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What Does The Diff Lock Actually Do?


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#1 webleymk3

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Posted 27 October 2010 - 03:10 PM

Does anybody know what the Diff Lock actually does??

A proper diff lock should lock all the wheels together such that if at least one tyre has traction the vehicle should be able to move. I tried it 'properly' today and almost got completely stuck (really close call!). When I got out to look, two of the wheels looked like they should have been fine. As I was on my own I couldn't check whilst trying to move but i wondered if anyone knew to what extent the wheels locked??

Thanks

Webbles(!)

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#2 bothwell_buyer

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Posted 27 October 2010 - 09:50 PM

I know the cobbles in edinburgh are slippy but having to use diff lock seems extreme. Have you checked your tread depth?? :lol:

Diff lock means different things to different models.

On the 4.1, it essentially locks the front and back...so when I do a 1/4 mile standing start sprint and the front wheels come off the ground, with diff lock I still get traction from the back wheels and the fronts don't spin so fast that the car bounces when it lands back on ground.

I believe later versions are quite different in operation... then one gets traction control systems for owners who have trouble controlling a 5 door dieselly oil burning 2 ton monster.

When it comes down to it, your selection of tyre plays a major part, and what tread is left. try going up to Crail one Sunday and you'll see what I mean.

#3 anchorman

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Posted 27 October 2010 - 10:10 PM

Hi Web

Its easy to get confused with terminology. There is no diff lock on your 4.3. It has a 4WD lock switch which does something quite different. On the nose of the rear axle there is a multi plate clutch which can be steplessly engaged up to a ratio of 55:45 front to rear. In fact the front transaxle and the rear drive axle have conventional diffs which means that like any other vehicle you can get one wheel spinning on a low friction surface.

However, this clutch is normally operated by the main ECU and it is programmed to give you the best combination of drive and economy. Your RAV ALWAYS sets off in 4WD (except when the steering is turned so as to avoid drag from the transmission) but as you gather speed it gradually backs off and becomes 2WD. If you floor the accelerator you engage the clutch again so normally you will not need a traction control (although it exists electronically on XT4 models and up with the VSC system).

There are times like when stuck in the mud or snow that the electronics get a bit counterproductive through clashing with each other and in that case you can operate the 4Wd lock switch. That forces the full 55:45 drive ratio and the traction control contiues to try to deal with left right wheel spin of the front and rear wheels. As you have found it isn't flawless and these are not true off roaders. You need a proper front/rear diff lock (of a usual third diff) and also left right diff locks on the axles.

As bothy says, the 4.1 has the former which is lockable and the 4.2 has an ingenious way of utilising the front diff for the rear axle. Early 4.2s also had a limited slip rear axle but this was dropped on later models.

The beauty of your 4.3 system is that it can be integrated into the VSC and electric steering to give astonishing capabilities for handling and safety.

Attached File  4WD.pdf   209.31KB   122 downloads

#4 bothwell_buyer

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Posted 27 October 2010 - 10:59 PM

Hi Web

Its easy to get confused with terminology. There is no diff lock on your 4.3. It has a 4WD lock switch which does something quite different. On the nose of the rear axle there is a multi plate clutch which can be steplessly engaged up to a ratio of 55:45 front to rear. In fat the front transaxle and the rear drive axle have conventional diffs which means that like any other vehicle you can get one wheel spinning on a low friction surface.

However, this clutch is normally operated by the main ECU and it is programmed to give you the best combination of drive and economy. Your RAV ALWAYS sets off in 4WD (except when the steering is turned so as to avoid drag from the transmission) but as you gather speed it gradually backs off and becomes 2WD. If you florr the accelerator you engage the clutch again so normally you will not need a traction control (although it exists electronically on XT4 models and up with the VSC system).

There are times like when stuck in the mud or snow that the electronics get a bit counterproductive through clashing with each other and in that case you can operate the 4Wd lock switch. That forces the full 55:45 drive ratio and the traction control contiues to try to deal with left right wheel spin of the front and rear wheels. As you have found it isn't flawless and these are not true off roaders. You need a proper front/rear diff lock (of a usual third diff) and also left right diff locks on the axles.

As bothy says, the 4.1 has the former which is lockable and the 4.2 has an ingenious way of utilising the front diff for the rear axle. Early 4.2s also had a limited slip rear axle but this was dropped on later models.

The beauty of your 4.3 system is that it can be integrated into the VSC and electric steering to give astonishing capabilities for handling and safety.

Attached File  4WD.pdf   209.31KB   122 downloads


nice explanation ---- but have you seen the state of the Edinburgh cobbles whilst they re-invent the tram?? Only Rome was worse and thats cos the cobbles are loose due to the Romans skimping on materials 2000 years ago. Edinburgh are re-fitting the roads with rails for the tram system - funny really as passengers will alight into the slow lane of normal traffic. But them what do you expect from an investment of squillions of pounds?

Webleymk3 - you could try keepig a spare set of wheels from a railway wagon to swap when the weather is poor. then you can use the excuse at work that leaves on the line/ snow on the rails/ etc - if need be, ask ancs to give you more examples. :lol:

#5 webleymk3

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Posted 28 October 2010 - 07:24 AM

Those cobble are a nightmare!!! I don't think the Romans even let it get this bad.. The railway wheels modifcation is on order :thumbsup: though so will hopefully resolve the inner Edinburgh transport problem!

I had done up a very steep muddy slope which she managed however as I turned off it onto the grass to turn round she ran into problems. Just started slipping all over the place. The back tyres would not have helped and I am in discussions with the dealer about getting new ones FOC as they are not in the great condition!

Anchs, thanks for the detailed response and attachment. Interestingly Mr T told me it WAS a diff lock! Eejit!

#6 junebug1701

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Posted 29 October 2010 - 04:49 AM

This site does a good job of explaining the various 4WD systems employed by Toyota, including the RAV4. It's meant for training Toyota sales people in the US, so it's geared toward North American models. The graphics and animations make it very easy to understand, which is good because it's meant for training Toyota sales people. :D

http://www.majormedi...fiedv5/4WD.html

#7 crofter

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Posted 29 October 2010 - 07:48 AM

Absolutely brilliant find jb.
Not seen it all yet but even a numpty like me can understand it.
A picture paints a thousand words, eh? :thumbsup: :thumbsup: :thumbsup:
Thank you.
Del

#8 GreyRacer

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Posted 29 October 2010 - 10:57 AM

Those cobble are a nightmare!!! I don't think the Romans even let it get this bad.. The railway wheels modifcation is on order :thumbsup: though so will hopefully resolve the inner Edinburgh transport problem!

I had done up a very steep muddy slope which she managed however as I turned off it onto the grass to turn round she ran into problems. Just started slipping all over the place. The back tyres would not have helped and I am in discussions with the dealer about getting new ones FOC as they are not in the great condition!

Anchs, thanks for the detailed response and attachment. Interestingly Mr T told me it WAS a diff lock! Eejit!



webleymk3. I assume your forum name comes from that model that you own. You are not a member of JGARC in Edinburgh by any chance.

#9 Big Kev

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Posted 31 October 2010 - 08:18 AM

Take note all ye south of Gretna.....it's all the EDINBURGH folk who are conversing re. rifles / airguns / weaponry !!!!!

Big Kev :eek: :lol: :lol:

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