4H to 2H Slow Operation

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Rodnic

4H to 2H Slow Operation

Post by Rodnic »

When selecting from 4H to 2H there is a delay in the actual 4WD disengage and the light keeps flashing. If this happens when transiting from dirt to a sealed surface the light keeps flashing until I stop and do the forward/back thing to get it to disengage. A real PITA. :x It seems to work OK if the change is done on a 'slippery' surface, albeit slowly.
Is this 'normal' and have others experienced this :?:
Jackofjr
Posts: 1384
Joined: Thu Dec 11, 2014 11:43 pm
Location: West Gippsland Victoria

Re: 4H to 2H Slow Operation

Post by Jackofjr »

Yep , it's normal , it's a pita . H4 to L4 it's the same flashes and beeps ,
I reported a couple of weeks ago somewhere on this forum , I went 4Wding for a day and changed from H4 to L4 about 10 times that day , I discovered when I stopped to select L4 if I went from neutral to P- park then to Drive or 1st Low , it went straight in no flashing / beeping .

Today I went bush again , the N-P-D change again worked well for H4 to L4 ,

2WD to H4 back to 2WD , was still a pita ,
Josh
Posts: 12
Joined: Tue Nov 08, 2016 12:54 pm
Location: Qld

Re: 4H to 2H Slow Operation

Post by Josh »

I have been experiencing the same when changing back from 4H to 2H. Previously it changed back to 2H after a short time but now when changing from 4H to 2H on two recent trips I can be travelling for over 400 metres with the flashing 4wd light only coming off when I went over a pothole in the road or rough road surfaces. Is this a common issue?

I have a 2015 Dmax auto.
Mike C
Posts: 32
Joined: Fri Dec 10, 2021 7:13 am

Re: 4H to 2H Slow Operation

Post by Mike C »

Mine does this and I just accept it as being part of the Isuzu 4WD system, to be truthful I liked the arrangement my older vehicles that used a transfer gearbox selector lever better.
mydmax
Posts: 1913
Joined: Sat Oct 12, 2013 8:36 pm

Re: 4H to 2H Slow Operation

Post by mydmax »

Rodnic
When changing from 4H to 2H you are asking it to disconnect the front drive shaft in the transfer box AND also to unlock the SOTF SPLINE connecting the front wheel axle/diff. Both actions must have the dog clutch (transfer case) and the SOTF SPLINE RING unloaded so it can slide off it's axle drive shaft. If the vehicle is leaning one sided or tyre flat a bit or recently had the wheels turning a corner, the may be some degree of binding/pressure on that spline and the electric driven fork cannot over come the the bond force.
With a slight movement it should always enter low and/or 4wd as the components are starting from , NOTHING loaded.
If you are carrying a load the reartryes may be at a smaller radius and so may cause wind up. Exiting uphill also does the same. With a bit of short hard poly pipe dropped under a wheel and drive over will allow a wheel to rotate and release the pressure.. Open door and place under rear the wheel. Good lube will also have a bearing on it. Add Nylon G70 to SOTF DRIVE BOX and Transfer to help. SOTF chmager only small amount. Total MLS is only about 120ml. So 10 ml drained and replaced would be enough.
garrytre
Posts: 685
Joined: Wed Feb 05, 2014 4:22 am
Location: adelaide hills

Re: 4H to 2H Slow Operation

Post by garrytre »

Yep, pain in the arse, fiddly, and if you don't have time to plan ahead, both 4H -> 2H, or 2H -> 4H often won't work.

You have to line up all the ducks in a row.

As Mydmax says, the whole drive line has to be unloaded. So no turns, no different tyre sizes or even different wear or pressures (= different rotational speeds), etc etc - just a straight line. Worse on bitumen. Then put your foot on & off the accelerator, alternating so the engine drives the car, the car drives the engine, etc etc. Just that bit in the middle, when nothing is driving anything, it'll click out.

For going from 2H -> 4H, similar. Anything not lining up will leave your 4WD light flashing. Or worse, not flashing.

That's a worry, because eg travelling over reasonably solid creekbeds, I suddenly got to a soft sandy bit, put the car into 4WD, all the lights stopped flashing, gunned it, lights flashed again and clunk, 4WD finally engaged in the middle of a wheelspin. Not happy.

Normally ie at home, I put it from 4WD then 2WD 3 times before I get to the bitumen. So I put it into 4WD way before I have to, then to the on & off the accelerator thing to make sure it's in. But when you unexpectedly need 4WD, very dodgey.

Mike C 'I liked the arrangement my older vehicles that used a transfer gearbox selector lever better.'
Yep, we've hammered that idea to death long ago. We hate the electronic, want the stick, but it isn't going to happen. :-(
If it ain't broke, fix it til it is.
mydmax
Posts: 1913
Joined: Sat Oct 12, 2013 8:36 pm

Re: 4H to 2H Slow Operation

Post by mydmax »

Garry
If the lights stopped flashing were they ON or OFF, when you applied power? Big difference, if OFF then the controller might be having a second try to engage and you have the system not in equilibrium to enable smooth takeup/engagement.
Below is how I see it all.
Having a stick operated 2h/4h and Low range is quite ok but the front diff is already turning, ie, being driven by the front wheels all the time with the front crownwheel rotating at wheel rotation speed. Therefore these vehicle have FW hubs fitted in most cases.

The Dmax and others vehicles stop the front crownwheel from turning while in 2WD, but to make this happen the innards of the front diff centre is always churning. The later ones after 2012 have the SOTF disconnect on the RHS. This means, with forward direction, the RHS differential side gear is rotating backwards as fast as the LH wheel shaft is rotating forward because the crown wheel is stationary, ie, double speed difference between side gear and SOTF axle shaft/connection ring.
If you select 4H, then the fun begins, The controller has to first begin to make the 4H synchro in the TC case begin to move so the front shaft and front diff is accelerated from rest and begins revolving at rear tailshaft speed and rear crownwheel speed. ONLY when the speeds are matched and the TC dog clutch locks into drive is the front diff matched in speed with the rear. When it is the SOTF spline ring begins to move via it's motorized fork and tries to slide the spline ring onto the RH axle now SAME SPEED and direction as the RH wheel. If all is at same speed it will lock and the the feedback loop tells the controller it is engaged and the 4H light stays solid ON. If it doesn't achieve this, the light will flash and possibly timeout after a failure to engage.
If you ask it for LOW range, the Transfer case has to then disconnect the 1 to 1 drive from GB to transfer case and select a dog clutch which now drives the both output shafts at a greatly reduced speed. This usually is heard as a clunk when vehicle stationary or slightly moving. Anything faster means it is like operating a speed boat prop drive while engine running to fast. Not going to happen. It Also won't change if the dog clutch faces hit each other because the DOGS are not lined up for engagement to occur. If the cannot slightly rotate the the unit will “time out” the attempt instead of burning the selector drive motor. After use, unless the system is unloaded the drivemotors for the SOTF spline or Low to High changer or 4h to 2h opposite action dog clutch will simply time out and not change as desired. If the steering is kept straight all should normalize with slow forward motion and any wind up can be reduced/eliminated by driving one wheel over a pothole or rock, OR opening door and placing a large round dowel or tube so the rhs rear wheel is allowed to rotate and unload. ie Same as for a conventional system.
People are just used to forcing the dogs together for engagement and forcibly pulling apart the dogs on stick only models,

A careful assessment of the lubes used in the SOTF changer and the transfer case will make things better for selection, especially if a service has been performed, ie wrong lube, and the lube fluid is not slippery enough or slows or inhibits change action. Thick oils will make the SOTF and transfer case motors work hard to excrete the oil from between vital sliding parts, especially in a short time frame.
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