I guess I figured that the only time you needed a proportioning valve was if you had drums on the back and discs on the front. I have bendix drums on the back and original drums on the front. When I had the original master cylinder (single resevoir) the brake pedal felt good and outside of having a collapsed rubber brake line, braked evenly. Now that I have a new master cylinder, (dual resevoir) I have bled the brakes and adjusted the shoes properly but the pedal just doesn;t feel right. I just can't get the right amount of pedal. Do I need a proportioning valve? If so, how do I determine the mix between the front and back? Does anyone know where I can get a good deal on a cell phone? (See, that just don't fit in at all!) Thanks guys, Gater
Gater, Sounds to me like the master cylinder still has some air in it after the install. You bled the master after it was installed using foot power right? I have had problems in the past and great difficulty bleeding a fresh master cylinder or two. I have heard of pre-bleeding a master prior to installation using some type of power unit but I have never seen the animal in question so I may not know a hill of beans what I am talking about. All I know is that installing a fresh master usually has been a very labor intensive process for me involving some very sore calf muscles until the pedal felt high and firm. I know...let's wait for Nate to tell all us garden variety shade-tree mechanics how to do it right. Andy
Generally they're used when the vehicle is fitted with disc brakes and the front discs are prone to locking up from weight transfer . Low or soft brake pedal shouldn't be affected by a proportioning valve or lack of same . I'd do the ' Stick Trick ' and see if that helps as it sounds to me like there's an air pocket . I assume you've triple checked the adjustments of all the shoes and the Bendix equipped wheels don't have a bo-boo like one inverted shoe .
Chiro, I bench bled the MC before installing. It came with a couple of hoses and adapters and instructions to use a philips head screw driver to pump the cylinder till all the air bubbles were gone. Then I installed it and, after wearing out my 12 year olds leg ( he started hiding from me when I went near the truck) I borrowed this neat air driven suction tool and pulled fluid to the farthest cylinder first then worked my way back to the nearest. Also, I jacked the truck up and ran out all the shoes till they were just swooshing when I turned the wheel. Nate, I think I will try the "stick trick" before I do anything else. The brakes are pretty good on the second or third pump but I may not always have time for a second pump. You never know when some jackass with a cell phone stuck in their ear is going to pull a numb nuts move in front of me. (Did I say cell phone?) Thanks guys, Gater
Always bench bleed your master before installing. This will save a lot of pump action from your 12 year old son. I remember being that 12 year old son and it sucked at the time. Here is the power bleeder that was mentioned above: http://buy1.snapon.com/catalog/item...&group_ID=1670&store=snapon-store&dir=catalog As you can see by the price it's really not worth buying unless you do this type of work for a living. I'm fortunate enough to have 2 at the shop that I can use anytime and they work great. If I were in your situation I would probably buy me a big ol bottle of brake fluid, turn it upside down and gravity bleed the system for several hours and see what happens. If that doesn't work then may go to your local brake shop and see if they have a power bleeder and let them give it a shot. As for the proportioning valve I would put one on any vehicle. They just help with brake transfer so much better. Always stay between a 60/40 and a 70/30 split. Higher percentage at the front of course. Hope all this helps.
Is your dual master cylinder for a drum/drum setup? If it is for a front disc/rear drum setup then you will not get good pedal unless you use a residual pressure valve in the line to the front. For drums use a 10# valve, they run about $20. The disc uses a 2# unit or none at all because the disc pads only retract by the amount of runout in the rotor but the drum brakes will, because they have pull back springs, retract all the way back. This means you have to push the shoes through a bunch of dead air space before they contact the drums. The residual pressure valve keeps pressure in the system so the shoes will clear the drum when pedal is released but not retract all the way back. If your master cylinder is for drums all the way around then the seats your flared brakeline fitting screws up against have the residual pressure valve built into them. Sometimes they go bad and can be removed by threading a screw into them and prying out. The problem is I don't know if they sell the seats anymore--they would rather sell you the whole cylinder. On your old single cylinder that funny little chinese peasant hat looking thing with the holes in it kept residual pressure on the lines.
CHEAP Pressure Bleeder O.K. , here ya go : http://www.performanceproducts4benz.com/productpage.aspx?pid=105048&name=Power+Bleeder now , go to scrap yard and get a spare MC cover , poke a hole in it and screw in a nipple , remove the Mercedes cap from this handy-dandy tool and connect the hose to your hommade MC cover adapter and have at it ~ You'll soon experiance what your brakes felt like in 1947...... firm & tight , high , rock hard pedal . this is *SO* cheap there's no excuse not to buy it . BTW : I didn't put any brake fluid in the bleeder so it stores neat & clean . When using this tool only pump up 3 ~ 5 PSI in it and always use a clean glass catch bottle and hose on the bleeder bolt , of course you all know to only use a box end wrench on bleeder bolts/nipples ! . If you've never touched them and they're really old & crusty looking , you can ensure they won't snap off by whacking each bleeder dead on with a flat faced hammer before putting the wrench to it . I always beel untill there's NO dirty fluid coming out the bleeder . You're supposed to change out your brake fluid every two years even if the brakes are working fine , doing so ensures you'll never buy another master cylinder nor wheel cylinder again . Certainly if your brake fluid is black , it's time to flush the system .
Okay, Whilst we are on the subject of AD brakes, I have a few questions. Since I have always had a friend with a really tired leg after I have replaced master cylinders I would like to know the proper procedure for bench bleeding one of our beloved and totally unsafe single reservoir master cylinders. Anybody help me out on that? Next question...the sequence outlined in the factory shop manual lists this order for bleeding the lines. Left rear, left front, right rear, right front. I always thought it was the longest line first and then the next longest line, etc. until the job was done. Correct me if I'm wrong because I haven't actually measured the lines, but it would seem to be that the proper order after eye-balling the lines in the truck should be left rear, right rear, right front, left front. Anybody help me out on that question??? Next question...would somebody please explain "gravity bleeding" and how to do it IF it actually works. And finally, whats the deal with the "stick method"??? How does that work and when exactly is it employed? Andy
Proper Bleeding Andy ; You're right , it follows the length of the brake lines from the master cylinder , follow that and you'll be fine . There _must_ be some freeplay in the clevis pin that pushes the master cylinder , this means your brake pedal return spring must return the brake pedal to the backside of the toe board with a " thump " or it ain't right and it -will- do you dirt . With the brake pedal released , you should be able to rattle the clevis pin , the pushrod should move in 1/8" ~ 1/4" but NO MORE before it begins to push the piston . I used to bench bleed back when I had a bench but there's a simple , less messy way you can do on any vehicle where you can look into the open master cylinder as you're moving the brake pedal with your hand..... I'm sure I don't need to remind you all to clean the floor 100 % hospital clean before you open the master cylinder ~ that tiny bit of dust you knock into it , will kill it . Anyway : mount the master cylinder , remembering to leave the mounting bolts loosey-goosey untill you've run the brake line connection in _by_hand_ so there's NO possability of cross threading anything , tighten the mounting bolts and then tighten the hydraulic lines using _only_ a flare nut wrench . fill the master resivoir with clean , fresh DOT 4 brake fluid and grab your good flashlight (the one with new batteries , dig) and shine it in the resivoir ~ you'll see two small holes drilled in the bottom of the resivoir , you're intested in the smaller one , near the outlet end of the master ~ gently push the brake pedal with your hand untill it takes up the slack and you feel the linkage barely begin to push the piston~ the front hole (called the by-pass port if you care) will emit a stream of bubbles so _STOP_ ! don't press the pedal down any further ~ just tap it and release , each time you bump the piston it'll emit bubbles or foam , keep on doing this untill no more bubbles/foam come out the tiny by-pass port then you can pump it ! -GENTLY- ! a few times , each time you depress the pedal a jet of brake fluid -WILL- come out that by-pass hole so push slowly and gently else you'll get an eyefull of brake fluid and that stuff burns your eyes like fire ~ guess how I know ? if you do get any in your eyes , flush with lots and lots of fresh water from sink or garden hose , low pressure tho' 'K ? . After a while , you'll feel resistance when you depress the pedal and it'll stop bubbling when it's released , get your slave , er child who's happy to help you and bottle bleed it . The stick trick is used when there's a bubble or what not you simply cannot get out , some cars have high spots in the lines or the bleeder bolts are not in the highest point in the wheel cylinder/caliper so by leaving the pedal depressed overnight , the bubbles will seek atmospheric equality and will , all by their lonesome , work back and burp out the by-pass port in the master cylinder ~ this port is covered when the brake pedal is released , that's why you need the stick . To perform the Stick Trick: get an old broomstick etc. and jamb it between the brake pedal and the seat , leave it overnight then carefully remove the stick the next morning and let it sit a few minutes before depressing the brake pedal , it should now be hard as a rock and give you great braking (within the confines of Huck brakes) Did this help ? . For those chuckling at my farmer ways , they're what was done when these trucks were designed and built ~ I have many years of field service experiance and more GM Delco factory training than you can shake a stick at ~ I'm glad it's coming in handy after all these years . I learned " The Stick Trick " from an old BMC Engineer . I really do think that pressure bleeding with the above referenced cheap pressure bleeder , is the way to go . By the way , I know many here have old Motos ~ try the ' Stick Trick ' on your hydraulic disc brake by wrapping a rubber band around the brake lever overnight , you'll be amazed at how firm and sensative it is to-morrow .
Geez, dad~ ...er, Nate! That was exactly how my dad told me to do it. Worked great! (back lines were first.) Kind of a bummer, because now I'll be doing disks up front and maybe out back. In other words, all my rebuilding of wheel cylinders and the master- new brake lines and shoes are out, and only with about 25 miles of wear and tear... Oh well, it was fun, this will be too! Great descriptive steps in the process, Nate! Thank you for the time you spend trying to help us get our dreams up and running!
?? new brake all 'round ? I wish you were closer as I'd love to dump my Huck brakes for a Bendix setup....
But would a 3/4 GMC work on a Chevy? (I'm down to only the back brakes now, as all of the front went with the axle...)
Hey VWNate1 I've been dealing with the same brake problem for three weeks now. I just bought a 1965 chevy C-10(three weeks ago), it had no brake pedal, so I checked for leaks and blead the system. It has front disc, and rear drums. From day one, I could bleed the rear all day, and it would have air all day. Replaced master cylinder, both rear wheel cylinders,steel lines, and rubber hose. I did all of this because I can not get a pedal, goes to the floor no matter what I do. I bench bleed the mc serveral times. I can't get basicaly no fluid out of either of the rear wheel cylinders. It's just air bubbles. So I disconnected everthing from the main steel brake line that supplys fluid at the rear before it connects to the brass T, and goes out left and right to the wheel cylinders. I connected a vacumm bleeder to this main line and got a solid stream of brake fluid. I connect the main line back to the rubber brake hose and T and get a stream. But I can't get basically no fluid out of either wheel cylinder. What am I doing wrong please? Thank You
Bleeding This is a head scratcher . If the MC is pumping O.K. , you should be getting good fluid transfer at the wheels . Are you maybe opening the bleeder screw too far ? I've done that and had air bubbles leak in past the threads ~ you should only have to open the bleeder 1/8 ~ /14 turn MAX. I assume you're using a clear glass bottle and a hose plus a box end wrench ? I like to use clear plastic hose when I can find it . So , if you got a solid stream of brake fluid at the T joint , there's some sort of leak between there and the wheel cylinders , perhaps some one installed the wrong typ of fitting ? you say everything is new so this problem is a basic one , it pisses me off when I miss a basic thing like this , maybe a freind should peek at it and give you a fresh perspective . Wishing I were there to help .
Thanks Nate, I used the stick trick on it yesterday, can't wait to get home after work and see how it works. I put the stick on after work yesterday. And you are so right, about having somone else look at it with a different perspective. Thanks again Nate
