DIY Geo? (NLC)

[Rich H]

Morning all,

Porker is pulling to the left after I changed all the balljoints and bushes on the front adn I'm sick of the crap garages round here. the only one I've found that is half good is miles away and a PITA to get to.

I get the string thing, just set up 2 parrallel strings and measure toe and the camber is relatively straight forward but what about castor?

The Porker is particually vauge around centre (It odes haev odd steerign geometry so I might be stuck with it!) so I want to measure castor properly, is ther an easy DIY way of doing it?

Thanks
Rich

[robin]

If you have a camber gauge you can, I think, compute castor angles by measuring camber change over known steering angle change. In other words if you measure camber at straight ahead, then turn 10 degrees right, then measure camber again, it will have changed. The change is, I think, due to castor angle; the more castor, the more camber change on steering. Whether or not you can compute the actual angular change depends on whether or not you're good at trigonometry .

Those optical 4 wheel alignment rigs must use the change in camber to measure the castor as they have no direct mechanism to measure the castor from the road wheel (at least none that I can see).

Cheers,
Robin

[Rich H]

OK I think I follow.... The camber gauge will likely be a plumbline and some maths though...

The symptoms are: vauge steering around centre, poor self centering (Like none!) and very sensitive to road camber, oh and the steering wheel is off to the left slightly.

The steering has only gone off to the left after I changed the balljoints and bushes on the LHS (which has cured a vibration so something was shot!) but the rest has been the same for a while. So I suspect the last align (9 months ago) was done with a shot bush or balljoint (They looked OK though)

[Mikie711]

Rich, suppose you find that it is out can you actually change castor angle on a Porsche?. Easy enough on an Elise within a certain limit.

[paulW]

I got one of these...

http://cgi.ebay.co.uk/Silverline-456976 ... 2eae54e7da

at local motor factors for £30, good for a quick easy camber check.

(though I cut mine down to size, so it would rest on wheel rim, not the tyre, as tyre bulges at the bottom, obviously.)

[Rich H]

Caster adjust is easy, the rear wishbone mount can be moved in and out by an inch total, I think that is what I disturbed when I changed the bushes.

Cheers for the link!

Rich

[Mikie711]

I use one of these and a bit of angle iron cut to length.

[Shug]

Impressively enough, the inclinometer in the iPhone is supposedly pretty accurate too - obviously only worth pointing out if you already have one...

Lots of free angle finder apps out there.

[Rich H]

Cheers - I'm looking for a digital angly finder now.

Ifone? I have a steam powered 5 year old Nokia but I'm due an upgrade...

[jj]

Phil was telling me a while back about guys using iPhones to geo cars -


http://18000rpm.com/ialign_for_iphone_a ... align.html

[Rich H]

Just lashed up a bit of string and some bricks...
Lined the string up with the centre of each wheel and did some vernier caliper measurements, not perfect but about what I expected!

Toe Front (degrees)
0.18 (out) L/R 0.57 (in)

Toe Rear (degrees)
0.32 (in) L/R 0.43 (in)

So the thrust angle is about right but the front toe is a mess! No wonder it's pulling...

the N/A is supposed to be:

Toe Front (degrees)
0.15 (in) (+/- 0.07)

Toe Rear (degrees)
0 (+/- 0.07)

I'm happy with a bit of toe in on the rear given it has 50bhp more than the N/A (Plus it's a nightmare to fix!) but I'll adjust the front if I can get the nuts undone! I'll aim for a smidge of toe in on each side.
Cheers

Rich

[thinfourth]

Have to do this on shrek while working on it i noticed the steering bar was banana shaped but the adjustment might end up being a big hammer until the front wheels point roughly forwards.

Once i have learnt how to do that then i can fix my focus which also has iffy steering

[Rich H]

Snow has stopped play

I was going to wind a 3/4 turn in on the LHS and 1/4 turn out on the RHS see if that helps, might have a look later.
By my reckoning the track arm is m12 so will have a pitch of 1.75mm so that should bring it into line.