1996 Rav4 Auto Grinding Noise On Turning ? Cause

[wilroda]

Hi. I hope you can help solve the problem with my much loved 1996 Rav4 gx auto. Its an import in great condition with 118k on the clock and no significant past problems.

About 6 months ago I started to notice a grinding type noise coming from the front of the car when turning at low speeds. I. E. roundabouts/car parks etc. This noise has got worse over the past few weeks but does NOT do it when the engine is very warm.

So far we have checked/ascertained the following.

CV joints all fine and well greased.

Tyres all good.

Diff oil changed. In good condition apart from two small slithers of metal on sump plug.

Car does not make the noise when the engine is off and when engine is warm/hot.

If the diff is damaged wouldn't it make the noise all the time?

I do hope someone can help with this as I am not sure where to go from here.

[gjnorthall]

Is the noise the same on both locks? Does the noise follow the speed of the car?

[wilroda]

It makes the noise on both locks but maybe more so on the Right.

I only hear it at very low speeds i e turning /parking. The noise " cycles" .

[gjnorthall]

So ............ the noise is there on both locks, at low speed when manoeuvring - it's not there when the engine is hot or the engine is off. My first check would be the steering pump belt - either loose or worn - the belt would be noisy when the pump is under load (ie on lock) but would improve as the belt warms up. Give the belt a spray of water and check for noise on lock - it will probably be much reduced for a few minutes! I would suggest changing the belt - belts which have been slipping will often be noisy even when re-tensioned correctly. It's a separate belt for the power steering pump on this particular model.

Check also the fluid level in the power steering fluid reservoir - the pump will be noisy on lock with a low fluid level.

[wilroda]

Thanks.

Did as you suggest and unfortunately it makes no difference to the noise.

Forgot to mention that the noise never occurs in reverse.

[gjnorthall]

Without listening to the noise, I don't know what to suggest further. You've checked several relevant things apart perhaps a brake disc / pad / calliper issue and transmission noises are not really an issue at low speeds (and the transmission doesn't "know" if the steering is straight or on lock). Might be an idea to get an opinion from a decent garage.

[wilroda]

Ok. Bit of an update with some conclusive facts.

Problem:

At low speed on 2/3 to full lock a mechanical cyclic grinding noise can be heard from the front of the vehicle when traveling forward ONLY. (D - Automatic Mode)

Conclusive evidence so far:

1) The problem does not occur in reverse under any condition.

2) The problem is always present when the vehicle is cold. And can be made to go away completely IF the vehicle is driven hard for 5/10 minutes. I.e. Warming everything up.

3) The problem is always present under normal driving conditions. I.e. not driving it hard.

4) All driveshafts and CV Joints appear tbe in good order with no play.

5) All wheel bearings appear to be in good order with no play.

6) The power steering system & gaiters look to be intact.

7) The power steering belt has been sprayed as above no avail.

8) The problem could not be replicated while the vehicle was up on 4 blocks with all wheels off the ground. I.e. No noises from steering on lock to lock while 'driving'.

9) Shock absorbers and springs all look to be in good order.

10) Front Diff & Transfer box oil drained and refilled. - Small metallic particles present in front diff oil, but nothing major considering the vehicle has done 118,000 miles.

11) Rear Diff oil drained and refilled - Oil dirtly, with black staining/sludge. No metallic particles present.

12) Vehicle has been driven gently 'off road' to flex the suspension to see if the noise could be induced. No noise was heard that related to increased suspension travel.

13) Driving forward onto our driveway if I hang out the back I can 'feel' the grinding with my hand on the rear diff. Thus indicating a driveline/transmission problem.1

14) All wishbone and mounting bushes are in very good order.

15) Exhast system in good order and is not rubbing.

Next times to tackle.

A) Drain and inspect Main Gearbox Oil

B) Remove Rear propshaft, inspect UJ's re-test eliminate propshaft.

C) Remove Rear Diff Pan Cover and visually inspect rear diff.

Does anyone else have any suggestions? I am curious as to the eletrical connector on the top rear of the Main Gearbox. What happens if I disconnect this and try to drive?

[gjnorthall]

This is a vast list you've worked through with further work planned. Don't know if you've already done it - but it may be worth getting someone else to take a look / listen - perhaps a decent local garage or car mechanic. The electrical connection you refer to is associated with the diff lock - this is automatically actuated on the auto - unlike the manual where you can operate the lock using a dashboard button. One member recently reported an issue with a clunk noise when manoeuvring on lock - this was on a 4.1 auto - the problem was "resolved" by disconnecting the diff lock system.

[wilroda]

Understood. I had thought this was the case.

I presume no damage is done if this is disabled?... And that it will drive on the front wheels ONLY?

It sounds easier than removing to the rear propshaft, so I will try this first.

Many thanks.

I will report back with my findings..

[gjnorthall]

No - the 4.1 is a permanent 4WD - the diff lock operates across the axles. It's the 4.3 that has the ability to vary the power sent to the rear axle. Theres no problem in disconnecting the diff lock - the problem comes with the diff lock engaged - it's a peculiar driving experience with the potential for transmission damage.

[wilroda]

Hi,

Ok. Thanks for your input.

So to clarify. I have good news. Disconnecting the electrical connector has completely eliminated the noise. :)

I need a bit of help understanding how this system works.

The electrical connect I believe controls the Central Coupling. Correct?

This central coupling is infact like running with an open centre diff. By disconnecting we are running in 2WD mode. I presume by default it drives on the front axle. OR is it the rear axle?

Can anyone point me at a schematic for how the 4WD system works on a 4.1 Auto Transmission so I can understand exactly what I have disconnected.

Next I need to identify exactly which component is causing the noise. :)

Thanks for your help!

[gjnorthall]

As I understand it - and I'm sure there are people on the forum with greater knowledge of the 4.1 auto ...........................the car is permanent 4WD and a centre diff allows the rear wheels to turn at a different speed to the front - an obvious necessity. On the manual gearbox - a manual system locks the centre diff so that the front and rear wheels turn at the same speed. This will allow the vehicle to get out of a tricky situation but it's otherwise virtually un-driveable. The auto box car features a system known as Electronic Controlled Hydraulic Multiplate Active Traction Intelligent Control - I guess this is a progressive clutch like device in the centre diff which varies the front to rear speed difference dependent on conditions (haven't a clue how the system detects "conditions"). If for some reason the system tries to control unnecessarily, the partial locking up of the centre diff will cause issues including abnormal strain on components.

There was a case on the forum earlier this year with some of the symptoms you mention but the noise was described as clunking. Disconnecting the diff actuator eliminated the problem. I'm unsure what happens with the diff lock system disconnected and would need checking out practically.

It's difficult to know what to do next, but it would appear to be a control / detection type issue rather than a mechanical problem. I haven't looked - but the Toyota online technical manual might throw some light on the detail - this is available on a pay per hour basis for downloading. Also might be worth searching the US forum - it's likely that the 4.1 auto was far more prevalent in the US than the UK.

[wilroda]

Hi,

Thank you for your input. Very helpful indeed.

I am keen to find out more about this: Electronic Controlled Hydraulic Multiplate Active Traction Intelligent Control.

More importantly, I am also keen to know of what type the actuator is.

Can anyone confirm which axle the vehicle will be driving on in this condition? I shall put it up on blocks tonight hopefully and check. I don't have a problem leaving it on two wheel drive. But need to understand the implications. Can you point me in the direction of this manual you speak of?

I will report back when I find out more :)

[gjnorthall]

The technical manuals are at http://www.toyota-tech.eu You can download the bits you want so an hours subscription goes a fair way. I spoke to someone usually knowledgeable in these things this morning. He seems to think that disconnecting the actuator does nothing - the car remains 4WD - what you've removed is the ability to apply a variable lock to the centre diff. The problem in your case appears that the actuator is getting a signal and is locking the centre diff unnecessarily and by disconnecting the actuator - this no longer happens. It will be interesting to see the result of your test.

Don't know why the text is underscored!

[wilroda]

OK.

So at the moment it is truely an open centre diff scenerio. I.e. It is unable to automatically distribute the torque between front and rear axles. Which would only really pose a problem in an off road situation where you would want this functionalitiy. I.e. the gradual locking of the central diff...

I'll take a look at the manuals this evening.

Will report back in due course!

[wilroda]

Ok.

Last night with the vehicle up on 4 blocks in 'drive' I can confirm that with the electrical connector disconnected all four wheels are driven.

If I hold one wheel still one each axle the opposing wheel spins. Both front and rear diffs therefore seem OK.

If we hold both rears still the wheels on the front axle speed up slightly.

Similiar situation on the rear if we hold the front wheels still.

So, I presume the centre diff is running in open mode with no intelligence with regarding to distributing torque between axles via the central coupling?? i.e. this is fine on the road. But less than idea in an off road situation..??

Is my understanding correct? Still need to understand how this acutator works on the central coupling..

[cheesymitten]

I have the exact same thing, i have a '96 2ltr rav4... clunk clunk clunk.. 

But i was also told that we r locked in 4wd.. hmm other than that, lovely lil thing to drive :)