6H bleeding brakes and still no luck

[gacksen]

spent two hours reading several posts but could not find any answer

changed the rear rubber hoses to braided ones the last days and tried to bleed the system today.
first bleed the tandem master with rubber hoses attached to the bleed screws into the reservoirs
until no air came out. have speed bleeders all around so started on the rear passenger side first.
then rear driver, passenger front and driver front side until no air came out of all the calipers just plain fluid.
have willwood fronts and started to bleed the inner valve of the caliper first. checked for
leakes of any kind and there seem to be none. system is not losing and fluid.

checked for any wilwood proportioning valve but there seems to be none in sight.

when i press the pedal it is full soft and brake light goes on. if i press it again say within 1 second
and pump the brakes will get pressure on the pedal and it feels normal but after waiting 5 seconds
pressure is gone and i would have to pump it again.

what i noticed with reservoir caps off the fluid in the reservoir tank for the front brakes stays level while
pressing the pedal. the reservoir tank of the rear brakes drops fluid down around 1/4 inch while pressing.
after some seconds fuild level will go up again. i guess it corresponding with the brake pressure.

is there and secret trick as i don´t know what to do else ?

[rcb280z]

1st thing I would do is re-bleed the master / "tandem master". Im not sure why you bled it to begin with unless you replaced that as well. If so, it should have been bench bled.
Did you install front calipers, doesnt say in your post if you installed new ones or if these are the old ones. If new or, you had the old ones off, make sure the bleeders are up top of the calipers.

[rcb280z]

Also sounds like you might still have air in the back brakes. Re-bleed those as well. What you are describing is air still trapped in the system.

[gacksen]

will try the master again. nothing has been installed except of braided hoses on the rear.after 4h i thought maybe there is air in the master thats
why the brakes won´t bleed so i bleed it with hose attached to the bleeder into the reservoir but barely bubbles had been comming up.
all bleeders are up to the calipers. don´t know how much fluid i ran through the system but it was quite a lot. strange thing is brakes worked
before so i don´t have any clue where the fault is. especially why fluid of the rear brakes drops down and comes up and fluid of the front discs stays
level all the time. should the fluid level be steady while pressing in both reservoirs or is there any movement up down normal ?

[rcb280z]

Should be steady that's why I say you still have air in the system. Worse case...bleed everything again. Anything you "cracked open" bleed again. You introduced air into the system somewhere, guaranteed.

[rcb280z]

I just checked my master to verify things and I get a slight movement in level, and I mean slight. If you are getting the 1/4" like you say then you have air still in the system. Sorry to sound redundant but........

[EuroDat]

How old is the master cylinder. The reason Im asking is old master cylinders don't like being pushed (pedal) to the floor.
Over time the section of the cylinder that doesn't get wiped clean by the plunjers gets pitted and corroded. This can damaged the rubber plunjer cups and seize the plunjer at the bottom of its travel. The front section could have this problem.

This could be your problem or making it a lot worse.
You can tap it with the handle end of a screwdriver and see if you hear it click when it jumps back.

Chas

[rcb280z]

Chas just beat me to my next question. Was getting ready to ask how old it was. In your first post I assumed you replaced it until you verified in post #4 it was not.
Post what fixes it gacksen.

[gacksen]

first of all absolutely great write up !

after 3 hours i skipped it for today. what i did had been the following :

1. switched back to the old rubber hoses on the rears just in case.

2. bled the master. first reservoir next to booster then the front one. clear hose from bleeder into reservoir. bleeder maybe 1/4 turn open. both reservoirs no bubbles at all. unknown factor is the bleeder as i did it by myself as girlfriend motiviation had been soso means kept pumping the pedal for some time. don´t think the bleeder will suck in air in the thread area but of course can´t tell for sure.

3. put the car on 4 jacks and for better access. started rear right same thing 1/4 turn speedbleeder open with clear hose in fluid canister.kept pushing the padal for 15x times. reservoir level then had been about 1/3. refilled the reservoir of rear brakes and repeated the process. pulled the handbrake some times but didn´t make a difference. unknown factor same as above would be the thread of the speedbleeder as i did it alone. don´t think it sucks air from the thread as the had been no fluid in the thread area.

4. repeated the steps on all 4x calipers twice. conclusion in the case nothing has changed at all. front reservoir for the rear brakes keeps on moving while fluid level of the fronts stays level.

As the car had been jacked up anyway and i had some time tried the following :

1. connected clear hose to fron´t left caliper and rear left caliper. opened the bleeder 1/4 turn and started pumping. of course fluid level will drop differently i guess due to the brake balance of front and rears so front reservoir will be low on fluid earlier compared to the rears. thought maybe there is something blocked due to the pressure imbalance but it does not seem so. made a picture of my front and rear calipers and can tell you...... brake fluid is the same hazzle as graphite grease [] two hours had passed and still no success on the brakes so i stared looking and found an old pressure bleeder that will be connected to a spare tire. when taking a look to all those brake lines espcially the rear one they are above the bleeder. as the pressure bleeder was meant to be used for reservoirs with a thread on it and those in the car doesnt have one had to use a different construction. checked the tire pressure and it had been 1.4 bar on the spare wheel. so searched for some clamps to get it kind of fixed on top but
wasn´t succesfull. ended up with big cable ties and i guess you know the rest of the story once pressure was on

after cleaning up the mess and thinking about what had been done in the past on the car. was in the workshop for new wheelbaerings
and they bleed the brakes without any problems. changed springs on the front dampers before that and drove the car to them with
brakes no bleeded they managed to get it done.

maybe just more pressure of an air pressure bleeders is needed to get rid of the air trapped in the rears ?

don´t know the age of the master....