Early A Disc Brake Help Needed!!

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66340SEDAN

66340SEDAN

FABO Member #3649
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First off I will tell you what I have, it's a 1966 Valiant with a manual disc brake swap from a 1973 Duster. All new or rebuilt parts, including all the brake lines. I have 11 inch cop car drum brakes on the rear, also running a Direct Connection proportining valve. I changed the master cylinder over to the newer 2-post style master cylinder with the adapter plate. I have not driven the car yet.

I went to bleed the brakes tonite and I don't have a hard pedal, it goes to the floor. I only get a pedal when I pump the brakes up, but after a few seconds the pedal goes back to the floor. I believe I have all the air bled out, no bubbles left. I did have a couple of leaks but got them fixed. I reused the stock brake rod that came in the car. I do have a Mopar Performance adjustable one but it looked like it was an inch or 2 too long so I went with the original.

Could it be that the stock brake rod is not pushing the piston inside the master cylinder in far enough? Anyone else who has done this could give me some insight? I am stumped and gave up for the nite. Any help would be great, I would like to get this car on the road soon before I have to store it for the winter!! Thanks, Keith.
 
Bad connection somewhere still? Did you change out the brake cylinders? How about the nipples? Bench bled the master? How are the seals in the 2 bolt master cylinder? A longer push rod may be the answer as you stated in your last paragraph. Maybe after some rest you''ll find the answer.
 
no insult intended, are the bleeder screws on the top of the caliper?

i have a 66 cuda and am using the stock rod and all works good. should be the same as a valiant
 
i was just going to say about the bleeders................that is exactly the symptom of bleeders not at 12 o'clock.
 
The bleeders are not at the 12 o'clock position but slightly lower, they do point up. When I installed the disc set up I mounted the calipers to the back side of the rotor instead of the front for sway bar clearance.

I did not bleed the master cylinder, the entire brake system is new and had no brake fluid in it. I didn't think this was a big deal because the whole system was dry.

When bleeding out the fronts, it seemed like there were no more air bubbles. Would it help to remove the front clapiers, with the hoses still attached, and holt them in a way where the bleeder is at the very top? Would this work better to get trapped air out? Thanks, Keith.
 
no. but you need to take the master off and bench bleed it. these are your brakes, everything must be done correctly. the reason you bench bleed a master is rid it of all air before you put it on the car.
 
The answer to the question was in your post. Your master cylinder is probably junk. The system is not holding pressure. So you either have a leak to the outside (which you should be able to find) or the master doesn't hold. Is the fluid level going down?

If you had air in the system you would have a soft pedal which would pump up, but then it would hold (although it might not be very hard). Also if you continue to bleed and you aren't getting air, it is a reasonable bet that air isn't the problem.

As far as bench bleeding goes, it saves some time, especially if you are filling an empty system, but once you have bled all the air out, it would seem silly to open a line. Also modern master cylinders will "gravity bleed" in time (as opposed to older cars where the master was under the floor and not the highest point in the system.) Over night should have been long enough.
 
I have to agree with c130Chief It sounds like the master is bleeding back by. was this a rebuilt unit? i had the same problem when helping my father in law with his van. Went through two rebuilt master befor we got a good one ! what a pain in the ...ya you know .
 
take the lines off the master, plug the master and pump the pedal. is it holding? plug just one then just the other. most likely you have a bad master.
 
It took 2 master cyls to get a good on my dart. I did the same swap and the first m/c was bypassing internally. I bought a Bendix brand new and I think it was like $30 and solved the problem. Drove me nuts though because I didn't think a new m/c could be bad.
 
I put on discs (KH small bolt ones) and did not bench bleed the master either, and I had a hell of a time getting the air out. Same problems as you're describing. Finally I had to bench bleed the master, but did it in the car with some old brake lines.

Just bend some short brake lines into the master and pump away.....air will come out like crazy!
 
Had the same type of problem and felt real dumb when I found the problem. One or the rear wheel cylinder arms slipped off the brake shoe. ( found the problem after taking a new master cylinder back to the parts house and bleeding the system a million times!:mumum:
 
hi i did this same convertion on my 65 a couply of years back.

now i have one question did you switch to a dual master or did you stick with the single? if you switched to a dual and are using the push rod from the single then there may be an aditional problem there. i beleave the single rod is not long enough for the dual master.
 
the rods are the same length. it soes sound like a bad master.

well, 66340sedan..........?
 
lonewolf said:
Had the same type of problem and felt real dumb when I found the problem. One or the rear wheel cylinder arms slipped off the brake shoe. ( found the problem after taking a new master cylinder back to the parts house and bleeding the system a million times!:mumum:
Click to expand...

Even worse is placing calipers on wrong sides. Line goes in at top and bleeder is then on the bottom. Never will get the air out. :glasses8:
 
www.mpbrakes.com
Has a really good tech info page for issues like this.
They have answers for disk brake conversions, which master cyllinder you need for certain swap applications, how to bleed, check pressure, trouble shoot.
 
Well, I got the brakes to work but the bleeders on both front calipers leak?? :( (real slow drip) I have the newer 2 post master cylinder and it is good, also the factory brake rod works fine. I have the calipers mounted to the rear but I popped them off and bled them with the bleeder in the 12'o clock position. I have a nice pedal but now I can't get the bleeders to stop leaking!! The bleeders are good, I ended up tighting one to the point where it feels like it will break. On one bleeder you can look where the bottom seals and it doesn't look like it seals all the way around, almost like the bleeder hole was machined crooked!? These are new/remanufactured calipers. Can the bleeder be sealed up with anything? Are my calipers junk?

One good note is I got to drive my car today for the first time with the new 340 4-speed and 4.10 gears, SUCKER HAULS ***!! :burnout: Pretty loud with open Hooker Super Comp headers, my neighbors didn't mind too much!! :mrgreen: I will bring it in tommorrow for the exhaust work.

If anybody has any ideas on the bleeders, that would be great! thanks again, Keith.
 
LOL If you had to take the calipers off to bleed them properly they are on the wrong side of the car.
Now.. the bleeder is a tube like fitting that holds approx 4 drops of fluid. If they are pointed downward the few drops will come out slowly.Switch them. Bleed them. Place rubber caps on the bleeders and drive it. Look for a leak in a couple days.
 
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