

89red911 · 09-16-2005, 07:36 AM

heres a little trick you can try take a hose and connect the clutch slave to one of the rear bleeders. open both bleeds and slowly pump the clutch this will do to things for you one if your lines are full of junk and pluged up the hose will pop off the other is it will push air back through the master and into the resivor.

you can also do this the other way to bleed the clutch.

rjm428 · 09-17-2005, 01:54 PM

well if i'm getting good bleed out of the front calipers and just a few drops out of the rear is it possible that a 77 911s has a proportioning valve. if it does have this valve is there a way to check it.

RoninLB · 09-17-2005, 02:42 PM

Quote:

Originally posted by rjm428

is it possible that a 77 911s has a proportioning valve.

No valve

if it was my car and the rubber caliper hoses had over 75k mi on it I would replace it before you Have to replace it.

the slower rear drip could be the way the car is jacked up. You're only dealing with a little bit of atmoshere head psi to begin with. A rough estimate is 2.31' of water = 1psi.

The bleeders may get dirty from road crap if not protected with rubber boots.

rjm428 · 09-17-2005, 04:50 PM

do you think that the rubber lines could be clogged? when we tried to pump up pressure we only got a few drops of fluid. we never did disconnect the rubber lines.
the other thoughts were possible master cylinder problem or just not using the correct bleeding methods (pump or vac ).

VincentVega · 09-17-2005, 05:17 PM

disconnect the rear rubber lines, they should be replaced if they are original and should help narrow down your issue.

Early_S_Man · 09-19-2005, 03:05 AM

Pre-87 cars don't have hydraulic clutch actuation, and pre-84 cars don't have propoprtioning valves!!!

I don't understand why people that aren't aware of when changes were made insist on posting problem scenarios that can't possibly exist for the stated year of the car!!!

Dixie · Dixie's Garage

Nothing personal, but I suspect you're doing something wrong. Why not try gravity bleeding the brakes? It's a pretty foolproof method...

Attach plastic lines to the bleed screws. Put the other end into a clean jar.
Fill the master reservoir.
Open the rear bleed screws, and leave them open.
Top off the reservoir every hour or so.
Close the screws when the jars have about four oz.s of fluid in them.