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MG Midget and Sprite Technical - Front Shock Arm Optimum Positioning

Optimum Positioning of the Front Shock Arms on Sprite/Midget Armstrong Front Shocks?

I’m refurbishing (for the 3rd and final time) my 60 Bugeye that is sort of a street driven autocross car.
I’ve owned the car since 1967 (when I bought it for $75) but it has not been on the road for the last 30 years.

IF any of you have the patience to wade through the following – I’d appreciate any advice, experience, theory, etc. you may have to help me with this question. Please excuse the imprecise/inaccurate terminology. My excuse is, it has been almost 60 years since I took algebra & geometry.

When I originally set the car up for autocross - in the late 60s – I remember playing with the positioning of the front shock arms in an attempt to best adapt them to the car which was lowered significantly and had had the shock arms shortened (cut and rewelded by a certified NASA welder) to get negative camber. I have NO idea how much I repositioned the arms from stock and in checking them find they are not even positioned quite the same. (I checked this by moving the arms to the ends of their travel then comparing the left and right shock arm angles.)

As I remember my thinking from 40+ years ago - I figured that - with the car lowered several inches - the shocks would be operating with the outer end of the arm significantly higher than stock (relative to the shock body). Therefore, the shock would be nearer to the end of the available range of travel. This would cause the pistons to have less travel relative to the outer end on compression – because the connecting rods in the shock body would be nearer to the end of their travel - where the connecting rod is less perpendicular to the bore. So I probably repositioned them to something like having the internal connecting rods perpendicular to the bore at rest with the lowered car???

Maybe someone can tell me what the stock arm setting is as a reference. Hopefully someone has some ideas on what the optimum setting is?

Thanks for any ideas or help.
S K Jones

You may have your card confused...🙂

The spridgets don't have the type of settings your refering to

There is only one setting and that's the toe, they do have kits that give the shocks more versatility

Considering you had the shock arms cut shortened and rewelded and there not an exact match


I would get another set of good lever proper spec arm arm shocks and go back to stock settings then do what ever mods your wanting to accomplish

Post some photos... we would love to see what you have
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Btw... you can now get truoin links and bushes with steeper negative chamber

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I think he is trying to "clock" them properly on the splines.
Trevor Jessie

It is not a normal "setting" I'm talking about - but one, can take the arms off and replace them at a different rotational position on the shock shaft. I'm aware of all the various ways of adjusting the trunion bushings and even have a set of adjustable trunions.
S K Jones

Trevor = you are correct. I'm trying to determine the OPTIMUM clocking on the shaft with a lowered car.
S K Jones

SK
I'm not real sure, because of not knowing how low/stiff your springs are but I would imagine that if you set it up so that you had about 2"droop from ride height at the end of the arm, that would leave you with heaps enough upwards travel BUT you would need to raise the droop bumpstops up high enough to make sure the arm rested on them at full drop to prevent the pistons in the shocks running out of travel and getting damaged
At 2" droop the springs would be almost fully unloaded---again depends on spring rate
Do your springs fully unload (come loose ) when the car is jacked off the ground
willy
William Revit

The positioning of the arm shouldn't change as the bump stops are still in the same place.

By lowering the car, all you are doing is reducing the amount of movement before the suspension hits the bump stops. The shock will still work fine, just over a slightly altered and reduced range of movement.

Malc.
Malcolm Le Chevalier

By altering the angle which the rocker is working at, the Pistons will have less movement, therefore less fluid moved. I would think that would have some effect on the damping.
Dave O'Neill 2

Unless you are going for out and out competition it seems more of a theoretical problem than one that needs any real correction. Assume the car is lowered by around 2", which is quite a lot for most circumstances. Then the changed angular position of the shock arm in relation to its spindle will only be a few does of rotation when at rest. The change to the linear movement of the shock piston arms will be measured in small fractions of An inch. Given that much of the time the suspension won't be anywhere near full travel then the damping movement from the mid point position is changed from a 90 degree tangent to have an 80 or 100 degree tangent will give very little difference to the amount of oil moved.

By the time the suspension is in its bump stops there is no damping movement left anyway.
GuyW

Now I understand.... I'd be curious what is to be gained from this modification

Instead of adjusting the rotation ... I'd think adding plates under the shock body would almost do the same thing... 1/8th to 1/4 inch thick steel plates and just stack them up

This way you still retain the the full dampening effect and the bump stop is still located in the same position you may have to shave the bump stop or build it up pending on what the objective is

Look into Peter cardwell at world wide auto??? In Wisconsin he has some cool adjustable lever arm shocks that will change the rides harsh vs Softness suspension ride to match your lowered suspension

Id think looking that much dampening of the shock by eliminating the travel of the piston would make the shock wear out fast due to the amount of reduced piston travel

In the words of star trek spock... ( interesting )

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AS to an answer to your question ... The only 2 people hear that could provide the answers your seeking is

Paul wilibrand??? (Incorrect) He owns an engineering firm

And Malcom who is a 1500 guru and a bbq grill /hot water boiler ??? engineer by trade

You might try speed racer (real name escaped me) on the mg midget experiance website... call him out directly as that group is primarily about repair not modification


Speed racer is just down the road from you in ashville? Or winston? North Carolina... that guy has forgot in the last 10 minutes what I spent 5 years learning... he used to race midgets, but I think his age forces him to set up race cars... he is a bill Billy thru and thru and has a big personality so be prepared for that... we slugged it out a few times, but he is a solid good guy.

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1500 guru eh? Thanks!

Did I provide the right answer then?!

:-)

Malc.
Malcolm Le Chevalier

I'd have to say your answer sounded good to me, as about as close to fact as I was able to spell your name correctly.


Haha

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William Revit

This thread was discussed between 21/02/2018 and 23/02/2018

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