School me - replace upper ball joint with heim joint

[leroy17]

Please school me on an idea that I have, however my technical knowledge on this is overshadowed by my thought for a solution.

My front suspension design has upper and lower A-arms. The lowers are now basically horizontal at ride height (have done adjustments due to significant lowering). However the upper ball joint is tall (where it mounts to the spindle) and places the upper A-arm in a 8ish degree upward angle at ride height.

So my thought was to replace the ball joint with a heim joint. This would basically place the upper A-arm on the same horizontal plane as the lower A-arm. Now I have achieved a lower A-arm angle and easier camber adjustment.

Obviously the taper in the spindle would be drilled for say a 3/4 bolt and all quality hardware used and the arm modified to accept the thread in heim joint.

Tell me the flaws in this solution which I presume may be on side load and shear strength.

Ball joint is a K6136.

[Shootnride]

I'm not sure that there is anything wrong with your idea so long as you use high strength components. But, have you considered just replacing the ball joints with some from a supplier such as Howe Racing. They have a selection of components that will pretty much allow you to build your own ball joints to suit your needs.

Just a thought.

https://www.howeracing.com/

Ted

PS: I have their ball joints in my SPF and am very impressed with the quality.

[Mark IV]

On a normal SLA suspension the upper and lower arms should NOT be parallel.
The roll center and instantaneous link center are determined by the upper and lower angles and where a line drawn from the ball joint center through the inner pivot points intersects the center line of the chassis.

[MikeFromPerth]

I would be worried that the suspension geometry will get messed up somehow?

[Gaz64]

If the upper and lower arms were parallel, then the camber would not alter during suspension movement.

That's fine in a straight line.

Now what happens when you corner.

The body leans, outside tyre is taking the load, and the car is leaning on the outside edge of the tyre, instead of the maximum about of tread that we could have on the road.

[ICCARS]

Originally Posted by Gaz64

If the upper and lower arms were parallel, then the camber would not alter during suspension movement.

That's fine in a straight line.

Now what happens when you corner.

The body leans, outside tyre is taking the load, and the car is leaning on the outside edge of the tyre, instead of the maximum about of tread that we could have on the road.

The camber would not change if the arms were of equal length, but unequal length arms have different pivot centers around their specific radius, hence the camber would change.

Leroy, can I ask if you have checked the actual geometry of your current set up to validate that there is an issue, as you really need to check to see if there is a problem with this set up before you change it and potentially make it worse, not better..

[xb-60]

You could well be making the geometry worse rather than better.
Just going back to basics, if your uppers and lowers were of the same length and remained parallel during up/down movement, then when cornering, your wheels would remain parallel to the centre plane of the car, and the wheels/tyres would be at an unacceptable angle to the road (because of the roll of the vehicle). Hence in a 'simple' double wishbone setup, there are significant deviations to the arm geometry and mounting points to achieve a better compromise....so back to the comment that you would probably be making the situation significantly worse.

Cheers,
Glen

[Gaz64]

Originally Posted by ICCARS

The camber would not change if the arms were of equal length, but unequal length arms have different pivot centers around their specific radius, hence the camber would change.

Yes, agree.

There are many variables as to amount of camber change during wheel travel.

[leroy17]

Thanks guys for your replies. I spent much of today's working hours at work...errrr.. Working and reading more and realising that the set up is not to be concerned about like I thought.

Will check over the weekend, however my initial measurements actually seem not bad now that I look at the overall set up and not just an angle. God bless the Internet and you guys for some heads up.

The basic alignment setting are 7degree anti dive, about 7 castor and a little negative camber with UCA which can be flipped for an additional degree of negative.

This is the stuff I enjoy about on working on an existing car, learning so much more than expected and being really hands on.

[Aussie Mike]

Importantly If it's mounted in single shear you should have a top hat washer on under the bolt head. In the case of a joint failure the body of the rod end wont be able to get past the washer and keep your wheels pointing in the right direction.

I made some rod end conversions for steering arms this way. You can see the top hat washer in this pic.



Cheers

[deano59]

you can buy castor and camber gauges pretty cheap nowdays . i have a longacre one i use on the racecar makes life pretty easier when playing around with the front end .

[mikeinatlanta]

Geometry issues aside. I have found that heims typically do not offer sufficient angle to accommodate a street suspensions geometry and travel. Have had the same issue with racing ball joints. If you go this route, be very careful to verify no binding at the extremes of travel, both steering and compression/rebound.

[Antny]

Originally Posted by mikeinatlanta

Geometry issues aside. I have found that heims typically do not offer sufficient angle to accommodate a street suspensions geometry and travel. Have had the same issue with racing ball joints. If you go this route, be very careful to verify no binding at the extremes of travel, both steering and compression/rebound.

^ this. Heims are great for the track, not so much on our decrepit roadways. Range of motion, longevity and harsh rides should be considered.