Xantia strut tops and caster angle

Mandrake · Unread post by **Mandrake** » 03 Mar 2006, 20:00

Hi All,

Trying to track down some tracking/centering problems with Dad's Xantia, and I've just noticed on the full body wheel alignment report that he had done some time ago that the caster angle is only 1 degree, and it should be 3 degrees.

According to the Citroen data (which I don't have in front of me to confirm at the moment unfortunately) it should be 1 degree for manual steering models and 3 degrees for power steering models (like his) and this is achieved by the direction of the mounting plate on the strut tops relative to the top section of the strut top.

The car has been crash damaged and repaired a few years before buying it so it is quite possible that the strut tops have been out and/or replaced in the past.

The question is, are the existing strut tops just rotated backwards, or are there two different versions of the strut tops to give the two different castor angles ? The service manual is not clear about this...

Anybody familiar with this ?

Another question - the rear end of the car seems a bit twitchy to me. On my car if I make an abrupt turn at speed the rear is always well behaved and stable, but on this car an abrupt turn at speed causes a sensation of the rear over-steering. Rear tyres are fine.

Could this be rear suspension chassis mounting bushes, or rear arm bearings ? The rear wheel camber measures fine but I notice when following the car down the road it looks slightly crabwise - with the back wheels slightly to the left of the front ones, and the rear right wheel seemingly angling in slightly, and yet nothing obvious showed up in the full body wheel alignment report, apart from the castor angle

Regards,
Simon

Mandrake · Unread post by **Mandrake** » 03 Mar 2006, 22:38

Hmm,

The plot thickens.... I've got hold of the books and checked the orientation of the strut tops, and they seem to be the correct way around for 3 degree caster - with two notches on the rubber block facing forwards and one notch facing back. So they are correct, and yet the caster is still wrong.

So that only leaves the location of the lower control arms ? Is there enough adjustment/play in the mounting bolts for the lower arms to move the bottom balljoint forwards or backwards and thus affect the caster ?

Regards,
Simon

jeremy · Unread post by **jeremy** » 04 Mar 2006, 10:15

Simon I think after severe body damage you can forget all the niceties of production line assembly and that you have to go back to first principals.

I'd start by doing a chasis drop. car on clean hard ground, then mark the location of symetrical components on the ground using a plumbline and chalk. then measure between them and if you like plot on graph paper. What you are looking for is things not being where they should be and in your case I'd be looking for front wishbone attachment points, measured from something convenient at the back - subframe mounts or bearings or something. Do remember that 2 mm over about 8 ft is actually a very small percentage innaccuracy and certainly in days gone by they were'nt built that accurately anyway.

The distance between the wheels itself isn't particularily important but the assemblies being parallel is. After all the Renault 4 (and other Renaults) were actually 4 inches longer in the wheelbase on one side than the other as the whole torsion bar/bearing assembly was made one behind the other!

I'm sure you can improvise camber and castor measuring tools. I did an Triumph 1300 which had been badly repaired by a main dealer who didn't notice a bend in a subframe by using a spirit level on the wheel face and made a simple woorden wedge so I could gauge the distance from level and transfer it from the good side to the bad side - you get the idea.

You are fortunate in having a good car to compare with - so when you have 3 measurements the same and one different you are in no doubt what should be going on.

Xantia has passive steering rear end like a ZX doesn't it? I would have thought this made it more susceptible to problems with wear or deterioration in the rear mounts.

Mandrake · Unread post by **Mandrake** » 04 Mar 2006, 10:34

Hi Jeremy,

Yes the Xantia has passive rear steering. My guess is it is the bushes that are worn, but I don't know how to establish if thats the case or not, other than by suck it and see....(and he doesn't have a lot of money to throw around on what is only an educated guess so far)

As for the caster problem, we did a comparitive measurement of wheelbase between my car and his, and the wheelbase on the right side of his (where it originally had the crash) is 12mm shorter than mine, and 8mm shorter on the left side

This is measured through the centreline of the wheels.

A little bit of trig calculation shows that if the caster was supposed to be 3 degrees but only measures 1 degree, and assuming its the lower balljoint thats too far back, it needs to be further forward by 17mm.

The camber and kingpin inclination are perfect, so the sideways location of the lower balljoint is correct.

Originally the lower right control arm was bent more than 20mm, but that arm has been replaced, however it's possible that it also stretched the mounting points of the bushes, although there is nothing obvious when we originally tried to measure it, and it doesn't explain the other side of the car, which wasn't damaged, and both sides measure very close to 1 degree caster.

Something still doesn't quite add up...

Regards,
Simon