[PMroamer]

Today I pulled into a snowcovered parking lot and when I tried to back out.... stuck. Why? Only the passenger side wheel turns in reverse so I'm left sitting there looking like a fool.Gonna have to call roadside assistance tomorrow just to unpark. Forward, both spin. Reverse..... not so much.
Whats up??


NOT HAPPY

 

[Dwight]

What happens with stability traction control turned off?

 

[Brian P]

Ummmm It's two-wheel-drive, but with a plain ordinary open differential.

If one wheel is on slippery stuff, that wheel is going to spin. It doesn't mean the other wheel isn't trying.

Get winter tires if you are going to be doing a lot of driving on snowy roads.

 

[keithwwalker]

Did you try the following?:
Lightly put on the brakes when reversing, to force the other wheel to turn?
Best with foot brake, but you can also do the same with the e-brake.

Also in emergency, try to let some air out of the tires, down to 20 psi to give the drive tires more surface area. Be sure to reinflate as soon as unstuck and don't drive fast after that.

 

[PMroamer]

I tried turning off the esc and nothing happens. I chipped down to the asphalt under the spinning tire,and even put down a whole bag of ice melt, and the one still on the snow doesnt spin so something else is going on. So I have a tire on snow not spinning, and the other on bare asphalt covered with ice melt salt spinning.
The tires only have 6000 miles on them and they work great the rest of the time. The snow we get here is light a fluffy and we're talking about an almost completely flat parking lot. I've been driving in snow my whole life and I can tell you, this situation is odd.
its weird and the guy parked right next to me in a two wheel drive pickup has pulled in and out several times since ive been sitting there. Just seems like if they both spin in forward on the same ground, they would both spin in reverse.

In regards to braking while applying the gas, the ebrake only locks up the rear so i'm not sure why that would help with a front wheel drive, and applying foot brakes would stop both drives tires equally so I dont know what benefit that would have.
Any other ideas? anybody in a snowy local wanna try backing up quickly somewhere slippery and see what happens???

 

[makevx73]

I tried turning off the esc and nothing happens. I chipped down to the asphalt under the spinning tire,and even put down a whole bag of ice melt, and the one still on the snow doesnt spin so something else is going on. So I have a tire on snow not spinning, and the other on bare asphalt covered with ice melt salt spinning.
The tires only have 6000 miles on them and they work great the rest of the time. The snow we get here is light a fluffy and we're talking about an almost completely flat parking lot. I've been driving in snow my whole life and I can tell you, this situation is odd.
its weird and the guy parked right next to me in a two wheel drive pickup has pulled in and out several times since ive been sitting there. Just seems like if they both spin in forward on the same ground, they would both spin in reverse.

In regards to braking while applying the gas, the ebrake only locks up the rear so i'm not sure why that would help with a front wheel drive, and applying foot brakes would stop both drives tires equally so I dont know what benefit that would have.
Any other ideas? anybody in a snowy local wanna try backing up quickly somewhere slippery and see what happens???

The PM, like so many other front or rear wheel drives, is essentially a one-wheel-drive vehicle. Basic differentials let the power go to whichever wheel on the axle is spinning. It stinks but that's the way it works.

The PM's ESC uses the brakes to try and slow the wheel spinning and move the power to the non-spinning wheel. Sort of like a limited-slip differential would. (Others join in here if you can describe it more accurately or simply?)

I'm not surprised to hear the PM's ESC system doesn't work in reverse. I don't think any of them do, although I've never given it any thought with either of two other vehicles I've owned with similar systems. This would, again, make it a one-wheel drive vehicle.

The suggestion of stepping on the brake and gas at the same time is basically a 'poor-man's attempt" at ESC/traction Control... It could work if the ESC doesn't in reverse?

You have me stumped as to why a tire on pavement will spin and and one on snow won't? Hopefully someone who knows something about this transmission will join in and have an explanation for this.

 

[PMroamer]

called the dealer today and they said it shouldnt do that and to bring it in. Good thing it still works properly in forward and somewhat in reverse since I'm good 2 hours of steep snowy mountain roads to get to the dealer down in denver. Could be worse.

 

[Chance]

The PM, like so many other front or rear wheel drives, is essentially a one-wheel-drive vehicle. Basic differentials let the power go to whichever wheel on the axle is spinning. It stinks but that's the way it works.

.....cut......

When equipped with open differential, I prefer to look at it more like a two-wheel-drive where the torque to each wheel is limited to the lowest of the two. As stated by others above, just because a wheel is not spinning it doesn't mean it's not pulling as much as the wheel that is spinning.

In my opinion using the word "power" in your statement above is technically correct but misleading. It is correct that the spinning wheel is getting more power but what we really want to know is how much force (as in traction) is being delivered to help move the vehicle.

 

[Chance]

....cut.....

In regards to braking while applying the gas, the ebrake only locks up the rear so i'm not sure why that would help with a front wheel drive, and applying foot brakes would stop both drives tires equally so I dont know what benefit that would have.
Any other ideas? .....cut......

I agree. Applying normal brakes doesn't help much if at all. To help, brakes would have to be applied to only the spinning wheel so that the non-spinning wheel will deliver greater drive force.

With an open differential on a vehicle without traction control, I only know of one way to improve driven force (traction). And it's essentially the opposite of applying brakes.

 

[rtz]

Some light reading on different types of differentials if anyones interested:

http://strangeengineering.net/flipbook/2014StrangeCatalog_LR.html#p=40

 

[rbisch]

Some light reading on different types of differentials if anyones interested:

http://strangeengineering.net/flipbook/2014StrangeCatalog_LR.html#p=40

Does Strange or anyone make a locking or limited slip differential for the Promaster gas or diesel transaxle?

 

[rtz]

This will be a likely source as soon as one becomes available: http://www.quaifeamerica.com/

 

[rbisch]

This will be a likely source as soon as one becomes available: http://www.quaifeamerica.com/

When do you think one could be available? My first choice would be the diesel.

 

[30 Ounce]

I seriously doubt Quaife, Strange, Dana or anyone will make a locking diff for a PM. A properly functioning traction control system will work better in all situations anyway. Something wasn't right with PMroamers TCS. It should apply brake to the spinning wheel which would force power to the wheel with traction. Of course if he applied the parking brake maybe it was frozen on like mine...adding to the problem.

 

[rbisch]

I seriously doubt Quaife, Strange, Dana or anyone will make a locking diff for a PM. A properly functioning traction control system will work better in all situations anyway. Something wasn't right with PMroamers TCS. It should apply brake to the spinning wheel which would force power to the wheel with traction. Of course if he applied the parking brake maybe it was frozen on like mine...adding to the problem.

A properly functioning traction control system does not work better in all situations.
Ford and GM have traction control systems and also locking and limited slip differentials.
On ice snow or mud I would prefer two wheels turning at the same time rather then then one wheel turning and the other braking.

 

[30 Ounce]

A properly functioning traction control system does not work better in all situations.
Ford and GM have traction control systems and also locking and limited slip differentials.
On ice snow or mud I would prefer two wheels turning at the same time rather then then one wheel turning and the other braking.

My last van (GMC Savana 3500) had a locking diff and it would lock in parking lots, especially when it was cold, and cause the rear end to break loose constantly. Then it would do the same thing in the summertime, occasionally, and sound like I was racing in the parking lot...then it would clunk as it locked or unlocked. You can keep you locking diff! Too primitive for me. And they don't actually lock if your going in a straight line.

There is a video I saw that had a 4WD with locking diffs and a 4WD Mercedes with traction control climbing a grade that had rollers on one side and smooth surface on the other. The Mercedes climbed it with ease while the other struggled to even get moving. I'll see if I can find it.

 

[rtz]

Here's one roller video. I think all the vehicles perform poorly:

 

[bobojay]

Seen that video before. Subaru has always had the bestest AWD system

 

[rbisch]

Forget the rollers this is the kind of locking differential I want.

 

[MJAB]

In Europe for Fiat Ducato (and Peugeot/Citroen twins) there is an option "Traction+" that, at low speed, uses ESC sensors and brakes to act like a locking differential.
http://www.fiatprofessionalpress.co.uk/press/article/5217

Fiat uses it also on road cars, for example Fiat 500L Trekking, Fiat Panda, ... and other commercial vehicles, like Fiat Fiorino (Qubo).
In the Doblò (Ram Promaster city) will be avaible in 2015.

But in North America Fiat 500L Trekking has not that option (well not only that, european 500L has also more ground clereance). Is there any safety law that doesn't allow this option?
Here a funny Fiat Fiorino Adventure (Trekking) advertisement of some years ago.

There are some "Adventure" models manufactured in Brazil that have a mechanical FWD locking differential manufactured by Eaton, the FWD ELocker, with electro-mechanical actuation system (and working at low speeds).
http://www.eaton.com/Eaton/OurCompany/NewsEvents/NewsReleases/CT_225960

You can find it also in Palio Adventure, Idea Adventure and Fiat Strada Adventure with Locker and now as Ram 700 with locker option in Mexico.