Dumb Questions

Submitted: Monday, Oct 13, 2003 at 11:15

ThreadID: 7775 Views:2523 Replies:5 FollowUps:8

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Jimmy

After reading an earlier post about dumb questions I began to think and realised I have quite a few of my own. I wonder if someone would be kind enough to indulge my simple mind and explain a few things for me.

How do auto-locking hubs work?

Do I need to service them?

Why do I have to reverse about two feet to disengage 4wd after changing from 4h to 2h ( the light on the dash goes out but the tyres are still trying to tear themselves to shreds on the bitumen unless I reverse)?

My vehicle smokes a bit A good strong puff of black smoke on acceleration a bit of blue (maybe Grey/blue) on start up and none at idle is this noraml for a 91 Turbo Deisel?

Is it benificial to lower the tyre pressures on a trailer if towing through soft sand?

How does a Suzuki get stuck up to the axles less than 5 metres from the entry to the beach?

Why was there a bloke doing circle work next to the flagged area at Rainbow beach (Sunshine Coast) in a brand new Subaru with shiny mags and low profile tyes?

Ok must go now and prepare my brain for the wealth of knowledge that may just be heading my way. If it may assist in the answering of the above my vehicle is a 91 Nissan Terrano 2.7 Turbo Deisel and this forum is the best!

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Reply By: Rhubarb - Monday, Oct 13, 2003 at 12:25

Reply By: Martyn (WA) - Monday, Oct 13, 2003 at 14:09

Monday, Oct 13, 2003 at 14:09

Jimmy,
Firstly, no such thing as dumb questions,somebody will always take information even if they won't openly admit to not knowing.
Auto locking hubs rely on the drive shaft from the axle spining an internal cam via some spring force that locks the wheel hub to the drive shaft, I can't find an easy way to describe the internals. When ever you are doing serious off road work it's always better to engage the hub in the locked position, when going down hills where the load can be on and off the hub it can disengage and freewheel, my mate had this proved a bit frightening the first couple of times it happened. He's also now on his third hub, smashed two of them, one was built up incorrectly by the mechanic, that didn't help. He's now changed them out and put the "normal" hubs on they are a direct replacement, no mods needed, cheaper as well. Means you have to get out of the vehicle one more time, so what...
All the smoking issues you mention are normal to a point, depends on the K's if you are looking at 200K on the pump and injectors could be getting close to needing a service. The black smoke on start up is the injector pump choke,plus a small amount of residual fuel leaking past the injectors when you switch off.
Suzuki stuck on sand, unlikely unless someone dug out the sand from under the wheels with a shovel, or taken the wheels off could also be an issue.
Sorry I'm not interested in the Subaru thing, don't know where Rainbow beach is, never mind the flagged area..........
Keep the shiny side up

AnswerID: 33597

Follow Up By: Jimmy - Monday, Oct 13, 2003 at 21:04

Monday, Oct 13, 2003 at 21:04

"When ever you are doing serious off road work it's always better to engage the hub in the locked position"

Sorry Martyn what do you mean by this? Is there a way to manually lock into auto hubs?

The Klms on the car are about 1600000 and from what you say the amount of smoke seems normal. thanks for the peace of mind

FollowupID: 24169

Follow Up By: Martyn (WA) - Monday, Oct 13, 2003 at 22:12

Monday, Oct 13, 2003 at 22:12

Jimmy,
If you look in the centre of the auto locking hub you should see the writing in the centre saying auto and lock, there will be a hex nut in the centre and an arrow you just turn the arrow until it aligns with the word LOCK, remember to unlock when you've finished. If I remember correctly the hex nut is the same size as the wheel nut so you just use your wheel brace to change the position. In my opinion I would get rid and fit the manual hub lock, again my opinion. The manual hubs are cheaper and in my opinion better. Hope this helpsKeep the shiny side up

FollowupID: 24176

Follow Up By: Martyn (WA) - Monday, Oct 13, 2003 at 22:27

Monday, Oct 13, 2003 at 22:27

Jimmy,
I suspect the auto hubs have been fitted instead of the manual hubs, I don't think the auto hubs where introduced until later 94 maybe 95. Mines a 92 and still has the manual hubs. Maybe somebody else knows.Keep the shiny side up

FollowupID: 24181

Follow Up By: Member - Oskar(Bris) - Tuesday, Oct 14, 2003 at 08:30

Tuesday, Oct 14, 2003 at 08:30

My Terrano is a '92 and has the auto hubs.
There is no manual lock on them.
The hubs can "slam" pretty badly (you would think they broke) if rocking the vehicle from forward to reverse in, say, a tight 3 pointer in soft sand. I have inspected the hubs and they seem OK (for now).
You have to reverse in 2WD to unlock the hubs.
I have never let the tyre pressure down on my trailer and have never had it bogged. Other people have had different experiences I suppose.
Re: Scooby-Doo ..... Idiots are everywhere, giving us all a bad name.
The idea of auto-hubs disengaging down hill seems pretty scary but it shouldn't happen.
Cheers
OskarMrs Oskar on Big Red

FollowupID: 24206

Reply By: Member - Ken - Monday, Oct 13, 2003 at 17:49

Monday, Oct 13, 2003 at 17:49

Jimmy

The need to reverse to move to move from 4H to 2H is due to to a thing called 'windup' that happens to 4WD'S that aren't of the constant variety.

It's a Tech Concept that is to hard to explain properly in this forum, however suffice it to say tat sometimes, most times and in some vehicles all the time, you are required to do the reverse thing in different variations to make the transfer from 4H to 2H.

In essence what you are doing by reversing is releasing 'windup' pressure in the transmission/transfer case.

Also this is why you DO NOT drive this type of 4WD on bitumen/hard surfaces.

Regards

Ken Robinson

AnswerID: 33627

Follow Up By: Jimmy - Monday, Oct 13, 2003 at 21:00

Monday, Oct 13, 2003 at 21:00

Hey Ken
I take it that what you are reffering to is different from diff wind up and is occuring between the front and rear diffs.
If the front wheels have a different rolling circumference to the rear and the vehicle is driven along hard packed sand while in 4wd causing the wind-up then driven through soft sand up a cutting should the drive through the soft sand usually be enough to dissipate the wind-up?
Thanks for your informative response

FollowupID: 24165

Follow Up By: Member - Ken - Monday, Oct 13, 2003 at 21:36

Monday, Oct 13, 2003 at 21:36

Jimmy

You are on the right track, but over to the side a bit.

This windup thing is very difficult to explain without making a dick of ones self unless one is an Auto Engineer, however I'll have a go.

Approx 2 yrs ago I had to undertake a 4WD course prior to going overseas for my employer.

During this course there was segment dedicated to windup.

They had a 4 wheel drive train (cut away version) demo setup so you could follow the theory line as the engineer explained 'windup'.

Now you are dead right about the difference between the front and rear diffs being the cause, why - not in this forum.

However the wind up takes place in the transmission/transfer area and can do so to such an extent the the transmission/transfer is totally lockedup and has to be tossed.

At this course we were told that driving on soft surfaces including hard packed beach sand allows the tyres to 'unwind' on a regular basis by undergoing little tyre surface slips as the tension builds .

Where as on bitumen etc the weight of the vehicle and friction doesn't allow this and hence the windup accumulates as the vehicle is driven forward.

The aforementioned engineer told a story of how he was given a vehicle so 'woundup' it was locked in gear. He stated that he managed to 'unwind' it by completing an intricate figure 8 sequence in reverse, however the transmission was damaged beyond repair from the stress of it all.

Now what you are experiencing is a tad of un released 'windup' when attempting to change from 4H to 2H etc. The reversing trick 'unwinds it and releases that tension.

In mine I sometimes have to reverse 10 - 20 feet on up to 3 attempts to release it.

So you aren't the lone ranger here. Just don't force the shift lever. It should glide when there is no 'windup'

Regards

Ken Robinson

FollowupID: 24172