Friggen Brake bleeding problem - Vacuum time?

[Shugalou]

Hey guys,

I have been searching and working on this for a while but I still can't build pressure in the system.

Here's what I replaced. New Booster/Master/Lines down to combo valve/Stainless Lines front and rear.

I have bleed the entire system and there are no bubbles coming out (unless trapped inside)

I checked the brake linkage and I am in the top hole - I know it's supposed to be the bottom but it won't work in that location as the brake light switch plate prevents it. This was how it was when I received the truck

I haven't pushed the pin in on the combo valve as I have fluid going to all corners - plus I can't located while it's installed - guess you need to remove to find this pin?

I have bench bled the master - both at the same time.

Is a vacuum bleeder required - do I have air trapped still or am I missing something else.

I'm thinking of rigging something up to close one system off to further isolate the problem

Any ideas are appreciated!

Thanks guys

[hatzie]

Make one of these...
https://www.google.com/search?q=BMW+...essure+bleeder

http://www.youtube.com/watch?v=Mdcn1USVQ-w

Here's how you use them with the commercial unit from Motive Power...

http://www.youtube.com/watch?v=QSDQCAXxkh8

Use the Motive Products 1105 master cylinder adapter.
http://www.jegs.com/i/Motive-Products/715/1105/10002/-1

[77 Big 10]

Disc & drum? Had someone worked on the brakes lately? If drum in rear, are they adjusted? Check if calipers are switched left to right with bleeder nipples at the bottom. If so switch them back.

[Breadfather]

I've also been dealing with a disastrous brake issue on my 77 k10. Re did everything on the rears as the brake warning light was on and it looked like the wheel cylinders blew out at some time. New drums, new cylinders, new hardware, new shoes, everything adjusted properly. Now, I can't get any pressure to the rear brakes. I pulled the combo valve and cleaned it out and re centered it. The brake light went out but came back after a few pumps of trying to bleed the rears. Removed prop valve and re entered, verified that air could come through the back section and re installed. I still could not get any fluid to the rear And again re tripped the valve. Figured out the rear section of the master cylinder was not putting enough fluid through so I replaced the master cylinder, and properly bench bled it. I still cannot get fluid through the back section of the prop valve. Gravity bleeding won't work, manual bleeding won't work, I am thinking the valve is bad. So before I buy a new prop valve from inline tube, any other ideas? I'm going to try the DIY vacuum bleeder to see if I can force the fluid through the system. I tried the mash on the pedal with the front bleeders open, no dice. I verified that the lines are not clogged or collapsed. Never had this much trouble with brakes on these trucks in my life.

[hatzie]

The hoses can and do break down internally. If you have a bad frame to axle hose chunks of rubber blocking the line will give you fits.

I always bleed the longest to the shortest. LR, RR, RF, and LF.

If you follow this one to the bottom you'll see how to make a pop bottle catch can.
http://www.ibmwr.org/ktech/pressure-.../bleeder.shtml

[Shugalou]

Thanks guys, so you think a pressure bleeder is what's needed? No brake drum or rotor work has been done. The truck has been sitting for a couple years now.

Breadfather I feel your pain...I wonder if air is trapped at the hi part above the diff in the rear?

[Breadfather]

Originally Posted by Shugalou

Breadfather I feel your pain...I wonder if air is trapped at the hi part above the diff in the rear?

I can't get to that point yet as the combo valve on the cross member won't even let fluid bleed through the rear section of it. I removed the line that goes to the rear brakes from the valve and let it sit for 40 minutes to gravity bleed, no fluid would come through. I tried to push the pedal very lightly to help it, and it trips the valve. I'm gonna try the DIY Vacuum bleed from the passenger rear, after I re center the valve to see if that works. If it doesn't, I'm going to get a new valve from inline tube. If that doesn't work, I going to cry.

[Shugalou]

Bread have you tried to c clamp the pin down and bleed? I've read that's the procedure.

I'm still stuck with mine took a break but I'm thinking of closing one circuit at a time to see if anything is even working...I hear ya I want to take it to shop and say just fix it but I can't give in...gotta be close.

[hatzie]

Originally Posted by Breadfather

I can't get to that point yet as the combo valve on the cross member won't even let fluid bleed through the rear section of it. I removed the line that goes to the rear brakes from the valve and let it sit for 40 minutes to gravity bleed, no fluid would come through. I tried to push the pedal very lightly to help it, and it trips the valve. I'm gonna try the DIY Vacuum bleed from the passenger rear, after I re center the valve to see if that works. If it doesn't, I'm going to get a new valve from inline tube. If that doesn't work, I going to cry.

Throwing parts at it will just get expensive.

My first guess is that the rear "rubber" axle-to-frame hose is may be breaking down internally so it's blocked up with flaps of itself. BUT. Till you do some tests it's just as much of a guess as a blocked up combination valve.

By all means buy a Combination valve and a rear axle rubber line but don't touch em till you run some tests.

Disconnect the rear brake line at the Master Cylinder. Fill the rear brake section... and see if you get fluid out the rear port. You might have to load the brake pedal 1/4" or so to unblock the rear output port on the MC. I've needed to do that on a new MC to get a good gravity bleed. No fluid at all means the MC is air locked... Re-do the bench bleed.

Test if the combination valve is bad... disconnect the big 9/16" rear brake line fitting on the tail end of the valve, center the valve, fill the master cylinder and see if you get fluid. No fluid? Check that the Combination valve is centered.

If you get fluid at the rear port on the combination valve re-connect the 9/16" fitting and disconnect the "rubber" axle-to-frame line from the steel rear brake line on the frame above the axle and see if you get fluid there. No fluid at the steel line means your blockage is in the steel line. If you get fluid replace the rubber line and bleed. NOTE you may have to have an assistant pump the pedal while you cover and uncover the end of the steel brake line with your thumb and a piece of inner-tube.

I've found the Mity-Vac to be a mixed blessing on brakes. Good for testing vacuum sensors, modulators, and the like. Not so good on brakes.

A pressure pot will push fluid through without an assistant... even if you have leaks. If the pressure in the pot drops with a supposedly closed system you can find the leaks without beating up the brake pedal.

Pedal pushing moves the MC seals along an area of the MC bores that never gets used in normal operation. These can be pretty rough on the seal cups... Pressure pot bleeding doesn't need you to move the pedal much, if at all.

[motornut]

does your e-brake work?
I've found if it's not close enough for the e-brake to work,then the reg brakes won't build pressure

[Breadfather]

i haven't tried the c clamp thing as the pin does not move no matter what is going on with the valve, which is making wonder about the functionality of the valve.

I get plenty of fluid in the rear line to the valve. I cannot get it to come out of the back section of the valve. Even after I have just re installed the freshly centered valve. That is again making me think valve issue. I blew air through the rear line starting at the 9/16 line that runs from the valve, air went through no problem pushing old brake fluid with it, so I don't think the rear rubber line is the issue. I cannot get the nut that connect to the rear rubber line loose without ruining the line(already rounded the nut) so that is when I did the air test.

I adjusted the e brake cable after doing the brakes and it does work. Right now the wheel cylinders will not even move as a result of the lack of pressure in the lines.

I think I will be wasting my time trying to vacuum the fluid through the again freshly re entered valve starting from the drivers rear bleeder, but I figure I would try before spending the $70 on the new valve.

[hatzie]

Originally Posted by Breadfather

i haven't tried the c clamp thing as the pin does not move no matter what is going on with the valve, which is making wonder about the functionality of the valve.

I get plenty of fluid in the rear line to the valve. I cannot get it to come out of the back section of the valve. Even after I have just re installed the freshly centered valve. That is again making me think valve issue. I blew air through the rear line starting at the 9/16 line that runs from the valve, air went through no problem pushing old brake fluid with it, so I don't think the rear rubber line is the issue. I cannot get the nut that connect to the rear rubber line loose without ruining the line(already rounded the nut) so that is when I did the air test.

I adjusted the e brake cable after doing the brakes and it does work. Right now the wheel cylinders will not even move as a result of the lack of pressure in the lines.

I think I will be wasting my time trying to vacuum the fluid through the again freshly re entered valve starting from the drivers rear bleeder, but I figure I would try before spending the $70 on the new valve.

That pretty much narrows it down.

If the light goes out then the metering portion of the combination valve is moving. The proportioning piston may be stuck.
You can disassemble it and try to free up the valve with some denatured alcohol before putting down $70 on a replacement.

[1970pelle]

Originally Posted by motornut

does your e-brake work?
I've found if it's not close enough for the e-brake to work,then the reg brakes won't build pressure

+1 on that, correct rear shoe adjustment.

I have in a pinch way to bleeding brakes by myself, on a brand new system. Doing this after you investigate the proportioning valve issue if there is one. The guys have you pointed in the right direction.

I used the glass jar way of bleeding the system, but rather than using a mityvac. I pull up another good running vehicle with good manifold vacuum, and tapped into it for my vacuum source. It pulled the brake fluid through the brake system fast, only took a minute or so each bleeder. It helps that I live at sea level also.

Good luck with it. Ken

[cdowns]

do you have a service manual? did you read how to properly bleed the brake SYSTEM? I FIND THAT THAT WORKS EXTREMLY WELL TO SOLVE THE PROBLEM

[Breadfather]

Originally Posted by hatzie

That pretty much narrows it down.

If the light goes out then the metering portion of the combination valve is moving. The proportioning piston may be stuck.
You can disassemble it and try to free up the valve with some denatured alcohol before putting down $70 on a replacement.

The I have disassembled all of that and re assembled I don't see how it could be getting stuck but that doesn't mean that it isn't. The little flare part on the red plastic proportioning piston, what keeps it from seating in on the back side? I think it is seating because there is no pressure on the rear side of the valve, but how to I generate pressure on the rear side to prevent it from seating? Could that big spring be too weak from being tripped for who knows how long? Looking at that diagram, it would seem to me that a vacuum on the rear side of the system would cause the piston to slide back and seat it again preventing flow? Or am I totally misunderstanding the operation of this valve?

Also, where can I get denatured alcohol?

[GRX]

Nice jar system. I spend $18 on a set of Russel speed bleeders. Makes brake bleeding a simple one man operation.

[1970pelle]

Originally Posted by GRX

Nice jar system. I spend $18 on a set of Russel speed bleeders. Makes brake bleeding a simple one man operation.

I use those on my Harley's makes my life much easier.

Also, where can I get denatured alcohol?

Any Hardware store Ace, Home Depot, Lowes, House paint store. I keep a gal around all the time, its very use full to have around. Not as harsh as Lacquer thinner, which I used way to much. A hard habit to break.

Ken

[Breadfather]

I'll pick some up and soak that thing in there for a while to see if that helps.

If that or the DIY vacuum bleed doesn't work, I'm getting a new valve.

[Breadfather]

Originally Posted by Breadfather

I'll pick some up and soak that thing in there for a while to see if that helps.

If that or the DIY vacuum bleed doesn't work, I'm getting a new valve.

Okay, tonight I pulled the combo valve and disassembled it and soaked it in de natured alcohol for a while. That didn't help, still no fluid through the rear section of the valve. Convince that the valve is the issue, I cut the red plastic metering or proportioning stem out of the rear section of the valve. The thought was I would be replacing the valve anyways I might as well see if I can get fluid to the rear while I wait for the new valve. I was able to get fluid to the rear brakes finally. After many headaches of getting all the air out of the lines, with the wife pumping and me bleeding I finally had a zero bubbles at the rear brakes. Everything else was bled as well. I noticed when we were bleeding the rears that the flow was still not that strong but better than before.

Once all the air was out, I started the truck up and put it in drive(on Jack stands with no rear wheels) and I still could not get the rear brakes to stop the axels. I figured if anything, they would lock up easy with the combo valve gutted. They did slow down more than before but would not stop, could this be the valve causing this because of my doctoring? Is it possible that the rear rubber hose could be causing this issue? I blew air through the rear lines and verified there is no blockage, but could this be the swelling I've heard about? I am 99% sure that the rear drums are adjusted properly as they are hard to spin and I can hear the shoes drag a bit on the drums as well.

New master, new rear steel lines, new rear everything in the drums.

[Breadfather]

Just installed new rubber rear hose and the flow is better but still can't get rear brakes to engage. I pulled one of the drums and had the wife push the pedal and I did not see the wheel cylinders do anything....could this still be a result of the prop valve since I gutted it? It is hard to tell if there are any leaks on the main rear steel line as there is so much other gunk and fluid on most of it or its behind heat shields, frame pieces, etc.....I'm about ready to start driving it around with no rear brakes.

New master, new rear hose, new rear axel lines, new drums, new everything in drums, still no rear brakes. They are adjusted properly.

[86c20]

on my 86c20 i have played hell with the brakes every time. what i have learned in the 9+ years. 1.when you change front calipers change front lines too. they are made cheep and you have to bleed it anyway. 2. air air air. it can take some time for the master to push the air to the rear. i have found that a grav bleed for a few hourse can save days of bleeding and your leg form pumping. 3. if the rear is not getting fluid first is check where the main line meets the rubber line if you have fluid there its the rubber if not its the prop vavle. 4. and this is the biggest one there is at lest on my pos.
ADJUSTMENT. it has to be spot on. i have done the turn tire and turn up till they just tuch its not enough its more till they drag bleed and back down. if using a adjust ment tool that goes over the shoes. to fit it to the drum norm it is really close. 5. ebrake. adjust the thing after you adjust the shoes then bleed. you would not think it would make a diff but for some reason it does.

disclamer. this is in no way the right way to do this nor the only way. nor does it aply to all the trucks just what seems to work on my rust bucket lol

[hatzie]

I'd replace the Combination valve now that you've gutted it. No reason to pay $70. Do an online search. Jegs has one for $59. http://www.jegs.com/i/Right+Stuff/96...FZKRHwodlzQAIw

I've gotten "new" parts that were non working. Don't assume that the MC is OK just because it's new.

I've had mixed results with Vacuum bleeders. My DIY weed sprayer pressure bleeder was $28 in parts not including the Motive Power MC cover. You can build a cover yourself out of flat plate and inner tube.

[craig113]

I copied the part from the article below. But the link to the whole article is http://www.classicperform.com/TechBo...t.htm#testprop It seems very good and covers alot of brake problems. I hope it works.

Test Combination/Proportioning Valve
Use a test light by attaching a clip to a positive contact on the vehicle and touch the point of the tester to the electrical connection of the combination valve. If the the light does not come on, the valve system is operating correctly and no further testing is required.
If the light does come on, this indicates that the pressure differential valve is stuck in the front or rear position.
Bleed the brake system to determine if the front or rear lines are blocked off. Set up one front wheel and one rear wheel for bleeding at the same time. Crack both bleeder screws and gently pump the pedal a few times.
The blocked side will trickle fluid out when the bleeder screw is cracked and the pedal pressed. An unblocked line will squirt fluid out the bleeder.
The lines that are clear must be left open and the blocked lines should have the bleeder screws tight to cause pressure to build up on that side. Be sure to use the standard bleeding procedures to prevent air from entering the system.
Slowly press the pedal with steady pressure a number of times until the light goes out; this will center the differential valve. You may also hear a pop come from the proportioning valve. This is the metering valve returning to its equalized position. When the light goes out, close the bleeder screw.

put a 2x4 under your brake pedal, to keep from over stroking you could get buy without the tool assist

[Shugalou]

Originally Posted by 86c20

ADJUSTMENT. it has to be spot on. i have done the turn tire and turn up till they just tuch its not enough its more till they drag bleed and back down. if using a adjust ment tool that goes over the shoes. to fit it to the drum norm it is really close. 5. ebrake. adjust the thing after you adjust the shoes then bleed. you would not think it would make a diff but for some reason it does.

disclamer. this is in no way the right way to do this nor the only way. nor does it aply to all the trucks just what seems to work on my rust bucket lol

This is good info here I'm guessing I left mine loose because there is little drag but just a touch when putting the drum on. Also I back off my ebrake cuz I'm not sure if it even works. Looks like further investigation is required.

[MTCK]

I've fought this type of problem on a couple trucks, and every time it has been air in the master cylinder. Bleeding through the lines never fixed it. A good bench bleed always did.