i think the best way to do this is lay out the facts...

all rotors turned (new bearings and seals in front)...
all calipers were fine...i cleaned them up and painted them with cast finish...
drained and flushed the system with fresh brake fluid...
bought a rebuilt master cylynder and bench bled it before install...

OK...i have bled a few brakes in my day but havent in quite a while and i have never bled a system that has been completely drained and flushed...
i got a good bleed on the mc at the bench and thought that it was going to be a peice of cake...my buddy got in to man the pedal and i went for it...
i started at the right rear, inside bleeder...pumped the pedal etc, just like always...
we worked at it for a while to no avail...i tried the outside bleeder...same thing...went over to the drivers side rear and again, same results...none...
i might add that after we worked at it for a while i put some fluid in a jar and ran my clear hose from the bleeder down into it and when i released the bleeder i got bubbles sometimes, but not every single time...

thats where i stand right now...any advise would be apreciated very much...SG

 

fill the master...leave master cover off....remove the bleeder completly from the caliper and wait for gravity to push the fluid through and the air out....give it enoughg time and it will come thru...shouldnt take more than a few mins though...continue to the next bleeder and proceed as above...no need for a helper...no need to pump the brakes....gravity will push it thru...if not then there is blockage somewhere.

you must leave the master cover off during gravity bleeding of a vacuum will be created under the cap and halt the draining process....during the entire procedure, never let the master go empty or dry.


[Modified by Jvette73, 9:33 PM 8/14/2002]

 

Did you bleed all four wheels? If the system is empty I would start out with all the bleeders open and gravity bleed the system. Then work your way around the car a few times. I don't think that you can really bleed the rear if the front is full of air.

 

Actually, front and rear disc brakes are completly separate. You could leave the fronts bone dry and bleed the rears with no problem. Of course your warning switch in the combination valve would be knocked off-center, illuminating your "Brakes" light. But air in one side won't prevent the other side from beingl bled if all is well internally (M/C, combo valve.)

 

i thought about the gravity bleed idea but i wasnt aware of removing the bleeder so i removed the rear brake line and removed the mc cover and it barely dripped out at all...then kinda stopped...

is it possible that my lines are blocked?
by the looks of the brakes when i started this job, the rears had been working very little if at all...
im thinking that i might disconnect them from the calipers and the mc and blow some air thru them tomorrow and see...whataya think?
i didnt even attempt to bleed the fronts which i KNOW were working and ill try that tomorrow too...

 

Exactly how long did you wait for the fluid when you removed the bleeder? Sometimes it will take a few mins to get flowing good. pull the bleeder then go make a sandwich or somethin. dont expect it to instantly begin to gush out. If it dripped a little and then stopped, most likely air was being pushed out. Use spit over the hole like the leaky valve stem trick. If the spit bubbles then air is being forced out. It just takes some time. After all though, you may have some blockage. I myself have never had a problem getting the fluid to flow when gravity bleeding. That goes for completely dry systems an a handfull of different vehicles including vettes.

 

i let it sit that way for an hour or so (each wheel)...
it dripped a little for a few minutes but after a while it either dripped even less or almost completely stopped...thats the rears...havent tried the fronts...

one of the reasons that i even did this project (other than the rotors were glazed) was beacuse it was stopping as tho all i had were front brakes...
but the rear rotors appeared to be fine (looked recently rebuilt) the pistons moved freely and they had no leaks...
i am now suspecting a blockage in the line...
remember too that when i tried to gravity bleed them...i disconected the short brake line from the rubber line at the axle (i also had replaced both of those short lines) so there is no blockage in the calipers...if it is blocked, it is blocked in the line between the mc and the axle...
hense i am considering disconnecting the line at the axle as well as the mc and blowing air thru the line from the mc end...
what the heck...it cant hurt anything and it will either fix the problem or eliminate the blockage theary (sp)...

 

Went through this last night with a 1980 C3...
Went through it a few weeks ago with a 1969 & a 1970... same issue.

The proportioning valve/switch is off center and is stopping the fluid from passing to the rear circuit.

The valve is very different based upon year. For example, a 1970 has internal springs that aid in recentering the valve, and it has a non-moving pin in the switch.

A 1980 has no internal centering springs (although it does have one spring), and it has a moving switch pin (plunger). The 1980 also has a an actual proportioning type component, whereas the 1970 does not.

If your brake warning switch light is known to be working, you can turn on the key so that the circuit has power, and view the light.... while viewing it, open a single rear bleeder screw with no other bleeders open.... pressurize the bleeder with compressed air in spurts until the light goes out. Make sure you have the cover sitting (but not clamped) on the master cylinder, and if you are not using DOT 5, cover your paint job.

To keep the switch from going off center again, bleed BOTH one rear bleeder and one front bleeder at the same time (two hoses, two collection jars, two open bleeders).

The early versions of the switch can be re-centered by closing all bleeders and pressing on the pedal until the valve moves internally.... the 1980 does not respond the same way.... compressed air is the only way I was able to get it to respond, and this was after removing the switch, disassembling it, and cleaning all of the sludge out of it to make sure it was functioning properly. (I have pictures)
After you get fluid in all four calipers, you can then re-bleed one more time following the "correct" order" if you desire.

If the valve is working properly, then the only way you can MANUALLY bleed the system is to bleed one rear and one front bleeder at the same time. Otherwise, when the pedal is pressed, the valve goes off center (as it was designed to do) and the circuit being bled closes, and no fluid will flow.

Of course.... pressure bleeding helps avoid most of these issues.

If you do not have compressed air, and your version of the valve/switch does not have internal centering springs (as in 1980), then you are between a rock and a hard place..... the system was not designed to be manually bled.

FYI.... a malfunctioning valve/switch will allow you to manually bleed the system because it is bound up inside and will not close off an open circuit when the pedal is pressed, or when gravity bleeding.

The 1970 switch even slid shut when gravity bleeding.

Hope this helps.
Tom

 

wow...this sucks! im supposed to leave for Carlisle sat and im having a hard time completely understanding this...
does anybody know about a 79 valve ?
can you post some pix tom?
where is this valve?
its begining to sound like i dont have a line blockage at all...hhhmmm...
thanx a lot tom...

 

I agree with Tom - and I think this is what Ken meant when he said
to make sure the fronts are not empty, too.

If the brake light circuit is not working, you could check this with a
volt/ohm meter by measuring the "ohms" to ground on the switch connector.
I think it is normally open (infinite ohms), and closes (~0 ohms) when
the imbalance is detected. Can anyone confirm this ?

 

Same thing happened to me-rear stopped flowing.

Close all bleeders, recover master cylinder and make sure you have enough fluid level fluid in it, and pump the brakes pretty hard possibly 10 times. This seems to reset the proportioning valve.

Then go back and gravity bleed the rears inside LR inside, LR outside, RR inside, RR outside. I did this and they started flowing real good again.

I used a clear tube over the bleeder to keep the mess to a minimum, an eye on what is coming out, and to keep the air off the bleeder by pointing the tube up from the bleeder so only fluid is on the bleeder.

Results were very good.

Brent....

 

SUCCESS AT LAST!! WOO HOO!...THANX TO YOU GUYS :yesnod: :)

1st of...thank you all for your help...heres what i did...

i bled the fronts first figureing that if the valve was stuck off center because the rear had leaked at one time then i might be able to fool it into thinking that the fronts were leaking (by bleeding them) and it would move back...
i dont know if that is even possible but that ws my conclusion and i went for it...
i couldnt resist hitting the pedal hard about ten times 1st tho (as suggested)...it made scense to me that you maybe could "shock" the valve back to the center...i dont know if it really helped or not but i figured that it couldnt hurt...
anyways...i did the right front 1st and got fluid fairly quickly...then the left front and everthing went good there as well...
man...i was feelin good :yesnod: :) as i headed for the rears...trying to keep positive about how it was going to go back there...
i went 1st to the right rear (of course) and started bleeding, with my friend Ron maning the pedal...
well...i was a tad disapointed as we started bleeding...
i didnt seem to be getting much response...i had been bleeding into a bottle so i got a cup and ran the hose down into it so i could see bubbles if there were to be some...
sure enough...there were...very few compared to the front...but they were there...after a while (probably, partaily because it is further away) i got a pretty good stream so i moved to the left rear...
WOW...big bubbles :yesnod: :lol: :) as tho you were blowing into it with a straw...both inner and outer...
OK...now i had three...one to go...i still wasnt thrilled about that one...
we bled that one several more times and got it pretty good but not as good as the others...even when we stopped i was getting a few little bubbles with every bleed...not a good "stream"...
i figured that it could go on that way forever so i called it good...

i ended up with a pretty good pedal and it stops pretty nice...at least for the short test ride and the 3 mile ride home (thru town)...
i think they will get even a little better when they seat and get a little "broken in"...

i was afraid that thr valve might be bad and they are $85 and i couldnt get one until monday...we're leavin for Carlisle late saturday night (early sunday morning" and it would have sucked :mad :rolleyes:
but thanks to all of you for helping me understand more about brakes and especialy about the proportion valve...we will be leaving on time :yesnod: :)