Locking trailer brakes causing control issues?

[brian_bp]

A discussion of the risk of problems with locking of the brakes on the trailer started in another topic (Towing prep package - photo request, in the 1998 - 2003 1st Generation Toyota Sienna section), and I think it deserves its own topic here in Towing & Hauling, since it is not specific to any generation.

[brian_bp]

If I recall correctly, there have been past problems with synchronizing the Sienna brakes with some trailers that have non-ABS braking systems. I have heard that some add-on trailer braking systems seem to cause more braking problems than they should by locking up the trailer brakes since the Sienna and trailer do not share the same brake cylinder. I wonder how the Sienna's ABS brakes work with non-ABS brakes on trailers with the trailer brake controller.

While there are many trailers with ABS, they are generally large commercial rigs with air brakes; I think it is reasonable to assume that anything towed by a Sienna does not have ABS. If anyone is aware of an exception, I would be interested to hear about such a system.

Some vehicles have built-in controllers for electric trailer brakes; this is generally just Ford, GM, and Dodge full-sized pickup trucks with optional towing packages, and in some brands only in heavy-duty models (F-250/2500 and up). Everyone else uses an add-on aftermarket controller, and that includes all of us with Siennas who have controllers. Aside from a couple of very obscure designs, add-on aftermarket controllers have no connection to the tow vehicle's braking system, other than a brake light signal.

There are electric brake controllers which ramp up braking power on a timed basis, entirely without regard to the actual deceleration of the vehicle. These cheap pieces of junk should never be used, and could indeed cause lockup or inadequate trailer braking problems; I'll assume that anyone driving a Sienna can afford a few dollars more for one of the most common current brake controllers, which would be any brand of proportional design.

Proportional controllers brake in proportion to how hard the tug is braking. Virtually all proportional controllers, such as the very common Cequent/Tekonsha Prodigy series, work on an inertial basis: they measure how rapidly the rig is decelerating, and brake the trailer in proportion so it does its share. There is no connection to the tow vehicle (Sienna in this case) braking system, except a wired signal from the brake lights, so that the controller only acts when the brake pedal is pressed. There is no issue of coordinating the Sienna's ABS system with the trailer, since it is irrelevant whether or not the Sienna even has ABS.

The brakes on a trailer are unlikely to lock up under any road or driving condition when using a proportional controller, because it only applies trailer braking force in proportion to how hard the Sienna is stopping; if there is inadequte traction for a hard stop (so the ABS needs to act), the whole rig does not stop hard, and the trailer brakes are not applied strongly.

[brian_bp]

Is uneven trailer braking a mechanic installation error, an ABS/non-ABS brake incompatibility, or a OEM design flaw? I don't know...

With a proportional controller, and reasonably working trailer brakes (e.g. not sticking on), the only factor left is setting the sensitivity (also known as gain) of the controller. It is easy to set, and once set needs no change as long as the trailer weight is approximately the same.

As I mentioned before, ABS is unrelated; I'm not sure what kind of design flaw is being contemplated.

[brian_bp]

I believe the general intent of a Sienna driver should be to safely slow the trailer being pulled, but locking the brakes on the trailer or Sienna could cause the trailer to sway and become unstable.

I agree. Locking the trailer brakes would be bad.

This is why I installed the Air Lite Suspension Air Kit - to enable better handling and stability when driving the Sienna and trailer.

I agree that adequate suspension is important to control, but I don't see how it would substitute for adequate braking, and even the best suspension cannot overcome the control challenge of a ton or two of unbraked trailer pushing the rear of the tow vehicle... and pushing it sideways if the Sienna and trailer are ever anything but perfectly aligned in a straight line when braking.

Yes, it will likely take a longer distance to slow the Sienna and trailer, but I feel our setup is safe for my needs.

To me, this is like noticing that rear-brake lockup in a vehicle without a trailer causes more control difficulty than front-brake lockup, and thus deciding to disconnect the rear brakes... :o it takes longer to stop, but stops will be straighter. This is not a whimsical comparison; I'm serious.

[brian_bp]

Okay, that's enough talking to myself...

discussion?