Is It The Diff? - 2!

[blackbob]

Hello I am new here, and would appreciate your thoughts..

Car is my wife's newly-bought, 1995 Rav automatic, 140k miles, MOT'd 3 weeks ago.

As well as a skidding, scuffing from the wheels which I gather is caused by the [lack of] centre diff, a new more sinister knocking has started from somewhere underneath, seemingly from the back.

Yesterday was the first time I had driven it like this, and I was so alarmed I drove gently straight home. In retrospect I wish I had spent more time listening, as I haven't yet found much wrong.

The propshaft, cv joints, diff bearings, and diff mountings all seem fine. The only possible problem I can see is definite play/end-float in the drive flanges coming out of the diff. I have taken the diff off the car, couldn't get the drain plug out but there is plenty of (clean) oil in it, there are no teeth damaged, no roughness in the bearings, just the play in the splines. Someone has been in here before, as one driveshaft is held on with ordinary M10, 17mm-head bolts, not the 14mm-spanner nuts/studs on the other side (all were tight).

I have not been in to the (drum) brakes, or indeed got the wheels off, but everything seems fine, the brakes are not binding.

I will just have to put it all together and go for another drive.. unless anyone has any ideas?

Thanks for any suggestions

Alistair

[gjnorthall]

The automatic has an auto controlled diff lock - disconnect the actuator at the gearbox and test drive the car. The diffs on Ravs are pretty bombproof provided the oil level and grade are OK. Diff mounts can fail resulting in a rear end knock - check -for a collapsed mount.

[blackbob]

Ok thanks I'll try that, went for a run this morning an there is a clattering which may well be the silencer (its rubber hangers are very soft). There is also a juddering noise during slow cornering, which is the kind of noise you might imagine a limited-slip diff might make, although I used to have a Trooper with one and it never made a sound.

Does this diff lock have some kind of clutch plates then, which might wear out, or make a noise if the wrong oil is used? Like a tractor with oil-immersed brakes, which make a horrendous racket if the correct oil with (I think they're called) anti-squawk additives?

The bloomin car was perfectly quiet when we first got it, these noises have appeared in a couple of hundred miles!

[gjnorthall]

The phenomenon you describe is known as tight corner braking. When cornering, the front and rear wheels need to turn at different speeds but if the diff lock is applied, this is not possible. The car will judder and sometimes will feel as if the brakes are being applied. Driving in this way puts undue stress on the transmission and can damage tyres. There was a case on the forum earlier in the year involving the diff lock engaging at random on an auto 4.1 Rav - the reality is that engagement of the diff lock is almost never required.

[blackbob]

So if I disconnect the electrics as you suggest. the car will still have 4wd with a central diff, but it just won't lock?

That sounds a good solution, I did wonder about taking off the propshaft like people do with Freelanders and Scenic RX4's, but that would defeat the object of having a 4x4, although it won't be used off-road, just useful when the snow comes!

I'll have a look, see if I can find that thread. Thanks.

[gjnorthall]

Correct - the car would be 4WD and drive normally. If this resolved the problem, you could either leave the actuator disconnected or dig deeper. Removal / disconnection of the propshaft isn't as easy as some other cars - something would need to be fabricated to seal the output of the transfer box!

[blackbob]

Yes I noticed that this morning - the shaft would slide into the back of the 'box, in the same way as, say, a Cortina. Showing my age..