Rear brakes not working - maybe the proportioning valve?

[Lugnutz65]

I can't get my rear drum brakes to work.

I must say how much I hate doing the brakes, brake lines and adjustments. Give me anything else, anything! Just not brakes.

I just installed a new CPP front disc brake kit with new spindles, rotors, etc. in my 1965 C10.
I have the Captainfab bracket (nice item) and a salvage yard 1995 Blazer booster and MC complete with the proportioning valve.

I did my research before choosing my booster and MC. The 1995 Blazer has front disc and rear drums. The Blazer front hard lines are 3/16". The rear brake line is 1/4" all the way back to the rear axle where it then reduces to 3/16" to the rear drums.

I bench bled the MC. Tonight I finished my hard lines and have no leaks. Front discs work great. I have nice pedal pressure. The rear lines don't bleed very well but I do get some flow. I just don't get any rear brakes. I adjusted the rear brake shoes. Still nothing.

I figure the rear brake cylinders are NOT getting pressure. So it's either a bad MC or possibly the proportioning valve? Any suggestions before I go spend money on something I don't need?

[LostMy65]

Brakes always frustrate me.
Can you just temporarily connect the fluid lines directly to the master cylinder and then check if the back brakes work? Kind of a process of elimination as to whether it's the proportioning valve or not.

[Lugnutz65]

Originally Posted by LostMy65

Brakes always frustrate me.
Can you just temporarily connect the fluid lines directly to the master cylinder and then check if the back brakes work? Kind of a process of elimination as to whether it's the proportioning valve or not.

Worth a try. I sure wish I had paid more attention as to HOW MUCH fluid was coming from each MC port when I did the bench bleed.

[LostMy65]

When I converted my 66 to discs, my backs would lock up before the front.
I ended up installing one of these:
https://m.summitracing.com/parts/sum-g3905
I know your issue is the rears not grabbing, but the valve above solved my issue. I installed it inline to the rear. Dialed it down until my back brakes quit locking up. Not only that, I could adjust my rear brakes for when my bed was loaded or empty.

[Lugnutz65]

Originally Posted by LostMy65

When I converted my 66 to discs, my backs would lock up before the front.
I ended up installing one of these:
https://m.summitracing.com/parts/sum-g3905
I know your issue is the rears not grabbing, but the valve above solved my issue. I installed it inline to the rear. Dialed it down until my back brakes quit locking up. Not only that, I could adjust my rear brakes for when my bed was loaded or empty.

I installed one of those on my 66 Galaxie (sold it since). Nice item. I'd just hate to buy it and then find out it was the MC after all.
Does a proportioning valve ever get stuck or ever need to be reset?
Thanks

[LostMy65]

Originally Posted by Lugnutz65

I installed one of those on my 66 Galaxie (sold it since). Nice item. I'd just hate to buy it and then find out it was the MC after all.
Does a proportioning valve ever get stuck or ever need to be reset?
Thanks

Yes, I think the proportioning valve you have has a pin in it that cuts flow to rear or front depending on if a failure occurs in the plumbing front or rear.
When it notices a drop in pressure it shuts off the fluid to the failed section.
There's a thread in these forums that demonstrates how to reset that pin.
I'll see if I can find it.

[LostMy65]

Here's the thread with a link to a 'how to'

http://67-72chevytrucks.com/vboard/s...=Proportioning

[Lugnutz65]

Originally Posted by LostMy65

Here's the thread with a link to a 'how to'

http://67-72chevytrucks.com/vboard/s...=Proportioning

I do believe the prop/combination valve is my problem.
I think the valve is off center. I will check tomorrow.
Thanks for your help. I will follow up with how things go WITH PICS!

I reviewed these 2 videos. The first is a promo video.
The second one is a little annoying because his explanation is not well prepared but he does explain things.

https://www.youtube.com/watch?v=qPLaPv8DITE

https://www.youtube.com/watch?v=pRtJ1QwZjWk

[PGSigns]

When I did mine on the 66 using about the same thing you have I had close to the same issue. One thing I did was to redrill the brake rod mount to the pedal 1" lower to give a bit more stroke. The I ended up having to pressure bleed the system to get the last bit of air out the back. After that no issues and stops great.
Jimmy

[LostMy65]

Originally Posted by PGSigns

When I did mine on the 66 using about the same thing you have I had close to the same issue. One thing I did was to redrill the brake rod mount to the pedal 1" lower to give a bit more stroke. The I ended up having to pressure bleed the system to get the last bit of air out the back. After that no issues and stops great.
Jimmy

Which would make sense if the front reservoir is for the rear brakes.
And that reminds me that many suggest adjusting the push rod engage sooner.

[jayoldschool]

Couple more things to consider:
1. That MC gets rear line to front port, (I believe)
2. If everything is plumbed correctly, rolling in reverse, and stepping HARD on the brakes will reset the switch in the prop valve.
3. Don't rule out a plugged rear flex line. Happened to me when I was doing the dual MC conversion.

[Lugnutz65]

Originally Posted by PGSigns

When I did mine on the 66 using about the same thing you have I had close to the same issue. One thing I did was to redrill the brake rod mount to the pedal 1" lower to give a bit more stroke. The I ended up having to pressure bleed the system to get the last bit of air out the back. After that no issues and stops great.
Jimmy

Thanks PGSigns,
I did drill a hole 1" lower on my pedal arm. Not everyone does that but my research showed me that the pedal ratio should be between 4:1 and 5:1 for a power assist disc/drum system. So that part of my setup is correct. I'm pretty confident I can sort out the proportioning valve thing after I give it a careful examination. It behaves like the rear lines are blocked by the piston in the back half of the PV. Update coming tonight.

[62stepside longbox]

Here is cpp's guide on getting the proportioning valve re centred.

[grubsster]

When I did mine I had the issue that jayoldschool mentioned. My flex line had collapsed. Changed out and worked great after.

[jchav62]

Originally Posted by LostMy65

When I converted my 66 to discs, my backs would lock up before the front.
I ended up installing one of these:
https://m.summitracing.com/parts/sum-g3905
I know your issue is the rears not grabbing, but the valve above solved my issue. I installed it inline to the rear. Dialed it down until my back brakes quit locking up. Not only that, I could adjust my rear brakes for when my bed was loaded or empty.

Did you run this along with a regular prop. valve?

[LostMy65]

Originally Posted by jchav62

Did you run this along with a regular prop. valve?

Yes

[Lugnutz65]

Spent over 1 hour last night testing different things. I fully believe my PV is bad AND perhaps my MC as well. I used a test light with 12V on the warning switch and it lit the lamp - which means the piston is out of position. I couldn't get the piston centered again so my NEW PLAN is to buy a new PV for just the rear lines. THIS ONE.

I also removed and tested my MC. The REAR BRAKE port (at the front) doesn't squirt a steady stream of fluid during bench bleeding. I disassembled, cleaned and reassembled the MC but I'm tired of having brake fluid dripping from my elbows so I'm ordering a new one.

I hope it will be fairly easy to use the new PV with 1/4" lines. If I need to downsize to 3/16", that will require a lot more work and creativity.

[The Rocknrod]

Good. That way you can dial in your specific rear weight and lock up instead of relying on a generic valve that may or may not be specific to you truck.

[Lugnutz65]

Just an update. My new MC arrived and the bench bleeding went well. I must say the bleeding procedure is much different than other MCs I've done in the past. Maybe that was my original problem.

The fluid doesn't shoot out in a stream like I'm used to, but I'm 100% certain that I've removed all the air. I should be able to finish the install tonight.

I'll post pictures once I have this done.

[The Rocknrod]

Originally Posted by Lugnutz65

... the bleeding procedure is much different than other MCs I've done in the past...

Do tell - whats the diff?

[Lugnutz65]

Originally Posted by The Rocknrod

Do tell - whats the diff?

All of the MCs I've ever bench bled were drum/drum old school. This step MC is more difficult to bench bleed according to these videos. I certainly had a hard time getting both ports to "squirt" a steady stream simultaneously. Still not sure until I test it on the truck.

Video 1

Video 2

[hotrodder]

My money is with the dudes that suggested that the rear rubber flex hose has collapsed on the inside. Been there.

[Lugnutz65]

Just some follow up. The rear flex hose wasn't collapsed. I'm convinced that my MC wasn't properly bench bled (even though I followed instructions). I'll take the blame on this one.

I did order and install a brand new 1995 Blazer MC. The rear brakes still wouldn't engage, so I took it off and did another bench bleed. Then it worked.

I eliminated the 1995 Blazer proportioning valve but used the bracket to mount the brake bias valve I bought from Summit Racing. The Summit brake bias valve is made by Wilwood (cast into the metal right beneath the Summit stickers).

I drilled 2 holes in the bracket and used some bolts and nylock nuts. Works for me.

More pics later. I still have a leak at one fitting that I need to fix. The brakes seems touchy even though I moved the pushrod down one inch. Just something I need to get used to I guess.

[Lugnutz65]

More pics. I think I sealed up all the leaks at the fittings. Too bad I had to use adapters with the brake bias. It would look a lot cleaner if I didn't need them.

One thing I can confirm - I HATE BRAKE FLUID. To say I took a bath in the stuff might come close to the mental picture I want you to have.

Just glad it's over and I can move on to something else.

I used a Captainfab firewall adapter to mount the booster.
1995 brake booster and MC
Summit Racing brake bias (made by Wilwood)
CPP front disc brake kit
Speedway pushrod extension and Heim joint