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Oversteer in left turns, neutral in right turns


Zaag
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Hi all,

My 1996 300tdi auto has developed somewhat odd behaviour... It became apparent during the recent snowfall here in Holland.

When there is little grip (ie snow on the road), the disco shows a tremendous amount of oversteer in left turns but shows its normal neutral / slightly understeered behaviour in right turns...

I consider myself an advanced driver with tons of miles on RWD cars, always enjoying their oversteered character but this is getting out of hand...

The problem already shows when rounding a roundabout at 10 mph In the snow (which go CCW here, hence a left turn).

The front axle has no problems and in right turns everything is OK, just those left turns.... My girlfriend already stated that she's too afraid to drive it like this...

Any obvious suspects?

What would be the first things to check?

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Tyre pressures and condition would be the first thing to check...

Then suspension bushes, particularly the right rear trailing arm bushes. Don't forget to check the condition of the mounting points too, at that age you might have a failed trailing arm to axle mount.

Check the A frame, both the ball joint at the rear axle and the bushes and mounting points where it bolts to the chassis.

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Something in the back of my head is saying to me "check the centre diff". I have no reason as to why it would make a difference left of right but have you got a viscous borg warner transfer box or lt230 (a lever to engage diff lock).

And like Dave said above, you need to check all your mounts, bushes, bolts are tight etc.

Do all your wheels spin freely when the axle is jacked off the floor ?

Gordon

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Only had time to take a quick peek and although there are some dry cracks in the traling arm bushes on the chassis side, they are not really desintegrating (yet).

Is it wise to opt for the poly bushes?

Will continue the hunt as it kind of feels like the rear axle is "steering", also in the dry.

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Condition of the rubber is less important than wear. You need to get a pry bar in there and see whether there is excessive movement. You need to check both ends of the radius arms and the a-frame bushes and ball joint.

This is a good candidate for your problems. Wheel bearing condition is another possibility.

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  • 3 weeks later...

Sorry that it took while to get back with photos but a pneumonia prevented me from spending much time with the Disco... :blush:

I did some further checking today but can't locate any noticeable play / war anywhere on the right side of the car...

Took some pictures with my phone so the quality is not all that but at least it gives some idea of the condition...

Trailing arm --> axle: can't get it to move with a pry bar...
002_zps7983a47f.jpg

Hub: I thought I noticed some bearing play with all wheels on the ground but can't notice any play that I can feel with the wheel removed:
001_zpscd670e1a.jpg

Sway bar --> axle: nothing unusual:
003_zpsdff8cf10.jpg

Sway bar --> body: the bush does open up a little with the wheel off the ground but it looks as if that is due to the amount of "lift":
004_zpsb7b86182.jpg

Shock absorber --> chassis: doesn't look unsual to me...

005_zps457a7288.jpg

Trailing arm --> chassis: nothing unusual?

006_zps0aa0eae1.jpg

The problem persists as before... GF almost lost control ths morning on a frozen over road in a 90 degree left turn at 10 MPH... it just slides out of control...

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You don't mention whether or not you checked the A-Frame bushes.

You will rarely notice bearing wear with the wheels off, rocking the wheels is the only sensible way of judging. Preferably with the car well supported on stands one hand on the top and one on the bottom. You might just be able to perceive movement, but you don't want much more than that.

As discussed very difficult to see from photos. There does appear to be a bit of a gap in the shocker top bush which is not great, but I'd be surprised if that is the problem you are having.

My money would still be on suspension bushes - possibly A-Frame.

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I tried for bearing wear with the wheel about half an inch off the ground and with the pry bar under it to try and rock the wheel but nothing worrying there.

To be honest, I didn't take a look at the a-frame joint yet but after looking at some videos about it on youtube, I think that that is the next suspect...

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The trailing arm bush in your last photo is long since expired - look at how the rubber is so swollen, specially at the bottom. I'd recommend replacing all the bushes that hold the radius and trailing arms to the chassis first and seeing how you get on, though removing the arms to check the axle-end bushes would be a good idea. Your damper bushes are also worn out - see the gap in the bottom of the damper eye? Remember to check the panard rod bushes and brackets.

A-frame ball joints d wear, but you can normally hear that before it becomes significant to handling, appearing as a single but significant clunk that can be heard and felt when braking or taking up drive. A-frame bushes don't tend to cause trouble.

I'm not a fan of poly bushes. They increase wear and strain on the other parts. Even the comp safari guys have found that the best bushes are the original spec ones.

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Spent some time under the car, together with a friend, and although I admit that many of the rubber parts, if not all, are up for renwal, we can't find anything so terribly wrong that it would cause this, yet unexplained, behaviour...

I also can't really think of what could possibly cause it... I'm inclined to think that if it goes wrong in left turns... it must be on the right side of the vehicle... or something so terribly wrong in the rear diff that it auto-locks under certain loads in left turns?

Took some more pictures of the left side and A-Frame (bearing in mind that the car was jacked-up on the right side of the vehicle thus putting some strange loads on various bushes):

left001_zps2b740fae.jpg

left002_zpsd5505e6d.jpg

left003_zpsde44165e.jpg

left004_zpsce715786.jpg

a000_zpsda2408c8.jpg

a001_zps783d02a5.jpg

a002_zps63bed563.jpg

a003_zps202fec9c.jpg

We stuck a pry bar into almost every nook & cranny but apart from some very minor sideways movement of the front bushes of the a-frame which appears to be in line with what I know from other cars, there's nothing out of the ordinairy...

I'm not afraid to spend money or time or effort on it as I've sworn not to let go of it before it reaches 500.000 km (it's on some 436.000 now) so I intend to get to the bottom of this and if it takes all new bushes, so be it... but my gut feel tells me that I haven't found the real cause yet.

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  • 3 weeks later...

Judging by the look of the trailing arm bush, where it mounts to the chassis, that would be my first suggestion. Replace the bushes at both ends.

Secondly, you mention the front axle is all OK but did you check the steering is working correctly, lock-to-lock?

I once fitted a used steering box that had developed a "notch" - meaning that a small change in steering wheel angle gave a big change in wheel angle as it went past this notch, which once or twice caused me the same oversteering problem.

Worth checking IMHO.

Good luck!

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  • 3 weeks later...

And back again...

Called in the help of a befriended logically thinking human being who also spent an hour or so under the car trying to find a "dedicated culprit" but nothing.

Yes, the majority of the bushes are due for renwal and that will be done but there should be an identifyable "something"... we drove the car in the snow and couldn't replicate the behaviour anymore... the only variable that was really different from when it went into the irradic oversteer is that it now had spent the night in our garage.

We decided to wander onto the ever-so-wonderful path called "logic" and the times that the car displayed this behaviour, was when it had spent the night outside at temperatures of some 10 degrees centigrade below zero which lead us somehow to the possible conclusion that the rear shocks, which of course also show a degree of wear, might have absorbed some moisture over time which, at the mentioned temperatures, freezes up inside the shocks and severely hamper the well functioning of said shocks. When the car spends the night indoors, they won't "freeze up" which explaines why we couldn't replicate it anymore...

Ordered some Terrafirma shocks from the UK and when they got in, I went to undo the old ones when the LH top mount decided to snap when I tried to undo the nut...

YIPPIE!

Ordered a new top mount from the UK, put the Terrafirmas on and... can't feel a huge difference... but the roads are clean now, temperatures are above zero... and an oil hose developped a leak...

YIPPIE!

Before I had the hose replaced, somebody slammed into the O/S door mirror and broke it... of course without leaving a note...

YIPPIE!

Took the mirror off while awaiting a new one from the UK and had the hose replaced...

On to new suspension bushings now! :-D

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Other than the trailing arms, you seem to have covered the bushes on the back end.

A couple of questions, (as I noted you have a lift) do you have a detroit/limited slip diff in the back? It is possible that you have a broken halfshaft causing weird driving characteristics.

Other than that, you need to start looking in all the same places at the front, not as likely, but well worth checking.

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Bad dampers can cause the trouble you have, but as I already said the bushes are shot, with clear signs or perishing, splits, wear and distortion. They are not just "up for renewal", they are in a bad way. Replacing all the bushes on the radius arms, trailing arms and panhard rod will sort the fault out, and replacing the damper bushes should be done along with the dampers themselves.

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