Problems bleeding rear brakes

[Broncojunkie]

Looking for some ideas here.

I just finished up the 5-lug, 8.8, sn95 booster/master cyl/caliper swap on my pace car. I ended up replacing the rear lines, as well as the front and rear rubber hoses. I went to bleed the brakes and I'm getting nothing from the rear (drums, not disc). I can bleed both front brakes, but nothing at all from the rear. I'm using a might vac pump because I don't have a helper, but I also tried using a 1-man bleeder bottle and pumping the pedal. Left rear bleeders open all night and that didn't work, either. Master cylinder was bench bled with no issues, as far as I could tell. Rear cylinders are brand new and I pulled both bleeder screws and made sure nothing was clogging them.

What am I overlooking here?

[AldeanFan]

Do you have a proportioning valve?

When you pump the brakes with the bleeders open does the pedal go to the floor?
Does it build pressure with the bleeders closed?

I’m not familiar with the sn95 brakes but isn’t that master for 4 wheel disks and you’re using rear drums? It should still push fluid anyway.


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[mudgepondexpress]

I will second the proportioning valve. I have never been a fan of the pump, pump, pump pressure, then bleed. I use the open bleeder, push it smoothly to the floor, close... over and over. Pumping seems to agitate the fluid and build up air bubbles. Yes it is a 2 person job.

Kenny

[ZephyrEFI]

I feel your pain. I'm dealing with only a faint trickle coming out of my rear brakes. There might be something here that can help you.

http://vb.foureyedpride.com/showthre...e-Brake-Lines-!

Specifically, I'm thinking of the stock prop valve thing where you use that tool to hold the combination valve in place so that it allows pressure to actually happen in the rear circuit. My car is a 1979 model too, and like you, i replaced a bunch of lines also. I'm going to try that procedure pretty soon here. If yours isn't resolved by then, I'll chime in here and let you know how it went. Good luck!

[Broncojunkie]

I actually do still have the original prop valve. Come to think of it, that's the only part I haven't replaced other than the front brake (hard) lines. I have an adjustable prop valve I planned on using, after gutting the old prop valve. But I decided to stay with the rear drums because i didn't want to fool with the e-brake cables. I was hoping the original valve would work without having to add the adjustable one.

[Broncojunkie]

A little back story on this car. I had collected about half of the 5-lug and brake swap parts, but plans to complete the swap were on the back burner. I had already replaced the master cylinder, both front brake calipers, the rear cylinders, pads, shoes, rotors, and drums with OEM parts. The brakes just never were right. Pedal was soft after bleeding multiple times, using different methods. I also replaced the new master cylinder with another new one, which seemed to help only slightly. But I was able to bleed them normally (it just never seemed to make a difference). I got frustrated and decided to go ahead with the swap... hoping that the combination of new stuff would take care of the problem. So now, it's a slightly different problem, but something still isn't right.

So now, I'm thinking the prop valve is the culprit. Question is, do I gut it and use the adjustable one I have or just replace it with a stock one?

[ZephyrEFI]

Wow, what you just said is the exact story of my car.

I'd try that tool to hold the combination valve in place and get the fluid moving in the rear circuit first.

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[Broncojunkie]

Wow, what you just said is the exact story of my car.

I'd try that tool to hold the combination valve in place and get the fluid moving in the rear circuit first.

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I evidently need some more guidance on this. Never knew there was such a thing!

[Broncojunkie]

I'm half tempted to pull it off and take it apart for a good cleaning. I mean, it is 40yrs old lol!

[AldeanFan]

Crack the line out of the combination valve that goes to the back brakes and see if you’ve got fluid there, if you do then it’s either the wheel cylinders or the rear flex hose.

If no fluid at the exit of the combination valve then crack the line entering the valve and if you’ve got fluid there the it’s the valve, if no fluid going in to the valve then it’s the master.


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[Broncojunkie]

Crack the line out of the combination valve that goes to the back brakes and see if you’ve got fluid there, if you do then it’s either the wheel cylinders or the rear flex hose.

If no fluid at the exit of the combination valve then crack the line entering the valve and if you’ve got fluid there the it’s the valve, if no fluid going in to the valve then it’s the master.


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I'll try this Monday (we're out of town for the weekend).

[ZephyrEFI]

Here's the tool. You put it where the brake light switch goes. It stops the other valve in the proportioning valve assembly from blocking off the rear circuit when you press the brake pedal. It's meant to do that if it detects a pressure differential, and this stop it to you can force pressure into the rear circuit.

https://www.summitracing.com/parts/clp-pv-tool

And yeah, they suggested to me that I take mine apart and clean it too. You can get a rebuild kit with new seals. Look in my thread for that link.

I'm going to do this on mine any day now, maybe even today.

[Broncojunkie]

Thanks for the link. It looks like this will keep you from "tripping" the pv, which will cut off the flow to the rear brakes. I'm also reading that the tool won't help if the pv is stuck in the tripped position. I'm now convinced this is what I've got going on. I'm going to see if I can take it off and disassemble it, clean it, and put it back together. I'll come back and post the results Monday.

[85WhiteGT]

I had the same problem when I replaced the hardline going to my rear axle. I was frustrated one night, sat in the car and pumped the pedal about 10 times in a row, heard a pop, and then finally got fluid to the rear brakes. I'm assuming that the proportioning valve reset itself somehow or just dumb luck.

[Broncojunkie]

Thought I replied to this earlier, but it evidently didn't stick.
I did some reading on this whole pv deal. The tool you posted is supposed to keep it from sticking, but won't fix one that's alway stuck. From what I understand, the pv can get stuck and cut off flow to the rear. That sounds exactly like what's going on. I believe I'm going to try and remove it, take it apart, and give it a good cleaning. I should be able to tell if something is froze up inside.

Thanks for the link and explanation! I'm pretty confident that's where the problem is.

[83gt351w]

When I did my sn95 brake swap, all was new, except the prop valve. I couldn’t get pressure to the rears, and I went to gut the prop valve, and it was full of 35 yr old gunk. I cleaned it, problem solved.

[Broncojunkie]

Just bored and still out of town, but came across this video that explains a lot.

https://youtu.be/xrjENVu1Bxk

[Broncojunkie]

When I did my sn95 brake swap, all was new, except the prop valve. I couldn’t get pressure to the rears, and I went to gut the prop valve, and it was full of 35 yr old gunk. I cleaned it, problem solved.

That's what I was wanting to hear! Thanks for chiming in!

[Broncojunkie]

Well, here's what I have going on now. I had the wife soak down the pv with penetrating oil earlier today, since I knew it would be a bear to get 5 old brake lines loose. I rounded off the first nut I tried. The others weren't cooperating much, either. I really don't want to start running new brake lines. The originals actually look like they're in great shape. And yes, I am using a line wrench!

I was able to pull the sensor from the top of the pv and the guts from the front. No fluid is coming out of it, even when hitting the brake pedal. I'm not sure if that is normal or what. I tried, again, to bleed the rears using the mighty vac while the pv was apart and still nothing.

I'm going to try bleeding the front calipers some more and see if I can get things moving. Any other ideas?

Edit: Forgot to add that there wasn't much dirt or gunk inside, that I could tell. It was a little dirty, but not what I expected. I sprayed a little brake cleaner inside to see if I could flush out what I could.

[Broncojunkie]

After fiddling with this thing half the night, I'm not sure what I did, but it's finally freed up. After bleeding the front calipers again, removing and checking lines from the mc to the pv, removing the mc and bench bleeding again (had it off because I wanted to recheck the rod and pedal function), tapping on the pv while the wife was holding pressure on it, I finally started getting fluid to the rear. All bled and I finally have brakes again!

That was an ordeal. Thanks, everyone, for the tips and help!

[ZephyrEFI]

Congratulations!!

So, that valve was stuck with the rear closed off?

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