Driving on Bitumen in Low Range central diff lock engaged

Submitted: Tuesday, Sep 11, 2012 at 21:38
ThreadID: 97970 Views:6945 Replies:11 FollowUps:15
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Hi

A question for someone with a good knowledge of Toyota 4WD systems. I have a 6 sp manual diesel 120 series Prado which has constant 4WD. High range has options for either the central diff lock on or off. However, Low range only has central diff lock on.

Last week I headed from St Lawrence (south of Mackay) inland to Capella up the divide. The road in mostly gravel but there are several very steep sections (20% slope for about 5 km) that are sealed. Was towing a camper and it was a tough pull. Got up there in High 1st but was wondering what the options were if the road got steeper!!!!

My question is can Low range with the central diff lock engaged be used on hard surfaces. The Manual instruction is vague suggesting its for use on snow, mud etc. My understanding is that with this central lock engaged provides the same revolutions to both front and back axles but obviously the front and rear diffs can allow for different speeds of inner and outer wheels.

Any thoughts appreciated

cheers

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Reply By: Bob Y. - Qld - Tuesday, Sep 11, 2012 at 21:54

Tuesday, Sep 11, 2012 at 21:54
OE,

Reckon if you couldn't get up in high range, then you'd have to use Low, or reverse all way back down again.

With open diffs it shouldn't be too bad, and you would be using a much higher gear in Low, so there would some slip, even on bitumen. And the weight of the camper would induce some slip too, if the range was THAT steep.

Is that the road over Funnel Ck, and past May Downs? Sounds interesting.

Bob.

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Can't remember most of it.

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AnswerID: 494735

Follow Up By: outback epicurean - Wednesday, Sep 12, 2012 at 10:54

Wednesday, Sep 12, 2012 at 10:54
Hi

Road goes directly from St lawerance, steepest long stretch of bitumen I have ever driven on. Warning signs about steep road but usually these are a bit conservative but not in this case.
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FollowupID: 770396

Follow Up By: Lyn W3 - Wednesday, Sep 12, 2012 at 14:04

Wednesday, Sep 12, 2012 at 14:04
Tried to drive a very lightly loaded Table Top truck over that road many years ago. Don't think I got anywhere near the top before I had to back back about 1/2 mile before I found a wide enough place to do about a 12 point turn and that was hanging the back out over the edge.

Bloomfield Track is a piece of cake compared to that road.
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FollowupID: 770407

Follow Up By: Rockape - Wednesday, Sep 12, 2012 at 19:03

Wednesday, Sep 12, 2012 at 19:03
Yep,
you should have tried to drive up it when it was gravel and raining. It has been improved a heap now.


RA.
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FollowupID: 770423

Reply By: V8 Troopie - Tuesday, Sep 11, 2012 at 22:19

Tuesday, Sep 11, 2012 at 22:19
I had this problem with my Mitsi Challenger, it has a too high ratio first gear to take off on a hill while towing a near max towing capacity trailer.
I fixed that by disabling the front free wheel hub lockers - they are actually in the diff housing and are vacuum operated.
A switch in the cabin lets me disconnect the vacuum relays so I can engage low range but only have drive to the rear wheels. I can tow then in low range on bitumen until the road flattens enough to use high range 2WD or 4WD.
AnswerID: 494739

Follow Up By: PaulyT - Wednesday, Sep 12, 2012 at 17:28

Wednesday, Sep 12, 2012 at 17:28
Tried to PM you but can't or don't know how.

I'm wondering if you care to part with a little more info like what year/model challenger, manual/auto and which auto, diesel/petrol, etc.

Over on newtriton.net we are trying to work out how it can be done on the superselect auto so any info you would care to part with would be appreciated.

Paul
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FollowupID: 770414

Follow Up By: V8 Troopie - Wednesday, Sep 12, 2012 at 23:53

Wednesday, Sep 12, 2012 at 23:53
Paul, dunno about PM on this forum either - I'm just a regular visitor.
Challenger is late 2010 model, still current I think, manual, diesel 2.5 4 cyl. motor.

Its not too difficult once the correct vacuum hoses & associated solenoid valves are identified.
Klaus
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FollowupID: 770445

Reply By: Shaker - Tuesday, Sep 11, 2012 at 23:09

Tuesday, Sep 11, 2012 at 23:09
Definitely don't use low range on hard surfaces unless you keep in a straight line, otherwise it will wind up badly 7 cause damage.
This is the one & only reason that I am changing out of my current Prado.
AnswerID: 494742

Reply By: Muddy.au - Wednesday, Sep 12, 2012 at 07:17

Wednesday, Sep 12, 2012 at 07:17
Search for " 7 pin mod" here or on Lcool, this tells you how to remove the automatic locking of the centre diff in low.
AnswerID: 494746

Follow Up By: MEMBER - Darian, SA - Wednesday, Sep 12, 2012 at 11:51

Wednesday, Sep 12, 2012 at 11:51
Ditto to Muddy - I did the ''pin 7 mod'' on my 100 series to allow me to decide if I want the centre diff lock in or out, when in low range (the existing dash switch allows that choice). Its a huge bonus to have no centre lock, when shifting heavy trailers on a sealed slope, while in low. As to whether the mod fits with a Prado, I can't say.
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Follow Up By: Member - Bruce C (NSW) - Wednesday, Sep 12, 2012 at 18:20

Wednesday, Sep 12, 2012 at 18:20
As far as I know.

Many Prados have a silicone coupling which locks the centre diff when the diff slip generates sufficient heat, and therefore many do not have a switch like the 100 series. I do not know which models this pertains to but this might be one of them.

Probably Lcool in the Prado section will have the required info as Muddy says.

On the 80 and 100 series you only have to remove the connector from the back of the transfer box, about 1 oclock position, to remove the auto engage in low range, as I have done.

4 WD is then engaged by the 4WD button on the dash as you say Darian, brilliant if low range is needed for getting going with heavy loads. Also the 80 and 100 series apparently have a syncro which enables you to shift to high range from low range once you get moving fast enough.

Cheers, Bruce.
PS. happy to be enlightened if I have got it wrong
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Follow Up By: MEMBER - Darian, SA - Thursday, Sep 13, 2012 at 08:43

Thursday, Sep 13, 2012 at 08:43
G'day Bruce - 'shift on the fly' is indeed the go in my manual GXL 100 - when taking off on a slope with my van, I start in low range and shift to high range while mobile, when convenient (up to high - back a cog = about the same gearing). As for the pin 7, or simply to pull the plug on the transfer - talk on Lcool suggests (as I recall) that the ABS and other protocols are left 'uninformed' re gearing status if using the plug pull method - don't know how much it matters - and such outcomes would depend on the model in question too I guess.
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Reply By: Member - lyndon NT - Wednesday, Sep 12, 2012 at 07:59

Wednesday, Sep 12, 2012 at 07:59
This won't be much help BUT, can you feel a difference in the steering with the diff lock engaged? If not it won't be a true diff lock (I think). LOL
I have front and rear lockers on my Troopy, manually operated, you know when you have your front one in.

Good luck with it
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AnswerID: 494749

Reply By: sweetnam - Wednesday, Sep 12, 2012 at 08:31

Wednesday, Sep 12, 2012 at 08:31
You definately run the risk of gear wind up and it can cause damage. If you find that you have to do it to get up a hill, the best option is put the passanger wheel line off the edge into gravel and crawl up the hill, that way 2 Drivers side on tar, passanger side on dirt (if the road allows you to)

With the centre diff locked, straight lines are manageable but cornering becomes the issue and is where the wind up occurs.

Have a read through

http://www.exploroz.com/Forum/Topic/9822/Using_low_range_in_Prado.aspx

AnswerID: 494752

Follow Up By: garrycol - Wednesday, Sep 12, 2012 at 11:01

Wednesday, Sep 12, 2012 at 11:01
You have the nail on the head - definite no no to drive on the hard stuff but if all else fails driving with a wheel in the gravel on the side of the road which should allow the slip the system requires.

Garry
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Reply By: brianc - Wednesday, Sep 12, 2012 at 09:46

Wednesday, Sep 12, 2012 at 09:46
The wheel diffs accounts for the difference in speed inner to outer as noted, but it is the difference front to back that the centre diff will account for. Hence the wind up with a locked centre, hence the answer - no.
AnswerID: 494756

Follow Up By: Polaris - Wednesday, Sep 12, 2012 at 17:02

Wednesday, Sep 12, 2012 at 17:02
Spot on there. The reason being is that when negoating a turn, the front wheels travel a larger arc than the rear ones do - hence the need for a differential. With the centre diff locked on firm surfaces, wind-up will occur and eventual damage to some components. The front CV joints are usually, but not always, the weakest link.
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FollowupID: 770413

Reply By: Member - Oldbaz. NSW. - Wednesday, Sep 12, 2012 at 17:01

Wednesday, Sep 12, 2012 at 17:01
If I was a mischevious old lad I would probably point out that such issues are not
even contemplated by those of us that drive part time 4wd (remember them?). They
were around in the days when the driver could still decide when to have 4WD, even
drive around all day in low range 2wd, on any surface, if the whim took them. No
wonder such frivilous pursuits are now denied the driver of the modern 4wd...just
too much fun..& far too practical...:))))).......oldbaz.
AnswerID: 494770

Follow Up By: garrycol - Wednesday, Sep 12, 2012 at 17:39

Wednesday, Sep 12, 2012 at 17:39
Same if you drive a landrover of any sort - full or part time - low range is available without centre diff lock being engaged.
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FollowupID: 770415

Follow Up By: Member - Bruce C (NSW) - Wednesday, Sep 12, 2012 at 18:30

Wednesday, Sep 12, 2012 at 18:30
Yep Oldbaz and Garrycool, 80 and 100 series have the same option open to them. All you have to do is remove one electrical connector from the back of the transfer case and 4WD, or the centre diff lock, is then selected from a switch on the dash, if the driver wishes.

The driver then decides if they will have 4WD or not, in any range, hi or low.

Cheers, Bruce.
At home and at ease on a track that I know not and
restless and lost on a track that I know. HL.

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Follow Up By: disco driver - Wednesday, Sep 12, 2012 at 18:42

Wednesday, Sep 12, 2012 at 18:42
Just remember that in 2wd low range all the torque is being applied to one set of axles (2 Wheels) only rather than to all 4 wheels. Low Range multiplies the torque at the wheels
This automatically increases the risk of blowing a diff or busting an axle in adverse conditions where wheelslip is not possible.

Unless it's a real emergency situation I definitely would not drive far on blacktop in low range with the centrediff locked.

Disco.
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Follow Up By: Member - Captain (WA) - Thursday, Sep 13, 2012 at 08:53

Thursday, Sep 13, 2012 at 08:53
Hi Oldbaz,

Toyota must have woken up to the problem, on the 200 the centre diff lock is manually selected. You can be in high or low range without the centre lock, great for reversing a van up a very steep drive.

Cheers

Captain
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Reply By: Rockape - Wednesday, Sep 12, 2012 at 19:25

Wednesday, Sep 12, 2012 at 19:25
Mate,
no one can state whether damage has been done or not but here is my bet.

I believe you may or may not have only caused very slight wear over that amount of tar seal and I wouldn't worry about it.

For instance our cruisers are loaded and run low range 4wd all the time.They would do about 2 K's on tar in 24 hours with hard 90 and 180 turns. They buck a bit under on the tar but the cv's last about 4 to 5 months which is normal for these vehicles even if they don't run on bitumen.

I accidentally drove a 25.280 MAN with a fully loaded trailer 100k on bitumen with the cross locks in and those diffs, hub reductions and axles weren't touched for well over 1.2 million K.

RA.
AnswerID: 494774

Follow Up By: gbc - Thursday, Sep 13, 2012 at 05:47

Thursday, Sep 13, 2012 at 05:47
My dear father made it from hervey bay to brisbane in an 80 series with the centre diff locked. Cost him a set of tyres but the cruiser is still o.k. to this day - amazingly.
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FollowupID: 770448

Reply By: Shaker - Thursday, Sep 13, 2012 at 09:36

Thursday, Sep 13, 2012 at 09:36
As a Prado 120 series owner, I think it is just mindless design from a company that obviously doesn't think of the end user!
AnswerID: 494791

Reply By: Member - Tony (ACT) - Thursday, Sep 13, 2012 at 11:35

Thursday, Sep 13, 2012 at 11:35
I was under the impression that the Centre Diff Lock is not a Diff lock as such just shares equal drive between the front and rear axles. Without it engaged there is 60o/o drive to the rear and 40 o/o drive to the front.

A diff lock locks both wheels to turn at the same speed.
AnswerID: 494795

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