47 Dodge breaks

[Guest copman87]

Hi all I'm new here. I picked up a Deluxe several weeks age and have now tried 2 master cylinders. No leaks and get a good pedal. Not lon after the pedal hits the floor but will pump up hard. Any body have a suggestion? Thanks copman87

[keiser31]

Adjust the brakes first, then bleed them. Start with bleeding the farthest wheel cylinder from the master cylinder and work on the next closest until you finally get to the closest.

[Ron42Dodge]

I agree with the need to bleed. Be sure to keep the master full while bleeding to make sure you don't draw more air into the system. Also be sure to bleed the rear passenger one extra good. That line is extra long and may have a high spot for air to pocket in.

When the pedal gets firm again, hold the brake for a while to see if the pedal slowly lowers. If it does, than you may have a leak some where in a wheel cylinder than isn't visable yet or a leaky line or a bad master again.

Do you have new lines and new hoses?

[Guest copman87]

Hi all I'm new here. I picked up a Deluxe several weeks age and have now tried 2 master cylinders. No leaks and get a good pedal. Not lon after the pedal hits the floor but will pump up hard. Any body have a suggestion? Thanks copman87

Thanks for responding. I put all new cycinders on, new break lines, hoses adjusted the breaks and put 2 residual pressure valves in. I got the master cylinder from Kanter

out of NJ. The first one was bad. Well with my luck I could get another bad one. Can't find any leaks. But I will go over the system again.

Enjoy your rides!!

[Guest Bob Call]

Why did you put residual pressure valves in a drum BRAKE sysem?

[Rusty_OToole]

Did you do a major adjustment? If you want your brakes to be first rate you have to contour the shoes to the drums using a sanding block and do a major adjustment (only after having the brakes apart). Later on you will need to do a minor adjustment to take up wear, maybe 1 or 2 adjustments in the first month. After the brakes are broken in you will need to do a minor adjustment once a year or less.

In other words when you rebuild the brakes you do a major adjustment to align the shoes to the drums. After that, a minor adjustment to take up wear once in a while.

If the brakes are adjusted correctly you will be impressed with how well they work. They were state of the art for their time.

[Guest copman87]

Thanks for the tip. I am going over the system again and recheck everything. This old gal runs great to. My friends including my mechanic friend can not believe I bought this for the mere price of $1,500.00. The body and frame are solid the paint faded and the inside is worn. But over all we are real happy. And thanks to all for your responses.

[Guest copman87]

That was a recommendation from a certified mechanic who does some racing. He uses some cars with out disc breaks and

has sucess using them as insurance against failing or inadaquate breaks. I'm going to rebuild the old master and see if that

makes a difference. If so I guess I got two bad new ones Thanks for the inout

[Rusty_OToole]

Pedal goes to the floor but you can pump it up, this is typical of brakes out of adjustment NOT master cylinder. There is so much clearance between the shoes and drums, you have to pump the wheel cylinders full just to get the brakes to touch, then you are OK.

The solution is to adjust the brake shoes. Chrysler products of that era are touchy about brake adjustments. The brakes are very efficient but must be set up right. Once they are set up right then only minor adjustments are needed occasionally to take up wear.

You have to get the factory manual and adjust them to specs using a special tool. It can be done without the special tool but it takes longer.

Don't waste your time rebuilding the master cylinder again if it is working correctly and not leaking.

[Ron42Dodge]

I will say I fought my brakes for a long time before I decided to invest in an Ammco 1750 brake tool which allowed me to set the brakes properly. But pumping the brakes did not make them any better prior. The shoes would make contact but not full contact. Now they are much better.

The tools are on ebay. A little pricey but the nice thing is you buy it, use it and then resell it and get most of your money back, or get into the brake adjusting business. But make sure all the parts are there before you buy it.

One other thought is the travel of the piston push rod. You can look down into the master cylinder with a flashlight and see the piston cup pass the ports in the bottom of the cylinder as well as brake fluid movement will ripple the the surface of the fluid. This is described in the free play section of the shop manual page 43 and 44. Your piston push rod may not be set quite right.

Edited October 27, 2012 by Ron42Dodge (see edit history)

[Guest Bob Call]

That was a recommendation from a certified mechanic who does some racing. He uses some cars with out disc breaks and

has sucess using them as insurance against failing or inadaquate breaks. I'm going to rebuild the old master and see if that

makes a difference. If so I guess I got two bad new ones Thanks for the inout

I assume this statement is in reply to my question about the check valves. The reason I asked is that it was my understanding that the purpose of the check valves is to keep calipers of a disc system at a point where there is a very minimum of space between the pads and the disc. My thinking is that on a drum system the check valves could keep the wheel cylinders extended and thus on properly adjusted shoes keep the shoes in contact with the drum causing overheating of the drum and extra wear on the shoes. Am I wrong?

[misterc9]

A residual check valve was used in the master cylinder of old drum brake systems. Its purpose was to help maintain a high brake pedal. It kept a small amount of pressure in the brakes to take up the "slack" in the system but didn't create a drag. Disk brakes dont need them as the pads ride right on the rotor and only pushed away by rotor runout. Disk/drum systems will only have them in the drum portion either in the master or in the line.

[Rusty_OToole]

The purpose of the residual pressure valve was to keep 2 pounds of pressure in the system. This was not enough to hold the brake shoes out but it was enough to keep the seals pressed tight to the cylinders and prevent leaks. It had nothing to do with maintaining pedal adjustment, that still has to be done by adjusting the brakes. By hand or by self adjusters depending on the design of the brakes.

Around 1975 they changed the design of the cups or seals to eliminate the residual pressure valve. The new type cups have a spring that goes around the lip of the seal to hold it tight. This is in addition to the spring that pushes them apart.