4H Button. What does it do? (1 Viewer)

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Joined
Sep 17, 2021
Threads
3
Messages
19
Location
Calgary, Alberta
New owner of a 1990 Prado SX5. New to the site as well but have got lots of very helpful information so far on a variety of subjects.

No owners manual came with which is just fine because the vehicle is from Japan and I don't speak or read Japanize.

I am working my way through a myriad of small items that need repair or don't work at all at all so thanks for your patience. I am certain this has been covered off before but my search is turned up nothing that answers the question.

When I bought the vehicle the guy I bought it from was older and very nice but his operational knowledge, short of driving the truck was, well, shall we say, rudimentary at best.

When I pushed the "HUB LOCK" button both the "HUB LOCK" and the "4H" buttons illuminated and the vehicle switched to four wheel drive with the front hubs locking up and the Tcase engaging. Some what confusingly, with the HUB LOCK button "not" pushed, I could push the 4H button till the cows came home and nothing happened nor did it illuminate. When I just pushed the 4H button, the back light on the 4H button did not illuminate, the Tcase did not engage and as such the drive shaft from the Tcase begin to turn.

Clearly, both processes of hub lock and T case engagement are working because the vehicle does switch in and out four wheel drive but "only" by activating the "HUB LOCK" button.

Just to save you from asking, yes, I can tell when it switches in and out. The driveline feels and sounds different in four wheel drive and on dry pavement in a sharp turn, the front wheels hop as they are being pushed by the rears. I did this test to ensure that the front CV joints on the front axles were not worn out which can cause them to click or grind in a tight turn if they are toast.

When I asked the old fella I bought it from why it was doing what it was doing, he said the 4H button is for vehicles that have "manual" locking front hubs as compared to the electric ones that are on my vehicle. He said the manual hub vehicle owners typically leave there hubs engaged 24/7 when the weather is inclement which then allows them to just simply push the "4H" when they want to engage four wheel drive while on the fly. He said the "HUB LOCK" button was there just to remind the drivers of the manual locking hub vehicles that their hubs are locked so they don't forget that they have them engaged.

See what I mean by kind of made sense but not really??????

If his story was accurate, then the HUB LOCK button would not be a button at all. It would just be an annunciator light that would come on when the manual hubs are locked and the manufacture would not have installed a button in the first place. My guess is he never really knew why it did what it did but the reason he came up with kind of made sense at the time so he stuck with it. Besides, the vehicle switches in and out of four drive with out a hitch so no problem, right???? WRONG! Sorry old fella but I don't agree!

I believe the HUB LOCK button and the 4H/four wheel drive Tcase engagement function are "supposed to work" independently. I think the HUB LOCK is supposed to engage the front hubs "only" and not simultaneously engage the Tcase as it is doing now. My thoughts are that this process, if working properly, would allow me while driving on crappy roads, to keep the hubs locked up (HUB LOCK button turned on) and when I have a need for four wheel drive mode, I can then push the 4H button which would then engage the Tcase sending power to the front wheels.

So after all this typing, I am now taken back to the title of this post. What is the 4H button supposed to do? Am I correct in my assumption as described above, OR , was the old guy really correct in how he thought it was supposed to work?

If it is supposed to work the way I think it is supposed to work then I have to start digging into how and why that HUB LOCK button is activating both the hub locking and Tcase engagement simultaneously and as equally as mystifying, why does the 4H seem to do nothing.

I can kind of see an advantage to the way it is working now but only as an optional choice of how to activate four wheel drive. Just conjuring up a scenario, I can envision driving with the roads unexpectedly turning to crap. Only having one button to push would reduce the terror of the somewhat holly crap, I need four wheel drive right freeking now moment.

Having said that, it still doesn't answer my original question of what does the 4H button really do.

My only answer is that the 4H is not working despite the back light coming on when the HUB LOCK button is pushed. If it is inoperative (not switching the Tcase on independently) then I just have to pull the switch and take a look as to why.

YOUR THOUGHTS PLEASE!
 
Yeah. At least you got down to it.
Thank you for this writeup on behalf of the next guy being troubled by a mysterious Tcase. 😄
My TCase is fully manual, but I always enjoy learning something new.
Thanks for the lesson.
 
@JuanJ …. “Electric hubs are not entirely reliable”.
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They work great right up to the point where you really need them. 😊
I do know that there problematic and the weakest link the chain but I bought this truck 2 repair and sell so as long as I can keep it stock and not spend any more money on it my back pocket will remain happy.
 
I've always heard it's not good to drive with front drive engaged without the hubs locked... If you want to drive in two wheel, but be ready, keep the hubs locked, but don't engage the front drive. When you need it, engage the front drive and the hubs are already locked.

Not sure where I heard it, but IIRC it's not great for the front diff to be driven from the driveshaft, but have no load on either of the axels.

Please correct me if I misremember.
 
The issue is solved and I really have nothing new to add. Just the same here's some related pages from a 70 series owners manual, just for reference...
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