HELP!!! Hellish problem with my trailer brakes.

[Stableduck]

Years ago I ran across a few cars and even my own truck that would lock up the rear (drum) brakes when first few stops, more so in damp conditions.
I changed the shoes out even though they looked new and it corrected the problem.
The materials used in the linings will brake differently

[keymastr]

Since the Tekonsha P3 is a proportional controller it uses inertia to activate the trailer brakes. There are specific mounting instructions on how to orient the controller so that it can sense the inertia change when you use the tow vehicle brakes. Just wondering if mounting it flush in the dash rather than the suggested vertical mount on the lower surface of the dash has anything to do with it. Maybe mounted in that way makes it think bumps are you hitting the brakes making them activate.

It's been awhile since I read the manual so not sure what they say about that.

[rodbuilder]

No, everything is ok in the "binding" department. Nite Eqpt in Pecatonica suggested that maybe the hoses are getting pinched, but my response to that is: If I hit the brakes and the fluid isn't being allowed to go back to the actuator, then why does it release when I back up.

And IF the hoses are getting pinched by the frame, please know that I have about 2500 miles on this new brake setup. I've hauled FIVE skid loaders on it!!! If a all 4 hoses were being crushed by the frame, how could they POSSIBLY survive and not get cut in two? They haven't because they all hold fluid!

It just doesn't make any sense!

I'm done messing with the darned thing! I'm going to let them mess with it on the 29th.

[rodbuilder]

Originally Posted by keymastr

Since the Tekonsha P3 is a proportional controller it uses inertia to activate the trailer brakes. There are specific mounting instructions on how to orient the controller so that it can sense the inertia change when you use the tow vehicle brakes. Just wondering if mounting it flush in the dash rather than the suggested vertical mount on the lower surface of the dash has anything to do with it. Maybe mounted in that way makes it think bumps are you hitting the brakes making them activate.

It's been awhile since I read the manual so not sure what they say about that.

I argued with the guy who installed it about that. HE wanted to mount it VERTICALLY on the right side of the dash!!! This guy has been in the trailer business for 25 years! I wouldn't have any part of his stupidity! I already had the square pocket cut out in the dash of my 2011 Chevy so it would fit in there and instructed him to do it MY way..................which was clearly stated in the instruction manual as well.

But the controller has NOTHING to do with my preset problem. You could run the brakes with the breakaway switch and they would still lock up until you back the trailer up!!

I am convinced that the problem is mechanical - not hydraulic, or electric.

[dayle1]

Yes it is not likely a pinched hose. But still worth pointing out that when applying the brakes, you have a 1200 psi pump to force the brake fluid into the wheel cylinders, overpowering the return spring and forcing the shoes against the drum. But when the brake pedal is released, the return spring is the only force available to release pressure.

Hope you post the actual solution after the 29th.

[JoeSR]

Rodbuilder,

Is there any chance that you have the brake assemblies on the wrong side of the axles?

From your picture, it looks like the wheel cylinder drives the secondary shoe and not the primary shoe. On all drum brakes that I have touched, the secondary shoe is smaller than the primary. The secondary shoe should be to the rear.

My drum brake knowledge is pretty old. So, take what I said with a grain of salt.

[Stableduck]

Originally Posted by JoeSR

Rodbuilder,

Is there any chance that you have the brake assemblies on the wrong side of the axles?

From your picture, it looks like the wheel cylinder drives the secondary shoe and not the primary shoe. On all drum brakes that I have touched, the secondary shoe is smaller than the primary. The secondary shoe should be to the rear.

My drum brake knowledge is pretty old. So, take what I said with a grain of salt.

It been years for me also, but I believe the brakes pictured where call self actuating.
As you apply the brake the wheel cyl pushes the primary shoe out contacting the drum which rotates into the secondary shoe (the long one) and pushes it against the anchor pin. Sort of wedging it in the anchor pin and the drum.
Which is why these brakes do not hold as well in reverse as the do in forward. (Old park brakes you could back up with them applied but not go forward)
That is why I mentioned possible brake lining issue or drum surface holding the shoe in the wedged position until it is backed up.
Just my 2 cents

[Old-Biscuit]

Originally Posted by JoeSR

Rodbuilder,

Is there any chance that you have the brake assemblies on the wrong side of the axles?

From your picture, it looks like the wheel cylinder drives the secondary shoe and not the primary shoe. On all drum brakes that I have touched, the secondary shoe is smaller than the primary. The secondary shoe should be to the rear.

My drum brake knowledge is pretty old. So, take what I said with a grain of salt.

Primary shoes are 'smaller' and go forward facing
Secondary shoes are the 'larger' ones.

[keymastr]

This may have no bearing but I know with my boat trailer the hydraulic surge actuator had a part that had to be changed if you went from disks to drums or vice versa or the brakes would lock exactly as you have stated. Maybe there is something in your system designed for disk brakes and it does not play well with your drums.

[KCFDCapt]

It sounds like the secondary shoe is wedging to the drum and not releasing. Remember the old parking brakes that used a lever to apply the rear shoe? They worked great to keep a car from rolling forward but were very poor at keeping it from rolling backwards. How many time have you backed out of a parking space only to find you had not released the parking brake when you tried to roll forward?

OK, enough of the history, now for the help. Things to check. Why is the rear shoe not returning to its travel position? Two things will prevent it. Hydraulic pressure and the other is binding linkage. Hydraulic pressure is easily checked by unscrewing a line at a connection - just like bleeding brakes. No pressure and still locked up? Must be mechanical.

If it is mechanical, check for obvious bend parts or linkage. Are all pivot points lubed and free moving? Can the shoes move their full travel without binding? The coils on the return springs should have space between the coils when properly installed. Have the return springs been reversed - the front spring on the rear shoe so there is not enough tension to pull the rear shoe back into position?

These are just suggestions of things to check before using the check book to fix the problem. Good luck on finding the problem and getting things running right.

[rodbuilder]

Originally Posted by Eric_H_E

I'm no master Mechanic and I am trying to learn. Is it the correct pump for drum breaks?

On second thought, if a hydrolic line is pinched or kinked, the pump is high pressure and can push the fluid by, but the spring does not have enough force to push back?

Ans: # 1 PLEASE don't uses that non-word "hydrolic" again!! (see the red line under it when you type it?) The word is hydraulic!! #2, Pinching of the hoses is the ONE point I've talked about with professionals that I considered, but I just don't think it's an issue because this new system has traveled about 3,000 miles so far and with that many miles on I would think that rubbing against the frame would have rubbed a hole through the rubber hoses by now. And if it was the cause why would the brakes release ONLY when i back the trailer up? It just doesn't make any sense! I''ll find out on the 29th when I have someone look at it in person.

On third thought, it sounds like with axles suspended it works as it should. When on the ground does not release. Suspension compressed kinks break line and thought 2 comes into play.

Ans: I wish I had 2 more jack stands so I could check it out this way!!!

[rodbuilder]

Originally Posted by Old-Biscuit

All of them locking up?

Piston forces Primary shoe outward which then levers secondary shoe out.

Fluid in wheel cylinder SHOULD flow back when braking is off by force of return spring
Which I bet it does........but secondary shoe is staying engaged against drum until you backup.

Have you disassembled one wheel braking assembly and checked for any 'friction/scouring' marks ---backside of shoe, face of backing plate etc

Got to be binding

What does inside of drum surface look like...any ridges?

Yep - only happens when the trailer is on the ground and moving. The drums look like new and are the ONLY parts that aren't new.

I'm going to have a shoo check out whether the lines are getting crushed by the frame but I REALLY don't think so because I took car to size up the clearance possibility before ordered the hoses.

This is a late model B&B 22 and 1/2 foot tilt bed and I wouldn't let even my ex wife buy one of these things, the way they are made. The "frame" is made out of 2"x4" tubing with a piece of 1/4" plate welded vertically under the 2x4 to reinforce it! Clearly an amateurish way to build a trailer frame, in order to make them as cheap as they possibly can. I could go on with this and talk about the hitch, lighting system etc., etc., but I'll stop there.

[twinboat]

My guess is that the check valve in the master cylinder ( used with drum brakes ) is holding to much back pressure. When you back up, the extra force on the primary shoe pushs the wheel cylinder in and open it.

Take the check valve out as a test. It should be in behind the brake line connection fitting, on the master cylinder. If the brakes don't lock, replace it with new.

If it still happens with a new check valve, get tougher return springs.

The check valve is in the drum brake system to keep some back pressure on the wheel cylinders, so they don't retract to far. If they retract, the first stroke of the master cylinder is wasted refilling them.

Disk brakes don't use them. The tight caliper seals hold the pistols in place.

[Old-Biscuit]

Originally Posted by twinboat

My guess is that the check valve in the master cylinder ( used with drum brakes ) is holding to much back pressure. When you back up, the extra force on the primary shoe pushs the wheel cylinder in and open it.

Take the check valve out as a test. It should be in behind the brake line connection fitting, on the master cylinder. If the brakes don't lock, replace it with new.

If it still happens with a new check valve, get tougher return springs.

The check valve is in the drum brake system to keep some back pressure on the wheel cylinders, so they don't retract to far. If they retract, the first stroke of the master cylinder is wasted refilling them.

Disk brakes don't use them. The tight caliper seals hold the pistols in place.

twinboat.......
Think you are on to something !!!

Forgot all about that dang check valve used ONLY on drum brakes

Boy that sure would explain the hydraulic pressure holding brakes until more force from backing up releases them


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