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Veteran
Posts: 282
 
Location: Henderson, T.N. | Hi guys, I have a 57 plymouth belv,that I got a cople of years ago has AAJ kit on the front with a GM booster and master cilinder. The problem the car is that the brakes are real soft. I have bleed them twice and I had a brake shop bleed them and it didnt change.The only thing I havent done is bench bleed the master cilinder.Should I try That next? I would try anything to get ride of that spongy pedel. Thanks |
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Expert
Posts: 1218
Location: Warren, Michigan | Yes I would try that next for sure. I had a bubble in my mastercylinder that drove me nuts for 3 months. |
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Regular
Posts: 71
Location: Kansas City, Missouri | I have had two sets of the front adapters. They were so miss aligned that it takes all
the pedal travel to bring the pads to the rotors. This makes the pedal low and spongy.
A simple test is to use a pair of vicegrips and gently pinch off both line and see if the pedal
is hard and at the top, or take the wheel off and watch for movement as some one applies
the brake. You should only see the pad move no more than .005 ths. |
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Elite Veteran
Posts: 690
Location: BELTSVILLE, MARYLAND 20705 | hellow, i had this problem . what i found out was that the huge rear wheel cyclinders take allot of fluid making the pedal soft.I changed the rear to a cuda/challenger rear and that solved the problem instantly. |
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Inactive by user's request
Location: Las Vegas, Nevada | Did any of you get the adjustable proportioning valve from Roger?
It takes some playing with, but you can find an acceptable balance.
You may want to look at this fellow's experience:
http://59sportfury.net/showcase/steinmaier/index.html
K. |
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Inactive by user's request
Location: Las Vegas, Nevada | Here's what I mean:
http://59sportfury.net/showcase/steinmaier/images/55.jpg
K. |
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Veteran
Posts: 282
Location: Henderson, T.N. | I have a 1985 new yorker rear end in my car so I would think that the rear and front would work good together. I dont think I would need a proportioning valve because the balince form front to rear is good theres just a real spongy peddle with almost no breaks. |
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Expert 5K+
Posts: 6203
Location: Big pimpin' | BadBelair, I've run into this at work...No matter how much you bleed the brakes, there's air in the system from somewhere.
I've seen BRAND NEW wheel cylinder's actually PULL air into the rear brakes when I tried to bleed them..Just bad parts.
Replaced, problem went away. You may need to bench bleed the hell out of the master cyl. though..
No matter what rear end you have in the car, a front disc., rear drum set-up WILL need a porportioning valve. Otherwise, the rear will lock up from 50/50 brake pressure being applied, when 70 front, 30 rear is needed....One cannot just bolt on front disc brakes and expect the factory junction block to apply the correct pressures..In factory form, the drum brakes got ALL EQUAL pressure to all drums, this is NOT the case with disc./drum set-up...
This, however, I don't think is your problem..You have air in the system from somewhere... |
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Expert
Posts: 1302
Location: Skaneateles,NY(summer)/Port St.Lucie,FL(winter) | I installed disc brakes in the front of my '55 DeSoto, stock master cylinder/power booster, stock rear drum brakes, silicone fluid, and NO proportioning valve. I used late '70's GM (Firebird/Camaro type) rotors, calipers, front flex hoses and had slightly modified front hubs machined. The stock rear breaks are totally rebuilt, from the backing plates out (2 1/2 X 12 shoes), with special attention being paid to fitting the arc of the shoes to the arc of the drums. Shoe adjustment was given close attention, and care was taken to get it right. The system works like Factory. NO spongy pedal, no excessive travel, and the system does not lock up un evenly. When pressure is applied to the closed hydraulic system, the fluid takes the path of least resistance. As the resistance increase in the front calipers, from pad contact with the rotor, the pressure increases to the rear cylinders until it is even throughout the system. The KEY to balance in the system is friction necessary to stop each wheel. If that is equal on all 4 wheels, then they will all work equally. There are a LOT of things in the equation...weight difference between the front/rear end, swept area of the front and rear/pads/shoes, volume of the calipers/cylinders, inside brake line diameters, etc. It appears that it was more cost effective for the Factory to include a proportioning valve, than to redesign/put into production properly balanced rear drums. Whatever the reason, the set up on my '55 appears to be perfectly balanced. The fronts don't lock up before or after the rears, and the improvement in pedal feel is great with WAY better brake response..with out a proportioning valve. Through no skill on my part, I might add. Even a BLIND squirrel finds an acorn ONCE in a while.
What you MAY be running into is an improper master cylinder diameter and/or air in the system, and /or flex lines that are spongy and expanding when the brakes are applied. If the inside diameter of your master cylinder is to small for the added volume of the front calipers, the the system will compensate by needing to increase pedal travel. Your GM master cylinder MAY be mismatched to the volume of your particular brake system. A master cylinder with a larger diameter will remedy that. By the same token, if the diameter of the master cylinder is to LARGE for the system, then the brakes will be REALLY touchy. However, I think you will find that there is air in the master cylinder, or trapped somewhere in the system, and/or your flex lines need to be replaced. If you are using silicone fluid, it does not respond well to "pumping" the pedal rapidly to bleed the system. Silicone fluid holds bubbles a LOT longer than regular fluid, and is best pressure or gravity bled...
Edited by 345 DeSoto 2007-12-02 8:36 AM
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Veteran
Posts: 282
Location: Henderson, T.N. | Well when I pump the brakes it helps a little but I did noticed that if Im going say up a hill when I gat to the top and hit the breaks the peadle seems a lot better?. Could I also have to much vacume or not enough? Thanks guys Im hoping to get in to this problem to night.
Thanks |
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Expert
Posts: 1302
Location: Skaneateles,NY(summer)/Port St.Lucie,FL(winter) | Are you sure the BOOSTER is working properly? Is the diaphram leaking (not holdind vacuum)...are there any vacuum leaks between the booster and the intake? With the engine off, rest your foot on the brake pedal with slight pressure, then start the engine. If the pedal goes down a bit, then chances are your booster is okay. If it doesn't, then chances are it's not working properly...or you might need a vacuum can... |
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Veteran
Posts: 282
Location: Henderson, T.N. | Would I still need it, its a corvett booster? |
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Veteran
Posts: 282
Location: Henderson, T.N. | ok I bled everything from bench bleeding the master to each wheel cylinder. The booster is getting something like 25incs of vacume. The brakes feel better but still soft peddle. Im I getting to much vacume? Should I try to adjust the rear brakes? Its a 1985 new yorker rearend,whats the best way of doing it?
Thanks guyus |
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Expert
Posts: 3035
Location: N.W. Fla. | Is the booster & M/C designed to work together or just 2 pieces thrown together? |
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Veteran
Posts: 282
Location: Henderson, T.N. | I asked the guy I got it from and he said it came to gether as one pice from AAJ. |
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Veteran
Posts: 259
Location: Detroit MI area | I know bleeding the the silicone fluid after I did the brake conversion was a bear. Took 9 or 10 times to get it right. I eventually used a clear plastic drain tube over the bleeder screw. Surprised how much air I could see in the fluid then.
Past that, did this car originally have power brakes? These cars had a vacuum tank on the inner fender. Gotta have one of those.
Two things I've seen-
The vacuum hoses on the tank were reversed. I won't say how I know about that one.
Original power brake cars have a booster trigger lever at the top of the brake pedal. It triggers the vacuum flow into the booster for the power assist. If it engages too early or is out of adjustment it'l bleed all the vacuum out of the system. That'll make for a lousy feeling pedal. I have no clue if that trigger gizmo is doing anything with the GM booster.
Jim Krausmann
Detroit
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Veteran
Posts: 282
Location: Henderson, T.N. | Hey,this car did not come with power brakes. Does that matter? |
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Inactive by user's request
Location: Las Vegas, Nevada | Dwight,
You can call Roger directly at 1-(503) 890-1469. He'll talk you through the problem and try to help you solve it, even though you weren't the person who bought & installed the kit.
Roger plans to have surgery soon, so you may want to call him before he's laid up for a spell.
Also, stock '57-'59 Mopars with power brakes used a different pedal assembly with an extra hole for the booster "trigger." But that shouldn't be an issue using the newer style M/C & booster.
What can cause a problem is if your car doesn't have the adjustable master cylinder push rod. The adjustable rod allows you to lengthen or shortern the rod to work with various master cylinders. My '59 AAJ kit uses the drum brake master cylinder with an adjustable proportioning valve for the rear drums, as both M/C reservoirs are equal size. I had to use the adjustable push rod and lengthen it when I installed the new dual master cylinder.
But please call Roger and discuss the problem with him.
K. |
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Veteran
Posts: 282
Location: Henderson, T.N. | Ok I pinched off the two front lines with vice grips and the peadle got a little better after a little pumping but not hard like I would have thought. Now what?
Edited by badbelair 2007-12-16 3:08 PM
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Regular
Posts: 71
Location: Kansas City, Missouri | Get someone to help you. Apply brakes and make sure front calipers are not working by turning the hubs.
Next, apply vicegrips to rear hose that goes to the rear axel. Check to make sure you can turn wheels when
brake is applyed. At this point the pedal should go down, when applyed, no more then to take out the free play.
Pedal should be hard as a rock. If not you have master cyl issues or air in line. Next remove vicegrip to rear
brakes. The pedal should go down maybe 1/4 in (all measurement are after pedal travel to take free play out)
it will not be rock hard, you will have a little movement because you will be forceing the shoes to fit the drums.
If you have a lot of pedal travel, check adjustment of rear shoes. Tighten them up to where you can't turn the
wheels. If you have no problems now the rear are out of adjustment. If they are still soft, check for air and
proper shoe fit to rear drum. If the shoes don't have the correct fit, you will have a soft pedal. It is forceing
the shoe to fit and that take pedal travel as well as makes it soft. You are distorting the shoes.
If rear is now correct, move to front. Remove vicegrip from one side. With some one in car, apply brakes.
You are looking for movement. The only thing you should see move is the pads. They should move no more
that .005 ths. The pads have to be parallel and perpindicular to the rotor or the pedal will be soft. It takes pedal travel to try and get the pads correctly in line. Plus your brake are poor because the contact area of the pads are
on one corner of them instead of the whole surface. You are using pedal travel and pressure to align pads instead
of stopping.
The easy way to check all this is with a set of dial indicators, but thats another story.
It is real hard to see the bracket twisting that is holding the calipers. I have two set of those brackets for the
front and both are out more that .90 ths. each. One way to check them is to remove them and use a straight edge
to confirm they are straight. The other thing is that the brackets are bolted to the back of the spindle. These
surfaces are machined but to no tolerance. I have three sets of uprights and none are the same, there is a difference
of from 30 to 110 ths. This put the bracket out of parallel and perpindicular with no way of fixing it.
I spent almost a year with two engineers trying to get mine to work properly.
I will try to keep helping you with this problem, It is so much easier to do it then tell how to. |
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AAJ brake question
