Technical Panda 4X4 Viscous or Solenoid?

[Ironwhip]

I see where you're coming from, but the Panda is such a versatile car that a small trailer would do no harm. I have an Ifor Williams 6'x4' with mesh sides and a rear ramp and it's excellent. Empty it weighs about 180kg, which is nothing, and I guess a max of say 200kg contents when it's full, so all up weight of less than 400kg, which is very little really.

Either way, sounds like you have a nice car!

That's a light trailer indeed. Your Panda can handle it without a blink!.

Here is my Panda 4x4 Climbing. I bought it a month ago. It was first registered in 2005 but only got 37380 KM when I bought it. There was one owner before me, and I heard that is a middle aged lady, thus the funky blue color and the red seats! The good thing is: the car was 100% maintained by the local Fiat dealer with a very detailed service history. :slayer: As part of the deal, I got four new tires of Vredestine Quatrac 3. I changed the exhaust pipe, too, but that's on me.

 

[R1NGA]

Footnote to this discussion from last week....

I had my 4x4 on the dyno again yesterday to check-up on the fuelling and timing for the Rotrex, now that I've got 2000+ miles on it. Good news is that all is well and a bit of fuel added here and there, and a touch of timing taken out there and here, has made things even smoother and more tractable. All good.

However, when we first put the car on the rollers, the chap gently let the car settle onto the dyno by driving forward in 1st gear really slowly - less than walking pace. Both axles were turning at exactly the same speed and I asked if the rear rollers were being actively powered to keep in sync with the front. Seems not - the car was driving the rear.

He stopped on the brakes, brought rollers to a halt and then pulled away again really slowly. The VC locked up almost instantly and there was almost no perceived difference in wheel speed that I could see from standing next to it. That VC clearly requires very very little differential before doing its locking magic. Very impressive indeed.

We talked about the modern approach using Haldex-style electromagnetic controls and its clear that these are pretty much mandatory now that ESP and Traction Mgmt are required across the board on cars these days - VC's just won't play ball in the same way of course. His view was that VC's are by far and away the best solution, as they're bulletproof and in his experience, 100% reliable.

Glad I have one!

Phil

 

[Ironwhip]

Wow!! Glad to know that you tested the VC on a roller platform. Makes me like my Panda 4x4 even more.

I also have a very good update. I just got an official email answer from GKN Driveline about the following scenario we discussed:

So if the front wheels are on ice and the rears on tarmac, you bring up the clutch, the fronts spin momentarily, the VC locks and the car drives forward. If it can't drive forward - say it's roped to a 3-tonne Q7 stuck up to its sills in clag which the little Panda had just driven across for example - then the car simply won't pull forward, same as it you tried to tow a bus on dry tarmac with a Panda. I guess.

So no, I don't believe the VC, rear diff nor prop will be damaged, as your scenario was I think working backwards rather than forwards, if you see what I mean.

Phil

First, the gentleman from GKN Driveline suggest testing the VC by putting the front wheels on low-friction surface, such as wet steel or ice, and the rear wheels on high-friction surface. The car should be propelled forward by the rear wheels, albeit that the vehcile will accelerate less than when all wheels are on high-friction surface.

About the hypothetical scenario we discussed, I asked GKN Driveline this:

"Would the VC be damaged if under the following (hypothetical) scenario?

The front wheels are on a low-friction surface, such as ice or snow, the VC was activated but the vehicle could not be propelled forward (such as when towing a very heavy trailer, or because of other reasons). In another word, power was transmitted to the rear wheels by VC, but the rear wheels cannot turn on the high-friction surface and the vehicle stays stationary."

The answer from GKN is:

"I wouldn’t exaggerate it, but if done only for a short period of time (~ 1 … 2 seconds) this shouldn’t be a problem to test the functionality. When the VC unit heats up to a predefined temperature (based on air content inside), it gets into the so-called hump mode, and the torque increases rapidly - caused by direct metal contact of the plates. This is an operating condition the unit should be able to handle (stall condition) a few times, but not permanently."


I hope this tip will help us maintain our Panda 4x4 and the VC unit.

I am yet to find a roller platform to test my 4x4.

Eric

 

[R1NGA]

Reckon that's answered this question completely then - nice one!

 

[Batfalcon]

I did the same test on mine some months ago. Both front and rear wheel were spinning at the same time on the dyno drums. In fact they also upgraded a little bit the performance of the engine.
Below the diagram of power & torque, before and after.

As far as the Viscous or Solenoid, I am under the impression that regardless of the system, all the cars have the Viscous coupling, but certain models have the Solenoid as well, activated by a push button right next to the big red alarm button on the dashboard, in case that the driver wishes to activate a 50 - 50 distribution immediately.

 

[R1NGA]

Out of interest, what method did he use to 'tune' the car? Directly through the OBD port in the car with their own software?

 

[Batfalcon]

I think so, yes. The ODB is placed down left of the steering column? He removed a cap there and connected a device, on which he downloaded the program.

http://www.youtube.com/watch?v=pUiOJIijj78&feature=youtu.be

 

[Herts Hillhopper]

As far as the Viscous or Solenoid, I am under the impression that regardless of the system, all the cars have the Viscous coupling, but certain models have the Solenoid as well, activated by a push button right next to the big red alarm button on the dashboard, in case that the driver wishes to activate a 50 - 50 distribution immediately.

Sorry, but no. All petrol 4x4s (in the UK) had viscous couplings until the time the Cross was introduced here. It, and the petrol models from that point onwards, dispensed with the viscous coupling, and instead used a solenoid to engage the rear drive - controlled via the ABS electronics to detect if the front wheels were spinning. The dash button (marked 'ELD' -- electronic locking differential') simulated a differential lock by applying the brake to one rear wheel or the other, preventing rear wheel spin in situations where one wheel loses traction (eg if one wheel were of the ground or if one wheel were on ice). It didn't turn 4x4 on or off.

 

[Batfalcon]

I didn't know that. Thanks for the reply.

 

[Batfalcon]

Does anyone know, where is this coupling located?

 

[Herts Hillhopper]

Hi Batfalcon

Take a look at this post from another thread and you'll see the answer:https://www.fiatforum.com/panda/332229-test-driving-buying-4x4.html?p=3308200

 

[Batfalcon]

Thanks for the reply H.H.

I do have a question though:

Suppose that having lifted the car (all 4 wheels), using a pair of BIG pliers, someone holds the prop shaft still.
Then if you try to spin both rear wheels to the same direction they should spin. Not freely but they should, right?
Because half the discs in the VC that are attached to the rear diff would spin inside the VC, but the other half (attached to the prop shaft), would remain still, am I right?

 

[R1NGA]

Theoretically, yes, what you describe will happen, but this won't prove whether the 4WD is working correctly. This topic has been discussed before in other threads and the conculsion is that the only true test is to put the front wheels on a VERY low grip surface (ice would be ideal, or slutchy wet grass perhaps), but keep the rears on grippy something. Pull away quickly to spin up the front wheels and then see if you move with some vigor. This will nip up the VC and pass drive to the rears. Easy test to do, but less easy to setup.

 

[Batfalcon]

Since it's rather impossible to find icy surface in Greece, this time of the year, I made the following test.

Left the Panda on a flat surface, without hand brake or any gear in the transmission.
I put 2 stones on the left side just to be sure it won't move, and lifted the rear right wheel.
It took all my strength to spin the lifted wheel just 1/4. Tried a little more and I managed to achieve almost 1/2 a turn.
It was so stiff, that I looked under the wheel, to be sure that it is indeed lifted of the ground!
All the above lead me to the conclusion that the car is continuously 4X4. There is no engagement or disengagement of the rear axle. The only thing that VC makes is to absorb the tensions between the axles, while the vehicle turns on any curve.
That's why we never "feel" the engagement or disengagement of the rear axle.
For the same reason it's impossible to spin the front wheels, instead the car launches itself forward, without any spin

 

[R1NGA]

You are correct Batfalcon - that's why I believe the VC setup is superior to the solenoid managed version, as it's passive, simple and way more resilient. Their demise was caused by the need for stability controls that can play with brakes and throttle (hence the rise of fly-by-wire throttles), but this requires full control of diff locking mechanisms. VC's just get on with it and cannot be controlled, hence the change of design in the recent models.

My car still has a FBW throttle though, which is annoying - I'm a bit too much old school for those!

So it looks like your car is OK!

 

[Batfalcon]

Indeed I never had a doubt for the status of the car. I was just curious, about the way the VC engages and disengages the rear diff.
So the answer is that in fact it NEVER disengages.
The whole story that was technically served to us regarding the 4X2 or 4X4 and how it comprehends the traction of each axle, is nothing but a fairy tale.
Fiat just figured out a way to reduce the tensions between the axles and served it with a technological innovation glossy wrap.

P.S. 1 Mine too has a FBW throttle.
P.S 2 Thanks for the discussion.

 

[Herts Hillhopper]

The VC is always partially engaged, yes -- during normal driving, about 95% front and 5% rear. If you lift any wheel off the ground it can be turned, but only just. Lift all 4 off the ground and turning one will make all 4 move in various directions. No fariy tale - this is how Fiat themselves describe it. It becomes 50/50 when the front wheels start to loose grip

(By the way, beware: if you jack up the 4x4 versions with VC and do any work on the car, it is important to chock the diagonally-opposite wheel to prevent car toppling of the jack, for this same reason)