Front ARB mount relocation

[Roy Kemp]

Hi gents,

Just following on from my blog post about front suspension mods, etc.

Got the car jacked up today and disconnected the front ARB mounts from the chassis. Now, I was expecting the whole lot to move forward to its own "natural" location, and this should mark the point where I refabricate the mounts.

As it happens, they didn't move forward at all, they actually moved back a couple of mm. Is it possibly my mounts have already been modified, or possibly built correctly in the first place?

See attached photos with measurements from the bottom of the chassis box section. Yes, I'm aware my car is filthy and I was using double-width bushes in a single width brackets.

So, bottom stud is about 190-ish from the bottom of the box section.

Can anyone compare/contrast what they have installed? S3 Phaeton with Escort suspension.

Cheers!

[Pete Clayton]

Doesn't look the car is on the ground, i'd have thought you need the suspension under normal load to get the position correct

[Roy Kemp]

I was sure I read previously that it was to be jacked up level before the ARB was disconnected.

[Pete Clayton]

You are right, i've just found the post from Dave Adams

[Dave Adams]

on my car it was far enough out that it bounced into position as i unbolted it all....

however i got the car to ride height (dropped it onto its wheels) then rolled it back a little and forwards, but in the end i measured from the shocker mount on my TCA to one of the chassis cross members rearwards of the front suspension to make sure the were equal. the chassis had already been measured by myself and found to be pretty good.

the other thing i elected to do was ensure the TCA mounts were sat at 90 degrees to the chassis mounts (not twisted) as my TCA on the N/S fouled the chassis once that was done i i checked the wheels for position in the wheel arches. they were very much improved in their position much more central.

after that i photographed the ARB mounts in relation to the ARB.....my ARB was touching one of the mounting bolts and it moved a little more when i cut it off. then i remade some mounts and welded them into position, once bolted back together the car sat as it should and the wheels were central to the wheel arches.

the only other issue i had was the shocker fouling the top wish bone and it had to be "adjusted " but my car was particularly bad.

[Dave Adams]

the N/S ARB mount on my car once unbolted....

And the O/S ......not as bad.

[Steve and Matt Pegrum]

I should think the best way to choose the ARB mounting is to measure/select the desired caster angle since that is fundamentally controlled by the ARB  - rather than relaying on a 'natural' position of the bushes since those are squashy, may have distorted and in the case of the escort TCA not be necessarily straight within the arm itself. It's also determined of course by the top wishbone and its mounting - which may or may not have been accurately made by Dutton.

I am presently considering the removal of the ARB and am intending to tack weld new chassis brackets & new fabricated lower wishbones in order to assess the Caster angle with the car on its wheels before final welding. You could do same with the ARB mounting

[Dave Adams]

in theory.......but Dutton already did that and then made the chassis to fairly good standards.....its pretty square....... its the brackets welded into place that are the issues.... we are not altering the castor angles away from an ideal standard set up NO we are fixing the poor job done by the factory.

by doing as i have suggested does not alter the castor away from where it should be but puts it back where it should have always been.

the TCA does seem to be in its correct position if it is allowed to just sit on the inboard mounts and everything around it correcting.....

[Dave Adams]

also the whole car is a series of compromises sometimes what is perfect is not going to work.....sometimes you just have to sort the bodges and end up with the best of compromises.

[Steve and Matt Pegrum]

If you detach/move the ARB mounting you will definitely change the caster angle. The question is whether it will be an improvement. The only way to be sure is to measure.

[Adrian Southgate]

The original issue was a discrepancy in the ARB mounting points between left and right on some Legerra's causing the N/S wheel to sit too far back in the arch. That's why Dave dropped his mounts and why I realigned mine.

I don't even know if it affects Phaetons, they may all be 'straight'. If you are fitting adjustable tension braces then it can be done without moving the mounts.

If the TCA bracket on the chassis is 1mm out it will have a magnified effect at the end of the TCA. I agree it will change the castor angle but whether thats beneficial or detrimental hasn't been tested. The aim was to equalise the distance between the front and rear wheels and match both sides of the car. This should have been beneficial as at least then the suspension would have been square (rectangular) to the chassis. 

[Dave Adams]

i have looked at a couple of S4 phaetons, they seem to suffer from the same issues.

[Roy Kemp]

Ok chaps, what can we agree on for a decent baseline castor angle then?

Starting to wonder if I can get my fab guy to make mounts that are easily adjustable!