Front Shock Shims?

[John Kuzman]

I removed the front lever arm shocks from my '59 Bugeye this weekend and shipped them off to Peter C. for a re-build. Upon removing the shock body from its mounting location, I found shims that were located between the shock body and the mounting platform in two locations on both sides. The shims resemble shims used for caster alignment on domestic vehicles, i.e. slotted shims. Is there any logical, or even illogical reason/need to shim the front shocks? Thanks.

 

[Morris]

Put in the shims to take out the shimmy?


Sorry for that one. Couldn't be helped.

 

[jlaird]

I don't remember any shims there. Maybe the previous guy was trying to adjust caster a bit, but why I wonder.

Experts please step in here.

 

[GB1]

I have never seen OE shims there either. My trick for A series was to carefuly ream out the holes that the shock bolts go through to slide them around. This gave a little adjustment, but I have not used shims.

Experts?

 

[Bugeye58]

Probably there as camber adjustment. You get about 1 degree negative camber for roughly 1/4" of shim. Far better to go with offset trunnions, or offset bushings. Shimming the shock moves the upper suspension pickup point, and can do funny things to the bump steer.
Jeff

 

[jollyroger]

Thank you Jeff. You are one one of the few guys who understand this concern. I have tried for years to explain this to other racers. Some just look at me like I am stupid....well I am stupid...I do race British cars. But I am not very stupid about suspension geometry.

 

[Bugeye58]

Jollyroger, that's why victory usually goes to those who do their homework!
Jeff

 

[tony barnhill]

What could it do to bump steer?

 

[jollyroger]

Well, Let me give it a try and keep it short.
In stock set-up the guys at Healey set the car to have a bit of positive camber)in static set). This gives the car good forward stability. As the car rotates into a turn the chassis will roll a bit(you want the car to roll) This moves the upper control arm up and drives it past horizontal. As it goes past horizontal it pulls the top of the tire into negative camber on the outside wheel(which is when you want negative camber, outside and only on a turn)
By shiming the shock you do move the upper control arm inward to creat static set negative camber. Depending on the ride height you also change the horizontal position of the upper control arm. This affects when the arm goes positive. All of this changes the relation to the pivot point of the tie rod/steering rack. The inner pivot point of the tie rod position is very critical when compared to the pivot points on both lower and upper arms.If this is not adjusted too you will get serious deflexion( usually pulling the tie inward when you hit a bump. Basically if you hit a bump, instead of steering straight the offending tire will kinda take a turn to the inside or outside or both(depends on the set-up). This can make the car a bit unstable at speed on bumpy roads. Before you make any changes to the geometry on a car you REALLY need to graph out what the changes will do. You will be glad you did. As usual I could tell ya more but if I did I would have to kill myself.

 

[tony barnhill]

Interesting....so, if that's the effect on hard driving, what's the effect on normal driving?

 

[Matthew E. Herd]

About the same ... it'll be unstable/uncomfortable to drive because the car will fight you over bumps, wanting to go its own way (which can be entirely random).

 

[tdskip]

Guys, who is Peter C. ?

 

[tony barnhill]

Ah, thanks...learned a bit here today

 

[jlaird]

Well, I learned a bit as well. Don't screw with the front end spaceing and spacers. Gesh, as Jolly would say......now I have to go kill my self. Kind of wish I understood all that.

 

[Morris]

Not that I ever plan on doing this, but couldn't you shim up the steering rack to counter act some of the bump steer?

Just curious to see if I am smart as I think I am. (answer: NO)

 

[jlaird]

And the rack mounts do indeed have shims under them.

 

[aeronca65t]

Wouldn't putting shims under the base of the lever shock affect camber rather than caster?

I agree that playing with suspension geometry can do crazy things with bump-steer. Whenever I see these "tuner cars" lowered down to within an inch of the ground, I wonder what they steer like?

Suspension is fun to play around with and sometimes the results are confounding. If you look at ~THIS PICTURE~ you will see that my green car is fairly flat, but the blue Spridget behind me is leaning more. His car often lifts a front wheel in turns and mine never does. Surprisingly, the blue car has much stiffer springs and sway bar than mine.....but it can be other variables. He is running sticky Hooziers compared to my DOT tires. And it could be just more aggresive driving too (picture taken at Big Bend-Lime Rock).

 

[John Kuzman]

Tom -

Peter C. is Peter Caldwell at World Wide Auto Parts in Madison, WI. He is the guru of lever arm shock re-builds. See info. at: www.nosimport.com

 

[GB1]

All spridgets have bump steer

see a bump and you better steer

 

[jcatnite]

I had forgotten how rough narrow 13" tires can be until I drove my Midget for the first time. Couple the small tire to a non power assisted steering box and the feedback can be overwhelming at times. I've learned to practiced the aforementioned method of bump steering.
JC