Free Wheel Hubs connected to diff lock?

[patrickr]

Hi chaps,

I recently bought a 1987 SC Hilux (4x4 duh). Everything is okay- interior needs some TLC, wiring needs some looking at, but other than that it seems mechanically sound :D .

So, yesterday I took it out to a local "4x4 track". Its more like a park with some humps, but that doesn't matter. I started playing around with the 4x4 and Low range and what not. First it took a bit of trail and error to figure out the shifting pattern on the transfer gear shift, but I eventually got it. Then, once I sorted all that out, I wanted to try the 4x4 for real, and so obviously I locked the front hubs. The thing is this- when I engage those hubs, the rear diff gets locked! I saw it with my own eyes- when taking sharp corners the wheels did the trademark "jumping" as with a diff lock on. With the hubs on free, none of this happens!

So my questions is this- what is going on??? I understood the front hubs to engage 4wd on the front wheel only!? The hubs are Aisin, and I had a look at the rear diff, and there doesn't appear to be any diff lock as such, although I am no expert in this area. Could you guys maybe give me some insight into this as I don't know what is going on

Regards,
Patrick

[Mud Dog]

Do not engage hubs and 4x4 on a hard or even semi hard surface unless you're moving in a straight line. You can do serious damage to the gear train.
What you were experiencing (the wheel hop) indicates that you had more than reasonable traction otherwise it would have slipped more smoothly. The reason is this, even though there is no diff lock and the wheels on an individual axle can still rotate at different rates while turning, (the inner arc is shorter than the outer), the arc between the front axle and rear axle also differ. You can see how much they differ if you look at your tracks left in sand when you turn. This different rate of overall rotation (the combined distance travelled by both wheels on the same axle) between the two axles results in axle wind-up (vehicles with a centre diff can overcome this problem) and has to be relieved somehow. Either a wheel slips or you snap a half-shaft / strip a diff / break a transfer box or a hub lock. If you can feel that the vehicle does'nt want to turn while 4x4 is engaged, it's a good indicator that you don't require 4x4 .... don't force it, something will give and next time it might not be that tyre that slips.

Consider yourself lucky that you learned this lesson without having to pay exorbitant 'school fees'.

[patrickr]

Wow okay yeah I reackon that is pretty lucky!!! that would have been a huge disappointment on my first outing!

So there is no diff lock, but axle wind-up.... Okaay I get that, but if i engage L4 on the transfer box, without locking the free wheel hubs, what does that mean? Are both axles (rather all wheels) being driven, or just the rear axle and wheels?

The reason i ask the is that in Andrew St. Pierre white's book, he recommends driving in 4wd on gravel roads. Okay maybe not recommends, but he claims that there is no detremental effect on the vehicle besides an increase in fuel consumption and maybe a bit more tire wear. Is this wrong? What is the general consensus in this regard?

[Mud Dog]

Wow okay yeah I reackon that is pretty lucky!!! that would have been a huge disappointment on my first outing!

So there is no diff lock, but axle wind-up.... Okaay I get that, but if i engage L4 on the transfer box, without locking the free wheel hubs, what does that mean? Are both axles (rather all wheels) being driven, or just the rear axle and wheels?

If the front hubs aren't locked, there is no drive connection to the front wheels. In the scenario you describe above you would have low range drive to the rear wheels only. The front diff and side shafts will be turning (extra friction, thus extra fuel consumption) but those turning side shafts are not driving the front wheels.

The reason i ask the is that in Andrew St. Pierre white's book, he recommends driving in 4wd on gravel roads. Okay maybe not recommends, but he claims that there is no detremental effect on the vehicle besides an increase in fuel consumption and maybe a bit more tire wear. Is this wrong? What is the general consensus in this regard?

ASPW would generally be right, if it's gravel roads with loose gravel ... not compacted stuff that is hard and so not allowing any slip of the wheels. Only very little slip is required unless it's a road with a lot of sharp turns. Using 4x4 on loose gravel, muddy or otherwise slippery roads (NOT TAR), can improve road holding, but it's a slightly different feel to 2x4, so get accustomed to it first before you try belting along the gravel at 80k plus. I would agree that there is a little more tyre wear, but it's really very insignificant. Fuel consumption will be noticeably a little higher.

What I do, especially if I know the gravel road is sufficiently bad in places where I would benefit from 4X4, I lock the hubs and leave it in H2 (2x4). When I get to the bad places I slow down to about 60 and slip the X-fer into H4 on the fly. I also slip it back out on the fly after the bad sections. When you do this (either in or out), do it while you're moving in a straight line (only needs a second or two), also try match the engine speed with the road speed ... that is, not under acceleration or deceleration .... slips in or out with ease. They say you can slip from H4 to L4 on the fly at very low speeds of about 4 kph but I would certainly not attempt it at speeds that are any higher.

Hope that helps.

[patrickr]

Yeah thanks Mud Dog that def. clears things up a hang of alot! Thanks for all your help mate. I was just worried that the bloke before me had installed a diff lock or some thing and had jypoed it up in some wierd cofiguration!

Okay that makes he a whole lot happier Now i just gotta worry about the interior... Eish :)

Anyways better get back to the rugby...... My bloed is nie blou nie, maar ZA is baie meer beter as Skaapies!

P.S. i didnt get an owners manual with my 'lux, but is there anywhere that I can download one from?

[Mud Dog]

There might be .... I seem to recall seeing something like that ... not sure if it was for the KZ though. A lot of the guys here have manuals and upload sections on request. If you can;t get hold of one, just post your queries here (use the appropriate forum e.g. "Technical Discussion") and someone is bound to assist.