Partial braking action

[Ahzmyrah]

I recently purchased a 1980 31 Excella and as part of getting it ready for use took it in to an RV service center to have the brakes checked and wheel bearings repacked since I did not know what they were like and wanted a baseline good feeling about taking it down the road. Turns out one wheel bearing race had spun because of lack of lubrication and the bearing and hub had to be replaced. The drum brakes showed wear on the riveted linings within 1/16" of the rivet heads so I replaced them as well. The problem is: When the brakes are applied you can feel the initial actuation but no additional braking force as the brakes are applied stronger. Pushing the actuator lever on the brake controller has the same effect, initial application and thats it no stronger braking action even with the lever pushed to its limit. The RV service tech has applied 12 volts directly to the brakes individually and they still only partially engage. Any ideas why this is happening? We have checked grounds, voltages, continuity, etc. Could all the brake magnets fail at the same time? The brakes are adjusted properly, could the shoes be installed wrong? Help!

[nickcrowhurst]

If someone had pulled the breakaway pin, and left it out for an extended period, this could have damaged all the electro-magnets through over-heating. ( I am only quoting what I have read. I have no direct experience of this) I would try one replacement magnet on a wheel to see if that works. If you still have a problem I would install one complete back plate assembly with new shoes and magnet, so as to give you a firm basis for further step-by-step investigation. One possibility, and I have experienced this, is that the Dexter parts manual incorrectly gave the part number for Excella brake shoes, and I wasted many hours attempting to get the wrong shoes to operate.
Nick.

[Ahzmyrah]

Thanks Nick - I'm not doing the work myself. (No place level enough on my property to jack and work on a 31 footer) The technician was going to try a new magnet on one wheel and see what happens. Also when something works until you start fixing it, it has to be something that was done in the fixing. I will follow up on possible use of wrong brake shoes. The Airstream manual for my unit says they are Kelsey-Hayes brakes so maybe we have a brand mix up causing the problem. We should be able to compare the looks and size of the old and new units and tell.

[HowieE]

Dwyer and Tekonsha each make a clip on amp meter that is great for checking brake current. You have to measure the current going to the magnet not the voltage.

If you clip the meter on each individual wire that goes to each brake you will see the current and can watch it as you ramp up the controller.

A good magnet should draw just above 3 amps at full application.

If you do see full current and still don't have good brakes I would look to make sure the shoes are in fact seated to the drumbs completely. New shoes often ride on high spots until the ware in. Way back in an earlier life we used to grind the shoes to fit the drumbs. No longer something about asbestos.

[axleman]

Originally Posted by HowieE

New shoes often ride on high spots until the ware in. Way back in an earlier life we used to grind the shoes to fit the drumbs. No longer something about asbestos.

In the Axle business this is called "burnishing in" (breaking in the shoes).

Once the shoes and drums are heated from use several times (we used to say 50 miles or so) they conform to one another and breaking is greatly improved.

The meter is a great tool to check amperage as mentioned, this may help explain the partial engagement, if less than 3 amps is noted!

Regards,
Henry