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73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: Breadfather on August 22, 2015, 11:28:27 pm
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okay, first off I apologize if this is a repeat but I have been reading for hours and can't find an answer to my issue.
The vehicle in my sig is what I'm working on. I bought is a few weeks back and the brake light was on in the dash and the brakes were week. The rear brakes were a mess and look like they had both leaked at some point from the wheel cylinders. So I redid everything on the rear, drums, cylinders, hardware, shoes, steel lines from the T. After the job I couldn't get them to bleed, there was no pressure. Plenty of pressure up front, but nothing in the back.
After a ton of time online, I was convinced the combo valve was the issue as I had the warning light on in the dash. After a ton of issues with the 5 brake lines I finally got them loose. Disassembled the combo valve and cleaned it out and re centered the switch thing. It was very dirty in there. Put it back on the truck. Refilled the master, gravity bled it at the master, then going into the combo valve. Front brakes gravity bled easily. But after 2 hours I still couldn't get anything out of the rear. If I start the truck the brake light stays off so I don't think the combo valve slid over.
After more dickering around I removed the line from the rear master and it just would not let any fluid out, nothing more than a drip every 5 seconds. The front one pours out. Is this is sign of a bad master?
These thing are driving me nuts as I've been working on the, for2 weekends now. I've never had this much issue with brakes before.
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I'd replace the MC too
Not expensive
Get a new one. Not a rebuilt one
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You could try to bench bleed the master to get all the air out but may be shot due to being empty with all the repairs that were needed. As roundhouse stated, they are not that expensive.
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Installed new master this morning bench bled it with no problems. The good news is that the flow from the rear reservoir is now what it should be and flowing well to the combo valve and the pedal feels much better than before so I'm sure I needed a new master or if I didn't it was only $34 new from Napa.
The bad news, I still cannot get fluid to the rear brakes. It flows well to the combo valve but will not come out the back section of the valve. I ran air through the lines before putting the valve in, and they are not blocked. I also ran air through the rear section of the valve before re installing it, and it came through. It was definitely reduced flow but it did come through, so I am assuming the reduction of air flow is how the valve is designed? Anyways, I bolted it back in and can't get fluid through the rear section of the valve and the warning light came back on after a very light pedal push to try and assist the fluid through the valve.
My diagnosis, the valve is also bad. Now I have to try and find another one. Anyone know if the PV-2 from Summit is a direct replacement? I don't want to have to redo lines or fittings. I'm gonna do some searching on here before I order it.
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The combination valve is just doing its job. Frustrating as it is, there is still air in the lines and the valve tripped to isolate the front from rear brakes. You need to recenter the valve and bleed.
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The combination valve is just doing its job. Frustrating as it is, there is still air in the lines and the valve tripped to isolate the front from rear brakes. You need to recenter the valve and bleed.
I cannot bleed the rears at all as it will not let any fluid through the valve. Even if I redo everything, and hook it back up, it will not gravity bleed through the valve. Am I doing something wrong? I have also noticed that the little pin on the front of the valve does not move no matter what happens.
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If you can get your hands on a vacuum bleeder try sucking the fluid through. I've got several proporting valves working again like that.
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All you have to do is open both front bleeders mash on the brake pedal to center the valve back and without letting the pedal up have someone close the bleeders. Then it will gravity bleed. Done this procedure more times than I care to remember.
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I don't know anyone that has a vacuum bleeder and buying one is the same as buying a valve.
I've tried the front bleeder mashing thing and it hasn't worked. Even when I know the valve is centered(after I remove it, disassemble, manually center it, and re install it) it will not let any fluid through the rear section of the valve.
There is no telling how long the truck was driven without rear brakes before I got it. By the look of the rears when I did them, it was a while. I am wondering if the spring inside of the valve is weak or if there is something else wrong inside of it. There isn't that much to it when you disassemble it but the red plastic thing that is attached to the switch section was a little bent when I pulled it out.
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Well im looking at the valve from inline tube, before I buy it, does anyone have any other suggestions on how to get this thing going assuming the stock valve is functioning? I've tried the open bleeder/pedal stomp thing and no dice. I don't have access to a vacuum bleeder and I don't think the DIY pressure bleeder thing will work as it seems like it would put the pressure in the wrong side of the valve.
Any other ideas?
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I don't know anyone that has a vacuum bleeder and buying one is the same as buying a valve.
I've tried the front bleeder mashing thing and it hasn't worked. Even when I know the valve is centered(after I remove it, disassemble, manually center it, and re install it) it will not let any fluid through the rear section of the valve.
There is no telling how long the truck was driven without rear brakes before I got it. By the look of the rears when I did them, it was a while. I am wondering if the spring inside of the valve is weak or if there is something else wrong inside of it. There isn't that much to it when you disassemble it but the red plastic thing that is attached to the switch section was a little bent when I pulled it out.
Got a shop vac? Wrap a ball of duct tape around some vacum hose, cram it in the end of the shop vac, tape the crap out of it, turn on shop vac, slip vac hose on brake bleeder, open bleeder, keep master cyl full.
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Can't you get a friend to cycle the brakes while you operate the bleeder? On-off-on-off...? I've tried lots of different ways of bleeding and there really isn't a substitute for the old-school two man way. I wouldn't expect gravity bleeding ever to get air out of the lines.
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If you absolutely have to do it alone, you can get a length of clear plastic tubing small enough to slip over the bleeder end and stay there without falling off. Run the tubing up and over a suspension member before letting it descend into your bleed receptacle. When you pump, you want the fluid to run uphill in the tube before falling into the receptacle. Basically, you'll have a column of fluid above the bleeder at all times. Open the bleeder and leave it open while you pump the brakes. Air bubbles will rise to the top of the column, while fluid is sucked back into the bleeder when you let off the brakes. It's harder to determine when the air is all out, but this is the only other method of bleeding that I've found to be close to practical.
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A hand held vacuum pump bleeder is not expensive
I've had to use em a few times
You could take the valve apart and remove the guts and reinstall
I don't think it's a proportion valve
I think all it does is turn on the light when the pressure is not balanced
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I'm going to try the shop vac thing but what I have had an issue with is that the fluid flows very well to the prop valve. Once it gets in the prop valve it flows out of the front section into the lines going toward the front brakes with no problem. The fluid flows to the rear section of the valve very well now with the new master, but it will not flow out of the rear section of the valve even if the rear brake line is totally removed from the valve. That is why I suspect a valve issue. Since I cannot get the valve to re center using the pedal, the only option that I see is to remove the valve, re center, re install, and see if I can suck the fluid through without tripping the valve. I have heard people talk about a pin that is supposed to stick out of the valve when it trips, the pin in the valve never moves, no matter what position the valve is in. Is this another sign of a bad valve?
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Previously, you posted there was a lot of gunk in the combination valve when you took it apart. What did you use to clean it?
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Sprayed it out with brake parts cleaner and re lubed all o rings with brake fluid.
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Have you tried taking off the bleeder fitting from the rear cylinder and checking to see if it's clogged? Then check to see if fluid will come out of the cylinder without the fitting. Replaced the bleeder fitting?
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The master cylinder push rod could be adjusted improperly
Closing off the rear port inside the MC ?
At this point I'd just gut the distribution block and see if that works
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The wheel cylinders are new and thus so are the bleeders. The rear line is free from obstructions, I have tested. The master cylinder is now new and fluid is flowing from the rear section of the master like a champ. Which brings me to the combo valve.
If I "gut" the valve in order to get fluid to the rear, and then re assemble it, do you think that will build up enough pressure in the rear section to prevent the valve from tripping again when I have to re bleed it? I am assuming that will affect the proportioning part of the valve and I will then have too much pressure to the rear brakes?
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Did you replace the rear rubber hose? I quickly read the entire post but I could have missed it.
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Maybe I missed it but are you holding the metering valve open while bleeding?
Pages 5-7, 5-8, and 5-16 in the 1973 Light Truck Service Manual.
The same procedure should apply to your '77
http://www.73-87chevytrucks.com/techinfo/7387CKMans//Service/ST_330_73_1973_Chevrolet_Light_Truck_Service_Manual.pdf#page=273
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Maybe I missed it but are you holding the metering valve open while bleeding?
Pages 5-7, 5-8, and 5-16 in the 1973 Light Truck Service Manual.
The same procedure should apply to your '77
http://www.73-87chevytrucks.com/techinfo/7387CKMans//Service/ST_330_73_1973_Chevrolet_Light_Truck_Service_Manual.pdf#page=273
Thank you for the link, it definitely helps me understand how the valve operates. It is making me more and more convinced that there is something wrong with the valve. The pin that is supposed to be sticking out of the front of the valve is and has never been sticking out of the valve since I've begun working on it. Nothing I have done has caused any movement in that pin. I think I am going to pull the whole valve again and soak it in denatured alcohol for a while to see if I can get it to free up, if not. It is new valve time.
As far as the rear hose, I do not think that is the issue as I have been able to push air and fluid through the entire rear section once I disconnected it from the valve.
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You are welcome.
I am bleeding the brakes on my '75 tonight or tomorrow.
I just need to whip something up to hold the metering pin pressed in while I bleed the brakes.
The metering pin on mine is covered with a rubber cap. I can feel it press in when I push and return when I release it.
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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.
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You have checked the hard brake line going from the prop valve back to the rear rubber line for leaks? I would replace the rubber brake lines on the front and the rear. They will swell on the inside and you can't see it until you take them loose and pump the brake. The fluid will either trickle out or not come out at all.
I just went through the same thing that you are doing with my truck. I replaced rear hard lines from the prop valve back, the rear flex brake line, the hard lines out to the wheel cylinders, new rear wheel cylinders, new rear brake shoes and all new hardware.
I replaced the front calipers, brake pads and front flex lines. I replaced all of the rubber lines with braided stainless lines.
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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.
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I would just go ahead and get a new valve. You likely want a pv2. I got mine from cpp and was very happy with their service.
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Make sure the rear brakes are assembled correctly and properly adjusted. Replace the combination valve.
If you bleed it at the master you get good pressure?
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Make sure the rear brakes are assembled correctly and properly adjusted. Replace the combination valve.
If you bleed it at the master you get good pressure?
Yep good pressure at the master great pressure up front. I thought gutting the valve would at least get me to be able to stop the rear wheels or lock them up...but not so. I put the wheels back on and drove it around today and the pedal is good, very solid. It stops better than it did before but I think that is because the new master...I'll update after I get new valve installed in a few weeks.
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Well remember the combination valve is not only a proportioning valve but also a metering valve so they're best not messed with. You can't really test the spring pressures and it's just not worth it. They're pretty cheap now anyway. I've purchased ones on eBay with no issue.
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You replace the wheel cylinders ?
Loosen the threads at each junction Starting at the MC
And have someone mash the pedal and see if it squirts out
If it does, move on to the next one
That way you can isolate where the blockage is
The rubber lines swell up inside
Or there may be rust or some thing blocking a line
You just have to me methodical and logical in finding it
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