Center Diff Lock

[ChrisG333]

Hi All

I wonder if anyone can help?

When pressing the Center Diff Lock button the light on the dash comes on, at the same time I can hear a faint buzz from under the car so I assume that the actuator / servo is doing something also i can hear a relay click in the engine bay.

When depressing the button the light on the dash goes out and again I hear a faint buzz type sound a bit like an electric motor from under the car for a couple of seconds but no buzzer or beeps sound in the car, which by reading other posts on here it should do this while the Diff Lock is disengaging?

Was just wondering what to check this weekend to see if it's working, I never go off road so it makes little difference if it works or not but as everything else works perfectly it would be a little anoying if this doesn't.

Thanks for any help.

Chris

[anchorman]

Hi

Buzzers and beeps only occur with such items as Hill Assist Control and Vehicle Stability Control but not with the four wheel drive button. There is a warning light.

When the four wheel drive button is off, the system is fully automatic. There is no centre diff', instead there is a conventional transverse front wheel drive gearbox and a drive shaft that is permanantly connected to the rear axle via a transfer box. The clever bit is in the nose of the rear axle. There is a multi plate clutch that is engaged by an electric servo. The servo can be steplessly engaged from zero to 55/45% front to rear. It works by twisting a helix through several degrees to vary the amount of clamping force on the clutch and therfor drive transmitted to the rear axle. The car starts in four wheel drive every time you set off. For this reason you will never experience front wheel slip under heavy acceleration and NORMAL traction control is completely unnecessary. As the speed increases and the torque from the engine reduces the servo backs off the servo and begins to reduce the drive through the clutch to the axle, eventually becoming completely front wheel drive to improve fuel consumption. The system is also connected to the vehicle stability control and will vary the drive to the rear axle in order to control a skid. You have no input to the normal or the skid control of the rear axle, it is all controlled by computer and varies dramatically upon throttle position, road speed and load.

However, it is not flawless and there could be certain times when you need to override the automatic sysytem. For instance, I have already stated that the car always sets off in four wheel drive regardless of whether you are on a dry road under perfect conditions or on ice. The exception is if you set off (eg from a junction) with the front wheels turned to full lock. The system will back off the drive to the rear axle from 45% to around 5% (easy to monitor because the car has electronic steering which is linked into the equation). This is to prevent wind up in the transmission that would normally be overcome with a third diff', it is self regulating and completely variable and automatic. Now imagine some difficult conditions. You are starting off on a steepish hill in the snow with the wheels turned on full lock. The computer cannot detect low adhesion and you may have problems starting because the it has backed off the drive to the rear axle. It will try to overcome the problem by applying the brake on any skidding wheel in order to obtain traction from a wheel with better grip. This is a kind of "reactionary traction control" to exceptional conditions. But if you have experienced ABS or traction control activity you will know that it is a bit intermittent and some throttle control is removed until the condition is stabilised. This would be a good time to use the manual four wheel drive switch. There are other examples but I can best summarise by saying if you appear to get stuck, use the manual override! You may never normally go off road but you will inevitably drive in the snow or even park in a field (such as a fete or other country event) at some time.

The symptoms you describe regarding noises are completely normal as the relays controlling the servo click in and the servo motor on the rear axle responds by fully engaging the clutch to its maximum of 45%.

As a matter of interest, if you engage it and set off you will find it switches itself off at about 25mph and it will not re-engage above this speed. This is to prevent any unnecessary wind up in the transmission described earlier. Don't worry, you can try it and it will not do any harm.

Hope this puts your mind at rest.

Regards

[Steve@Aberdeen]

Nicely written, Anchorman - good piece of "word engineering" (as a colleague recently commented on one of my reports).

[anchorman]

Nicely written, Anchorman - good piece of "word engineering" (as a colleague recently commented on one of my reports).

Why thankyou!

A good example of why use 2 words when 200 will do!!! ;)

Regards

[ChrisG333]

Hi

Buzzers and beeps only occur with such items as Hill Assist Control and Vehicle Stability Control but not with the four wheel drive button. There is a warning light.

When the four wheel drive button is off, the system is fully automatic. There is no centre diff', instead there is a conventional transverse front wheel drive gearbox and a drive shaft that is permanantly connected to the rear axle via a transfer box. The clever bit is in the nose of the rear axle. There is a multi plate clutch that is engaged by an electric servo. The servo can be steplessly engaged from zero to 55/45% front to rear. It works by twisting a helix through several degrees to vary the amount of clamping force on the clutch and therfor drive transmitted to the rear axle. The car starts in four wheel drive every time you set off. For this reason you will never experience front wheel slip under heavy acceleration and NORMAL traction control is completely unnecessary. As the speed increases and the torque from the engine reduces the servo backs off the servo and begins to reduce the drive through the clutch to the axle, eventually becoming completely front wheel drive to improve fuel consumption. The system is also connected to the vehicle stability control and will vary the drive to the rear axle in order to control a skid. You have no input to the normal or the skid control of the rear axle, it is all controlled by computer and varies dramatically upon throttle position, road speed and load.

However, it is not flawless and there could be certain times when you need to override the automatic sysytem. For instance, I have already stated that the car always sets off in four wheel drive regardless of whether you are on a dry road under perfect conditions or on ice. The exception is if you set off (eg from a junction) with the front wheels turned to full lock. The system will back off the drive to the rear axle from 45% to around 5% (easy to monitor because the car has electronic steering which is linked into the equation). This is to prevent wind up in the transmission that would normally be overcome with a third diff', it is self regulating and completely variable and automatic. Now imagine some difficult conditions. You are starting off on a steepish hill in the snow with the wheels turned on full lock. The computer cannot detect low adhesion and you may have problems starting because the it has backed off the drive to the rear axle. It will try to overcome the problem by applying the brake on any skidding wheel in order to obtain traction from a wheel with better grip. This is a kind of "reactionary traction control" to exceptional conditions. But if you have experienced ABS or traction control activity you will know that it is a bit intermittent and some throttle control is removed until the condition is stabilised. This would be a good time to use the manual four wheel drive switch. There are other examples but I can best summarise by saying if you appear to get stuck, use the manual override! You may never normally go off road but you will inevitably drive in the snow or even park in a field (such as a fete or other country event) at some time.

The symptoms you describe regarding noises are completely normal as the relays controlling the servo click in and the servo motor on the rear axle responds by fully engaging the clutch to its maximum of 45%.

As a matter of interest, if you engage it and set off you will find it switches itself off at about 25mph and it will not re-engage above this speed. This is to prevent any unnecessary wind up in the transmission described earlier. Don't worry, you can try it and it will not do any harm.

Hope this puts your mind at rest.

Regards

Hi

Thanks for the explanation.

I think you might be refering to the later models?

Mine is a 1994 (4.1).

Reading lots of posts on Ravworld and here the general consensus seems to be that it is operated via a vacuum hose which is opened by a solinoid via a relay when the switch is pressed, when the C-Diff is disengaging there is meant to be either a beeping noise or buzzer sounding until it fully disengages.

Mine does not make any noise other than the faint buzzing for a few seconds that I refered to in my earlier post.

But many thanks for taking the time and the trouble to reply.

Chris

[ian2144]

Hi

Buzzers and beeps only occur with such items as Hill Assist Control and Vehicle Stability Control but not with the four wheel drive button. There is a warning light.

When the four wheel drive button is off, the system is fully automatic. There is no centre diff', instead there is a conventional transverse front wheel drive gearbox and a drive shaft that is permanantly connected to the rear axle via a transfer box. The clever bit is in the nose of the rear axle. There is a multi plate clutch that is engaged by an electric servo. The servo can be steplessly engaged from zero to 55/45% front to rear. It works by twisting a helix through several degrees to vary the amount of clamping force on the clutch and therfor drive transmitted to the rear axle. The car starts in four wheel drive every time you set off. For this reason you will never experience front wheel slip under heavy acceleration and NORMAL traction control is completely unnecessary. As the speed increases and the torque from the engine reduces the servo backs off the servo and begins to reduce the drive through the clutch to the axle, eventually becoming completely front wheel drive to improve fuel consumption. The system is also connected to the vehicle stability control and will vary the drive to the rear axle in order to control a skid. You have no input to the normal or the skid control of the rear axle, it is all controlled by computer and varies dramatically upon throttle position, road speed and load.

However, it is not flawless and there could be certain times when you need to override the automatic sysytem. For instance, I have already stated that the car always sets off in four wheel drive regardless of whether you are on a dry road under perfect conditions or on ice. The exception is if you set off (eg from a junction) with the front wheels turned to full lock. The system will back off the drive to the rear axle from 45% to around 5% (easy to monitor because the car has electronic steering which is linked into the equation). This is to prevent wind up in the transmission that would normally be overcome with a third diff', it is self regulating and completely variable and automatic. Now imagine some difficult conditions. You are starting off on a steepish hill in the snow with the wheels turned on full lock. The computer cannot detect low adhesion and you may have problems starting because the it has backed off the drive to the rear axle. It will try to overcome the problem by applying the brake on any skidding wheel in order to obtain traction from a wheel with better grip. This is a kind of "reactionary traction control" to exceptional conditions. But if you have experienced ABS or traction control activity you will know that it is a bit intermittent and some throttle control is removed until the condition is stabilised. This would be a good time to use the manual four wheel drive switch. There are other examples but I can best summarise by saying if you appear to get stuck, use the manual override! You may never normally go off road but you will inevitably drive in the snow or even park in a field (such as a fete or other country event) at some time.

The symptoms you describe regarding noises are completely normal as the relays controlling the servo click in and the servo motor on the rear axle responds by fully engaging the clutch to its maximum of 45%.

As a matter of interest, if you engage it and set off you will find it switches itself off at about 25mph and it will not re-engage above this speed. This is to prevent any unnecessary wind up in the transmission described earlier. Don't worry, you can try it and it will not do any harm.

Hope this puts your mind at rest.

Regards

I thought all Rav 4's were permenant 4 wheel drive......and my local dealer thinks so as well !!

I asume the above info is all in the hand book then?

Ian.........

[chatman]

I thought all Rav 4's were permenant 4 wheel drive......and my local dealer thinks so as well !!

I asume the above info is all in the hand book then?

Ian.........

I believe the 4.1 had the this option my 4.2 model and 4.3 models are permanent 4X4.....and newer models have HDC....

[anchorman]

Hi

Buzzers and beeps only occur with such items as Hill Assist Control and Vehicle Stability Control but not with the four wheel drive button. There is a warning light.

When the four wheel drive button is off, the system is fully automatic. There is no centre diff', instead there is a conventional transverse front wheel drive gearbox and a drive shaft that is permanantly connected to the rear axle via a transfer box. The clever bit is in the nose of the rear axle. There is a multi plate clutch that is engaged by an electric servo. The servo can be steplessly engaged from zero to 55/45% front to rear. It works by twisting a helix through several degrees to vary the amount of clamping force on the clutch and therfor drive transmitted to the rear axle. The car starts in four wheel drive every time you set off. For this reason you will never experience front wheel slip under heavy acceleration and NORMAL traction control is completely unnecessary. As the speed increases and the torque from the engine reduces the servo backs off the servo and begins to reduce the drive through the clutch to the axle, eventually becoming completely front wheel drive to improve fuel consumption. The system is also connected to the vehicle stability control and will vary the drive to the rear axle in order to control a skid. You have no input to the normal or the skid control of the rear axle, it is all controlled by computer and varies dramatically upon throttle position, road speed and load.

However, it is not flawless and there could be certain times when you need to override the automatic sysytem. For instance, I have already stated that the car always sets off in four wheel drive regardless of whether you are on a dry road under perfect conditions or on ice. The exception is if you set off (eg from a junction) with the front wheels turned to full lock. The system will back off the drive to the rear axle from 45% to around 5% (easy to monitor because the car has electronic steering which is linked into the equation). This is to prevent wind up in the transmission that would normally be overcome with a third diff', it is self regulating and completely variable and automatic. Now imagine some difficult conditions. You are starting off on a steepish hill in the snow with the wheels turned on full lock. The computer cannot detect low adhesion and you may have problems starting because the it has backed off the drive to the rear axle. It will try to overcome the problem by applying the brake on any skidding wheel in order to obtain traction from a wheel with better grip. This is a kind of "reactionary traction control" to exceptional conditions. But if you have experienced ABS or traction control activity you will know that it is a bit intermittent and some throttle control is removed until the condition is stabilised. This would be a good time to use the manual four wheel drive switch. There are other examples but I can best summarise by saying if you appear to get stuck, use the manual override! You may never normally go off road but you will inevitably drive in the snow or even park in a field (such as a fete or other country event) at some time.

The symptoms you describe regarding noises are completely normal as the relays controlling the servo click in and the servo motor on the rear axle responds by fully engaging the clutch to its maximum of 45%.

As a matter of interest, if you engage it and set off you will find it switches itself off at about 25mph and it will not re-engage above this speed. This is to prevent any unnecessary wind up in the transmission described earlier. Don't worry, you can try it and it will not do any harm.

Hope this puts your mind at rest.

Regards

I thought all Rav 4's were permenant 4 wheel drive......and my local dealer thinks so as well !!

I asume the above info is all in the hand book then?

Ian.........

I couldn't tell you about a 4.1 but it seems from the above that it is switchable.

4.2s are definately permanent and all 4.3's are as described above, i.e. part time automatic 4WD/2WD.

Ther is a US option for a permanent FWD only.

Regards

[ChrisG333]

Hi

Buzzers and beeps only occur with such items as Hill Assist Control and Vehicle Stability Control but not with the four wheel drive button. There is a warning light.

When the four wheel drive button is off, the system is fully automatic. There is no centre diff', instead there is a conventional transverse front wheel drive gearbox and a drive shaft that is permanantly connected to the rear axle via a transfer box. The clever bit is in the nose of the rear axle. There is a multi plate clutch that is engaged by an electric servo. The servo can be steplessly engaged from zero to 55/45% front to rear. It works by twisting a helix through several degrees to vary the amount of clamping force on the clutch and therfor drive transmitted to the rear axle. The car starts in four wheel drive every time you set off. For this reason you will never experience front wheel slip under heavy acceleration and NORMAL traction control is completely unnecessary. As the speed increases and the torque from the engine reduces the servo backs off the servo and begins to reduce the drive through the clutch to the axle, eventually becoming completely front wheel drive to improve fuel consumption. The system is also connected to the vehicle stability control and will vary the drive to the rear axle in order to control a skid. You have no input to the normal or the skid control of the rear axle, it is all controlled by computer and varies dramatically upon throttle position, road speed and load.

However, it is not flawless and there could be certain times when you need to override the automatic sysytem. For instance, I have already stated that the car always sets off in four wheel drive regardless of whether you are on a dry road under perfect conditions or on ice. The exception is if you set off (eg from a junction) with the front wheels turned to full lock. The system will back off the drive to the rear axle from 45% to around 5% (easy to monitor because the car has electronic steering which is linked into the equation). This is to prevent wind up in the transmission that would normally be overcome with a third diff', it is self regulating and completely variable and automatic. Now imagine some difficult conditions. You are starting off on a steepish hill in the snow with the wheels turned on full lock. The computer cannot detect low adhesion and you may have problems starting because the it has backed off the drive to the rear axle. It will try to overcome the problem by applying the brake on any skidding wheel in order to obtain traction from a wheel with better grip. This is a kind of "reactionary traction control" to exceptional conditions. But if you have experienced ABS or traction control activity you will know that it is a bit intermittent and some throttle control is removed until the condition is stabilised. This would be a good time to use the manual four wheel drive switch. There are other examples but I can best summarise by saying if you appear to get stuck, use the manual override! You may never normally go off road but you will inevitably drive in the snow or even park in a field (such as a fete or other country event) at some time.

The symptoms you describe regarding noises are completely normal as the relays controlling the servo click in and the servo motor on the rear axle responds by fully engaging the clutch to its maximum of 45%.

As a matter of interest, if you engage it and set off you will find it switches itself off at about 25mph and it will not re-engage above this speed. This is to prevent any unnecessary wind up in the transmission described earlier. Don't worry, you can try it and it will not do any harm.

Hope this puts your mind at rest.

Regards

I thought all Rav 4's were permenant 4 wheel drive......and my local dealer thinks so as well !!

I asume the above info is all in the hand book then?

Ian.........

I couldn't tell you about a 4.1 but it seems from the above that it is switchable.

4.2s are definately permanent and all 4.3's are as described above, i.e. part time automatic 4WD/2WD.

Ther is a US option for a permanent FWD only.

Regards

Hi All

Seems to be some confusion here.

The original thread was regarding the "Centre Diff Lock" operation, not the 4WD.

When switching off the Centre Diff Lock I don't get a beeper or buzzer sounding which you are meant to.

So I asked if anyone might know if I have a problem and where to start looking, all the fuses are OK and when the switch is operated i can hear a sort of short buzz coming from under the vehicle which shows that someting is happening but not necassarily working correctly.

Thanks

Chris

[anchorman]

Hi Chris

I did get confused because you didn't add your model type to your profile. I know that 4.2s are permanent and 4.3s are automatic. I confess that I never imagined that 4.1s had an electric engagement switch.

Are you concerned that the 4WD isn't working or only that there might be a problem with the electronics? You can check the 4WD by jacking up a rear wheel, engaging a gear and switching the diff lock switch on and off. You should be able to turn the wheel with it off and not with it on. If it works I wouldn't worry about the buzzer.

I think the comment from Ian is just curiosity about 4.3's not confusion about your problem.

Regards

[ChrisG333]

Hi Chris

I did get confused because you didn't add your model type to your profile. I know that 4.2s are permanent and 4.3s are automatic. I confess that I never imagined that 4.1s had an electric engagement switch.

Are you concerned that the 4WD isn't working or only that there might be a problem with the electronics? You can check the 4WD by jacking up a rear wheel, engaging a gear and switching the diff lock switch on and off. You should be able to turn the wheel with it off and not with it on. If it works I wouldn't worry about the buzzer.

I think the comment from Ian is just curiosity about 4.3's not confusion about your problem.

Regards

Hi Anchorman

Thanks for the reply.

I'll take your advice over the weekend.

One question - I'm assuming that I jack the vehicle up, engage the Diff Lock and then try and turn the airborne wheels by hand?

Thanks for your help.

Chris

[anchorman]

Hi Chris

I did get confused because you didn't add your model type to your profile. I know that 4.2s are permanent and 4.3s are automatic. I confess that I never imagined that 4.1s had an electric engagement switch.

Are you concerned that the 4WD isn't working or only that there might be a problem with the electronics? You can check the 4WD by jacking up a rear wheel, engaging a gear and switching the diff lock switch on and off. You should be able to turn the wheel with it off and not with it on. If it works I wouldn't worry about the buzzer.

I think the comment from Ian is just curiosity about 4.3's not confusion about your problem.

Regards

Hi Anchorman

Thanks for the reply.

I'll take your advice over the weekend.

One question - I'm assuming that I jack the vehicle up, engage the Diff Lock and then try and turn the airborne wheels by hand?

Thanks for your help.

Chris

Chris

I presume with the diff lock disengaged it runs in front wheel drive?

If so jack up one rear wheel and make sure the fronts are firmly chocked. Then do the engaged/locked disengaged/free (may be a bit stiff due to the transmission) test described.

Good luck