On 8 Mrz., 04:30, Brian Bange wrote:
I just towed my new (to me) Cobra for the first time and when I
brake even moderately, the tires lock up on the trailer, then let
go, then lock up in a repetitive cycle of about 3Hz. What do I
do?

Brian

HGi Brian
In your case, most likely the wheels are too big in diameter.
Overrunning brakes are a self regulating system, and they are servo-
sustained.
Self regulating means, that a trailer with a certain weight needs a
certain diameter of the brake drum and a certain diameter of the
wheels.
The dynamic wheel diameter for a trailer with wheels with 4 bolts can
be between 572 and 602 mm, so the difference between minimum and
maximum diameter is just slightly more than one inch.
The dynamic wheel diameter is the diameter with 100 km/h ( about 60
miles an hour.) Here the wheel is about 12 mm( 1/2 inch) more in
diameter as the trailer resting.
As mentioned before, the brake is servo sustained. This is done with a
certain position of the brake shoes inside the brake drum. So, a
certain amount of the
force of the turning wheel is used to sustain the brake force.
If your wheels are too big in diameter, this servo system just
receives too much force from the wheel and overreacts, blocking the
wheel. This means no force anymore to the servo brake, = brake opens.
Wheel turns again = too much force to the servo brake = blocking
again.........
If you tell me the wheel size you currently use and if you have a
brake drum with 4 or 5 lugs, I can give you some advise
The whole system is designed to work perfect at 90 % of the maximum
weight of the trailer. It will run up too light and brake too weak at
50 % and it will run up hard ( and brake weak again ) with 100% of the
trailers maximum weight.
Alfred