C5 Bobbing Up & Down

johnway · Post by **johnway** » 19 Jun 2011, 12:20

Hello,
My C5 is behaving in a most amusing way - having replaced the rear trailing arms and putting it all back together I found that the rear end was too high once the car had been fired up. Not to be outwitted, I immediately set about checking the LDS fluid level in the tank ( it was low) and then playing around with the rear height sensor position on the rear anti roll bar. I managed to get the right height but then the BHI began to engage and the car started to go into a height search mode, bobbing up and down. I should mention at this point that my labours have all been made using ramps and a trolley jack, so the car has not been level. To stop the motion I have disconnected the battery. My next plan of attack is to mount the car level on 4 ramps, re-connect the battery and set the suspension to it's lowest height on the console switch and release the front and rear pressure nipples after 30 mins. That should fully depressurize the system, put both ends at their lowest level height and I should then have an accurate fluid level check at the tank. Fingers crossed that after re-tightening the nipples, adding any necessary fluid, starting the engine and setting the console height setting to normal, the car will rise to it's proper height and stay there. Any comments/advice ??

All the best,
John.

Post by **myglaren** » 19 Jun 2011, 12:39

Only that mine started doing that after I had had the front raised to access the sump drain.
Drove the car to the front of the house and it stopped and has been fine since - two weeks now so I assume it is OK.

dnsey · Post by **dnsey** » 19 Jun 2011, 12:56

If it persists, I'd suspect a dead spot on the height sensor, causing the system to hunt.
I can think of two possible tests: either swap front and rear sensors, or temorarily add a resistor (say 10% of the total track resistance) in series with one end of the sensor track - the height will then be stable, but incorrect, of course.

boristhespie · Post by **boristhespie** » 19 Jun 2011, 15:31

What about the thing in the middle of the car undertray.

My c5 got stuck up on a day trip in France. Was great. The sister in law (miserable French git) bounced all the way back in the back. Hit her head on the ceiling too.

Cost virtually nothing for a new one.

I feel good now having recalled that. Aaaaah funny. Unfortunately i will soon be seeing her miserly pus soon. Sorry can't help myself.

fred1 · Post by **fred1** » 20 Jun 2011, 09:22

Hi,

As already said by dnsey it is almost certainly worn spots on the height corrector causing hunting.

Had similar experience that again appeared after work on the rear arm bearings.

Easy to fix by replacing the appropriate height corrector.

They are about £35 each from Cit and easy to replace - release the link arm ball joint, release electrical connector and undo one bolt (I think you need an 8mm AF spanner from memory). Then just refix and connect up - no other adjustment needed as long as you do not disturb the attachment to the axle cross member at the other end of the link arm.

Access is easier if it is on a hoist but not too bad under the car -JUST REMEMBER TO JACK UP & SUPPORT CAR ADEQUATELY !!

John

Post by **Paul-R** » 20 Jun 2011, 10:02

My C5 does the up-and-down can't-make-up-my-mind trick at the front if I park with the front wheels turned. I think there was an ECU update for this but, to be honest, it's now second nature for me to park with the wheels straight.

It's probably not much help to you though as your's has the back end bobbing.

Have you tried Citraerobics? This involves simply cycling from the very lowest to the highest positions whilst staionary a few times.