problems going from 2WD to 4WD

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garrytre
Posts: 669
Joined: Wed Feb 05, 2014 4:22 am
Location: adelaide hills

problems going from 2WD to 4WD

Post by garrytre »

In the past I've had problems with going from 2WD to 4WD, that seem to have resolved themselves over time.

Now I think I have a different problem going from 2WD to 4WD, although who knows, maybe from the same basic cause.

Travelling at 10 - 80km/hr, put it in 4WD. Sometimes works normally. But sometimes the 4WD light flashes for about 3 seconds like it should, but then doesn't stop flashing, and I get a beep beep about 2 Hz, for up to 15 seconds. Then the beep beep stops, flashing continues for ~3 seconds, then the light stays steady. I presume that by then the car is in 4WD.

The Isuzu dealer indicated this is not unknown, and reeled off a few causes that they've found. The car bottoming out, actuator hose dislocated, some electrical thing - I didn't understand.

So the question - has anybody else had this? Why. How was it fixed?
If it ain't broke, fix it til it is.
mydmax
Posts: 1807
Joined: Sat Oct 12, 2013 8:36 pm

Re: problems going from 2WD to 4WD

Post by mydmax »

Garry
Slightly flat tyre will cause a difference in speed and confuse the SOTF System.
Different front to rear tyre sizes or actual loaded driving dia will also, if significant. Wheel speed sensors may detect speed differences and inhibit a change 2 to 4.
Love to learn how bottoming can cause it. WoW!
Unless the transfer case synchro system can match the front crownwheel speed with the rear , ie, both front and rear drive shaft shafts rotating at same speed the SOTF system will not engage. While normal driving, the front crownwheel does not rotate. The diff side gear fixed to one side wheel, (L Side in yours I think), is rotating, but differential action means the opposite side gear is rotating backwards until full transfer speed is achieved. Transfer then has to begin turning the front drive shaft, make crownwheel turn up to speed, same as rear, then the diff gears are effectively stationary BUT all revolving inside the crownwheel housing. When all is at same speed and going same direction, the previously rearward turning side gear small exit shaft can be locked by the SOFT sleeve to the opposite wheel. Now in 4WD.
In 2wd the front crownwheel doesn't rotate, just the guts of the actual diff is always doing it's thing though, one side going backwards.

I added about 20ml of Nulon G70 to my SOTF oil, drain same out to fit it in. All around 120ml. Same Nulon in Transfer case to enhance change.
Only time mine is change stalled, is when totally stopped and the transfer Dog clutch faces are not slightly rotating to allow/effect engagement. Roll a bit fixes it.

Does yours have a vacuum hose actuator?????? Mine are both electric motor driven Forks. Dealer may never have seen one yet.
To work and not then work electricals have to be ok then not ok then fix themselves again and again. Hmmmmmm.
Hope this all make sense. Cheers
garrytre
Posts: 669
Joined: Wed Feb 05, 2014 4:22 am
Location: adelaide hills

Re: problems going from 2WD to 4WD

Post by garrytre »

Ross

>Slightly flat tyre will cause a difference in speed and confuse the SOTF System.
I've had all sorts of flattish &/or different sized & wear spares on the car, and resultant refusal to engage, even tested to 1km. But the beep - beep warning thing never occurred until just a couple of months ago. At the moment, I have a nearly new set of tyres, all 40psi, and it happens with 1/2 ton on the back, or with no load, either way intermittently. So I don't think effective wheel diameter is the issue.

>Love to learn how bottoming can cause it. WoW!
Yes, I had a !!?? moment.

>Does yours have a vacuum hose actuator
and that too - I thought it was an electric motor.

>To work and not then work electricals have to be ok then not ok then fix themselves again and again
Yes, intermittent fault from dodgey contact.

anyway, thanks.
G
If it ain't broke, fix it til it is.
mydmax
Posts: 1807
Joined: Sat Oct 12, 2013 8:36 pm

Re: problems going from 2WD to 4WD

Post by mydmax »

From memory, a bit fading at times, if the action of the SOTF gearing cannot close the feed back contacts or they are dirty, the change controller won't send "OK" to the controller to confirm the change fork has completed it's full movement and locked the front axle to the diff/ crownwheel. May be worth removing the loom and switchy bit on the SOTF to see all is well.
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