No brake fluid getting to rear

[chief poncho]

So I'm in the process of bleeding my brake system for the first time with all new calipers, lines, master cylinder etc.  Was a completely dry system.  Fronts bled fine, but I can't get any fluid to the rear.  I've tried bench bleeding the master cylinder, vaccum pumps to suck the fluid to the rear etc.  I tried pulling vaccum directly on the line ahead of the calipers and still nothing.  I'm suspecting the proportioning valve, but it looks like its centered.  I'm going to play with it a bit more.  Anyone ever have a master cylinder that was weak to the rears, but worked up front?  Seems to push fluid when bench bleeding, but not nearly as much as the front.  Even if the master cylinder wasn't pumping fluid I should be able to suck the fluid through with the vacuum.  This is getting very frustrating.  Been working on it for a couple of days.  Pumping the brakes to bleed the rears didn't work either.  I guess I could try another master cylinder too.

[firebirdparts]

I've never seen a master cylinder that wouldn't move fluid against no resistance.  I wouldn't think that's it.  Do make darn sure you have a hole there from the reservoir down to the back piston bore.

[chief poncho]

It definitely has the hole there in the back reservoir.  I think it has to be the proportioning valve.  I hate messing with brake fluid.  I also need to make sure I don't have any air leaks in the system and that everything is sealed up tightly.  That could be the other issue.

[Warren Seale]

Remove the brake light switch in the proportioning valve then using a pick try to center the shuttle.  If it is already centered then you must have a blockage in the rear brake line.

[Wallington]

x2 was thinking the same. You can see down inside if it is centered or not. I just picked up one of the nylon bleeding tools, nice and cheap and potentially saved some dramas, although not once had an issue bleeding the brakes. One less thing to check anyway.

And follow the brake lines along the floor and make sure none have been flattened from driving over things or bad jack positioning!

[highway star]

I have the same issue, replaced all parts of the rear drums up to the rear line going into the proportioning valve. With the rear line disconnected at the prop. valve and a hose/fluid connected I was able to use a mityvac at the rear cylinders and pulled fluid through. No fluid to rears with the brake pedal. I suspect an issue with the prop. valve?

[chief poncho]

Ok, so prop valve was part of the problem.  Was able to remove the switch and use an awl to get in there and move the bar back into position along with opening the front brake bleed valves.  Popped right back to center.  I also purchased a little bleeder tool from Amazon that screws into the switch hole and holds the bar centered. 

I was then able to disconnect the brake line where it comes in over the rear axel and draw fluid through.  However, I'm still not getting any fluid to the rear brakes.  Tried the MIghty Vac on the valves for awhile last night, also checked for leaks throughout and also pumped the brakes for a good 15 minutes with no fluid coming through.  I'm really suspecting the master cylinder.  Its been sitting on a shelf for at least 6 years and maybe the seals aren't good anymore.  It was brand new.

[ryeguy2006a]

I bought a MC from a parts store and it sat for a few years and it was completely rusted in the bore and wouldn't bleed. I'd say that is probably your issue too.

[Warren Seale]

Ok, so prop valve was part of the problem.  Was able to remove the switch and use an awl to get in there and move the bar back into position along with opening the front brake bleed valves.  Popped right back to center.  I also purchased a little bleeder tool from Amazon that screws into the switch hole and holds the bar centered. 

I was then able to disconnect the brake line where it comes in over the rear axel and draw fluid through.  However, I'm still not getting any fluid to the rear brakes.  Tried the MIghty Vac on the valves for awhile last night, also checked for leaks throughout and also pumped the brakes for a good 15 minutes with no fluid coming through.  I'm really suspecting the master cylinder.  Its been sitting on a shelf for at least 6 years and maybe the seals aren't good anymore.  It was brand new.

Does fluid come out of the rear side of the proportioning valve when the line is disconnected from it?  If yes, then try to suction fluid throught the rear line with it being disconnected from the valve.

Also this is a good time to check to make sure your brake light and proportioning valve switch are working.  If the shuttle were shifted off center then the light should have been on.

[chief poncho]

Does fluid come out of the rear side of the proportioning valve when the line is disconnected from it?  If yes, then try to suction fluid throught the rear line with it being disconnected from the valve.

Also this is a good time to check to make sure your brake light and proportioning valve switch are working.  If the shuttle were shifted off center then the light should have been on.

Ok, so I am getting fluid out of the rear side of the prop valve now.  I can place the mighty vac at the rear brake line outlet where it goes in over the rear axle and pull fluid through.  However pumping the brakes does not push any fluid through that line.  When I reconnect that line to the rear caliper lines, I can't pull fluid through to the calipers, though either.  I was about to remove the lines feeding the calipers and see if I can pull the fluid through there.  Regardless, pumping the brakes does not seem to be pushing fluid through the rear lines at all.  I checked the booster rod length and it seems ok.  I'm also thinking of removing the MC again and trying to bench bleed it one more time on the assumption that there might still be some air in there.  The fronts seemed to bleed easily with little issue. 

[chief poncho]

Alright, so I took the MC off again and did another bench bleed.  I was able to get more air out of the rear side.  I was also finally able to push fluid down through the MC to the rear calipers.  Now...the question is after I get it all back together, will I be able to pump fluid with the brake pedal???  I did buy a new MC just in case this last effort doesn't work.  I'm keeping my fingers crossed.

[firebirdparts]

You might want to dismantle it and look down the bore and see what kind of shape it's in.

Back in the olden days, it was perfectly normal to rebuild masters.  I suppose you could consider honing it and putting it back together, but that's not why we used to hone stuff.  Whether or not it works is going to depend on the surface roughness you're dealing with.

[twov8sandat4]

Are you running rear discs?  What calipers if disc? what master cylinder?  disc/disc or disc/drum?  I am having the exact same problem as you.  I just converted to rear disc, and the master is supposed to be for it.  Too cold now to continue the troubleshooting.  Will resume in the spring.

Thanks.

[chief poncho]

Ok, found the issue!  Not sure its 100% corrected, but found a big problem that when fixed seems to have helped a lot.
1.  I'm running a Right Stuff rear disk conversion - It's essentially the factory setup used on the 2nd gen TA's with GM calipers.
2.  I'm running an original style master cylinder - it is supposed to be compatible with the Right Stuff setup.
3.  I'm using a 4wdb prop valve from Inline Tube - it is designed to work with the original master cylinder.

So I found a few problems so far.

1.  The rear caliper bleed valves need to be cracked more than a 1/4 turn to get fluid through them.  I was trying to both pump and pull with the vacuum pump through the bleed valves with only about a 1/4 turn.  I was pulling air through the threads, but not actually pulling any fluid through.  The bleed valve needed to be turned almost a full turn to get fluid through it.

2. When I bled the front brakes the bar in the proportioning valve cut off flow to the rear brakes since the system was completely dry and there was no fluid in the rears.  I had to reset the prop valve bar by using a pick to recenter it through the switch hole.  I then purchased a tool off of Amazon that would hold the bar in place.  After that I was able to push brake fluid through the prop valve with a syringe, but still wasn't getting fluid to the rear brake lines when pumping the brakes.  Here is the tool:  https://www.amazon.com/gp/product/B09G68TRKT/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&th=1

3.  Whenever I installed the MC on the brake booster, I was not able to push fluid to the rear brake lines.  I loosened the MC and verified that the Brake Booster push rod was engaging the MC slightly when I would tighten it down.  I checked the push rod on my original booster and verified it was the same length as the one installed in my new booster.  It was.  However, the push rod was deeper in the original booster by about 1/8 of an inch.  I was perplexed.  I messed around with the push rod in the new booster and found that if I rotated it slightly while pushing it in, it fell into place.  I believe it was notched in a way that the bottom pin actually had to slide into position for it to go all the way in.  Guess what?  That corrected the problem with getting fluid to the rear brake lines.  After that fix I was able to get fluid to flow all the way through to the rear calipers using the syringe and pushing it through the opening in the rear well of the MC. 

So I think I was dealing with a number of problems.  The biggest being that the MC was partially engaged and not able to pull fluid down into the rear position since I was not getting full travel of MC piston.  Hopefully this fixed the problem.  I still have some air in the rear system that I'm working on correcting, but the brakes seem to be functioning now.  What a PITA this effort was.  Granted I've never done a fully dry brake system before either.

[chief poncho]

Doing a little more research and I may need to switch out the MC for optimal braking too.  I can't find anything directly stating the MC needs to be changed, but I can buy a replacement 2nd gen disc/disc MC that will fit the car.  I probably should do so.

[chief poncho]

Ok, so I confirmed with the rear disc kit manufacturer that using the Disc/Drum MC is ok, but if the pedal still feels a bit soft, I can replace it with a 1" bore piston disc/disc MC that will provide a bit more pressure to the rear brakes.  The Right Stuff part number for that MC is DBMC05.