I'm kinda stumped by this one: I have been helping my brother get his car up and running after sitting for 21 years. Unfortunately the car is an O/T Mopar ('73 Charger), but I thought I would ask this a general question because a power brake system is a power brake system is a...well you get the idea. When we got the car, the first thing we did was get the thing running (after a long fight), then we tackled the brakes. We replaced the front pads, calipers assemblies, rear wheel cylinders, shoes, etc. We also replaced the master cylinder and the power booster. The brakes have been bled, adjusted, etc......but when you step on the brakes...the car does NOT STOP. The pedal just goes to the floor. If you pump the pedal, the pedal will become hard and does not seem to fade if you hold it. If you take you foot off of it however, then step on the brakes again....all the way to the floor. We aren't loosing fluid anywhere and there is not much in the system that can fail. The only thing I can think of that could have some influence is the Intake/Carb change......causing a vacuum issue. We ditched the original 2bbl intake setup and went with the Edlebrock Performer 4bbl set up. With the vac hose to the stock location....nothing. even if I move it to the port on the carb itself.....no difference. Am I on the right track?....What am I missing here? Help? Clayton - Mr.ModelT
Give this a try....."only way i know to test a booster, is to turn engine off. use brakes several times till pedal is hard. then with brake applied,start engine. the brake pedal should then soften.if the pedal stays hard the booster is bad" Usually a bad booster will just give you a very hard peddal, this sounds more like a bad master cylinder.
I will certainly give this a shot! The unsettling part is.....I have 3 boosters: 2 originals (that I believe are good) and 1 re-mfg.... All 3 have the same results in the system. ..even more unsettling, I have 3 Master Cylinders....2 new ones and an original. Sames results with any of these.
Are you 'cross bleeding'? This car 'may' have a system that is tied right front/left rear, left front/right rear. Some cars had that as a 'safety feature' (why do I feel like Joey from Friends with all the ' marks? lol). Other than that, are you bleeding with engine on or off? If you are doing it with the engine on, you may be feeling the booster amplify a bad circuit. I'd bleed them with the engine off, and see if you get a pedal. I just had to do this on an OT Dakota- woo hoo. Good luck bro. I love your ON topic car too btw. JK
I have just been bleeding it the ol' fashioned way. I don't know if the car is set up as a "cross system", but it won't hurt to try. I am bleeding it with the engine off. and the pedal is decently hard. When the engine is running however.....nothing. Thanks for advice..and the kudos on the T
Did you 'bench bleed' the master? Meaning, they have these goofy hoses that come with them sometimes, and you screw the hoses into the fittings, then run them back into the master cylinder, fill it with brake fluid then press the plunger in and out until there is just fluid coming out of the hoses and back into the master cylinder... does that make sense? The only other thing I can think of is you don't have vacuum to the power booster- there should be a goofy looking tree thing in the back of the intake or you're pulling it from the wrong port on the carb, perhaps? My dad has a car similar to the one you're working on- if you're still having issues maybe I'll slide over there and check out the visuals if you need. JK
Hey MrModelT. I'm no brake expert but here are my thoughts. You've installed 3 different master cylinders. You've installed 3 different brake boosters. (Thats a lot of brake bleeding and fluid!). In all cases you are bleeding the brakes w/ the motor off. You conclude your bleeding when the brake pedal feels stiff and seems to engage the brakes a certian length of pedal travel. Then you fire the motor up, press on the bake pedal and it travles clear to the floor and the brakes do not hold the car in place. Have you tried to operate the car w/ the booster not pluged in to a vacume source to see what happens? Are the brakes actually engaging? I'd think that the brakes should work w/ or without a vacume source. I know that w/out the vacume source the brakes will be very stiff, but should still work incase of a booster failure or sudden loss of vacume. After all, you can pump fluid through the lines w/ the motor off, the pistons should be moving somewhat. The info you gave about pumpking the brakes several times is a key. I had an old VW fastback w/ a bad master cyl. and would have to pump the brakes at least three times to get them to hold. The moment I took the pressure off the pedal, they instantly began to fade and the pedal moved toward the floor. I still, to this day, give my brakes a double pump when comming to a stop, and I sold that P.O.S. Fastback 15+ years ago. I'd suspect that either the master cylinders are all bad or there is still air in the lines somewhere. I just replaced the master cyl. in my Scout. I bench bled it, installed it, bled it and had sad brakes. I took off the master cyl. again and found that I had not done a very good job at bench bleeding, for there was still air in the system. Now the brakes work as designed, and yes my Scout has a power brake booster. I would test the brakes in a controled maner, by trying to use the brakes w/ out a vacume source to see if the brakes are actually working. I suspect air is still in the system. Try bench bleeding again, adjusting the rear dums again and bleeding the entire systems starting from the most distant wheel from the master cyl. and move your way from wheel to wheel until you reach the wheel closest to the master cyl. My brother and I usually have a cadence, where he'll be sitting in the seat, I'll be bleeding the wheel cyl. I'll hook a clear hose to the nipple, which goes into a jar of brake fluid. I'll crack the nipple open and yell "PRESS". he'll shout "OK" and hold the pedal down, giving me time to close the nipple off. I'll yell "RELEASE" when the nippled is closed and he'll yell out the number of pumps we've completed. After about 5 or 10 pumps, I'll jump up and check the fluid in the resivour. We'll contiune this until I see pure cream soda (w/ out bubbles) colored fluid flowing through the clear tube. Then I'll move to the next distant wheel and start the process over again. When you find out the cause, please let us know. I'm curious.
...Not yet We have been playing around with it and have made some progress, but not completely fixed the problem yet. We bled the system considerably, but still no change. I pulled out the test (spare) master and booster and put the new ones back in...nothing. Pulled the metering/control/proportioning valve out and switched it out for the cleaner spare from the parts car and eureka! The brakes WORK!..sorta. If you pump the pedal a few times (before you want the brakes to ACTUALLY work) the pedal gets hard and stays as such. If you take your foot off and don't touch it for a few seconds (10 or 15) then apply the brakes...pedal goes to the floor. I think my next step is to bleed the system 'till the cows come home...just run a whole jug of DOT 3 through the system till the there is no more air. Also need to adjust up the rear brakes because the metering valve cuts power to the front discs by 50% and applies 100% to the rears in gentle and average stops. During a "panic" stop, it delivers 100% to all wheels. ...Back to the shop I go!
Mr Model T, I think you are on the right track now. You can forget about the booster,it will not cause what you describe. You need to bleed this thing! Also check the rod that connects the booster to the brake pedal and the rod that goes between the booster and the M/C. If either is too long you are not gonna be able to bleed the system properly. One more, did you say you adjusted the rear shoes? They need to be adjusted before you can sucessfully bleed the system. lastly, you would nod have a 'cross' system unless someone put it in that way, but not from the factory. Good Luck. Normal Norman
So here is a quick up date. Went through the ENTIRE system again, then bled the DAYLIGHTS out the system. We topped off the Master, hooked up a chunk of rubber hose to the bleeder screw, stuck the hose in a clean plastic cup and ran the contents of the master through until no air came out. Refill master and repeat at all 4 wheels. No air......system is full.....metering valve is clean..... STILL... .....NO..... ..............BRAKES!!!!!!........ The pedal still just goes to the floor...pump it a few times and it's hard....let it sit for a sec....goes to the floor. I'm lost here!
Sorry Norman....read your post and I swear I answered you back ... M/C rod....... Adjusted Rear brakes........Adjusted Brake system.........Bled (Did it again last night just to be sure) Still nothing.....bupkiss......nodda......zilch......NO BRAKES.... I am a real loss here......anyone have any input on this?
I think you are pumping the clutch pedal. OK, maybe not. A few back to basics checks. Are you sure the left and right calipers and or backing plates have not been swapped at any time and the bleeders are at the bottom, and not the top? Second, you can test the master for pedal hold by plugging the brake line fittings. Remove the brake lines, install the correct plug (or crimp a spare brake line) and slightly crack the fitting loose to bleed the master. With the plugs in, the pedal should be rock hard, and all the way up since no fluid is being moved. If that works, pull one plug and re-install one brake line and repeat the bleeding process, isolating the front/rear to see where exactly the problem lies.
I am quite sure the calipers have not been switched, but as a side note...the bleeder screws are at the top. The calipers don't let you switch sides very easily and all factory service literature illustrates that the calipers are mounted properly with the screws pointed up. I will certainly make up some plugs for the other brake fittings and do the bleeding process you suggest......I can only pray to the Gods of Stopping Power that it works and solves this!
If you can pump up the brakes and have a hard pedal, then release, wait a few seconds, and have the pedal go to the floor, you've got a displacement problem, or air in the system. I'm ruling out defective masters and boosters because you've done that. If you haven't used a pressure bleeder, now is the time to use one. NOT one of the cheapy "garden sprayers", but a genny brake pressure bladder bleeder. The metering valve (NOT the proportioning valve) holds pressure off to the front discs till about 100 psi master pressure, then allows full psi. It's purpose is to allow the rear drum shoes to overcome their return springs and make drum contact the same time the front pads touch the rotors. These were used in the 70's, pretty much disappeared, then returned briefly in the 90's when pedal "feel" and bench marking became important. Most have a button that must be pushed while low pressure bleeding that bypasses the hold off feature, otherwise no pressure will build in the fronts. When bleeding, you MUST SLOWLY FULL STROKE the master while bleeding each wheel, with or without a pressure bladder. Do one wheel two or three times, then move on to the next. It's best to use a tygon tube connecting the bleed screws to a container. Hold the tubing higher than the bleeders and you can clearly see any air present in the fluid. Your '73 Charger should be plumbed with a vertical split, meaning a front/rear system. Front drive cars in the 80's starting using cross split LF/RR RF/LR systems.
I will certainly give all this a shot this weekend hopefully. I have enough extra fluid to bleed it through several times...just gotta get the bleeder. That is what I thought. I have two...pulled the spare apart and cleaned it out then switched them out.....no change. Had my brother try to pick up a new one, but they told him that because they are so damn reliable and almost NEVER fail...they don't make new or re-mfg them. ...don't think that is the case, but haven't been able to find new ones yet.
Are you sure a previous owner hasn't modified the brakes? If so the specified parts might not be sized right. Just a thought. I can't think of anything normal you might have missed.
Wow, what a head scratcher. I like the suggestion of using a special tool. I also like the idea of the metering button. I've never heard of the meter before, but its stuff like that which could be the culprut. My brothers 53 had the opposite problem. His pistons expanded and then never retracted. So his brakes were on all the time. I cant wait to find out what the issue was.
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