The Rodding Roundtable
Motorhead Message Central => Rodder's Roundtable => Topic started by: BFS57 on January 28, 2010, 08:29:53 AM
Hello;
The other day, I decided to put some new disc pads and wheel bearings on my 57. It has a upgraded system (5 years ago) to power disc/drum with a duel 8" booster and corvette style MC.(From Speedway)
Well, after I did the bearings and new pads, NO BRAKES!! What the heck!
Discovered a leaking rear break area but that was just loose where the backing plate bolts on to the end of the rear end housing.
Have spongy pedal while bleeding, start the engine (Vacuume in the booster) and Breaks (pedal) on the floor!
Still no breaks!! Bleed the snot out of them, Still no Breaks! Does this mean, my master is ka-poot? Someone mentioned that some kind of crud might kad worked it's way into the booster, the fluid coming out is kind of nasty looking.
Anyone got any handy hints of any kind of test or "words of wisdom"?
Everything worked fine (or seemed to) before I tore it down!/
HELP!!!
Bruce
Did you bleed the master first?
Hello;
Did the master removal and inspection. Found tons of gritty crud inside! Time for a new one!!!
Don't know how I am going to go about flushing the lines yet!
Bruce
lasso a friend with a strong leg & bleed til clean fluid comes out.
Hello;
While the Master is off, I'm thinking I want to hook up the compressor to the lines and just blow until clear. Next I have some spray cleaner I am thinking about spraying in the lines to try to clean them out.
Anyone have a better way to go about this?
Bruce
you might also want to rebuild the front calipers .. if they are gm style they are not hard to do...
the varnish and crud build up behind the seal and prevent the designed in kick back on the piston.. increases mileage... pads last longer also...
why???
this is the caliper seal groove.. \_| the seal fits in the top... when the piston is pushed out.. the seal flexes slightly.. when pressure is released.. the seal tries to straighten up... pulls the piston back just enough.. just a thought...
just curious--are the calipers moving when you apply the brakes
Quote from: "BFS57"Hello;
Next I have some spray cleaner I am thinking about spraying in the lines to try to clean them out.
Bruce
Be careful of the cleaner you use if it comes in contact with the rubber parts ie: cups, seals and o-rings. It's best to use just clean brake fluid.
Hello;
Ken, Yes the calipers were moving. But the pedal was spongy without the booster and after the engine was running, the pedal went to the floor but I still had "some" stop. Kind of like if I made the rod from the booster to the pedal longer, it would be better.
After I took off the master and took it apart, I saw so much gritty crap in the piston area that it is pretty much a given that this master is in dire need of a good cleaning. I searched for a local rebuilders but couldn't find any located in Orlando. I know there has to be someone here but they make it difficult to locate them either on the net or by phone book. So, I have opted to buy a rebuilt one or look at a new one. Am using CarQuest for parts, they seem to have pretty good parts at decent prices. I got the wheel bearings, disc pads and grease seals from them.
Bruce
Hello;
been working on this now for this afternoon. Got the new master on, brakes bleed, rear shoes adjusted. When the car is not running, (booster not working) the pedal seems good but a slight bit spongy! When I start the car (booster working) the pedal goes down to the floor with no effort!
What the heck is going on? Could I have a bad booster too?
Someone please give me some pointers!
Bruce
Quote from: "BFS57"Hello;
been working on this now for this afternoon. Got the new master on, brakes bleed, rear shoes adjusted. When the car is not running, (booster not working) the pedal seems good but a slight bit spongy! When I start the car (booster working) the pedal goes down to the floor with no effort!
What the heck is going on? Could I have a bad booster too?
Someone please give me some pointers!
Bruce
I wouldn't be surprised if you got a bad MC, even if it's "new". I went through the same thing a few years back and finally took the car to a friends shop. He knew right away the MC was bad, even though I had a "new" one on it from Murrays. He said it's very common now to get bad ones, plural, from these places.
A spongy pedal is air in the lines. where it's coming from is a different thing.
I agree with Frank. Air is either coming in from a leak or you may need to find a pressure bleeder to purge the lines.
Hello;
Is there a way to test to see if it is the booster????
When I first mounted the master, I took the little plastic fittings and lines and did the bench bleed on the car with the pedal. I noticed that I couldn't get rid of the air bubbles coming from the front reservoir. I pushed the little plastic ends in, held them, had someone pump, and then it was (or so I thought) just fine.
I'm so puzzled why this is happening, I guess that I remember that you could buy parts that worked right out of the * box!
Bruce
A bad booster will not make the pedal spongy. It may suck fluid out of the master cylinder without a visible leak. But only of the master cylinder seals are bad.
If you can borrow a pressure bleeder, that could be the quickest way to see if you have another problem. I use a miteyvac also but I don't feel that it is as good as the pressure bleeder. Good luck!
A bunch of yrs ago I came up with a one person bleeder. I took a i qt glass mayo jar with a metal lid (washed it first) drilled two 3/16 holes in the lid. Raising a child with asthma I had 100' left over nebulizer hoses. I put one 8' hose into the lid, extending just enough to seal. I attached a few hoses together to reach the farthest away wheel cylinder and made sure it reached the bottom of the jar. I would loosten the bleeder nut on whichever wheel I was bleeding, slide the hose over said bleeder nut. Start the car, pop the top off the master cylinder and make sure it's full. Disconnect the vacume advance hose off the carb base and attach the short hose. Stand close by and repeatedly refill the master cylinder till the jar was either full or I thought it was completely flushed, at which time I'd go tighten the bleeder nut, reattach the vacume advance hose and Walla! Flushed and bled in just a couple minutes. It can be moved to any wheel of your choice, empty the jar and start all over. :D
Quote from: "BFS57"Hello;
been working on this now for this afternoon. Got the new master on, brakes bleed, rear shoes adjusted. When the car is not running, (booster not working) the pedal seems good but a slight bit spongy! When I start the car (booster working) the pedal goes down to the floor with no effort!
What the heck is going on? Could I have a bad booster too?
Someone please give me some pointers!
Bruce
brand new pads and shoes... before you break them in by driving the car a few blocks may have a soft pedal... the surface of the pads and shoes is not pressed flat and worn smooth that happens in the first few applications of the brakes...
oh... and the best 20 bucks i ever spent was for this brass bodied brake pressure bleeder..
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92474
i have changed out the standard hose for some silicone vacuum hose i got off a saab turbo car. this unit also if you look carefully when you have it in your hand.. can be unscrewed to clean the internals..
most parts stores also sell the same thing.. but they get 40 bucks for it..
Q: did you turn the surface of the drums and rotors???? are they smooth or is there a small ridge at the edge ????
Theory) if there is a ridge at the edge of the rotor or drum.. there has been wear.. rotors wear faster at the outer edge than closer to the middle.. brake drums wear also.. but when they wear... they also take on a bell shape... slightly.. both of these wear patterns cause brand new shoes and pads to only contact the braking surface.. this will cause a spongy pedal..
i will ask .. if your pedal is up... and still spongy.. but it does not go to the floor... take a few block drive.. if its safe to do so... then come back and check the adjustment on the rear shoes.. you can do that with a screw driver by going through the adjustment slot.. pushing the star wheel forward .. then levering it toward the back.. see how far it moves.. got more than 1/8" of movement .. you might want to tighten them up till you get it down to about 1/16" its kinda up to you.. as the self adjusters will usually take up the slack after you back up a few times...
i am also taking it that there is no play in the rear axle bearings... up and down play..????? that will cause all kinds of weird braking problems.. as the drums are not centered do to the offset.. when the brake pedal is depressed.. it has to center the brake drum by lifting the car a fraction of an inch before the brakes can get tight...
you can test the booster for proper operation...
warm up the motor.. so its easy to start..
motor off.. pump the brakes 3 or 4 times... till you are sure there is no vacuum left.. with your foot lightly on the brakes.. start the motor.. see if the pedal pulls down or drops slightly.. almost instantly.. this indicates the booster is getting proper vacuum..
take your foot off the brake pedal... let the engine run for 20 seconds more... shut the engine off... push the brake pedal 3 more times.. it should be higher each time as the vacuum is used up...
if the pedal does not get higher as the vacuum is used up.. sometimes you only get one full and one partial assist..
this instant loss of boost when you shut the motor off... indicates a bad booster.. if it passes the previous test..
if your pedal stays hard... on both tests... i would look for a vacuum restriction.. or a totally blown booster...
~~~~~~~~~~~~~~~~~~~~~
one thing i have found lately.. the plastic bleeder hose adaptors that screw in.. need to be tightened with a wrench to prevent air leaks.. i take it that the plastic is too hard..
with the brake bleeder .. i have found that not loosening the screw very much is better... loosen it more than a turn and it leaks more air around the threads...
and for the last thing... i have found .. that just barely cracking one bleeder screw at a time... and with your hand.. rapidly patting the brake pedal....
you can build up line pressure but since you are not passing the fill port in the master.. there is no fluid being pulled back... this squirts fluid out at the wheel... and works really well.. after some practice... since i work alone.. and most of the time.. my brass bleeder pump is buried in the tool pile .. its just faster...
there are also speed bleeder screws available.. these have a check ball and a spring.. loosen them slightly.. and you can pump the pedal to speed bleed the brakes...
i really love what they use in professional racing classes... a pair of check valves and 2 hoses to each caliper.. this keeps the fluid circulating.. in the bottom hose out the upper hose... it properly done.. the bubbles will come out in the master cylinder...
i hope that this has helped..
Hello;
Just to bring us up to date on this! I finally took my car to a shop (claiming to be a hot rod shop). They put a power bleeder on and bleed the snot out of the system.
At that point, I had pedal (very low) next the shop adjusted the rear brakes and adjusted the distance between the booster and master. I paid my bill and drove it around the corner (thank god) to my work. When I arrived, the rear passenger side wheel was SMOKING!!, I jacked up the car and loostened the adjuster on that wheel as I couldn't turn the wheel by hand (in neutral) and did the same on the other wheel.
I drove the car home that evening, good thing it isn't too far (10 miles) I begin noticing the motor working harder and the car not free coasting like usual. Had the smell of brake burn going on! I knew that the booster rod was pressing on the master causing brake drag! I drove it back the to my work the following morning. That next morning I had good pedal when I stated out but soon the pedal was way up at the top! and the brakes were dragging. When I got to work I felt the wheels and they were warm, not blazing hot, but warm, the engine was working harder to make the car go.
When I got to work, I pulled the master top off and the fluid was at the brim! (I thought those guys knew what they were doing!) So, I used a paper towl to wick the fluid down to around 3/8".
Next I took the master loose to adjust the booster rod back down. To my suprise the adjuster in the booster was out about 3/16" so I adjusted it back down to about 1/16". Got in and didn't have good pedal at all!!
One question I have is I know they make a tool to find the exact measurement between the booster and master but I have only seen it at CPP (Classic Performance Products) What do you guys use to get this measurement???
I am going to my work today to try to get this thing working right! Meanwhile, I am noticing a leak at the front line going into the master so I am pretty much resolved to put a new fitting in there because the old one was not too good and I thought I could get away with that but once again, can't fudge this stuff!! (Why did the shop say I had no leaks?/)
Bruce
I made my own tool, it's similar to the CPP tool.
Quote from: "enjenjo"I made my own tool, it's similar to the CPP tool.
Hello;
Don't tell me about it, give me more info, unless it is some sort of secret society thing I know nothing about.
Bruce
A link to a post I made about it.
http://www.roddingroundtable.com/forums/viewtopic.php?t=2609&highlight=brake+booster+tool
Hello;
I'm back! Still can't get this thing to work right! Got my second master, an aluminum copy of the cast iron corvette style with 1" bore ect. Got it mounted, power bled, and have been "FIGHTING" FOR PEDAL EVER SINCE!
When the brakes don't "drag" the pedal is low but works but I doubt if I could "lock em up" if I had to! When I adjust the pedal travel or booster rod till I have Good pedal, It seems though the brakes want to drag!
Am I overlooking something? I adjusted the rear drum brakes as far as I can go. Of course the rear cylinders and the master all are made off shore so I have my doubts!
Anyone had this problem?
Bruce
I want you to try something for me. with the pushrod adjusted right, which you say gives a soft pedal, clamp the front brake hoses shut, and see what happens to the pedal then. Don't drive it this way, for testing purposes only.
Was the other master cyl. an inch also? If you give it a quick pump do you have more peddle.
With the mc/booster rod
What I do is , with the m/c pison in it,s rested state against the rear circlip ,take a measurement from the m/c bolt mounting face to the activating rod seat of the m/c piston.
I then,at the booster, measure the distance from the tip of the activating rod to the m/c face of the booster.
If the rod is too long you will get blocked compensating ports in the m/c, evidence of this is lack of steady drip at the wheel bleeders once open,other symptom is hard pedal and locking brakes.
Rod too short gives excessive pedal travel.
Frank.
Hello;
Enjenjo, What am I looking for while clamping my front brake hoses off? I found a pair of "insulated" clamps that will do the trick, I just want to understand just what it is I am looking at when doing this?
Question; I know that most power brake conversions use a "combination" valve. I have the front lines from the master going to the front disc and the rear out of the master going to an adjustable proportioning valve.
What is the difference in the two different ways to plumb this system for disc/drum?
You know, If I keep this up, I will be a brake EXPERT!! (or at least know way more than the guys I took my car to)
Bruce
Unless I missed something, there is no mention of a residual pressure valve (RPV) in the rear drum brake circuit.
Depending on the year of the 'Vette master cylinder, I'm assuming it is for 4-wheel disc brakes, so there would be no RPV built into the master.
Drum brakes require an RVP. .....Without one, a lot of pedal travel gets used to bring the brake shoes out to contact the drums.
Another thought:
Since you are not using a combination valve, you may want to consider adding a "metering" (aka "hold-off") valve into the front brake circuit.
The metering valve is often a component of the combo valve, but they are available as a stand-alone valve. .....ECI is one supplier.
The metering valve delays application of the front disc brakes until the rear brakes have enough fluid pressure to overcome the shoe return springs and allow the shoes to contact the drums.
If you have a firm pedal but feel the rear brakes are not as good as they should be, your brake shoes may not be fully contacting the drums.
Years ago, it was common practice to "arc" the linings to match the radius of the drums. ......This practice has just about disappeared, but if your drums were refaced (cut) or if new shoes have been installed, there may be a mismatch of the arc, and only a small portion of the brake linings are contacting the drums.
QuoteEnjenjo, What am I looking for while clamping my front brake hoses off?
I'm trying to isolate the problem to find out where to look. What we are looking for is a change in the pedal feel.
Hello;
Bruce Dorsi;
I thought you only had to use hold off valves if the master was in the frame level not up above on the firewall? I also have been driving this car with this exact set up for 5 years without any problems until I decided to put in new wheel bearings and front disc pads, thats when everything went to hell in a hand basket!
Upon taking the master apart (old one) I found it had enough gritty, rusty, cruddy junk in it to warrant replacement! Thats when the fun begun!
I also had to replace the real wheel cylinders as one was leaking and the shoes were deteriorated (as in linings coming off the metal!)
I checked the output from the new master to the old one and the inside diameter of the new one was the same as the old one. I am considering changing my whole set up now as this doesn't seem to want to cooperate and I am getting frustrated trying to get back what I already had!
Next I am trying Enjenjo's thought to clamp off the front brake hoses to isolate front from rear circuits!
Bruce
Quote from: "BFS57"Hello;
Bruce Dorsi;
I thought you only had to use hold off valves if the master was in the frame level not up above on the firewall?
A hold-off valve is not the same as a residual pressure valve.
Here's more info:
http://ecihotrodbrakes.com/brake_facts.html
just a thought from the side lines...
what kind of calipers do you have???/
i would like to know... if they have caliper slide bushings.. and if the calipers are free to slide on the bushings..
on other cars.. i have found that some other tech had greased the caliper slides with silicone dielectric tune up grease.. this locked the caliper slides so tight... when i tried to get them to move.. not even with my 30 ton press could i budge them....
why are caliper sides important...
on calipers with pistons on one side.. when the piston is pushed out with the hydraulic pressure from your foot moving the pedal.. the inner pad is pushed against the inner rotor face... for the brakes to actually work properly... the caliper has to slide a bit so the squeezing force applied is equal on both inner and outer pad...
~~~~~~~~~~
if the caliper side is locked.. the piston has enough force to distort the caliper or bracket... and depending. the bracket or caliper may bend back.. this bending to squeeze the rotor if it is enough will result in a low pedal....
i am wondering... since you have a kit for the disc brakes.. if any spacers could have fallen out.. washers in the brackets installed wrong...
were the wheel bearing races installed all the way in..
any chance that a spacer got left out on the spindle.. or something that moved the rotor centerline so the caliper does not line up perfectly.. or that it is changed enough to keep the caliper from sliding properly...
can you pull the front wheels and see if there is any gap between the pads and the rotor when the brakes are not applied........
can you use a C clamp and retract the piston and see if the caliper is free to slide... use care... you don't want to bend the rotor... or warp it..
why did you change the wheel bearings.. were they worn..
do you still have all the old parts you took off.. for measurements.. or part number examination??
these are only thoughts..
~~~~~~~~~~~~~~~~~~~~~~~~
Hello;
Wayne;
My calipers are from a 69 Chevelle. As far as they go, They are moving, sliding back and forth over the rotor. I replaced the wheel barings because I could feel at least one was bad. I had a guy do the wheel barings, he used a tool to drive the races down into the wheel and I am pretty sure that the bearings were proper for the application as I called the maker of the kit and they recommended the part number I got.
I do know that the guy that did the wheel barings did grease the bolts that the calipers slide on with some kind of grease and I think he put some anti sieze on the threads of the bolts. Mean anything?
I still have to do the clamp off of the front brake lines and try that.
I will make a better inspection of everything you have mentioned, just to rule out any problems there.
Bruce
I have been following this post with great interest. With that said I have either missed or it has not been up about calipers being on the wrong side of the car. A quick easy check is as follows . Check the position of the bleeder screws...... If both bleeders are between 11:00 and 1:00 on a clock face they are mounted right .......... If one or both are mounted between 5:00 and 7:00 they are mounted wrong . Take both and swap sides ( left side goes on the right wheel ...... and right side goes on the left wheel.)
Next bleed brakes and start engine check pedal travel for firmness. ALSO should have just on caliper that is mounted wrong ..... Remove it go to your friendly parts store and tell them you want a caliper for the side of the car you removed the caliper from . Before You leave the parts store get the counter man to show that he gave you the right part . This may prove to be the trickiest part of the whole endever. :roll:
Hello;
thanks for the info on the caliper mounting. Let me assure you, these calipers are mounter right. This car has been driven daily for almost 6 years and during that time the brakes have always been SUPER! It is only after I got a wild hair up my * to put in new wheel bearings and disc pads that I am now seeming to have some sort of a problem with the brakes not functioning as they had in the past, a thing I find hard to believe as before I had brake power enough to throw you out the front window!!! Now I can't even trust it to stop!!!
Bruce
I'm just curious...have you had the wheels off the ground? Do the tires spin freely? Just kind of thinking out loud.....
If this car operated for 6 years then something has changed. Caused either by some new part, or something unwittingly damaged by the mechanic. Or just a coincidental failure after the other work was done.
Charlie
pinching off the brake lines... the rubber hoses lets you know... if the problem is at the master cylinder or at the wheels...
1A: pinch off the left front first...
1B: test the pedal ... hard or soft...
2A: pinch off the right front next...
2B: test the pedal hard or soft...
3A: pinch off the hose to the rear end... above the axle...
3B: test the pedal hard or soft..
now... i tend to use 3/16 inverted flair unions
http://contentinfo.autozone.com/znetcs/product-info/en/US/ags/BLU-3C/image/8/
and 3/16 inverted flair plugs to block things...
http://contentinfo.autozone.com/znetcs/product-info/en/US/ags/BLF-60C/image/8/
both of these use are threaded 3/8-24 threads on the fittings..
warning.. pinch the rubber brake hose/line off hard enough to close it... but not enough to CRUSH it..
what makes me thing that there is something wrong at the front is all this happened after you did the front brakes...
perhaps.. the pads got installed wrong.. or the wrong pads.. there are some variations... including some D52 pads.. for rear disc brake applications.. with a stud/ raised area to keep the caliper piston from turning... just in the right spot to give one fits.... front brake calipers don't need this..
somethings wrong up front... have somebody who is a brake mechanic for a living take a look at it..
if you weren't on the far side of the country i would stop by..
Did you have the rotors turned or replaced with the pad change?
Hello;
I am contemplating finding a brake specialists but don't know any around here in Orlando. Guys say that they are but I can tell that they don't have what it takes to diagnose my problem.
Yes, I believe that something is wrong with the front brakes. I will try to look at the old disc linings and see if the new ones are right. They seemed right as the spring clip retainers fitted right and seemed right I still have a feeling that this may be internal as when I took the master apart there was so muck gritty rusty crud inside I just wonder if any of that junk was inside the calipers? When the guy that put on the new pads squeezed the pistons, he didn't use a tool to do it, just a large "C" clamp and he didn't do it slowly, he did it quite rapidly which resulted in the master going out. It wouldn't suprise me if I had to replace the two front calipers also.
I did not have my rotors "turned" they looked pretty good so I opted not to have that done. Maybe I should?
Unfortunately (fortunately) my work schedule is pretty intense right now so I don't have a lot of time to devote to really chasing this problem. I just take some of the suggestions and try those and then try some other things as time permits.
I hope I didn't discourge you. You should turn the rotor and drums, or replace, every time you replace the pads. The rotors could have to much run out. This would push the piston into the bore farther. You would need move fluid for it to come out far enough hence an addition quick pump. Even then the new pads will have to from to the old rotor grooves. Same goes for the rear. You may want to start over. New shoes and pads. Turn the rotor and drums.
Mike
dirty fluid from the brake calipers being pushed back into the master can damage the master...
full stroking the master cylinder after a brake job can also damage a master.. as the SOFT seals are run across corrosion in the bore where there has been no wear.. ON old master cylinders..
pinching off the front brake hoses... like i described on my previous post.. will give you an idea if the system has problems with the calipers shoes or not..
or have for even more work.. take the front wheels back off.. and have someone work the pedal... while you watch the calipers work.. see if one or both have excessive movement when being applied.. they should just barely move.. less than 1/16" .. just barely noticeable..
and i am sorry to say that there are a lot of people who call them selfs auto mechanics.. or auto techs.. who don't really have a clue other than just changing parts till the problem is solved.. that is one of the reasons i try so hard..
i will now let you handle this.. you might want to copy and print the text from this thread...
but i really don't think that the master cylinder is the problem after you have readjusted it to avoid the locked up brakes.. you might want to also examine the rears.. after the lock up...
Sent you a PM--did you get it about a guy in Titusville
Hello;
Wayne, if my calipers are moving more than a 1/16" what should I be looking for to correct this? The times I was bleeding, I am pretty sure that they were moving more than a 1/16!
Bruce
A lot of good info has been posted about your problem. I would only suggest that you take a methodical approach to the problem. I worked for a major brake manufacturer for over thirty years and while I get stumped from time to time, believe me.....I think I've seen it all. So, for what it's worth, here's what I would do.
First, buy some brass plugs (flared style...not pipe plugs) and plug both ports on your master cylinder. Then try pumping the brakes. You should not be able to pump them. If you can, you either have air in the master cylinder or it has an internal bypass usually caused by a bad seal.
Next, try the suggestion of pinching the hoses. First, pinch them all and you should have much the same results as the above test. The pedal should not move much if at all. Then release the clamps one at a time, testing your pedal each time you remove a clamp. When the pedal goes to the floor, you have found where your problem is.
I believe you mentioned earlier that you had the line for the rear brake connected the rear port of the M/C. In most systems, this is wrong. The rear piston is the first one that "sees" pedal movement and is usually plumbed to the front brakes.
Next, there was mention of a residual pressure valve. Usually, this valve can be found behind the brass cone shaped fitting just inside the port on the M/C. I looks like a little rubber plug but it has a slit cut in the face of it to allow most of the fluid to return to the M/C while keeping a small amount of pressure in your rear brake system. (Usually about 5 PSI.) As someone mentioned, if your M/C is for a four wheel disc car, odds are that it does not have this valve. This could be part of your problem.
Lastly, I believe you said that the calipers were from an older Chevelle. If so, I would not suspect that they are the cause of this. But, if they are from a mid-eighties car, you may have "low drag calipers" which require a different type of M/C. The low drag calipers were designed to pull the piston back further away from the rotor than older designs. This was done for fuel economy reasons. To compensate for this, the M/C used was called a "quick take up" master cylinder. It had a two stage bore in it. A larger bore in the back and a smaller bore toward the front. You can visually see this when you look at the cylinder. It is fatter toward the firewall end. The idea was that the bigger piston in the back would move more fluild under less pressure. This higher volume of fluid would move the calipers further and quicker. When the pads came in contact with the rotors, pressure would build causing the pressure to transfer through a valve to the front (smaller bore) portion of the M/C. From then on, braking would work just like the old design.
Sorry for the rambling explanation but I have seen "low drag" calipers put on cars with the old style cylinders and the results were much as you have described. The small bore on the standard cylinder just can't move enough fluid to make the pads move far enough, quick enough before you run out of pedal. You indicated that you think you have a lot of clearance between pads and rotors which would lead me to think that you may have low drag calipers...just a thought.
I'll continue to watch this thread and perhaps I can send some photos if you would like.
Good luck!
A lot of good info has been posted about your problem. I would only suggest that you take a methodical approach to the problem. I worked for a major brake manufacturer for over thirty years and while I get stumped from time to time, believe me.....I think I've seen it all. So, for what it's worth, here's what I would do.
First, buy some brass plugs (flared style...not pipe plugs) and plug both ports on your master cylinder. Then try pumping the brakes. You should not be able to pump them. If you can, you either have air in the master cylinder or it has an internal bypass usually caused by a bad seal.
Next, try the suggestion of pinching the hoses. First, pinch them all and you should have much the same results as the above test. The pedal should not move much if at all. Then release the clamps one at a time, testing your pedal each time you remove a clamp. When the pedal goes to the floor, you have found where your problem is.
I believe you mentioned earlier that you had the line for the rear brake connected the rear port of the M/C. In most systems, this is wrong. The rear piston is the first one that "sees" pedal movement and is usually plumbed to the front brakes.
Next, there was mention of a residual pressure valve. Usually, this valve can be found behind the brass cone shaped fitting just inside the port on the M/C. I looks like a little rubber plug but it has a slit cut in the face of it to allow most of the fluid to return to the M/C while keeping a small amount of pressure in your rear brake system. (Usually about 5 PSI.) As someone mentioned, if your M/C is for a four wheel disc car, odds are that it does not have this valve. This could be part of your problem.
Lastly, I believe you said that the calipers were from an older Chevelle. If so, I would not suspect that they are the cause of this. But, if they are from a mid-eighties car, you may have "low drag calipers" which require a different type of M/C. The low drag calipers were designed to pull the piston back further away from the rotor than older designs. This was done for fuel economy reasons. To compensate for this, the M/C used was called a "quick take up" master cylinder. It had a two stage bore in it. A larger bore in the back and a smaller bore toward the front. You can visually see this when you look at the cylinder. It is fatter toward the firewall end. The idea was that the bigger piston in the back would move more fluild under less pressure. This higher volume of fluid would move the calipers further and quicker. When the pads came in contact with the rotors, pressure would build causing the pressure to transfer through a valve to the front (smaller bore) portion of the M/C. From then on, braking would work just like the old design.
Sorry for the rambling explanation but I have seen "low drag" calipers put on cars with the old style cylinders and the results were much as you have described. The small bore on the standard cylinder just can't move enough fluid to make the pads move far enough, quick enough before you run out of pedal. You indicated that you think you have a lot of clearance between pads and rotors which would lead me to think that you may have low drag calipers...just a thought.
I'll continue to watch this thread and perhaps I can send some photos if you would like.
Good luck!
Quote from: "BFS57"Hello;
Wayne, if my calipers are moving more than a 1/16" what should I be looking for to correct this? The times I was bleeding, I am pretty sure that they were moving more than a 1/16!
Bruce
have somebody pump the brakes.. while you look at the calipers...
find out why they are moving more...
take them apart.. examine stuff.. see if there is a lump on the top center of the inside pad that is hitting the top of the piston... causing it to press only on that spot first..
here is a picture of the WRONG smaller brake pads...
http://contentinfo.autozone.com/znetcs/product-info/en/US/pfc/0154-20/image/8/
look at the left upper shoe.. there is a small dent that sticks out and locks into a groove in the seville rear caliper piston... stops it from spinning.. if these shoes got installed on the fronts.. the piston would press only on this and you would have the problem that you describe..
you need to see if the pads are sitting flat against the rotor and against the caliper...
it is quite possible that you have quick take up calipers like the new guy described.. but they worked before... and the system failed with just a pad and wheel bearing change..
just curious.. how tough was it to retract the pistons???
i think you are going to have to take the caliper bolts back out of one side... examine everything.. make sure the caliper slides are free to slide and greased.. with white grease.. or sil glide..
just because the bolts will go through.. does not mean the caliper slides are free to move..