Brake question

[suntennis]

Are you sure the rear brake cylinders work? Did you ever check them?

[4852dodge]

Make sure your rear wheel cylinders work before you go any farther.

[Herr Otto]

When I obtained the truck a year ago it came with rebuild kits for the cylinders and I rebuilt them at that time but never really watched them in operation. I will do as you suggest and see if each cylinder operates with the drums off and the pedal pressed down.

Thank you

[MBF]

On the off chance the rear cylinders are working, don't step on the pedal with the drums off-you'll pop the cylinder(s). I'd bet that both of the rears are seized, or that you have a pinched off metal line, or internally collapsed rubber line in the rear. Once you've determined that the rear brakes are working and properly adjusted you can address the issue with the proportioning valve. Mike

[Herr Otto]

How do I determine which rear cylinders are working? I know at least one is working on each side as I can stop each wheel from spinning by hand if someone appies the brake. They just will not completely stop if the truck is jacked up and it is in gear. When I rebuilt the cylinders a year ago I also replaced all the brake hoses.

Thank you

[Merle Coggins]

Did you perform both the major and minor adjustments on the rear brake shoes? It's possible that both wheel cylinders are working at each wheel but there's not enough friction material making contact to stop the wheels under power. The major adjustments are made by turning the ecentric anchor pins, which move the heal of the shoe out closer to the drum. The minor adjustments are the cams in the middle. These move the toe of the shoe out. If the heals are out of adjustment just the toe will contact the drum and won't have enough friction to stop the wheels.

Merle

[Herr Otto]

Merle, I did follow the instructions on how to do a major and minor brake adjustment. I know the shoes are not new and will need replacing in the future but I do feel there is enough material left to do their job.

Thank you

[Herr Otto]

If in fact I end up replacing the rear shoes, where is a good place to purchase them and what should they cost?

Thank you

[Don Coatney]

If in fact I end up replacing the rear shoes, where is a good place to purchase them and what should they cost?

Thank you

Check with these folks.

[Merle Coggins]

I think I got mine from Bernbaum or Roberts.

[desoto1939]

If in fact I end up replacing the rear shoes, where is a good place to purchase them and what should they cost?

Thank you

iF YOU HAVE THE RIVETED LINING THEN YOU CAN REPLACE THE LINING YOURSELF.

iF THEY ARE BONDED THEN YOU WILL HAVE TO SEND THEM OUT TO HAVE NEW LININGS BONDED TO THE METAL BACKING.

A RIVTING TOOL WILL RUN AROUND 20-30 DOLLARS AND THE SHOES MAYBE 20-30. The rivets around 25 cents each. So if and when you have to replace the linings again the only cost is very minimal if you can do the work.

I can replace a set of rivited linings back on the shoes in about 1 hour or less.

USe a c clamp to hold the lining in place on the shoe and align the holes put several rivits in the holes then start at one end and work towards the other end. move the c-clamp past the next set of hole and then clamp down the lining. Then set the rivets and continue until you have all the rivets set.

Rich HArtung

[Herr Otto]

I have bonded linings.

Thank you

[Herr Otto]

With a drum removed and someone stepping on the brake pedal I can see the brake cylinders are operating but with minimal movement. They are probably only pushing out 1/8" each. Any ideas what would cause such little movement or how to fix this. Like I said in earlier post, I successfully bench bled the master and then the whole system with good squirts out of every bleeder with no air. The pedal does not feel firm at all.

Thank you

[Don Coatney]

With a drum removed and someone stepping on the brake pedal I can see the brake cylinders are operating but with minimal movement. They are probably only pushing out 1/8" each. Any ideas what would cause such little movement or how to fix this. Like I said in earlier post, I successfully bench bled the master and then the whole system with good squirts out of every bleeder with no air. The pedal does not feel firm at all.

Thank you

I wonder it the volume of the wheel cylinders exceeds the volume of your master cylinder? Has this brake system ever worked as it is setup on this vehicle?

[Herr Otto]

It worked better than it is now but I never felt that it was 100%. The new master cylinder definately has less volume than the one I took off. Accordinging to O'reilly's auto parts it is the correct part number for the replacement.

[Don Coatney]

You really need to post pictures of your set-up!

[Herr Otto]

After much research and speaking to people from master power brake and NAPA, I purchased this http://www.napaonline.com/Search/Detail.aspx?R=UBP36359_0270674277 master cylinder from NAPA. My problem now is determining which is the front chamber and which is the rear. The master cylinder is for manual brakes and each chamber is the same size. The threads going to the front chamber are 1/2" and the rear are 9/16". When bench bleeding with the cap off you can surely see the front chamber has a much more powerful stream. Any suggestions are welcome.

Thank you,

Otto

[Herr Otto]

My question is , which chamber should feed the rear brakes and which one for the fronts?

[Allen I.]

Decent general information...

http://www.auto-repair-help.com/automotive_maintenance/master_cylinder.php

[rustyzman]

I could not get the link to work for me, but...

The line connected to the larger reservoir is for the front brakes. Likely the one closest to the actuating rod.

You may very well have the same master I have. Mine fits 70's to early 80's GM products, 4 wheel drum 1 ton. 1 1/4" bore, both circuits. I have noticed on mine as well that my rear brake action is not as powerful as I would like. However, I also have to break in my linings a bit more before I call it bad. I have plenty of pedal stroke as well with no binding in my adapter.

Interested to see what you find with yours.

Could you also post the NAPA part number?

[MBF]

Just to add my 2 cents here and its just an educated guess. The design of a disk / drum system requires two very different volumes of fluid to actuate the front and rear brakes-hence the two different sized reservoirs. If I remember correctly, the early 80's Chev wagon that I had had very small wheel cyls on the rear. What I'm saying here is that the master was designed to work with a large volume piston setup on the front, and with smaller drum cyls of the rear. I think if you measured the volume of fluid coming from each reservoir on a bench bleed single stroke you'd see that only a small portion of the total volume is sent to the rear.

Mike

[Herr Otto]

The NAPA master is UP36359. I believe this has finally taken care of my braking problem. I have a good pedal and the rear brakes stop the wheels from rotating when jacked up and in gear. This was very painstaking as I had tried 4 different master cylinders.

Here is what I learned:

1. On a manual master cylinder with 4 drum brakes, the chambers will be equal in size, their chambers are also smaller than power brakes.

2. Typically but not always, the chamber closest to the firewall will be for the front brakes.

3. Drum brakes require a 10 lb. "Residual Valve" either built in the master or external ones can be added. Rebuilt masters will not have these valves built into them, only "NEW" masters will come with them built in. The purpose for the "residual valve" is to keep pressure on the brake shoes so they do not have as far to travel, elininating a soft feeling pedal and pumping of the brakes.

4. The original master on my truck was a single chamber with a 1 1/4" bore. My "New" dual chamber has a 1 1/4" bore and the residual valves built in it.

I purchased 2 external Residual valves that I ended up not needing. If anyone is interested in them I will sell for the price I paid plus shipping.

$9.95 ea. plus shipping. They were never put on the truck.

Thank you all for your help,

Otto

[HanksB3B]

Knowing how frustrating a problem like this can be I hesitated to say anything (that"s a first? ) You wouldn't know if you saw my truck in person (and I've gotten better since being on the P15-D24 forum) but I don't know a lot when it comes to modifying working mechanical parts. I really like the idea of things like a Volare Front Clip, A taller differential ratio and disc brakes. I hope I get there someday, but I wondered why you opted to go with a dual master cylinder because I didn't think you installed front disc brakes. I'm not up on the Freeway yet like Merle and honestly with the drivers out here in LA not sure if I want to be. My truck would have to do at least 70-75 before I'd even consider doing that. I would not like to exceed 2,100-2,500 rpm to do so and I'm a ways away from accomplishing that. At 40mph my truck keeps up with local street traffic and stops very well with an all new and original spec braking system.

One question: Did the UP36359 fit with no modifications to the truck?

Thanks,

Hank

Edited October 23, 2010 by HanksB3B

[Herr Otto]

I opted for the dual chamber master because I already had to get a new master cylinder and I figured why not go with what is considered safer. With a dual master it is like having a back up system if one of the chambers goes out. This is less than ideal but it is better than having no brakes at all. Since 1968 any vehicle manufactured in the U.S. has to have dual chamber master cylinders.

I also will most likely will not be doing much if any expressway driving.

The previuos owner already switched the brake pedal to one from a 1965 Coronet, therefore the master was now mounted on the firewall instead of the frame. This master was the type with 4 mounting bolts. I had to drill two different holes for the new NAPA master shown in the picture.

This is probably the first time I feel that I can actually contribute to this forum instead of always asking for help.

[Dave72dt]

Askig questions is also a valuable contribution. Exposing problems that other may have but are afraid to ask helps everybody, especially when the problemis solved and relayed on to others.