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4WD System in Prado KZJ78

masterl

New Member
Joined
Jan 15, 2019
Messages
1
Country Flag
kenya
Good morning/afternoon/evening guys,

I have some questions concerning the KZJ78 Prado 4x4 system.

I got a 1995 Prado at the beginning of the year and I'm the third owner. I must admit that I didn't know a lot about the car then and may have missed a few critical checks during purchase.

Anyway, those are bygones and I am where I am.

The problem I've been having is that the front wheels were previously not being powered, even after switching on all the buttons (H4, Hub Lock, and even in low range). After searching in the forums, the first culprit was the electric hub locker which we replaced but still the issue persisted. So we opened up the front diff and found out that some of the gears were completely worn out (or removed by previous owner. Some do that). So once that was fixed the front wheels are now being powered, but with concerns as spelt out below.

The bone of contention now is when and how the 4x4 system should be engaged.

So I come here looking for a clarification (call it schooling) of how exactly the 4x4 system should work in the KZJ78:

a) What does the H4 button do? Or what should it do? My expectation would have been with the H4 button pressed, the car should power all wheels. So if I raise the car and "drive" it, all the 4 wheels should move. This is currently not happening

b) Can H4 button be used independently of the hub lock button? I took the car to the dealer and they insist the hub lock button should be pressed along with the H4 button for the 4 wheels to turn.

When I press H4 and Hub Lock, all the wheels are powered but the left front wheel spins much much faster (not sure why) while the right spins like it's someone is applying brakes on it sporadically. If I hold the left front wheel, the right front wheel spins more consistently.

So back to my question, if I have to turn the hub lock button for the 4 wheels to be turned, then what's the purpose of the H4? My expectation is that the hub lock is just that, to force the front 2 wheels to turn at the same speed.

c) Should the front wheels spin when I engage low range? Currently I also have to press the Hub Lock button to spin the front wheels even in low range. As above, the front wheels do not rotate at consistent speeds

d) The dealer mentioned that there should be actuator next to the front diff and it appears to have been removed. Is that an/the issue?

e) Suppose I find myself in a ditch where the rear wheels are suspended while the front wheels are on solid ground with perfect traction (it has happened before) what mode should I use to get myself out? Since I found that I can stop the front wheels spinning by simply holding the wheel even when it's on low range and the hub lock button is pressed, my confidence in the offroad capability was seriously eroded.
 
Hello masterl,

I have my electronic hubs removed, and have manual engaging hubs installed on my LJ78.

(4H button: on ; Hublock button: on) = 4wd**

I will try to answer some of your questions:

a: The H4 engages the front differential. If you only press 4H without hubs engaged you will be spinning the differential gears and shafts without locking them to the wheels. I don't really see the point of the 4H button, It should have been one button(engage diff drive and lock hubs as one button.. anyways)?

b: No. You will be spinning dead weight in either option.

c: No, if you put in Low range depending on 4wd** , you will be in 2L if 4wd** is engaged you will be in 4L, if 4wd** is not engaged you will be in 2H, if you are in High range with 4wd** on then you are in 4H.

d: there are only 2 systems, that I know of, in the 4wd** system for activation, the engaging motor in your hubs and the 4H engaging mechanisms located in your transfer case. Not sure what he is talking about " actuator next to the front diff" You should be able to find and follow the wiring going to your hubs behind your front brake dust covers.

e: Never use 4H or Hublock buttons independently (on: off;off: on). In the scenario put in 4wd**, made sure you are in low range 2nd gear and crawl out. If you loose traction try to reverse and get a better driving line.
 
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