New Trailer Coupler Takes Off With a Clunk

[isaacs]

Last year I fitted my 2002 single axle trailer with a new new Demco surge brake coupler; this is a replacement for the original one made by Titan.

Everything works fine except every time I leave a stop sign or traffic light the coupler bumps or slams itself back into its "non breaking" normal position. My old one did the same thing and eventually bent the bolt that it slides on making it dangerous to use so I replaced it. I know there's an adjustment with a spring on it but the instructions say to not touch it.

Does anyone have a solution for this? Thanks, Bob

 

[76SeaRay]

I have the Titan one (1976 model) and rebuilt mine. I don't remember a spring adjustment but there are two shock absorbers in mine. I think the idea is that they never really get fully compressed so there is little motion when you take off. Since this is a new coupler, I am going to guess that you do not have enough brake fluid or there is air in the brake lines.. I would start there..

Mine was a pain to bleed the brakes and get all the air out.. There is usually a small orifice in the back of the master cylinder that only lets a little brake fluid at a time so it is hard to compress the cylinder to force the fluid in and air out.. I had replaced everything new on mine including brake lines and the brake assemblies.. I wasn't in a place where I could offload the boat to work on the brakes but that would make it a lot easier.. Mine was doing what yours is doing until I rebuilt it...

 

[Alumarine]

Like 76searay said sounds like there's no fluid or air in the lines.

When it's disconnected from the vehicle try and operate the mechanism by hand.

If it's easy to operrate there's a problem.
I take the ball mount off the vehicle and use that with a pipe to give me more leverage.

 

[isaacs]

When I put the new coupler on, I used the breakaway lever with a pair of vice grips to do the bleeding. I pumped a ton of brake fluid through the system and I was careful not to allow any air to enter the system either from the master or slave cylinders. My goal was to purge all the old fluid out of the lines and cylinders and it seemed to work.

However, after reading your posts I'm wondering if my brakes are worn or out of adjustment; the extra brake shoe travel required at the wheels would translate into a lot of travel at the master. Thanks alot guys, you just gave me a bunch of work to do! Why do I get this funny feeling that by the time I'm finished I'm going to have a whole new brake system? Would new disk brakes require a different coupler?

 

[Alumarine]

On some couplers you can add a fitting for disc brakes I believe.

Try adjusting your brake shoes and see if that helps.

It can be difficult to bleed brakes by yourself unless you use the right procedure.

 

[isaacs]

On some couplers you can add a fitting for disc brakes I believe.

Try adjusting your brake shoes and see if that helps.

It can be difficult to bleed brakes by yourself unless you use the right procedure.

Yup, I'll try adjusting when I feel up to it. Hopefully the adjusters aren't all rusted up.

 

[Horigan]

...Would new disk brakes require a different coupler?

Disc brakes typically need a different master cylinder with a different piston diameter. The coupler will also have a backup solenoid valve to block the pressure when backing up (triggered by your reverse light power). If you go the disc brake route, I would recommend a version with a three port solenoid that blocks master cylinder pressure AND ports the brake system pressure to the reservoir. This is required if you have to back uphill.

However, I would try adjusting the shoes first. This should make a vast improvement in clunking in my experience if the shoes are out of adjustment.

 

[76SeaRay]

I really had to pump my cylinder hard (pry it actually) due to the orifice fitting in the back of the master cylinder that only allows a very small fluid jet through at a time. Took a long time to bleed them. Make sure you have that orifice fitting if it calls for it since that controls how hard and quick the brakes set up. Relative to the backup solenoid, there are new surge brake backing plate assemblies that do not set up automatically when you back up so you might want to consider those if you do a full brake job. I put those on mine instead of using the back up solenoid. They seem to work fine on my trailer (tandem axle for a 22 foot boat so has some weight to it).

 

[Chris51280]

I have the same setup and used a vacuum gun at the brake. You have to do switch sides a couple of times since there is a t off. Make sure you don't suck the reservoir dry and keep filling it. Also, do you have the one with the free backup system? I don't have to put a pin in mine when backing up. Make sure your brake shoes are adjusted.
I would start by taking the drum off and inspect the cylinders. I had to change mine.