Steeper descents dangerous behavior

Yes, my Rubi beats every Jeep I've ever had. The first one was a '74 CJ-5, 3-speed manual, 304 V8 AMC engine, no limited slip at all. The good thing was, as young as I was then (20's), that Jeep taught me to drive off-road. So now, in this Jeep, it's bliss.
Either the problem we are experiencing is only in a few Jeeps, or thousands of other drivers aren't really noticing as much when driving. Maybe only a very few Jeeps have the issue. And on mine, it does not set off any engine codes or CELs. If it did, I'd know and be able to read them w/the Tazer.
I eagerly await your report of descending Tazer-less!
 
XT Carol said:
Yes, my Rubi beats every Jeep I've ever had. The first one was a '74 CJ-5, 3-speed manual, 304 V8 AMC engine, no limited slip at all. The good thing was, as young as I was then (20's), that Jeep taught me to drive off-road. So now, in this Jeep, it's bliss.
Either the problem we are experiencing is only in a few Jeeps, or thousands of other drivers aren't really noticing as much when driving. Maybe only a very few Jeeps have the issue. And on mine, it does not set off any engine codes or CELs. If it did, I'd know and be able to read them w/the Tazer.
I eagerly await your report of descending Tazer-less!
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I would still like to know where you read that using tap shift alone, in a downhill situation would hold the speed.
Even the manuals I drove years ago, did not activate some engine compression, it did initially when shifting down but never did I have any of them hold a certain speed going downhill, eventually gravity does what gravity does and either you have to brake or shift
 
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jeeeep said:
I would still like to know where you read that using tap shift alone, in a downhill situation would hold the speed.
Even the manuals I drove years ago, did not activate some engine compression, it did initially when shifting down but never did I have any of them hold a certain speed going downhill, eventually gravity does what gravity does and either you have to break or shift
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Yes, you are correct. Simply being in a certain gear doesn't guarantee speed will not increase, if the hill is steep enough. As that happens, engine RPM increases proportionally. But if the engine is still "holding back" (no up-throttling), RPMs rise but the reported mpg stays at "99". So the throttle is still "closed" (using old-school terminology from carbureted engines).
But when this begins to happen, the RPM goes up dramatically, the driver feels the acceleration, and the mpg display drops way down to 18 for instance. You can feel you're getting no hold-back, and aggressive braking has to be applied. Or engine RPM will continue to rise to even above 3K.
In what you are describing, as you notice your selected hear is too tall on a given descent, just downshift manually one gear and continue.
To demonstrate to someone, I'd have them ride with me up into mountains, not extreme just the usual dirt forest road w/few curves perhaps. Then descend attempting to use only engine & geaing. Which is the usual way of doing it. If I picked the right gear, little or no braking would be needed. Maybe a light touch on the curves.
I'm so used to it now that I can replicate it fairly easily, especially on a warm day. It's a weird feeling driving, something I'd think would get almost enyone's attention. So perhaps it's just a very few of us who suffer from it.
 
XT Carol said:
Yes, you are correct. Simply being in a certain gear doesn't guarantee speed will not increase, if the hill is steep enough. As that happens, engine RPM increases proportionally. But if the engine is still "holding back" (no up-throttling), RPMs rise but the reported mpg stays at "99". So the throttle is still "closed" (using old-school terminology from carbureted engines).
But when this begins to happen, the RPM goes up dramatically, the driver feels the acceleration, and the mpg display drops way down to 18 for instance. You can feel you're getting no hold-back, and aggressive braking has to be applied. Or engine RPM will continue to rise to even above 3K.
In what you are describing, as you notice your selected hear is too tall on a given descent, just downshift manually one gear and continue.
To demonstrate to someone, I'd have them ride with me up into mountains, not extreme just the usual dirt forest road w/few curves perhaps. Then descend attempting to use only engine & geaing. Which is the usual way of doing it. If I picked the right gear, little or no braking would be needed. Maybe a light touch on the curves.
I'm so used to it now that I can replicate it fairly easily, especially on a warm day. It's a weird feeling driving, something I'd think would get almost enyone's attention. So perhaps it's just a very few of us who suffer from it.
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Sounds like you believe the jeep should have hill-holder, like a tow-haul, mode that will lock in at a certain speed using gearing and engine compression. Jeep won’t.

No automatic I’ve ever had would do that except for my big 2005 Ford diesel that actually had those features and they were awesome. Every other automatic I’ve had would accelerate going down hill unless I’m in 1st and even then it would accelerate to high RPMs and would require breaking depending on how steep the grade is. If you want slow controlled speed without breaking you need to be in 4lo and in 1st gear, maybe 2nd, but even 2nd will accelerate to high RPMs and may need braking. This is how all my automatics behaved.
 
Ddays said:
Like Mike said, I've never owned any vehicle, manual or auto, that held an rpm while going down a hill except our diesel Ram using the exhaust brake. Short of some device to limit it, physics demands the vehicle increase speed. This thread confuses me.
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OK to you both, perhaps I'm expecting too much. Before this Jeep I had a 2005 Liberty w/the diesel engine & 5-speed auto transmission. It was a pretty good little 4-wheeler, good torque, HI & LO range, limited slip. It had none of the descending features of these new ones. But it would descend very steep slopes, using only engine holdback. I used the foot brake to come to a complete stop, but otherwise it'd "walk" down about anything. It never speeded up on its own like this new one, with no input from the driver.
 
Mike Pierson said:
Sounds like you believe the jeep should have hill-holder, like a tow-haul, mode that will lock in at a certain speed using gearing and engine compression. Jeep won’t.

No automatic I’ve ever had would do that except for my big 2005 Ford diesel that actually had those features and they were awesome. Every other automatic I’ve had would accelerate going down hill unless I’m in 1st and even then it would accelerate to high RPMs and would require breaking depending on how steep the grade is. If you want slow controlled speed without breaking you need to be in 4lo and in 1st gear, maybe 2nd, but even 2nd will accelerate to high RPMs and may need braking. This is how all my automatics behaved.
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That's interesting about your Ford diesel. I wonder what it was doing to prevent speed from increasing? Do you think it was applying the brakes, as these do in Hill Descent mode?
 
XT Carol said:
OK to you both, perhaps I'm expecting too much. Before this Jeep I had a 2005 Liberty w/the diesel engine & 5-speed auto transmission. It was a pretty good little 4-wheeler, good torque, HI & LO range, limited slip. It had none of the descending features of these new ones. But it would descend very steep slopes, using only engine holdback. I used the foot brake to come to a complete stop, but otherwise it'd "walk" down about anything. It never speeded up on its own like this new one, with no input from the driver.
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You are expecting too much I think. Also, your liberty was way lighter and the diesel has better compression so it stands to reason it will naturally slow down easier.
 
XT Carol said:
That's interesting about your Ford diesel. I wonder what it was doing to prevent speed from increasing? Do you think it was applying the brakes, as these do in Hill Descent mode?
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It was made to tow and haul heavy loads. The tow haul would change the gearing and combined with the compression of the engine would hold the speed and RPMs down.

Regardless, Jeeps, with possibly the diesel being the exception, just depend on gearing.
 
XT Carol said:
That's interesting about your Ford diesel. I wonder what it was doing to prevent speed from increasing? Do you think it was applying the brakes, as these do in Hill Descent mode?
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Just to mention in passing, I'm fairly familiar with diesels, gearing, exhaust brakes, etc. since I live full-time in a 38-ft diesel pusher Class A & tow the Jeep behind.
I think it's just that I've never experienced in any other vehicle what this one is doing. Maybe it's totally normal?
 
Don’t appreciate how you created this thread to imply that jeeps are unsafe because they speed up so much going downhill that you have to brake too excessively.

Not true. Fake news. End of story. Even you can’t decide if you’re losing your mind or not.

I’m constantly amazed at how Jeeps can be modified and built up and they are still a safe, enjoyable vehicle for everyday driving. That’s why they are the best.
 
It was my impression that hill descent mode would also enable pulsating braking (noisy), similar to the anti-lock braking system. I have seen demonstrations of this on YouTube. But I have never tested the feature.

It is not realistic to expect a small engine to provide a lot of stopping force, and particularly through a torque converter. If the torque converter has a locking feature then it could be far more capable.

Someone mentioned BMW transmissions, and indeed this same transmission is used in many European cars, which are nothing like a Jeep.

The Jeep ECU can control things such as gear selection, but it not clear what other external controls are available for this general-purpose transmission.
 
bobfriesenhahn said:
It was my impression that hill descent mode would also enable pulsating braking (noisy), similar to the anti-lock braking system. I have seen demonstrations of this on YouTube. But I have never tested the feature.

It is not realistic to expect a small engine to provide a lot of stopping force, and particularly through a torque converter. If the torque converter has a locking feature then it could be far more capable.

Someone mentioned BMW transmissions, and indeed this same transmission is used in many European cars, which are nothing like a Jeep.

The Jeep ECU can control things such as gear selection, but it not clear what other external controls are available for this general-purpose transmission.
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Yes, try Hill Descent sometime. It definitely makes a bit of noise working. But in the right spots, it's nice.
 
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