Rear wheel alignment/geometry

[Paul Deslandes]

A friend's pre '95 de Dion Vx 7 car appears to have strange rear wheel alignment. Are the rear toe and camber determined by the de Dion tube end plates, the ears or a combination of both?

 

I'm certain that camber is fixed by the ears but is the same true of toe and are there different toe angles available? Thus far the factory has been unable to give a sensible answer. Also, are the ears 'handed' or universal and the same both sides?

 

As far as we can tell, the tube is straight, the end plates are true and parallel and the ears are identical either side, but the toe (in), wrt the car's centre line, is significantly greater on one side than the other.

 

Ta

 

Paul

[Pendennis]

Common fault pre watts linkage Paul

 

Yes the camber is set by the ears and DD, alignment and toe is also set by ears and DD. You can shim to suit, but that is a static setting which changes immediately the car moves over uneven ground or starts to corner. Basically pre watts linkage cars rear wheel steer to a degree which some swear by

 

HTH

[Richard Price]

Are the rear toe and camber determined by the de Dion tube end plates, the ears or a combination of both?

 

Yes, all of the above.

I think the factory spec is 20 or 30mins toe in, which is set by the DD tube.

The Tube should have flanges that are parallel in the vertical plane.

It's not unusual to find that a DeDion tube is a little bent. depending how they've been knocked, from what I've seen, its most common that a bent tube will give more toe in, and more negative camber.

Additionally, if a tube is bent, then its also possible that one of the trailing arm mounts in the chassis is also bent.

 

The ears should be parallel in toe, but tapered depending on the amount of negative camber.

whilst the most common ears in recent years have been 0.5 (or is it 0.25)° to suit crossply tyres, and 1.5° to suit radials, I'm pretty sure others have been supplied at one time or another (I've got three ears here that measure 0.7°).

Additionally, 2° ears are now available as used on R300 race cars.

[SLR No.77]

And the ears are not handed.

 

Stu.

[Q Catcher]

I've just rebuilt my car with new de Dion & ears and ... the rear toe-in is different from one side to the other. On the geo check one was 14 mins and I've forgotten already what the other was, but it was several mins less. And that's with a Watts linkage. (I didn't really pay enough attention, 'cos I was really interested in the front at the time.)

 

The ears are supposedly 1.5 deg negative camber, but they are in fact both slightly greater.

[Pendennis]

Sounds like your de dion tube is not symmetrical to the chassis. You could run a string down the middle and measure off the brake discs, adjust trailing arms to get equal. You should also check it's butt is central to the chassis, if not you could shim to suit.

It would be foolish to presume the tube, A frame, ears and arms when all bolted together would result in a perfect alignment

[Paul Deslandes]

I'm inclined to agree that maybe the tube is misaligned although, given the length of the tube, the radius arm lengths/locations would have to be hugely different to make even a small angular toe difference. Measurements were made with a string frame and done fairly carefully.

 

The rear steer with roll is more pronounced if the higher radius arm fixing points are used, compared to the lower points which result in an almost horizontal arm.

 

Time for another measure methinks!

 

Thanks for input.

[Pendennis]

If the trailing arms had rod ends you would be able to dial it out, maybe worth considering rectro fitting them, it's not difficult

[Paul Deslandes]

I think I'd prefer to correct the problem at source, i.e. fit the correct ears or properly aligned de Dion tube. To pull out the amount of error that we're seeing would mean a trailing arm length difference of about 12mm!!

[Pendennis]

OMG, must be the A frame that's the cause 😳

[7 wonders of the world]

Check the chassiss is straight,

 

Check the trailing arms are the same length / straight

 

Check the end plates on the the DD tube are parallel - clamp steel sections on the plate and measure at a set distance compare with a measurement plate to plate slightly bent DD tubes are not uncommon.

 

Check A frame is true,

 

Check DD tube A frame mount is central and then the tube is centralised with A frame - washers on front mount etc

 

Check location of trailing arm chassis mounts - all 4

 

Check location trailing arm mounts on DD tube,

 

All these items will have a tolerance and all are handmade, as good as Bruce and his guys are there will inevitably, though rarely slight deviations from these tolerances.

 

Once you've sorted the cause I would however look to rose joint your trailing arms to dial it in perfectly at least you know then it is correct.

 

The DD if true and correct has no effect on camber / toe this is determined by the selection of 'ears', CC offer different ones for cross ply (ACB10's etc) or radial tyres.

 

Edited by - 7 wonders of the world on 24 Jun 2014 20:58:23

[Pendennis]

I don't think the lug mount type ears are handed but I can assure you the radial mount ones are

[Paul Deslandes]

I didn't know there were different types. I thought they were interchangeable even if not identical although the method of manufacture, and hence appearance, has changed over the years.