Weird brake problem - cannot build brake pressure.

[suburbanfireman]

I really hate to post this because I will look like an idiot.  I have a 68 charger (basket-case born with 4 manual drum brakes) that the previous owner switched to manual disc front / drum rear using 1976 Dart rotors / calipers.  I've almost finished a complete teardown / rebuild over the last 7 years.  I ran all new brakelines, new rear wheel cylinders / brake shoes, new loaded front brake calipers, new front rubber brake hoses, and brand new (not rebuild) manual disc-brake master cylinder (1-1/32 bore).  I bench-bled the master and bled all lines properly.  When I step on the brake pedal it drops to approx 1-2 inches from the floor (where the back brakes kick in) - the pedal will not get firm (even when I tried to pump it).  It acted like a bad master cylinder, so I replaced it yesterday and re-bled everything - still doing the same thing!  I removed the brake lines and plugged the master cylinder - rock solid pedal (after I tightened a loose plug / sprayed brake fluid all over my painted fender ).  This rules out the new master cylinder.  I hooked the back brake line (still plugged off the front) to the master - still have solid brake pedal.  After I hook the front brake line and re-bleed - the calipers will squeeze the rotor (I spun the front wheel) and stop the wheel but pedal drops almost to the floor!!  FYI - I am not getting any more air when I bleed the front brakes (only fluid).  I checked all lines / fittings for leaks.  I am out of ideas - replace the calipers??  Can the distribution block go bad??  I've done at least 50 brake jobs - never ran into this situation.  Sorry for the long post - just trying to be as descriptive as possible.  I need to finish these brakes so I can start re-wiring with painless kit.  (Only 39 days left until Chrysler Classic at Norwalk - my goal is to finally participate!!)  Thanks.   

[cdr]

you need to isolate if it is the front or rear that is causing the problem,they make a clamp for clamping rubber hoses & not damaging them.clamp rear rubber hose & see if pedal gets better

[suburbanfireman]

I sort of did that with the plugs.  When I plugged the master cylinder and removed the brake line for the front brakes - pedal felt fine.  I now have working rear brakes.  At this point I can assume the the problem is isolated within the front calipers / front brake lines / or the distribution block.  Do I need to switch to a larger diameter brake line for the front disc setup?  I replicated new brake lines copying what I had on the car when I bought it - I'm not sure if it was set up correctly by previous owner. 

[cdr]

make sure that the calipers are not springing back ,ie at the floating points,or the pads not sitting parallel to the rotors,get someone to push the brake s & watch the caliper & see how much movment it has

[cdr]

also you can take the calipers off & put a block of wood where the pads go & see if that tightens up the pedal,if it does you have a caliper mounting issue

[bobs66440]

The master needs to be for front disc / rear drum unit if that's what you are running. It should have a smaller front reservoir for the rear drums than the rear one for the front discs. Also, make sure the master bore size(s) are matched to the front caliper and rear wheel cylinders bore sizes. And you should be running a combination valve, not a distribution block. There's a difference. All the components should be taken from (or specific to) one donor car or application to simplify things. That way, you know it's all matched.

It almost sounds like the master doesn't have enough volume for the calipers...make sure all the bore sizes are compatible and that the lines are run to the correct reservoirs.

[suburbanfireman]

Thanks guys.  To address the recent responses -

I do have a disc / drum combo master cylinder (bigger reservoir for front brakes) Fenco NM 1627. 
I will pull the wheels off tomorrow and check the pad movement to see if it is a mounting issue. 
I might be calling the "distribution block" the wrong term / name.  I will attach a picture of what I have.
I don't know if the privious owner grabbed all the parts from one donor car - Here is what I do know for sure I have 1-1/32 inch bore on my master cylinder, I have A1Cardone (O'Reilly Auto Parts) parts #16-4103 & 16-4104 loaded front calipers.  I have to figure out what bore my rear brake cylinders are - any quick tips to figure it out would be appreciated.  I will try to get back to you with that info.   

Thanks for the pointers - I ran out of ideas, and I hate throwing expensive parts at a problem - hoping that they fix the situation.

[resq302]

Bob has a very valid point.  You could be bottoming out the front part of the piston in the master cylinder which controls the amount of fluid going to the front brakes.  If that is the case, then you either need a larger master cylinder that is matched to the system OR find out why you are not getting enough of the same pressure down to the front brakes.  Remember, if you are using a disc/drum master cylinder, the area for the drum part is a lot smaller than what the disc area is.

[b5blue]

Have you installed an adjuster to correct proportioning to the rears, if not that may be your problem. 

[bobs66440]

That's a combination valve you have.  

I did a little research and, according to the Oreilly site, the calipers that are compatible with the 1627 master are the 16-4102 and 16-4103. I don't see a 16-4104 available. It's also showing that the compatible rear wheel cylinder for those parts is 15/16" bore, and the same for  a '68 Charger. So, based on all the info you have given, all the parts should be compatible.   

[cdr]

i know you know this but i just had to say it when you have the wheel off also make sure the calipers are on the correct side,the bleeders should be at the  top

[bobs66440]

That's a possibility 

[cdr]

i have seen that done many times by very experienced mechanics not paying attention,it can happen--oopps 

[suburbanfireman]

Sorry I did not get back to the project today - called into work a 24 hour shift today.  I will tackle this brake debacle on Tuesday.

To address Bob's research (thanks for looking it up) - the #16-4104 caliper is just the "loaded" version of the 16-4102 & 16-4103.

To cdr - I'm almost positive that I mounted everything correctly.  (My bleeders are facing upwards)  To all - don't ever worry about mentioning these "obvious" things to me.  Firefighter's are not the sharpest knife in the drawer - most normal people run away from fire!!

To b5blue - I did not install an adjuster yet.  The car did not have one when I bought it, and the brakes worked without it before teardown.  My uncle converted his 1967 Coronet to front disc using the same master cylinder that I'm using without an issue.  If I can't figure it out, I might add an adjuster to my setup this week.

NOTE - I had a reputable "car guy" tell me that my combination valve may be "stuck" inside??  (I did use a vacuum bleeder kit when I originally bled the brakes.)  He asked me to draw him a picture of my combination valve, and once I did he told me that he knew how to fix it.  He said I need to pull the combination valve apart and reset the plunger inside.  He claims that is why I have back brakes, but barely anything on the front.  (Hell, I didn't even know that it could be taken apart!)  Has anyone ever tried to reset / clean the combination valve on their car?  I will try to search this website for more info between calls tonight.

I want to thank everyone for the advice - it's appreciated. 

[cdr]

TO RECENTER THE P VALVE pop the brake pedal with your foot pretty hard about an inch or 2 a couple of times

[FLG]

Is the rod that runs from the booster to the cylinder properly adjusted and not preloading the MC?

[bobs66440]

NOTE - I had a reputable "car guy" tell me that my combination valve may be "stuck" inside??  (I did use a vacuum bleeder kit when I originally bled the brakes.)  He asked me to draw him a picture of my combination valve, and once I did he told me that he knew how to fix it.  He said I need to pull the combination valve apart and reset the plunger inside.  He claims that is why I have back brakes, but barely anything on the front.  (Hell, I didn't even know that it could be taken apart!)  Has anyone ever tried to reset / clean the combination valve on their car?  

I had the one on my Mustang apart. They are rebuildable...that one was at least. Basically, it's just a shuttle valve inside that moves to shut off  fluid to the front or rear when low pressure (leak) is sensed. Once the leak is fixed, the even pressure from both circuits when the pedal is depressed is supposed to re-center (reset) it.  I imagine it's possible for one to get hung up, but I don't see how that would cause a low pedal. If it's restricting fluid, I would think it would cause just the opposite. Unless having the valve all the way to one side causes the other side to have more room and thus more space for the fluid to go. Therefore causing a low pedal. Just thinking out loud here...

[ACUDANUT]

I had that problem before. It was a bad proportioning valve. Beautiful car you have. I want to see more pic's.
I wish I got paid to sleep. 

[suburbanfireman]

PROBLEM SOLVED - I re-bled the front brakes last night using my Phoenix vacuum bleeder.  Then I followed CDR's advice and "popped" the brake pedal a couple of times to center the proportion valve.  I had improved pedal, but it still would not hold constant pressure.  I then went under the car and hit the proportion valve with a brass hammer a couple of times - then "popped" the brake pedal a couple of times - then tapped the proportion valve again.  The valve must have reset because my brake pressure improved instantly.  (It makes sense that things might be a little corroded inside the proportion valve - it sat on a shelf (dry) for almost 2 years during paint / bodywork!)  I noticed that the pedal would "squish" about 1 inch before it felt like I had decent brake pressure - so I got underneath the car (yet again) to see if the rubber lines were moving / bulging during brake pressure.  That's when I realized that I am a retarded!!  While looking at the back of my passenger wheel / caliper I noticed that the bleeder was located at about 1-2 o'clock (not directly at the top).  When CDR asked if the calipers were mounted on the wrong sides, I assumed that the bleeder would be near the bottom of the caliper (if mounted incorrectly) not ALMOST at the top of the caliper!    I switched the calipers, re-bled the system - guess what - the brakes are perfect! 

I'm pretty sure that my proportion valve did get stuck - that is why things improved after I reset it.  I also think that I might have gotten all of the air out of my front (incorrectly mounted) calipers using the vacuum bleeder - that is why I had decent brake pressure despite my best effort to screw everything up. 

THANK YOU to all members for their time / advice - apparently I need it!!  Moving on to wiring today - I'm sure that I will have more questions.

TO MODERATORS - feel free to erase this thread.  Not happy being immortalized on the web as an IDIOT.  (What can I say - I can restart your heart  using a cardiac defibrillator & IV drugs but don't ask me to set up your brakes!!)

TO ACUDANUT - you had to go there!  It is nice (if we get to sleep) but we run ambulance + fire so a quiet night is a rarity!  Too many old / sick people (not to mention an assisted living faculity).   The only time I ever hear that line - it's coming from a cop.  Did I guess right??!!  If so - you could change your screen name to ACUDONUT

[b5blue]

 

[ACUDANUT]

Damn, your on to me.

[cdr]

PROBLEM SOLVED - I re-bled the front brakes last night using my Phoenix vacuum bleeder.  Then I followed CDR's advice and "popped" the brake pedal a couple of times to center the proportion valve.  I had improved pedal, but it still would not hold constant pressure.  I then went under the car and hit the proportion valve with a brass hammer a couple of times - then "popped" the brake pedal a couple of times - then tapped the proportion valve again.  The valve must have reset because my brake pressure improved instantly.  (It makes sense that things might be a little corroded inside the proportion valve - it sat on a shelf (dry) for almost 2 years during paint / bodywork!)  I noticed that the pedal would "squish" about 1 inch before it felt like I had decent brake pressure - so I got underneath the car (yet again) to see if the rubber lines were moving / bulging during brake pressure.  That's when I realized that I am a retarded!!  While looking at the back of my passenger wheel / caliper I noticed that the bleeder was located at about 1-2 o'clock (not directly at the top).  When CDR asked if the calipers were mounted on the wrong sides, I assumed that the bleeder would be near the bottom of the caliper (if mounted incorrectly) not ALMOST at the top of the caliper!    I switched the calipers, re-bled the system - guess what - the brakes are perfect! 

I'm pretty sure that my proportion valve did get stuck - that is why things improved after I reset it.  I also think that I might have gotten all of the air out of my front (incorrectly mounted) calipers using the vacuum bleeder - that is why I had decent brake pressure despite my best effort to screw everything up. 

THANK YOU to all members for their time / advice - apparently I need it!!  Moving on to wiring today - I'm sure that I will have more questions.

TO MODERATORS - feel free to erase this thread.  Not happy being immortalized on the web as an IDIOT.  (What can I say - I can restart your heart  using a cardiac defibrillator & IV drugs but don't ask me to set up your brakes!!)

TO ACUDANUT - you had to go there!  It is nice (if we get to sleep) but we run ambulance + fire so a quiet night is a rarity!  Too many old / sick people (not to mention an assisted living faculity).   The only time I ever hear that line - it's coming from a cop.  Did I guess right??!!  If so - you could change your screen name to ACUDONUT

you are not stupid, YOU OWN A CHARGER,we all make mistakes,the reason i know about these things is because I HAVE MADE LOTS OF MISTAKES LOL and i am sure to make more

[bobs66440]

I'm glad you figured it out!

I must be a little thick, though. I don't quite understand this quote..." While looking at the back of my passenger wheel / caliper I noticed that the bleeder was located at about 1-2 o'clock (not directly at the top).  When CDR asked if the calipers were mounted on the wrong sides, I assumed that the bleeder would be near the bottom of the caliper (if mounted incorrectly) not ALMOST at the top of the caliper! " Were the bleeders near the top or bottom when you looked at it? They should be near the top.

[resq302]

Glad to hear you got the issue resolved!   

[suburbanfireman]

Yeah Bob - when the calipers were on incorrectly the bleeders were almost at the top (about 2 o'clock if looking at the pass wheel from underneath the car).  I assumed (not sure why) that the bleeders would have been way lower (more towards the bottom) if I had the calipers on the wrong sides - kind of assumed they would look obviously backwards.  Once I switched them to the correct sides the bleeders were directly at the top.  Thanks again for all the help. - Tim