M400 Rear Brake getting hot

lip · January 19, 2018, 03:11 PM

Hello!
I've done my rear brakes, new brake cylinders, new springs, new adjuster cable, new adjuster. Just the drum and the shoes stayed in because they were still in good shape.
After reinstalling, I had an issue with the right side. When I installed it, I adjusted the brakes to be easily turned by hand. After a few miles the right side was getting hot. I mentioned that the adjuster tightened the brakes till they got stuck. When I turned the starwheel back from behind, the wheel got free again. I marked the starwheel position, made a trip of a few miles and the starwheel was turned by the adjuster arm and the brake was stuck again.
Any ideas what could be wrong? Maybe the adjuster arm is not bent correctly. Is there a manual how the adjuster arm has to touch the starwheel?
I hope you can understand what I mean.
Thanks for your help.
Best regards from Germany.
Lloyd

Rickf1985 · January 19, 2018, 05:21 PM

Does this have the emergency brakes on the rear wheels and if it does is that adjusted correctly?

DaveVA78Chieftain · January 19, 2018, 06:54 PM

Did your rear brake setup look like this:

Bendix Duo-Servo Brakes

or like this:

Bendix Twinplex

postman · January 19, 2018, 10:45 PM

Quote from: DaveVA78Chieftain on January 19, 2018, 06:54 PM
Did your rear brake setup look like this:

Dave which one do you have?

DaveVA78Chieftain · January 19, 2018, 11:47 PM

Bendix Twinplex was used on the early M-400 (RM-350) chassis that had dual Hydro-Vac boosters

Bendix Duo-Servo was used on the later M-400 chassis that had the Hydroboost system (like mine)

postman · January 20, 2018, 12:14 AM

AW! Come ON! two bleeders!

Me thinks it is near better to get kicked in the head by a fresh shoe'd mule!

Guess i be lookin tomorrow.

lip · January 20, 2018, 08:05 AM

Dave, I've got the Bendix Duo-Servo Brake - first pic! Parking Brake is well adjusted!

Rickf1985 · January 20, 2018, 09:21 AM

My next question would have to be was the parking brake adjusted before the service brake? If the service brakes are adjusted up first then the parking brake will not adjust out far enough without brake drag. It is also a possibility that the shoes are worn worse at the top than at the bottom from going too long without adjustment. New shoes may be in order. The last possibility is that the drums may be worn beyond limit, have you had them measured? Something is causing that top of the shoes to travel too far which is causing the adjuster to keep doing it's thing.

lip · January 20, 2018, 09:42 AM

Is it possible, that the adjuster arm is bent so it is turning the starwheel where it should not?

DaveVA78Chieftain · January 20, 2018, 09:50 AM

Left rear side (USA Drivers Side) view. (USA Passenger Side) Right rear side would be a mirror image (e.g parking brake lever and adjustment assembly is mounted on the rear half of the backing plate).

When the operator steps on the brake pedal, pressure applied by the hydraulic wheel cylinder pushes the upper parts of the shoes outward. The primary shoe wedges against the rotating drum while the drum tries to pull the shoe along with it. This self-energizing action pulls the shoe even more tightly against the drum, multiplying the braking force.
As the primary shoe shifts inside the drum, its lower "foot" pushes against the adjuster, applying force to the secondary shoe and forcing it outward against the drum.
This, combined with the action of the rotating drum, forces the top of the secondary shoe against the anchor post, which stops the shoes from rotating further and binds them more tightly against the drum.

This shoe "rotation" allows the adjuster cable to pull up on the adjustment lever that turns the star wheel. As the shoes "wear" the "amount" of shoe rotation increases thereby "increasing" the amount of "distance" the adjustment lever travels. This results in the star wheel turning which increases the length of the adjuster which "reduces" the length of shoe travel. This automatic adjustment based on shoe wear and adjuster compensation maintains a balanced condition. If the components are not in their proper placement anywhere on the assembly or are not moving freely, improper operation results. Almost forgot, this adjustment operation is more prevalent when the rig is being driven in reverse as the adjustment assembly at the bottom is pulled away farther from the anchor point of the adjustment cable.

I do not recall for this specific application, however for many applications, the "Primary" shoe (facing front) braking surface is longer then the "secondary" shoe (facing rear) braking surface.

That's how it works and Rick indicated some things that may prevent it from operating properly.

For reference, while not applicable to your front disk brake application, here is the front lefts side assembly view (no parking brake) for any application that used it (does show the components behind the parking brake lever more clearly):

FYI: Parts info at the bottom of my description web page: http://dave78chieftain.com/M400_76.html

Rickf1985 · January 20, 2018, 02:53 PM

The adjuster arm should be basically flat so it is more lifting up than anything. The only bend I could think of that would cause it to do what you are saying is if the part that contacts the star was bent under the star and was pulling out instead of up. This would have to involve a lot of bent parts in addition to that arm for it to be able to get down low enough for that to happen. And those arms just don't bend easily, you need a hammer to bend one.

RANGERRICK · January 20, 2018, 07:19 PM

If you did remove the brake shoes did you put them back in the correct spot.In most cases their is a secondary shoe and a primary shoe.

postman · January 20, 2018, 08:26 PM

Pic of my passenger side rear backing plate

postman · January 21, 2018, 02:21 PM

Anyone have a recommendation about a manual with comprehensive instruction on M400 Bendix Duo Servo brakes?[size=78%] [/size]

DaveVA78Chieftain · January 21, 2018, 02:28 PM

Dodge Service Manual

turbinebronze · January 21, 2018, 06:26 PM

This may sound silly but I think the adjusters are right side and left side specific. If the wrong side adjuster was installed, it could automatically adjust the brakes while driving....
(if I remember right...it's hell getting old.)
Just my 2 cents, Craig.

DaveVA78Chieftain · January 21, 2018, 07:30 PM

Quote from: turbinebronze on January 21, 2018, 06:26 PM
This may sound silly but I think the adjusters are right side and left side specific. If the wrong side adjuster was installed, it could automatically adjust the brakes while driving....
(if I remember right...it's hell getting old.)
Just my 2 cents, Craig.

Yep, that's why I list separate P/N's on my web site