caster measurement

[gvy]

Hi.

Recently I got my front suspension from under the car .
I made some shackles to lower the front 1.3 inch (33mm).

See attached thumbnails:

[gvy]

I mounted the suspension back under the car and put some neoprene rubber spacers, where before some sort of other spacer plate was. See photo...

After that, I had to do a proper wheel alignment, because the lowering of the car had set the alignment completely wrong.

I set a little Toe in . ( about 0',20).

[gvy]

Now,

Before the changes, the car was driving straight on even if I didnt hold the steering wheel.

Now the car is driving straight on when holding the steering wheel straight,so that is OK.
But when I release the steering wheel it turns itself a bit to the left, and the car pulls to the left.

I suspect that this has something to do with the caster?
The toe in is in my opinion OK, because when holding the steering wheel straight , the car drives straight. Also the car is handling good.

Second question : How can I measure DIY myself if the caster is within tolerance and if it is the same on the right and left . (I suspect something is wrong)

What can cause a change in caster here? (I didn't change the washers in the upper control arm)
Personally, I can think of two reasons :

1 . Lowering only the front causes possibly the caster to become a bit more negative ....
2 . The neoprene rubber plates, I put between chassis and suspension is not pressed in evenly when attracting the four bolts ( that attach the front suspension to the chassis), causing a different caster left and right.
If, for example the front bolt is attracted harder and the neopreen is pressed in front a little more than the back, then the suspension is may be tilted a bit, changing the caster? I dont know...

Any thoughts are welcome.

Is it the caster that causes the pulling?
Can I measure it some way?


Geert

[Redskinsjbs]

It sounds like a caster problem, although it may also be a camber problem. If one wheel has a different camber than the other, it is essentially a different diameter and can cause a drifting. I don't think that this is the case in your situation because it seems to be more voilent of a turn . . . simliar to torque steer in a fron wheel drive car.

I don't know of a way to measure the caster at home, but I would find a shop with an old guy who has been doing alignments for a long time and talk to him. I don't trust the fancy gizmatic machines because the operators always seem like it is their first time operating the machine.

[gvy]

I guess I found an interresting self to make tool for measuring the casterangles directly on the axis of the ball joints.

The metric frame caster tool is attached to the upper and lower balljoint. The angle finder reads caster directly, whether the wheel is exactly straight or not.

It looks way more acurate to me then the method of measuring cambers while turning the weels right and left .

I have to weld it together but it looks plain simple. I just need to find an "angle finder tool"


Geert

[ghcoe]

Originally Posted by gvy I have to weld it together but it looks plain simple. I just need to find an "angle finder tool" Geert

- Harbor Freight Tools - Quality Tools at the Lowest Prices

Any time you change the position of the steering arms you are going to change the steering geometry. The alignment is set at suspension rest. Going down the road your suspension geometry is constantly changing in response to arm and tie rod cycling going over bumps.

[gvy]

Originally Posted by ghcoe Any time you change the position of the steering arms you are going to change the steering geometry. The alignment is set at suspension rest. Going down the road your suspension geometry is constantly changing in response to arm and tie rod cycling going over bumps.

Yes,

That is why I did set the toe in al over again after lowering with shackles
But what is a bit strange is why the car and steering wheel (after setting toe in correct) is pulling to one side?
I just guess may be it is the caster on the left and right that isn't the same anymore?. I am not sure of it.
That is why I want to measure it some way.

Anyway, A car with a correct suspension geometry set at rest, should drive straight on , on a good road... Mine did before the suspension was out to install the shackles. Now it pulls, so I have to find a solution

Geert

[Paul]

Did you align the front tires to the rear tires as well, or did you only check the front tires to each other for Toe?

[ghcoe]

Originally Posted by gvy Yes, That is why I did set the toe in al over again after lowering with shackles But what is a bit strange is why the car and steering wheel (after setting toe in correct) is pulling to one side? I just guess may be it is the caster on the left and right that isn't the same anymore?. I am not sure of it. That is why I want to measure it some way. Anyway, A car with a correct suspension geometry set at rest, should drive straight on , on a good road... Mine did before the suspension was out to install the shackles. Now it pulls, so I have to find a solution Geert

Lowering the suspension is going to throw out your camber because the lower arm is longer than the top arm. So lowering would push the bottom of the wheel out and pull the top of the wheel in because the arm arcs are different. It does not take much to throw everything off. Even just the slight curve of the road bed can make the car pull to one side or the other. George.

[RallyBob]

Originally Posted by gvy Anyway, A car with a correct suspension geometry set at rest, should drive straight on , on a good road... Mine did before the suspension was out to install the shackles. Now it pulls, so I have to find a solution Geert

I've seen this before. If you have a slightly bent lower a-frame, then the caster can be off. However, the standard front leaf spring attachment is so rigid, it will hold the lower a-frame in position. By adding the shackles, you have perhaps just released a 'bind' in the suspension that was previously there!

The car will pull to the side of the car with less positive caster. So you probably have to increase positive caster on the left side (more shims towards rear of upper a-frame).

[gvy]

George.

My Camber is within tolerance : ( for the GT it is -0° 15' to +1° 45')
In my opinion even a different camber (wich I have not) will normally not cause a car to pull.

Further, The car keeps steering itself always a bit to the left, so not one side or the other).

Bob,

I think the same.
I am working on a way to measure the caster.
This way I hope to actually see what I am changing
But Caster is a bit hard to measure

Geert

[gvy]

I did a quick measurement
I turned my left wheel completely to the left and camber becomes negative
I turn my wheels straight : camber is about 0
I turn my left wheel completely to the right and camber becomes positive

So I think I have a problem : It looks like a negative caster.

Am I thinking right?

Geert

[gvy]

So today, I made a small simple tool to measure the castor of my GT front suspension.

I simply mount the tool between the upper ball joint and the lower ball joint.
Normally this gives me directly the castor angle.

I dont claim it is super accurate, but because of it's simplicity it does OK.

But .

As suspected , I did measure a negative castor of -3°...... Not so good...

The good news (I think) is that the thick tooted washer( to set the castor on the upper control arm) is in front and the thin washer is in the back.

So normally changing them should increase the castor.

However , I am afraid that maybe it wont be enough since I have a negative caster of -3°.
Can I do other stuff to increase caster?

[RallyBob]

Originally Posted by gvy However , I am afraid that maybe it wont be enough since I have a negative caster of -3°. Can I do other stuff to increase caster?

I have had some GT's with bent suspension crossmembers, and with incorrect caster measurements beyond normal shimming capability.

I corrected the caster by removing the upper a-frame, and cutting some material from the upper pivot tube (which the a-frame attaches to). Then I added extra shims to correct for the shorter pivot tube, but of course at the opposite side of the tube!

Bob

[MonkeyNutZ]

It could be that your shackles are allowing the leaf springs to shift to the left or right.

[gvy]

No.

I did some changements in the middle of the spring and the bridge.
The spring stays free. (it actually can go up and down in the middle).
But it can't shift to the left or right.
I'll take a photo later on.

Geert

[gvy]

Bob,

I can' t see a reason why I should not put both washers on the backside to increase the castor to the max ?

OK, then the center guide sleeve tube will sit and turn directly against the inner sleeve of the front side of the A arm
So what???
The only difference is that there normally is the iron of the washer between them?

suggestions?

Geert

[gvy]

OK ,

I dismantled the upper A arms.
Left side went OK.
right side , I encountered the infamous bolt from hell

I had to cut it out with a cutting disc. After that my father machined two new tubes on his lathe to reinstall in the rubber bushings. Those are still in good shape (renewed them 17 years ago...)
I searched and bought a new bolt . M12x220mm 12.9 ( 2.8€)
And this time I used a lot of grease before installing those boltS.

So,

First I made two wedges ( 3mm ) and put them between the chassis and the suspensionbridgemounts, so the suspension bridge turns over a bit. (very very little of course)

On the left side (drivers side) I machined a shimming of 19mm and there is no shimming on the front side to get maximum castor.
To install it I even had to widen the A arm a bit
I also shortened the pivot tube a bit.

On the right side I could simply put the oem wide shimming in the back and the small shimming in front.

I measure on both sides a castorangle of +1.5° now.
I measure on both sides a camber around 0° with a little difference.

Now, everything is measured and installed with the car in horizontal position.
In the front on jackstands , In the back on its wheels but on 2 concrete blocks of 14 cm.
I also used my front spring compressor and compressed the spring as if it stands on its own wheels, while installing. Very important when using rubber bushings....

Hope It wil work fine now...


Geert