I have always thought that a vehicle's cruise control once set, is supposed to hold on that speed regardless of the landscape of the road (ups, downhills, whatever) unless you're really going down a steep mountain or something. Well, my cruise on my '04 does not hold going down hill on the interstate or something. For example, if I set it at 65 and start going down hill a few minutes later, it will gain speed going down the hill up to 75 even.....not good when it comes to cops. So anyway, I'm goign to have this checked when I go for my appointment at the dealer, and I called about it today. The service guy told me that 'no vehicle will hold speed on cruise going downhill.' I was like 'then what is cruise control for?' He said its supposed to gain speed going downhill because it can't brake. I told him I own a '93 f150 and it holds its speed on cruise control, and that every other vehicle I've ever driven does too. I've never noticed one not holding its speed. He claims that he's never seen one that does hold it's speed. I think he's crazy and lying to me, I'm not stupid. What do you guys think about the cruise, isn't it supposed to hold?

This is the 2nd time this service dept. has fed me this crap, if you remember yesterday my post about brakes and a different guy telling me the manual says they are supposed to squeek. If I find out the cruise definitely should hold, I may be having a talk w/ someone higher up so that I can ensure that my truck gets looked at and fixed the first time when it goes in for all these little problems. Sounds like idiots trying to feed me full of it like I'm ignorant or something and they think I'll just go along w/ whatever they say.

 

I'm 50 years old, and have driven dozens of cars (close to 50 different cars) with cruise control, and none of them will hold speed going down hill.

It's a physical impossibility.

The cruise control pulls the throttle open, and closes it, to maintain a steady speed on level ground, and try to maintain speed on uphill grades.

On downhill grades it will close the throttle all the way, but without applying the brake it will not slow the vehicle down.

How could it?

 

Certain vehicles..."not the f150" will auto down shift on down hill grades with the cruise set.

My moms mercedes downshifts with the cruise set, but my f150 runs away if you don't reach down and hit the o/d button.

 

He is right and you are wrong. Your wasting your time taking it in.

The vehicle is not suppose to hold a certain ammount of speed going downhill. It will back off of the engine and "coast" but not brake. This has been discussed before and many have simply used the O/D button to slow down with the cruise engaged.

 

I must have gotten the only truck then that will hold speed going downhill, cause I set my cruise at 75, and that is where it stays, doesn't speed up one bit. It works perfect for me.

 

An object in motion tends to stay in motion. 5500 lbs of pickup going downhill isn't going to stay exactly at it's set speed. The cruise control can only do so much.

 

Indeed, there are other mitigating factors with your '93 that allow it to not gain speed on the same grade. Some that come to mind would be the increased rolling resistance, increased drag, possibly increased compression braking because of the different transmission, rolling resistance of the tires, etc.

The cruise control on the F-150 has no ability to slow the vehicle, other than closing the throttle. If you are going the same speed at the top of the hill without the cruise control set, the vehicle will do the exact same thing. Let off the gas, and if the grade is sharp enough, it'll accelerate.

I'd recommend not taking it back to the dealership for the matter again. You're wasting your time.

-Joe

 

The cause of the difference in results is the location.
Places with no real mountains the cruise holds nicely. Places where there are real grades gravity takes over.
No cruise, not even one that can drop a gear, will slow down in the Cajon pass.

That said, this cruise control, probably because of the drive by wire, is the 'tightest' I have ever used.
Chris

 

Actually there are a couple of systems on the market currently that will actuate the brakes to maintain a max of 5 mph over the speed.... those are typically the systems that also have active cruise control that will actually reduce speed and brake in response to a slowing vehicle in front of them. I believe it was the high-end Mercedes vehicle I remember seeing it on, but I could certainly be mistaken.

Needless to say, a Ford truck is NOT one of them.

-Joe

 

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You ask for advice on this site, folks give it and you can go with the answers or not. That having been said I recommended you do exactly that in your last thread (going to someone higher up) BUT NOT IN THIS CASE. The answers given by all the gang about gravity and your cruise control are correct and if you insist on bringing your truck in for that reason they WILL look at you like your crazy.Gravity makes the rules ( just ask the fine folks at NASA ) Good luck with the other issues though ...

 

I see what all you guys are saying, but I've had my '93 f150 for 9 years now, daily driver, and I've used cruise frequently on it. I'm telling you it holds it's speed going down hill. I live in mid TN, there are flats, hills, and mountains and I have been all over the state in it to different scapes. I don't expect it to hold completely or any going down a high % grade, but when I'm going across 'hills' on the interstate and my '04 takes off to 75 instead of 65 for example while on cruise, that is not what my '93 will do. The '93 holds steady. It may downshift or shift into another gear to maintain it's speed, but it maintains. I know it doesn't 'hit the brakes', that would be dumb to think that. If my '93 didn't hold, I wouldn't have even ever noticed that my '04 doesn't. I do realize the difference in weight between the trucks though. My question to the dealer is simply 'Is the cruise supposed to hold on this truck?' because I know my '93 does, so why does a truck built 11 years later not hold? If I had a digital video camera I'd go out this afternoon in my '93 and record it holding going down a hill and post it. Besides that, my '04 has even held before going down a hill, but it only holds about 10% of the number of times it happens.

 

gotta agree with the rest...it has to do with weight, resistance, gearing, etc.

My 92 mustang seems like it holds going downhill until I increase the effect of gravity

 

vader,

I can handle that if that's the case, I just want to find out for sure the answer.

 

None of us are claiming that your '93 doesn't hold the speed, but it's not because of the cruise control. Your '93 has more drag, rolling resistance, etc. than your new one does. When it crests the top of the hill and starts to head down, the cruise actuator backs off the throttle to maintain 75. What happens from there is based on the resistance of the vehicle (air drag, rolling resistance of the tires, frictional losses through the bearings and transmission, etc). If the acceleration component of the gravitational force is strong enough to overcome the combined drag forces, the vehicle will accelerate despite having the cruise control set. If the acceleration component of the gravitational force can't overcome the drag forces, the truck will not accelerate, but may appear to hold its speed. It's mere coincidence.

Here's another way of looking at it.... take that mountain grade, straighten the road out, and park both trucks at the top of it. Shift both into neutral, and start them coasting down the hill. Your '93 may coast up to 55 mph before it's drag-limited. Your new one may coast at 90 before the drag forces stabilize the speed.The new one needs additional drag forces (brakes or downshifting for engine compression braking) to maintain 75 mph, where the '93 needs to give her some gas to reach 75 mph on the downgrade to help overcome the drag forces.

Have I beat this dead horse into a bloody pulp yet?

The really short answer is that the dealership is correct on this one.

-Joe

 

I'll throw in my 2 pennies...

I already took my new King Ranch back to the dealer twice for this same reason. Took it up with the service manager the second time because I didn't want to believe it. Both times my invoice was marked with the same analysis, "Design characteristic of new transmission functions". Their short answer is that the overdrive gearing has changed enough that there is virtually no drag on the engine, so no compression braking. They could only suggest I take it out of overdrive on the steeper descents. Sure enough, that helps but not too much.

I have a '99 F150 that holds the cruise speed steady on the same hill that I drive the KR on daily. So I did the test mentioned by GIJoeCam, I took my 99 out of drive at the top of the hill going 60 and let it coast down the rest of way. It gained about 8 mph more by the time I got to the bottom. Then I did the same thing with the KR, and it gained over 15! That proved the "rolling resistance" to me.

Between the hill test and the dealer explanation, I've decided to live with the "flaw", and instead treat it as a "feature" of the new Ford. Every car/truck I've owned has had some characteristic that you just have to accept, just like family...