This is a bit of a continuation from my last thread ( https://www.c3vr.com/vrforums/master-cylinder-question_message421197.html ) but this question is more specific to brake bleeding so I started a new thread.  Anyway, I can't seem to get the fronts bled properly - they just spit a little fluid, no solid flow at all, no matter how many times I do the pump and bleed.  (I asked my wife to do some pedal pushing tonight)   I've also supplied the bleeder with a generous vacuum source and same thing - it will pull some fluid through but not much.  It almost seems like there is a blockage somewhere.  Could this have anything to do with the proportioning valve?  I didn't touch it, but did disconnect, remove, and re-install the line that goes from the valve to the right front wheel.  

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Sometimes the threads around the bleeders will allow air back into the system. I had to put some thread sealer on mine and the bubbles stopped - solid stream of fluid. Also make sure not to open them too far. 1/4 turn should do it. 

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Disconnect the line from the M/C to the pro valve if the break fluid flows pretty good it's probably the valve, which I would & do replace on theses old C-3's. 

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Dave, remember the service manual mentioned about forcing open the proportioning valve. knotacare might have a point about the valve being bad or even plugged/restricted. 

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Joel Adams
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Thanks, guys.  I'll focus my attention on the pro valve next.  Any suggested vendors for a replacement?  I've even had a hard time finding one on some of the online catalogs - I guess some call it a "distribution block" others "proportioning valve" and still others "proportion valve".  Would love to know where others have purchased theirs.  

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Dave here is a link to what I used.....................

http://www.ecklerscorvette.com/corvette-brake-proportioning-valve-1974-1977.html

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This is where I get mine

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I bought the brass one, but I like your price better.

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Dave, I just got done bleeding my brake and my blood.......actually my sweat. I would rather pull the engine/transmission and body than do the brakes again. I did them myself.....tough to do. I had previuosly bench bled my new master cylinder in the vise. I have completely new stainless steel brake lines and new brass diverting blocks. Also all new stainless steel flex hoses. I had flow to the front brakes. There are actually two bleeders on all 4 calipers. The rear brakes I couldn't get any flow. I even opened the connection off of the proportioning valve. I then connected up a pressure power bleeder to the MC. I pumped up the pressure to 15 psig. I left the bleeders completely out of the rear calipers. I finially got flow to the rear by pumping the pedal. I'm using dot 5 silicone fluid (purple). I put the Russell check valve bleeders back in and opened individually each one less than a quarter turn. I pumped slowly in on the brake petal and held it down for at least 10 seconds. I did this for all 4 bleeders in the rear about twelve time apiece. I then went back to the fronts and repeated the same procedure. I almost filled a Mason jar with the purged brake fluid. When I came into the house my wife had to dry off my sweat when she saw me (she's a keeper). Well anyhow that's about the worst job of my project so far. I sure hope everything works out for you. Oh and by the way the pedal is as hard as a rock

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Well, you're definitely a step or two ahead of me!  Glad you've got a hard pedal now after all that effort.  Hopefully I'll be there soon, but I took a step backward tonight.  Removed the M/C and the proportioning valve.  I'm going to re-bench-bleed my M/C and also make sure the lines and calipers are full of fluid before I go on.  

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Dave be very careful on the material of the O rings. Just make sure it's compatable with American brake fluid. Years ago I had an MG and used American brake fluid. The British used natural rubber in the MC, which turn into gum. Not long after the fluid addition.............I was without brakes. It takes a lot of white knuckle driving to make it home with no brakes. I then rebuilt my MC. It's not very hard to do. The only special tool needed is a hone to reface the cylinder. 
Buna N does work with Dot 4 fluid. Just make sure they are not real rubber, and also make sure to use the proper ID OD and thickness of the rings 

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 Don't know if this could be your problem or not but I replaced my leaking master cylinder with a rebuilt O'reilly's a couple of weeks ago. Could never get a firm pedal after bleeding 3 times. It would almost go to the floor, sorta like stepping on a ripe plum (courtesy of C W McCall. lol). Drove the vette over to close to Dallas for a bunch of major work. Almost there, traffic stopped due to an accident. I hit my brakes...and guess what! NOTHING..TO THE FlOOR! Luckily there was a median strip between the concrete wall an the two lanes of stopped traffic in front of me. Long story short... the master cylinder was CRAP! Might want to consider that as possibly your problem

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   I know the voices aren't real, but they have some pretty cool ideas...

  Dang, Dwain! I guess you took it to Rich's place?

Another wild idear I have on it....take the bleeders out of the front calipers completely, and see if the holes for the fluid where the bleeders thread in are stopped up. I have definitely seen this in calipers, both rebuilt, and old ones on the car. Crud builds up there over time, and sometimes, it just won't allow fluid to pass thru the bleeders. I'm not talking about the bleeders themselves, but the holes in the calipers. But...I have also seen bleeders that were crudded up enough to not allow flow.
Just because the calipers are rebuilt doesn't mean they were cleaned really well before.
It's worth a look-see, anyway.


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Joel Adams
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It's interesting to see the research tangents I get to go on for this car.  Tonight I got to research o-ring material types that are compatible with DOT 4 brake fluid, thanks to Corvette440!  I came up with a little bit different info, though: most sources said to stay away from Buna N (also known as nitrile) and use something like EPDM, which I have no clue where I'd get a "variety pack of" those.  I'm using Valvoline synthetic DOT 3&4 and interestingly, they say that fluid is actually compatible with natural rubber!  (http://www.valvoline.com/pdf/valvoline_brake_fluid.pdf)  I think most of the o-rings you get at the parts store or hardware store, though, are just regular old nitrile.  The existing o-rings look like they're still OK so if I can't find any EPDM I may just put it back together with the originals (after I blow out the passages)

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EPDM rubber (ethylene propylene diene monomer (M-class) rubber),^[1][2] a type of synthetic rubber, is an elastomer which is characterized by a wide range of applications. The E refers to ethylene, P to propylene, D to diene and M refers to its classification in ASTM standard D-1418. The M class includes rubbers having a saturated chain of the polymethylene type. Dienes currently used in the manufacture of EPDM rubbers are dicyclopentadiene (DCPD), ethylidene norbornene (ENB), and vinyl norbornene (VNB). EPDM rubber is closely related to ethylene propylene rubber (ethylene propylene rubber is a copolymer of ethylene and propylene whereas EPDM rubber is a terpolymer of ethylene, propylene and a diene-component).

The ethylene content is around 45% to 75%. The higher the ethylene content the higher the loading possibilities of the polymer, better mixing and extrusion. Peroxide curing these polymers give a higher crosslink density compared with their amorphous counterpart. The amorphous polymer are also excellent in processing. This is very much influenced by their molecular structure. The dienes, typically comprising from 2.5% up to 12% by weight of the composition, serve as crosslinks when curing with sulphur and resin, with peroxide cures the diene (or third monomer) functions as a coagent, which provide resistance to unwanted tackiness, creep or flow during end use.

EPDM rubber is used in seals, glass-run channels, radiators, garden and appliance hose, tubing, washers, belts, electrical insulation, vibrators, and speaker cone surrounds. It is also used as a medium for water resistance in electrical cable-jointing, roofing membranes, geomembranes, rubber mechanical goods, plastic impact modification, thermoplastic, vulcanizates, and many other applications.^[3][4]

EPDM exhibits satisfactory compatibility with fireproof hydraulic fluids, ketones, hot and cold water, and alkalis, and unsatisfactory compatibility with most oils, gasoline, kerosene, aromatic and aliphatic hydrocarbons, halogenated solvents and concentrated acids.

The main properties of EPDM are its outstanding heat, ozone and weather resistance. The resistance to polar substances and steam are also good. It has excellen

Typical properties of EPDM vulcanizates are given below. EPDM can be compounded to meet specific properties to a limit depending first on the EPDM polymers available, then the processing and curing method(s) employed. EPDMs are available in a range of molecular weights (indicated in terms of Mooney viscosity ML(1+4) at 125 °C), varying levels of ethylene, third monomer and oil content.

it has electrical insulating properties.

Typical properties of EPDM vulcanizates are given below. EPDM can be compounded to meet specific properties to a limit depending first on the EPDM polymers available, then the processing and curing method(s) employed. EPDMs are available in a range of molecular weights (indicated in terms of Mooney viscosity ML(1+4) at 125 °C), varying levels of ethylene, third monomer and oil content.( This was copied from wikipedia)

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I was also wondering if Vitron (green) O rings would work. Vitron is sold at auto parts stores. They have variety packs. These O rings are used for Aircondioning seals that use sythetic oil (POE) for R134A. I purchased a packet at Advance

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Fingers and toes crossed for you Dave. If it don't work go for the pressurized MC setup..........I think that's plan C.

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Thanks, Larry.  The digit crossing didn't work out for me - still have a soft pedal.  BUT, I think I'm making headway.  I found a serious problem on the fronts: I did not install the hoses with the copper washer at the caliper.  With my vacuum pump I think air was being sucked in through that interface.  There is still another problem, though.  I'm pretty sure my prop valve is off-center again.  When I was working on them earlier today I did the rears first.  I actually had some pedal after I was done with those.  But then I moved on to the front and with the lack of pressure in that circuit I think the valve got off center.  I can tell by the fact that I have a full M/C, lid is loose, and no fluid is even dripping out of the disconnected hard line where it would attach to the front left hose.  So anyway, tomorrow I will buy some copper washers, put everything back together and try again!   I'm hoping I can get the valve re-centered by opening the back bleeders and slowly pushing the pedal.  We'll see.  Still realize that guy might need to be replaced.

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Dave for what it's worth: I used a digital cliper to check the copper washer but this was after I tightened them in place. So, here is what I came up with .400 inside diameter, .627 outside diameter, .075 thickness. I tend to get very exacting (go overboard) with things. You (in my mind) can't over engineer.   

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Man, folks were not kidding when they said this is one of the toughest jobs on a shark. I'm getting closer, but still not there yet. I replaced the M/C with a different one from Autozone, bench bled it and now I'm bench bleeding it again, because there were still bubbles coming out after it was on the car. And those cheesy plastic bleeder fittings that come with a M/C are apparently one time use only so now tomorrow I'll be buying another bleeding kit. I'm also going to put plugs in the outlets and test - the pushrod should be rock hard if it was done correctly.

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Dave, I hate to tell you that the gravity bleeding is futile. Maybe it might work for you....I only hope for your sake that it works.

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Hat's off to ya, Dave...I'm getting frustrated just READING this...and YOU'RE doing all the werk!

Anyway....here's what I would suggest at this point. You have to determine WHERE in the system the problem is. So...start with the master. Disconnect the lines, and verify you have fluid UNDER PRESSURE coming out of both fittings there. Not just fluid running, but fluid under pressure.
Then, connect the lines back up, and go to the next junction...the p-valve. Disconnect the lines to the front brakes, one at a time, and verify fluid under pressure. If you have good pressure coming out of the master, but not out of the p-valve, you'll need to replace the valve. Cross leakage inside of the p-valve will not cause the problem you have, so even if you left the seals off, you should still get pressure from both ends.
If you happen to get pressure on both the fittings coming out of the p-valve, then your problem HAS to be in the lines to the front calipers, either the hard lines, or the "new" flex lines. Make sure there is nothing restricting the flex lines....they can get crap in them from the factory, or by sitting on a shelf. If they get twisted, they can collapse, too, so just be sure they are free to flow.
From everything I have been reading, your rear brakes will bleed with pressure no problem, but the fronts are just dribbling. If the master is working, the only other possibility would have to be the p-valve, or a restricted line/hose.

When I say "under pressure", I don't necessarily mean under full pedal pressure...just enough to determine there IS pressure...the kind that might skwert ya in the eye, so be careful.

I would also seriously start thinkin about renting/loaning/buying/building a pressure bleeder....

Good Luck...hope ya get it figured out & fixed soon. I would have already beat the he!! out of it at this point... 


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Joel Adams
C3VR Lifetime Member #56    
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Thanks, Joel and Larry!  Yep, good advice about starting at the M/C and working down from there.  That's definitely my plan.  I almost think it has to be in the M/C or valve since I'm having problems with both fronts.  (and I know the single front hard line from M/C to valve is OK).  Unless there are problems in more than one line which I guess could happen.  A couple more questions: 1) when you say test under pressure, can I do that with a "thumb test" or do I need to rig up some kind of gauge?  2) Pressure bleeder: I've heard the $60 parts store versions have a hard time sealing to the old GM cast iron M/C's - any truth to that?  You're probably referring to the professional version, but I'm not sure I'll be able to find one of those in my usual list of "tool loaner" friends.  But I think I'm done with the sucky sucking (MityVAC) method - I think it's causing more problems than it's solving.  Thanks again - I'm pretty sure I'll nail this eventually.  All part of the fun! 

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Sounds like you're having a nightmare with these brakes..can't say I haven't had my share of them myself..those brass washers ..seals usually don't come with hoses anymore..not sure why because they used to but a few years ago I noticed that they didn't come with them..I think the biggest problem is..if they are not included they should be a suggested part as they really only work once..maybe twice if you have to..don't feel bad about not putting them in..I can't count how many times I do stuff like that and knock myself up and down once I figure out what I did wrong..hopefully with the brass washers installed the brakes bleed out as easy as they can..one thing I do to help bleed is leave old hoses on the front and get the back done ready to bleed..then I pinch off the old hoses in the front with vice grips and bleed the back completely..then install new hoses on the front and it usually bleeds out pretty fast..I have done this a couple of times and haven't fought it as much as I did it without being pinched off...also...when I bled the front I jammed a small screw driver in between the pad and rotor of the rear on both sides..this keeps the rear pistons from moving..makes all the pressure go to the front instead of using some of it to go to the rear..this part was for when you pump the pedal to bleed..I may have done the same thing to the front at the same time but can't remember...the reason I did this was to increase the amount of fluid flow to the caliper that had the bleeder open...btw..I didn't use any type of power bleeder to do this even though I have you 2...I have used the old hose dipped in a milk jug tool immersed in brake fluid and just pump away..really works as it pushes out the air and sucks in fluid at the same time..really hope this helps as it did work for me.

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My first parade at Carlisle 2010

Dave, put yer thumb/finger over the hole, and make sure there is enough pressure to blow some fluid out..a good stream, not just a dribble.

Don't know about the $60 bleeder sealing, but my $300+ one leaks a bit, too....that's what rags/paper towels are for...



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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Dave, this is what I used. It comes with J hooks (4) wing nuts (4) and 2 dinky chains. The best thing to create a good seal is to forget the J hooks and chain junk. Use two C clamps instead so that when you pump up the pressure it doesn't squirt from unsealed gasket areas. Here is the link:.............

http://www.summitracing.com/parts/MVP-0105/

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The real prollem with the leakage from the pressure bleeders is folks thinking you need 30-40 psi to get the job done....truff is, 10psi is all ya need. I don't think I've ever pumped mine much over 15psi. Mine leaks mostly because the rubber gasket is old, has had brake fluid on it for 10 or more years, and it's just swelled, and mooshy. I really should get a replacement....one of these days...

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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

x2 on  this trick. I use a 1/2" thick piece of flat steel that is 2" wide and 4" long on the bleeder cover and secure it with one C clamp in the middle over the divider wall in the casting. Pump up to 12-14 psi and start bleeding.

The copper washers will get hard over time, even unused new ones. If you anneal them they become soft again and will seal better. I put a piece of tubing or a welding rod in the vise, place the washers on the rod, heat until glowing and quench in a pan of cool water. It makes them soft and they seal easily when the bolt is torqued to spec.

Thanks guys!  Lots of good advice out there.  Think I'm getting closer on this thing.  Tonight I redid the bench bleeding of the M/C.  I'm very confident it's right this time and the part is good.   No bubbles at all, no matter which way it's oriented and there is almost no give with the ports plugged.  I re-installed and hooked up the outlets.  I'm in the process of trying my gravity bleed method right now.  I'm doing front and back on the driver side simultaneously.  The back is dripping like mad, but it was more or less already bled.  The front is dripping, but more slowly.  I know there is a good chance that this won't work, but I figure what's the harm in trying.  I'll try the pass. side tomorrow and see if I have a hard peddle after that.  I'm sure it's even less likely it will work on the pass side, but we'll see.  I'm a little worried that my earlier tries of using the vacuum bleeder could have collapsed my new front hoses.  There were a couple of times I tried applying up to 20" Hg.  in an effort to get fluid to flow to the fronts.  Hmmm. 

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WhoHoo!  Hard pedal, finally!   Gravity bleeding actually seems to have worked.  I was most worried about the pass side front, but after about 15 minutes fluid finally started flowing.  I let it drip drip drip for about a half hour after that (inner RR was going at the same time) and then let the outer RR flow for a few minutes and then double checked all bleeders were tight and voila! hard pedal.  Thanks for all the advice and support, guys.  Think I'll go crack a beer to celebrate.  

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Joel Adams
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Dave, I am so happy that things worked out for you that I might have a beer and smoke a cigarette in your honor...............NOT really I hate beer and don't smoke, but you get the idea! I really appreciate people who never say die. You never gave up and found and admitted to a slip-up. As you mentioned other sites picking on people, it's great that it's not done here. Now on to the next challenge 

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Yep!  And that next challenge (all I have left, really) is dropping in the engine and then getting it running.   Can't wait for that fun and excitement.  Thanks again, guys!

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Hopefully dropping in the engine goes smoother! Glad you were able to get things working like you wanted! Betcha it was a lot easier workinc on that master cylinder and proportioning valve with the engine out! Great job!

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