Low range with centre diff unlocked

Submitted: Friday, Dec 18, 2009 at 18:12

ThreadID: 74500 Views:5936 Replies:6 FollowUps:13

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Tenpounder (SA)

I have a Series 90 Prado V6 manual. As you know, this has constant 4WD, with a centre diff which is automatically (electrically) locked when in 'High Range Locked' and in 'Low Range Locked'. For slow speed manoeuvring with the caravan, I'd like to be able to unlock the centre diff while in Low Range.
I know it can be done, and I read that it's easy, BUT will someone please give me blow by blow instructions for a 'switch-operated diff unlocker' that will give me 'unlocked low range'.
Or is it harder than I thought?

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Reply By: MEMBER - Darian (SA) - Friday, Dec 18, 2009 at 18:19

Reply By: Mal58 - Friday, Dec 18, 2009 at 18:56

Friday, Dec 18, 2009 at 18:56

Hi Tenpounder.
The series 90 Prado comes in two versions of centre diff lock. One is mechanical and the other is electro-mechanical.

The purely mechanical one, there is no way you can go into low range without the centre diff locked.

For the electro-mechanical one, I believe that you can engage low range and have the centre diff unlocked.

Now I am not 100 % sure what models had the electro-mechanical arrangement, but I think it was only the auto Grande in the post 2000 build.

Is your's one of those ? If so, then there is a switch already that you use to lock the centre diff.

If not, then sorry, I don't believe that there is way not to have the centre diff locked when in low range.

Cheers,
Mal

AnswerID: 395630

Follow Up By: Tenpounder (SA) - Friday, Dec 18, 2009 at 19:26

Friday, Dec 18, 2009 at 19:26

Thanks, Mal. The difference between models may help to explain why the Haynes workshop manual is on a par with the latest Telstra help menu in this area. It sounds as though a March 1998 build GXL may well be a mechanical lock.
If you are wrong, Mal,I hope someone will set you right, but thanks for your contribution whichever way

FollowupID: 664205

Follow Up By: Mal58 - Friday, Dec 18, 2009 at 20:37

Friday, Dec 18, 2009 at 20:37

Hi Tenpounder,
Jan 1998 to Dec 1999 was the second revision of the 90 series Prado.

I have a January 1998 build GXL so mine is the same as yours.

Sorry, it's a mechanical engagement for the transfer case, so it is not possible to enage low range without centre diff lock.

Cheers,
Mal

FollowupID: 664216

Follow Up By: PradOz - Saturday, Dec 19, 2009 at 10:16

Saturday, Dec 19, 2009 at 10:16

Hi Mal

I am not sure about those dates? I think second version went to Nov 1999. I have the Dec 1999 model which I was told and have read before was first of the next series (2000 model). Also was told that when I enquired on a trade in one day and this was not a toyota dealership.

Not that it helps the original question; however, I do reverse my van up my short steep driveway with my Prado in low range. For the distance and time I feel the safety and ease of it outweighs any other risks. I can do it so much easier and quicker and always 1st go. cheers....

FollowupID: 664291

Follow Up By: Mal58 - Sunday, Dec 20, 2009 at 09:41

Sunday, Dec 20, 2009 at 09:41

Hi PradOz,
You may be right about Nov 1999 was the end of the second revision and Dec 1999 onwards being the beginning of the third revision.

I think the main differences were that the third revision 90 series Prado's had the white lenses(no globes in them though) in the top section of the tail lights, the "fog" lights in the front bumper bar, a catalytic converter and an oxygen sensor in the exhaust, the split second row of seats and of course the electro-mechanical engagement for the centre diff lock if an auto.

Cheers,
Mal

FollowupID: 664412

Reply By: Graham Watson - Saturday, Dec 19, 2009 at 10:20

Reply By: bbuzz - Saturday, Dec 19, 2009 at 20:08

Reply By: Member - Teege (NSW) - Sunday, Dec 20, 2009 at 08:41

Sunday, Dec 20, 2009 at 08:41

Chris
I have an August 2000 build auto Grande. It has an electric switch to engage the centre diff lock. It can be very difficult to disengage if I happen to leave it in for general driving. Has never actually locked up on me but I have spent up to 10 minutes reversing, throwing the steering around and doing whatever I can to get it out. On those occasions it makes quite a bang when it does disengage - clearly can't be good for it. Consequently I am quick to disengage it these days as soon as the need for it has passed. I know this doesn't help you, but it might explain why there are different stories floating around.

teege

AnswerID: 395779

Follow Up By: Member - Graham H (QLD) - Sunday, Dec 20, 2009 at 10:33

Sunday, Dec 20, 2009 at 10:33

Be careful or it will make a really big bang before you get it out.

As locking it in turns all the wheels at the same speeds it will ruin something pretty quick if you turn a few too many corners with the poor tyres scrabbling away at the bitumen.

Also makes cornering an interesting exersize.

FollowupID: 664419

Follow Up By: Member - Teege (NSW) - Sunday, Dec 20, 2009 at 21:57

Sunday, Dec 20, 2009 at 21:57

Graham
I have to disagree with you. The centre diff lock, as I understand it, only locks the drive between the front and rear axles - it locks the ratio of the drive to the two axles. (I think, something like 60-40 front to rear, but I'm not sure about that) It does nothing to the front or rear diffs and therefore has no major effect on the respective speeds of the right and left wheels. To lock the wheels I would require front and rear lockers as well. The vehicle is fitted with electronic traction control which continues to operate when the centre diff lock is engaged.As I said in my previous post, it clearly is not good for it to leave it engaged, so I take it out as soon as possible.

teege

FollowupID: 664538

Follow Up By: Member - Graham H (QLD) - Monday, Dec 21, 2009 at 09:38

Monday, Dec 21, 2009 at 09:38

Well whtaever but I accidentally hit the button on my 100ser and when I backed out of my drive the tyres were chirping and left huge black marks on the drive then when I got to the corner it had a strong desire to go straight ahead.

FollowupID: 664588

Follow Up By: Member - Timbo - Monday, Dec 21, 2009 at 15:32

Monday, Dec 21, 2009 at 15:32

That's because the centre diff lock will lock the front and rear axles together...
As you turn a corner, the front wheels take a wider arc (longer distance) than the rear wheels which tend to cut the corner. I think you'll find that Toyota would specifically recommend against driving with the centre diff locked on a firm surface (ie. bitumen).

It would be the same situation as driving a part-time 4WD in 4WD on the road (ie. no centre diff, just a dog-clutch that locks the front propeller shaft to the rear propeller shaft).

FollowupID: 664636