Sudden jerks from trailer brakes

[T and C]

Sometimes this forum amazes me. During my last trip I encountered a new situation that had me worried and completely at a loss to explain. I had just towed my TM over the Donner pass and down to Sacramento on I-80. I turned onto an off ramp to switch to US-99. It was one of those ramps where you circle around 270 degrees to enter the slow lane of the new road.

Suddenly there was a sharp jerk from the rear of the truck or trailer. I immediately pulled over to check out the trailer. I had no idea what had caused it. I evaluated some possibilities:

1. I had run over something on the road. However, there was nothing on the road behind me and nothing dragging under the trailer.

2. I had hit a pot hole. But there weren't any. I had stopped in a wide place at the base of the off ramp and could see most of it.

3. I had dropped a wheel off the pavement. However, there was a wide, paved shoulder on the ramp so that could not be it.

4. I had a flat. But a check of the tires showed that the tires were ok.

Needless to say I was puzzled by this. A CHP officer pulled up behind me and we discussed all these possibilities and he agreed that there was nothing on the road, etc..

The one common factor was that the four times that this happened over a one week period of towing was that I was on a tight curve every time. Once on the off ramp, once driving up to the Yosimite area, and twice in the Kern River canyon going up to Lake Isabella from Bakersfield.

I went on line this morning to ask the other members for help in figuring this out. I decided to read the new posts first, and then I read this:

Originally Posted by PopBeavers
On my 3008 GMC 2500HD truck, when tow haul mode is engaged and the ABS brakes activate, the on-board computer in the truck pulses the electric power to the trailer brakes.

I call this virtual ABS.

Not all tow vehicles have this feature. My 2002 Chevy 1500HD does not.

My Ford F150 has a version of this. It is part of the anti sway feature. It will automatically apply brakes on one side or the other to bring trailer sway under control.
__________________
2006 TM 3023
2010 Ford F150 SuperCrew FX4

I'll bet that is it. I also have a 2010 F-150 with the sway control feature. When I go around sharp curves the truck computer thinks the trailer is swaying and activates a brake on one side. The "jerk" only lasts for a second or so, and once it did it twice in succession, real fast.

Do you think I'm right? Or not??

And thanks to PopBeavers and MHatcher.

Tom

[T and C]

Here's another factor in this puzzle: When the anti-sway control is on, how does the truck computer know the position of the trailer??

Tom

[Mr. Adventure]

Originally Posted by T and C

Sometimes this forum amazes me. During my last trip I encountered a new situation that had me worried and completely at a loss to explain. I had just towed my TM over the Donner pass and down to Sacramento on I-80. I turned onto an off ramp to switch to US-99. It was one of those ramps where you circle around 270 degrees to enter the slow lane of the new road.

Suddenly there was a sharp jerk from the rear of the truck or trailer. I immediately pulled over to check out the trailer. I had no idea what had caused it. I evaluated some possibilities:

1. I had run over something on the road. However, there was nothing on the road behind me and nothing dragging under the trailer.

2. I had hit a pot hole. But there weren't any. I had stopped in a wide place at the base of the off ramp and could see most of it.

3. I had dropped a wheel off the pavement. However, there was a wide, paved shoulder on the ramp so that could not be it.

4. I had a flat. But a check of the tires showed that the tires were ok.

Needless to say I was puzzled by this. A CHP officer pulled up behind me and we discussed all these possibilities and he agreed that there was nothing on the road, etc..

The one common factor was that the four times that this happened over a one week period of towing was that I was on a tight curve every time. Once on the off ramp, once driving up to the Yosimite area, and twice in the Kern River canyon going up to Lake Isabella from Bakersfield.

I went on line this morning to ask the other members for help in figuring this out. I decided to read the new posts first, and then I read this:



I'll bet that is it. I also have a 2010 F-150 with the sway control feature. When I go around sharp curves the truck computer thinks the trailer is swaying and activates a brake on one side. The "jerk" only lasts for a second or so, and once it did it twice in succession, real fast.

Do you think I'm right? Or not??

And thanks to PopBeavers and MHatcher.

Tom

My $.02:
1) A manual pulse of the trailer brakes (with the controller lever) is an old anti-sway maneuver they used to tell you about.
2) The traction control system in the tow vehicle both senses the varying speeds of individual wheels and uses brake pulses to help you regain control. It's possible that the slower speed of the inside wheels suggest a skid condition mandating a brake on the outside wheels to compensate (I once discovered a low tire on a front wheel after the traction control system pulsed for no otherwise explainable reason).

An easy way to test this would be to go around the whole cloverleaf to successfully duplicate the situation, then switch off traction control and try again.

My owners manual does not specify anything about left versus right side.

At any rate, this can only be measured in the truck. I doubt that the TM with the Bargeman connector relays this level of information back tot he truck.

I have never had this experience.

Either:

1. I just have never been in that situation.

2. GM does not have this feature, but Ford does.

fwiw, I don't use my brakes as much as I used to in this situation. The transmission automagically down shifts when I press the brake. Once automatic down shift is engaged, I frequently no longer need the brakes for the turn, unless I approach an obstacle.

[MudDog]

I once had the emergency break-away connector pull out on a tight turn, which immediately applied the brakes on the trailer.

Since them I'm more careful about how I route the break-away cable to make sure there is enough loose slack for tight turns in both directions.

I'm not sure how sensitive the break-away controller is. Could enough slack be taken up to start pulling the plunger out, but then before it pops out completely enough slack is given back and it stays in?

[ShrimpBurrito]

Originally Posted by MudDog

I once had the emergency break-away connector pull out on a tight turn, which immediately applied the brakes on the trailer.

Since them I'm more careful about how I route the break-away cable to make sure there is enough loose slack for tight turns in both directions.

I'm not sure how sensitive the break-away controller is. Could enough slack be taken up to start pulling the plunger out, but then before it pops out completely enough slack is given back and it stays in?

This is exactly what I was thinking when I read this thread, as I too have had this happen. If what you are experiencing is happening consistently when you turn in one direction and not the other, then I would pay particular attention to this possibility.

Of course, as Mud Dog/Jim speculates, is it possible the plunger pulls out just slightly and then goes back in? I don't know. When mine pulled out, it stayed out until I pressed it back in.

Dave

[T and C]

Originally Posted by ShrimpBurrito

This is exactly what I was thinking when I read this thread, as I too have had this happen. If what you are experiencing is happening consistently when you turn in one direction and not the other, then I would pay particular attention to this possibility.

Of course, as Mud Dog/Jim speculates, is it possible the plunger pulls out just slightly and then goes back in? I don't know. When mine pulled out, it stayed out until I pressed it back in.

Dave

I thought about the break away plunger the first time it happened. I inspected it and it seemed to be in the normal position. There was/is plenty of slack in the cable. Now that I think about it. The "jerk" happened on both right and left turns.

Tom