braking question

[dm2776]

does anyone know what would cause the truck to brake while pulling a trailer. we were buzzing along about 60 mph when the cruise control went off and starting loosing power. could not get cruise control engaged after that. so it appears there was some braking going on somewhere (without using the brake pedals..could not get it re-engaged until I took the trailer off

 

[DocFather]

Are all of your brake lights operating correctly - truck as well as trailer?

 

[danemayer]

The trailer has an emergency break-away circuit designed to stop the trailer if it separates from the tow vehicle. If the switch failed or the activator came unplugged the trailer brakes would engage.

 

[dm2776]

i will check truck trailer is in the shop due to this problem. they are trying to say it was loose lug nuts but when i dropped it off they said the brakes had locked up. and i don't think it was the lug nuts as that should not have affected my cruise control

 

[dm2776]

thanks i will start googling that to see what happens if still attached and brakes go one..that sounds more like what happened

 

[danemayer]

thanks i will start googling that to see what happens if still attached and brakes go one..that sounds more like what happened

If you had brakes that were working well and the break-away circuit activated, it would apply significant stopping power. At a low speed it would lock the wheels and drag the tires on the pavement. If you continued driving with trailer brakes locked up, it wouldn't take very long before there was serious overheating of the shoes, drums, magnets, and perhaps the wheel bearings.

Cruise control normally shuts off when you touch the brake in the truck. I don't know, but I supposed it might also be programmed to shut off if it detects a loss of speed.

 

[evolvingpowercat]

There is a small cable connected to a break-away switch that when the plunger pulls out it applies 12 volts from your trailer batteries directly to the trailer brakes. This is separate from your brake light circuit, so generally if the break away switch operates it would not be "seen" by the tow vehicle, with the sole exception being the trailer brake output of the Trailer Brake Controller. If the controller was factory OEM module it is possible it might "see" the 12 volts being applied by the break-away switch and shut off the cruise control and perhaps even give you other notifications depending on how fancy your information center in your tow vehicle is.

It is always important to make sure there is enough slack in the break away switch cable that it does not operate un-intentionally when making a sharp turn, and to check to make sure that the break away switch did not get un-intentionally activated.

 

[olcoon]

While at the rally, I heard of a similar issue. Symptoms sound very similar, the truck had "issues" and went into "limp" mode, and could only be driven about 20 MPH, when unhooked, the truck ran fine, unfortunately I don't remember what the issue was, but it wasn't cheap.

 

[Bob&Patty]

To the OP. You have been given some advise. But kinda "blind" advise. It would really be helpful if we knew what truck and trailer you have. When you post about an issue....we need to know what you have.

Its the old saying....information...information...information.

 

[dm2776]

Sorry. I have a 2008 ford f450 with tow package and 2013 cyclone 3712. I dont think cable would have been pinched as driving about 60mph on a very very straight road. Very wet but straight. If I ever find true cause will be sure to post. Going to call ford to see what they might can tell me

 

[porthole]

Cruise control normally shuts off when you touch the brake in the truck. I don't know, but I supposed it might also be programmed to shut off if it detects a loss of speed.

All cruise controls will disengage if the vehicle falls below a set parameter in it's ability at maintaing the set speed. Safety feature.

 

[pegmikef]

All cruise controls will disengage if the vehicle falls below a set parameter in it's ability at maintaing the set speed. Safety feature.

I know mine always did when I was pulling my Edge M21 (5,000 lbs) up long or steep grades with my F150.

 

[Bohemian]

TFLTRUCK.com

This site does tow testing on all the pickup trucks up and down the Eisenhower Tunnel Interstate section. A very steep long grade of interstate highway. They use cruise control as part of the test procedure. Take a look. Measure brake temperatures after the runs down the mountain. Comment of drivability, etc.

 

[wdk450]

I just wanted to throw out one more possibility for the cruise control shutting off, but I don't know if you have this: Diesel Exhaust Brake (like Jake Brake). Enabling my exhaust brake automatically cuts off my cruise control - it is wired that way. So maybe there is a fault in the exhaust brake circuit (if you have one) that is causing this.

 

[recumbent615]

I have experienced this several times - and have yet to find the exact issue - other than every time it happen it was when the weather was wet so I attributed it to something getting wet. Mind you my issue never caused the brakes to come on or the truck to go into "limp" mode, only the loss of cruse control. but know that if the truck goes into "limp" mode and runs at a lower power, you will not have cruse control under those conditions. When it happens the computer should latch the error code that caused the issue and any autozone can read those codes off the computer for you. Other Auto Parts stores may be able to do that as well.

 

[Jim.Allison]

There is a pressure switch mounted on your master cylinder that is a redundant cruise control switch (bottom side). It is in the closed position as a default, meaning that pressure has to be applied to open the switch. It is an inexpensive part and is easily replaceable. It should be the only pressure switch attached to your master cylinder so it is easily identifiable. Slip connector off, replace pressure switch, slip wire back on. Done. No brake bleeding required. Go test your old one with ohms meter for continuity. if no continuity then you found your problem. If you have continuity then you may have still found your problem, the switch just may be functioning at that moment. This is the most common cause in Ford Super Duty cruise control failure either intermittent or permanent failure.

BTW Occam's Razor dictates; in the absence of certainty—the fewer assumptions that are made, the better. "solve simple problem with simple repair, do not solve simple problem with complex repair. Good luck.