Hi every one J

New to the site and wanting to pick people’s brains about a very strange problem with my Octavia, any help advice would be great!

1.8 t 4x4

2003 (53)

120,000 miles

 

I bought the car as spares or repairs due to intermittent oil light illumination! After reading on the TT forum  (had not found brisk Skoda) I dropped the sump found a rather bunged up pick up pipe so replaced this and the oil pump and pressure switch, 10,000 miles later engine still sounds lovely.

However I have this very strange fault! When turning to the right it feels like the near side front wheel is wobbling! I put this down to a wheel bearing or drive shaft, and have changed both and the tyres (replaced all 4 with a good make).

 

This helped some 5,000 miles ago but has got worse of late with the added addition of sometimes wandering in a straight line as if being in high winds (on a motorway) again I have done the obvious and had a 4 wheel laser alignment. If you apply hard power say 60-70 on a motor way you get the wobble.

Now in heavy rain a few weeks back, the car I can only assume felt it needed to apply more power to the rear, as it felt like the 4x4 was more active, my guess was slight loss of traction and it engaged more?

 

This is when the fun started it sounded very mechanical and droned quite a lot and seemed to vibrate heavily though the prop, by backing off the throttle (coasting still in gear) and then re-applying it seemed the 4x4 system cut out and the drone/vibration left.

I have had the transmission fluids and haldex unit oil/filter changed and they reported the oils to be in good condition and no metal particles etc.  On regular day/conditions the diff in the rear seems very quiet and the prop doesn’t vibrate.  So I presume the problem is front gearbox/transfer box!

 

Possibly a worn diff?  Any help really appreciated J

 

 

Hello, welcome along

 

When turning to the right it feels like the near side front wheel is wobbling! ...

ball joint ?

Now in heavy rain a few weeks back, the car I can only assume felt it needed to apply more power to the rear, as it felt like the 4x4 was more active, my guess was slight loss of traction and it engaged more?

that would be a reasonable assumption ..

 

This is when the fun started it sounded very mechanical and droned quite a lot and seemed to vibrate heavily though the prop, by backing off the throttle (coasting still in gear) and then re-applying it seemed the 4x4 system cut out and the drone/vibration left.

I have had the transmission fluids and haldex unit oil/filter changed and they reported the oils to be in good condition and no metal particles etc.  On regular day/conditions the diff in the rear seems very quiet and the prop doesn’t vibrate.  So I presume the problem is front gearbox/transfer box!

 

Possibly a worn diff?  Any help really appreciated J

Possible

The Haldex unit has two diffs in one casing, the haldex clutch unit, and coupled behind it the rear axle unit

The rear axle unit has a set of pinion gears and an open differential

Have you changed the oil in this ?

Typically droning from a haldex tends to be one of three things:

Electric pump fail on the haldex unit

Low oil in the rear casing unit leading damage to the pinion gear teeth, and then possible damage to the rear open diff

Get the car on a scissor post ramp - the type where all 4 wheels are off the ground and clear to rotate

run the engine, engage gears at a low speed - with no front grip the haldex unit should engage - all four wheels should turn

You should then be able to hear whats going on

My money would be on electric pump fail, as you have no droning on 'normal' driving

Thanks for the info about the electric pump, the car is due an mot this week so will try and get it on a ramp at the same time and see what it does, and if there is any adverse noises!

forgive me for coming across a little thick what is the purpose of the pump? does this engage the 4x4 on the rear and how does it all work? if I turn the esp off, via the button on the dash will this overide the 4x4 and cut it out?

The haldex diff system uses clutch plates which are pressed together due to the oil pressure within the casing, which is generated by the electric pump

If left to its own, the clutch plates will press together and transmit the torque through the diff

However, the controller on the side releases the pressure within the casing, reducing the friction of the plates and controlling torque transmission

The controller recieves input from the ABS and engine ECU, and acting on this decides how much torque to transmit

As programmed for VW, according to their 'just enough' 4x4age philosophy the controller will only allow enough torque to stop slipping wheels, and will then back-off engagement

The system normally operates will a 20% torque transmission to the rear axle, upping to circa 50% under acceleration, and more it slip detected

The only time the system completely opens the diff and disenages all rear axle torque is under braking - this is done to reduce the risk of oversteer

The ESP button on the dash only affects the ASR traction control function, which overrides the vehicles throttle input as a method of reducing slip

It has no effect on the 4x4 system

Other manufacturers who deploy haldex, such as Land Rover, Mercedes, BMW, Volvo, GM, etc tend to programme the diff to behave more like a mechanical diff, with much more engagement more of the time

There are several aftermarket products which allow you to override the factory programming

I have killed the box in mine and it is known to be the weak link on the 4x4 as the haldex is usually very good. When it went it was over the course of 30-40 miles with weird noises and a strange wobbling sensation. Hope it's not the box though as that gets expensive..