The Stovebolt Site Forums The Shop Area Driveline 1955 GMC drum brake problems

Hi everbody

I am from Hamburg Germany and I got a problem with my rear drum brakes and my parking brake hope that somebody is able to help.The truck is original except the Heidts Mustang II front suspension with disk brakes and a new master cylinder with 7” dual booster.

1. During city cruises under warm weather condition my rear drum brakes are chafing / a bid slightly braking sometimes more or sometimes less, I disassembled both brakes cleaned them and reassembled but no help , I checked the function of the springs and the brake cylinders but found nothing

2. The parking brake is uneven braking and I missed the 2 years road check/ inspection sticker( in Germany the car needs every two years a check to be street legal). So I lift the rear and adjusted the park brake cable , with park brake handle two notches pulled and both sides start to brake but that did not solve the problem of uneven braking , I did this two times but it was both times the same result.
I attached some pictures to see the drums removed and my installed master cylinder


Hope that somebody could help to trouble shoot .

Thanks Giorgio

Hy Giorgio, welcome, could you tell us if your master cylinder was originally designed to be used in a disc/disc, disc/drum, or drum/drum braking system? When you installed the master cylinder onto the brake booster did you make sure there was a clearance between the master cylinder piston/plunger and the booster pushrod while the master cylinder was fully at rest?

I'm noticing a couple of things.


1) There is no wear pattern on the shoes. Have they been engaging the drum?
2) The adjuster doesn't look like it has been adjusted?
3) Are the front brakes plumbed to the "Front" output on the proportioning valve?
4) Is it possible that you are boiling brake fluid because the assembly isn't shielded from the exhaust pipe?

Hi
the master cylinder was bought and installed by the previous owner , i do not know how to identify which kind of master cylinder is installed.


and Marc

1) yes they have engaging the the drum
2) foto is before first disassembling the adjuster moves freely now
3) I have to check now we got storm and could weather conditions , i will do when the weather is better
4) I have installed super 44 exhaust that ends below the cab and is electrical controlled and I got the brake problem also when the supper 44 is switched on and the exhaust pipe near the master cylinder is only bid warm and the boiling point of my used barke fluid is 240°C

I agree that it appears as though the rear shoes have not been rubbing the inside of the drum. That adjuster is not turned out as far a I would expect to see

You should adjust the service brake function using the star wheel adjuster before you adjust the parking brake.

I do not know this tool could you send me a picture or a link, please?

Here is a link for a drum brake adjusting tool from Amazon. [Link]

Here is a link for the “1955 Chevrolet Truck Shop Manual” for adjusting your brakes. Your ‘56 will be the exact same as the ‘55.
http://chevy.oldcarmanualproject.com/shop/1955truck2/55ctsm0510.htm

Thanks a lot Phil for the manual and the link. I will try to find the tool in Germany, if not I can make this tool if I know the width of the measurment bracket ( its very easy if I got all measurements)
As I read the width is 1 7/16" so 35,56mm , right?

They were probably telling you the measurements of the packaging and not the actual tool. The tool is double sided, one side straight and the other side bent to aid access to the star wheel. Each side basically looks like the blade side of a large flat blade screwdriver. It”s about 12-15 mm wide and about 180 mm long. I have used a large flat bladed screwdrivers before but the tool makes it easier.

The tool is just a standard brake adjustment tool. We in the US can buy them in any auto parts store so I’m sure it shouldn’t be hard to find. Good luck!

Giorgio, brake adjusting “spoons” are available at every place that sells tools, including every auto parts store. Not a rare tool at all.
Phil’s fingers work faster than mine.

Just a note: you may need to free up the adjuster. I just removed one of my front drums and had to pry it off the shoes, as the adjuster had frozen and wouldn't move as I tried to loosen it. Pull the spring off and take the adjuster assembly off and clean/lubricate it (not too much oil).

I use anti-seize lubricant very sparingly on the adjuster thread and the stub shaft that goes into the other side, but avoid getting any on the outside of the adjuster so it doesn’t get on the brake shoes. Been doing it for years with great results.

I found the tool but not at our auto part stores ,I found on Ebay Germany.I thought it is a gauge but it is a tool to turn the adjuster.
Thnaks a lot to you both.

The springs seems to be weak but as I looked for new ones I found them only in the states with 50 $ shipping costs, are these springs in my drum brakes not used in many truck and cars over years or are they so special ?

To be able to find the springs in Germany could give me the information in which other cars and truck they are used , I looked on rockauto because they are always cheap in shipping costs to Germany but they do not have a hardware kit for the 1955 GMC truck and all other pictures of hardware kits the springs in the 50's looked different.

As i have the new springs in hand I will disassemble the brakes again and clean and grease the adjuster until its easy working.

Thanks guys for all this informations.

Giorgio

Brakes for your truck are the same for GM trucks up into the early '70's. But unless the springs drop out or don't take much effort to remove, they're probably OK. I don't see an issue from the pics you posted.

If you really need them, put a post in the parts wanted forum here, and maybe a fellow Bolter has some to spare that he'd be willing to mail to you.

[on edit] AC Delco 18K1597 hardware kit from RockAuto should fit your truck. The adjuster springs look a little different, but should work fine. Not bad pricing at a little over $6 for both rear brakes.

Thanks for the information , I will order it its not a huge price.
As soon as it is a above 15°C in Hamburg I will have a look on my brakes.

Thanks a lot Kevin