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Discussion Starter #1
I swapped my rear end out to a 8.5 4.11 posi from a 8.2. Added right stuff rear disc kit / and PV valve at the time of swap. Why not? Makes sense right?

Worked fine for few 100 miles. No issues. Driving around breaking in the diff and the rear brakes start to drag. I made it home with red hot discs. Assumed the issue was a failed brake hose. Replaced the hose coming from the chassis, calipers, rotors, and pads. No pedal ever since.

I have since replaced the master cylinder twice. I bench bleed it before I put it on. Tried bleeding the brakes with a friend a few time with no luck. Bought a pneumatic bleeder that hooks up the air compressor. Use a little grease around the bleeder and I can drain the master in about 1-2 minutes. I have bled the brakes so many times I cannot remember how many now.

I do not have any leaks that I can see. I have checked checked and re-checked and gone thru about 2 gallons of DOT3 fluid.

I obviously have a leak somewhere. No physical leaking from brake lines/hoses. Master is brand new and bled. Can a PV valve cause this? I bought PV72 from right stuff when I did the swap.

Any ideas?
 

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Is the PV for a Disc/Disc setup? I had a CPP one on my car and it was set up for Disc/Drum, I had to remove a little valve in it to make it disc/disc. I just googled it, and it looks like I could be used for both. Look on Right Stuffs site and see if you have to mod it for Disc/Disc, like I did
 

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If you are literally losing fluid I'd remove the MC and look into your booster to make sure brake fluid is not leaking back into the booster thru the rear MC seal.
 

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Discussion Starter #6
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Is the PV for a Disc/Disc setup? I had a CPP one on my car and it was set up for Disc/Drum, I had to remove a little valve in it to make it disc/disc. I just googled it, and it looks like I could be used for both. Look on Right Stuffs site and see if you have to mod it for Disc/Disc, like I did
Thank you I will contact them. I looked before and it did not have any little valves like the disc/drum PV that came off of it.
 

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Discussion Starter #7
If you are literally losing fluid I'd remove the MC and look into your booster to make sure brake fluid is not leaking back into the booster thru the rear MC seal.
The master that came off was leaking out of the back a small amount. This a manual brake setup. No booster.

Another thing to add, the internal piston in the valve could be stuck to one extreme and needs to be reset. Here is a decent discussion on this - Anyone know how to reset the brake proportioning valve?
I will check this out. I do not believe it is stuck if I can pull fluid easily to all for corners with the vacuum canister bleeder. right?

I had a similar problem on my camaro, used a mityvac a bunch of times, no luck no pedal at all. Ended up getting a pressure bleeder and was able to get a great pedal.
Capri-Tools-Vacuum-Brake-Bleeder - From amazon is the one I am using.

I am going to go back to just having a buddy pump the pedal for me. The vacuum bleeder pulls a lot of air from the bleeder threads unless I cover it with grease.

For the pressure bleeder did you just tap the cap or something? All the pressure bleeders I see are for late model stuff that already has a threaded port on the reservoir.
 

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I use this pressure bleader, works great

.
 

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I don't use vacuum to bleed brakes. I've had trouble pulling air past the wheel cylinder cups and through the back of the master cylinder. So if you used vacuum to pull the air out of the system it may not have worked as planned. The Pressure bleeder is the way to go and you may have to re-bench bleed the master if the Vacuum bleeding system was used..

This is the process I would use if your car was brought to me. Fill the master cylinder to about a 1/4" from the top and install the cover. You have a person inside the car to press the brake peddle. You open the brake line at the master cylinder before the person presses the brake. Open the brake line a half turn press brake peddle down and close off the line before the peddle stops traveling down. Hold the peddle there for 10 seconds or so. If any air went into the tube it can have time to float back up to the top. Then release the peddle. This pulls the air that was in the tube back into the master. Do it a second time. Any air bubble that was in the tube should be right there ready to come out as soon as the peddle is pushed in. Go to the next line at the master and do it the same way. After that you pressure bleed the system. The furthest bleeder away from the master first, but don't just crack it open see no air and close it. You have to give it time for an air bubble to travel the entire distance from the master to the bleeder. Then go to the next closest wheel and bleed it but you only have to bleed it from where the brake line T's near the rear differential, over to the wheel you are bleeding. On the front wheels, open the bleeder long enough for the air to travel from the master to the bleeder on both wheels.

With using the pressure bleeding system, the wheel cylinder cups and master cylinder cups are facing inward in the correct direction so when the fluid pressure is applied it forces the cups to seal against the bore, same as if you're stepping on the peddle. If you apply vacuum it can pull air past the piston forcing the lip of the cup to move away from the bore and allow the air to enter the system. I feel the larger the piston or cup, the better the chance of air contamination. So the master cylinder would give the path for the air to enter in the case of this car. It would be difficult to pull air past a disc brake piston or seal.

One of the other things I was taught at an early age is, brake fluid absorbs moisture or water. I am pretty sure every auto technician has heard "Never use brake fluid from and open container". That's because it gets contaminated from moisture in the air. In the pressure bleeders pictured above the air is pressurizing the fluid and seems like it forces whatever moisture is in the air to mix with the brake fluid. I know these pressure bleeders are used in automotive shops as well, not just home use. I also know they are easy to use and the Mightyvac version has excellent adapters to fit the master cylinders with quick disconnects and shutoff valves that prevents the brake fluid from spraying all over the car when the unit is removed. I just don't know how much contamination is occurring, so I really have no clue as to why those pressure bleeders are sold as such or used as such. I use a pressure bleeder that has a top and bottom housing with a rubber bladder in between. This design prevents the moisture in the air from coming in contact with the fluid being pressurized. The air pressure pushes the rubber bladder against the fluid forcing it to the master, never making contact with air.

Ok there is one other thing I've learned over the years. This one you have to be careful and you have to trust the person in the car not to push the brake peddle so fast it squirts out of the master. You can take the top off the master cylinder and have someone move the brake peddle ever so lightly in and out ( like clicking the brake light switch on and off). You look down inside the master as the person does this and watch for tiny bubbles rising from the holes at the bottom of the master. If there is a string of tiny bubbles rising up then you still have air in the master and the bleeding procedure I mentioned above should be performed. If your getting a bubble once in a while or a string of bubbles and then one or two then you should be good. Those bubbles will work there way up and out in about 15 minutes of drive time. I hope this helps.
 

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Discussion Starter #11
The issue is in the rear. I pinched the hoses off and was able to get pedal. I have tried vacuum bleeding again, followed right stuffs instructions about setting e-brake tolerance and gravity bleeding before bleeding whole system. As soon as your crack the bleeder fluid drips out. There is fluid there.

Still soft pedal when back is not pinched.

I'm sure it's done stupid little thing but usually it shows up sooner.

Ordered a Motive pressure bleeder. #0105. Hope it works. I have never had so many issues with a set of brakes.
 

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Are the brake fluid bleeder valves on the top side of both rear brake calipers?.... or is one (or both) of these valves on the bottom side of the calipers?
If one (or both) of the bleeder valves are located on the bottom side of the rear calipers, you will not remove all of the air while bleeding the rear calipers.
 

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It has been my experience that nothing works any better than the regular two man bleeding . One pumping the brakes and the other bleeding from underneath. It's not as fancy and is harder but we quit using anything except the old school way. We also bleed the brakes two or three times. We will bleed the brakes and try to drive the car a bit. Then we go back in a day or so and bleed them again. We usually do it three times. We have a guy who works in the Q and A lab at Nissan and he says that if there is any air in the system it will usually work it's way to the calipers. The second or third bleeding usually takes care of it.
 

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Discussion Starter #14
I bled with a the motive pressure bleeder and I am able to get about 1/4 peddle after a few pumps. It will hold 15-20 seconds easily but when I come back after a couple minutes the pedal goes the floor the first stroke.

I have the calipers off the disc and clamped with an old brake pad and C-clamp and the bleeder pointing straight up.

Master has been bench bled and hold pressure when plugged. I checked every single line connections and wiped them dry. They still appear dry after pumping up the pedal and waiting a few hours. I do not believe the PV valve is the cause because fluid is getting to all four corners. I do not have a preload condition and have about 1/8 of play before the pedal engages the master cylinder pocket. (T56 hyd clutch bracket (3/16 or 1/4 inch steel) between firewall and master cylinder. )

I guess because I am staring to get some pedal I will try and bleed one more time. If that doesn't work I will try another master because it has definitely been "overstroked" once or twice during the bleeding process.

I look out for more ideas if not I might have to just take to a shop assuming I can even get it out of my sloped drive way safely. My wife is going to kill me if I keep working on this thing every single weekend.
 

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I'll take a stab at it but it seems because you have not seen a fluid leak the culprit is somewhere where there is an accumulation of air in the system where the leak is. Not sure if this is relevant but when I was bleeding my 100% new system was was pumping that EZ Vac till I couldn't move my hand any longer. I didn't have a fluid leak but I did have a loose fitting at the Tee above the differential. I would get some vacuum going on the pump but it would drop quickly. All I was doing was pulling air back into the system.
 

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Is anyone available to observe all of the rear rubber brake lines as you pump the brakes and apply pressure to the system (with all brake bleeders closed). The issue might be caused by a portion of the rubber brake line that is "ballooning" as pressure is applied. I had this happen to a buddy of mine.
 

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Discussion Starter #17
I have tried all the above methods now and found to leaks, bulging hoses, etc. I am taking to a local shop. I will update the forum with their resolution. Thanks for all the advice.
 

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Ok - - - I've posted this before : WHAT Brand of new M/C do you have . . . ?
At work we had a fleet of Ford Trucks (doesn't really matter - brakes are brakes) . I was in this "small garage" , maybe 6 years , (doing Fleet work on company trucks & cars at the 'Copper Mine') . We always used "Raybestos Brake Parts" - - - m/c, wheel c, pads, shoes, e-brake cables, hardware kits, . . . . everything. Then, they change 'vendors' . . . . the new vendor says : we only use "Wagner Parts" .
Our Boss told them NO - we want Raybestos ! Then, he did give - in .. . . we started using Wagner. At that time we also started returning a lot of "bad Brake Parts" - - - I would get a NEW M/C - bench bleed, install, remove, - - bench bleed again, install, and that new M/C would still by-pass , straight outa th' Box. We DID make that vendor Change over to supply all Raybestos brake parts from then on .
It says right on their Box - - - "Raybestos - Best In Brakes" - - - It will make a believer outa you . . . . . . 9 - 10 mechanic's with almost 4-5 guys doing brake jobs every day . . . . . .
you learn to use the good stuff . Plus, for brakes . . . I buy new not rebuilt, m/c , wheel cyl. , valves , ect. Brakes are easy too do . . . . don't beat u'r head around . . . . be smarter than those things . . . . . just my 2cents. And, Be Safe out There .
 

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Discussion Starter #19
Local shop discovered that he lines running to the PV valve were not routed correctly. It now has a small amount of pedal if you pump the brakes but still goes to the floor. They are going to switch the master out again..... The confirmed there are no leaks, bulging hoses, etc but still don't know why there is not a firm pedal. The car will stop but will not lock the brakes.

Could a PV valve be damaged and cause soft pedal if the rear master outlet was connected to the rear outlet? That is how it was connected for the last 15 years with no issues.
 

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Discussion Starter #20
Mechanic changed the master cylinder. It stops now. The pedal feels much more spongy but it will lock the tires up. The pedal Almost goes to the floor.

Anyone with manual brakes have this type of pedal?

The PV valve was routed wrong. The rear outlet from the master was hooked to the outlet on the PV valve. Maybe that's why the brakes pedal was so hard before.

Any thoughts?
 
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