Ok, need help.Brake pedal on the floo,r all new brake booster , MC , porp. valve, lines. Problem, I bench blead the MC, then the brakes, good pedal, back drums work fine, but new front disc won't release. Took the MC off from the booster and adjusted the rod back to make sure it wasn't too long, they are still tight. Thinking of removing the 2 lb. residual valve to see if that lets them release? Any other ideals?? Thanks for your help.
I'd first check that they release if you crack the bleeders. If they do not then the problem is in the caliper or mounting. If they do then you know you have a line pressure problem. Crack the fitting at the brake hose next- if they release you know the hose is good. Then you have some figuring out to do.
Sometimes the inside lining of a flexible brake hose collapses and lets fluid into the caliper but not come out ? You can loosen the banjo nut or whatever bolt secures the hydraulic fitting to one of your calipers in front Posted using the Full Custom H.A.M.B. App!
My best guess is;Wrong MC,ya got a drum brake MC,get disk MC or take res/valve out of MC so it had none
Do you have your calipers mounted right? If the bleeder is in the wrong place, you can't get all the air out.
#1 Do you have free play in the pedal, when locked up ? #2 If you do have a free pedal when the brakes are locked up, loosen the master cylinder from the booster, when locked. This will do to things, it will indeed tell you weither it is the mechanical hard pedal****embley, or a malfuntion in the hydralic system.
I think you got double residual valves, one in the MC and the other is the 2lb. one, remove the 2lb. one and it will work ok, I had the same problem with two MC good luck Leen
31Vicky's got you on the right track here. It should be fairly easy to isolate the problem this way. If the caliper isn't physically sticking I'd be suspicious of the residual valve, especially if it's plumbed to the front wheels only.
This is where I would start. If it changes nothing , proceed to 31Vicky's advice. Also ,how about a detailed description of your brake system such as firewall or under floor mount booster m/c , any inline residual valves and pressure and loctions of those etc...?
Some years back I executed a complete brake job on an older Aston Martin. Subsequent test drives nearly ended in disaster when all axles locked up and sent the car into a screeching halt. Problem turned out to be faulty brake boosters (yes, there are two boosters, one each for front and rear calipers). One booster had been****embled incorrectly by a previous owner. Why didn't the brakes lock up before my rebuild of the calipers? Because the calipers couldn't retain pressure as they were leaking so badly. Live and learn. Posted using the Full Custom H.A.M.B. App!
Just what I'm thinking too. That's why I'm going to remove the 2 lb tomorrow and see what happens. I did take the MC away from the booster and no change, so t's is a hyd problem. I didn't buy the set up, I'm helping a friend , that He bought, so I'm not sure of the MC, but it's the "corvette" style one everyone sells.
Does the pressure get relived when you loosen the the front brake line at the master cylinder ? Also the internal push rod between the booster and the master cylinder also be incorrect ! since I believe you said the booster and the master cylinder are not a OEM matched****embly. Meaning are both pusrods correct length. internal and external ?
I've seen calipers so badly in need of rebuilding that they seized up when the vehicle was moving, when the pedal was depressed, after someone put in new pads w-OUT rebuildin the calipers --
For once everyone is on the same page with solid ideas of what the issue could be. I'd organize the list of what the guys gave you above and work down the list one step at a time. He didn't get the residual valves reversed by chance putting the 10# in front and the 2 # to the rear? When I was working on brakes daily most of the brake problems caused by do it yourselfers trying to do their own brakes was parts put in the wrong places or mirroring one side with the other and having parts reversed.
Oldsman is likely onto the problem. Had similar issues on my coupe (front disc, rear drum, residual pressure valves in both lines). Turns out the push rod was simply too tight. You're gonna need 1/4 - 3/8" inches "free play" in the MC pushrod for everything to work right.
Ok, update, I removed the front 2 lb. residual valve and the brakes work fine. I think the new MC already had a valve in it. Bleed them again and I also had backed off the inter rod so I had to bring it out to take up the slack. Work great now. thanks for the info again guys. You can always count on someone here having Been There / Done That.
Ok, now,,,, a drum /drum master will will have a built in residual on both ports. Removable too. A disk/drum master will have a built in residual on the rear/or drum port only. Which master do you have? http://www.speedwaymotors.com/Unive...Cylinder-1-Inch-Bore-Corvette-Style,4316.html This is set up for disk/drum brakes in its OEM vettte application. All this is leading to your theory of having too many residual vales and combined residual pressures. First, do you have the fronts hooked up to correct port? Your current theory would say no. Secondly, I don't think that residual valves can add their pressures together. Thus for the sake of discussion - a ten pound residual at the master and a 2 pound in line would not equal 12 pounds in the caliper. It can only be the larger of the two as a max residual pressure. If my thinking is correct here, (I might be FOS) this also would not support your theory.
Same problem years ago, it took a while to find but the bolt that retained the hose on the caliper was too long on the banjo fitting. The bolt bottomed out in the caliper. Seems odd but under pressure the fluid would enter the caliper but could not exit. I removed 1/16" from the bolt and everything is fine.
residual valves cannot add their pressures together, whatever the higher pressure residual valve is will over come the smaller one. no one mentioned if the valves in the lines were installed backwards, trapping pedal pressure in the line after applying the brakes then releasing them. they only should be installed in one direction and are usually printed with "inlet:" for the master cylinder side and "outlet" for the wheel side.
Glad you fixed the problem. If the master cylinder is on the fire wall you don't need a residual valve with disk brakes.
I believe they are really misunderstood, Based on all of the brake problem threads we see, it must be harder to outsmart brake fluid than I ever thought possible. Brake fluid always does what it's told to do, it always obeys, it never misbehaves, that is according to the laws of physics. (Note the use of absolute terms; always and never) Now components on the other hand, well they can be problematic, the components are supposed to do what they are designed to do. The components require an input and then deliver an output or result. All you can do with components is verify that is is receiving the required input and then verify it's result is what is was designed to do. It can only be hard to fix if you don't know what the input is supposed to be, can't verify this input, or don't know what it's designed output or result should be. Every part can be broken down into this almost oversimplification - A nut and bolt is a component that falls into this, a simple rod also a component, a inverted flair fitting, a brake caliper, everything mechanical ever though of fits quite nicely into this simple breakdown.
To throw in my 2 cents, I have seen an out of adjustment mechanical brake light switch cause brakes to drag because it prevented the brake pedal from fully returning.
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