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MG Midget and Sprite Technical - front suspension and ride hieght

ok guys, pls have a look at the picture attached, it shows both sides of my front suspension...

First thing to notice is that the RH side (in the picture) is higher than the LH side, this would explain the 20mm difference i have from one side of the car to the other... i have tried to fix this by re-arranging the springs at the back but it made no difference.
As far as i know both the front springs are std and the same.. but who knows ?
i can get over this by lowering the RH side slightly..

Second thing in the picture is the angle of the top and bottom susp arms (both sides) and the steering arm, i would have thought these should be level, rather than pointing down...
i have GRP front, doors and rear section and also my engine and gearbox is lighter than std... do i need to lower the suspension to bring the arms level to counteract the weight loss ?

Went for a "spirited drive" today down some back roads and it seemed a bit twitchy when encountering bumps.. possible bump steer caused by the steering arms not being straight ?

is my analysis correct ? can i just lower both sides (by differing amounts) to sort this out or does that lead to other issues., or is what i have normal ?


Andy Phillips (frankenfrog)

Andy, pretty sure slopey steering arms are normal and that bump steer is part and parcel of the 'interesting' 1950s suspension design (if suspension geometry was even a consideration in the olden days!)

Malcolm
Malcolm Le Chevalier

How's your lever shocks? The front lever shocks are integrated into the front suspension as this is not a double wishbone design, the lever is the upper control arm. If shot could cause suspension sagging on one side and the terrible handling you are experiencing. How are your bushings? Do you have a manual to go by? That would help you become familiar with the proper suspension setup and setting of toe-in, proper spring free length, and position of steering arms. These things all effect suspension geometry. Keep in mind this is an antique design and even a freshened up suspension will leave much to desire in comparison to modern suspensions. That's why we like tinkering on them an modifying them, ohh so much. ;)
Ron Koenig

Hi Ron,
Full suspension freshen up done, i have had all the parts off and stripped, new std rubber bushes fitted , new pins and brackets, everything that can wear has been renewed, front and rear.

My lever arms were shot, so i removed the valves and filled them with oil to just use as a top arm and made my own tube shock conversion following this guideline http://npmccabe.tripod.com/spritetubeshock.htm
I planned to fit a Peter May top arm conversion, but not got round to that yet.
Maybe the tube shocks are too stiff? they are new and originally used on mitsubishi lancers from mid 90's...


Toe in set at 3mm .
wheels are alloy 13 x 5.5j with 165/65-13 tyres.

never driven a spridget before so not sure what to expect..... and this one has been a year in being sorted out, only drove it very calmly to a show around christmas time and this is the first time i have been confident enough to give it a good testing..

Andy Phillips (frankenfrog)

oh, and 10mm of wheel spacers each side....
Andy Phillips (frankenfrog)

Your RH truion is 180 degrees backwards. Turn that around and your good to go.

The truion (not spelled correctly) is the part that the lever shock attaches to and sits on top of the king pin

Its a very common mistake

Prop
Prop and the Blackhole Midget

as you probably know by now I'm not technical expert but I do have a little (unfortunate) experience of front springs thanks to a certain main parts supplier

are you sure those front springs are standard free length and standard rate

I don't know what weight difference you have over a standard car with all your changes from standard

the rh pic does look higher, I've no idea why but the cars never stand scrutiny with a tape measure anyway - could it be that those front springs are not closely matched(?)

difficult to see on yours but I did notice on mine, which sits just above factory ride height I think, that the bottom wishbone pans sit roughly horizontal - I'm not sure if yours are slightly pointing down
Nigel Atkins

having just looked at my car dismiss the last sentence, another false memory, the pans are not horizontal I must have been imagining another car's set up or just barmy as usual
Nigel Atkins

both springs were the same length when off the car... but not sure of the spring rate....

ive had an idea though... if i change the springs over, one side to the other, it might make the drivers side higher (RH drive car) which could then become level when i sit my 90kg inside it...

i'll give that a go before looking at other changes, but i'm still convinced that the steering rods should be more level...

As for the weight difference, i read somewhere on a forum that someone replaced their metal frogeye bonnet with a GRP one and the weight difference made the ride height go up by an inch...

Prop, i dont think its the trunnion as the wheels are upright , if the trunnion was 180 degs out wouldnt the wheel get a very noticeable positive camber on that side ? i'll double check anyway...
Andy Phillips (frankenfrog)

If Its not a reversed trunnion link... id say disconnect the tube shock.. re hook up as.factory orginal and have a looksy...it could well be a mis-adjusted tube shock...its a mistake id make

I doulbt its a Soft spring...id say the spring is not sitting well before id consider a soft spring

Im assuming the cars body is straight and not bent from a crash...check the front frame rails to make sure they have

AN UPWARD BEND....
AN UPWARD BEND....
AN UPWARD BEND....

they should not be straight or level.

Prop
Prop and the Blackhole Midget

Andy - the steering rods should be pointing down. Here's a pic from mine (before the engine went in) showing they slope substantially. Even with the extra weight of the engine they're not anywhere near level..




graeme jackson

and another with the engine in place..




graeme jackson

Took off the springs today, they are exactly the same length at around 9 3/4"
i tried to test the spring rate using a big bucket of water, a tape measure and a set of bathroom scales but it wasn’t accurate enough to be of any use (surprisingly!).

Did find one thing though,,, the spring seat ( the part that bolts into the bottom A frame) on one side was bent, the other side is ok. Also, one of the bottom A arms has some damage....I have very old A-arms, they don't have drillings for an ARB...and the damaged one has been repaired by welding, though it looks to be a good job.

so i swapped springs and spring seats over to the other sides.

now the left side of the car (the right side of the original picture i posted) is still higher than the other side, but 5 mm less....

so i suspect maybe there is some dimensional difference with the A Arms also....

i'll look at the chassis rails at the front Prop,, i didnt notice any damage when i was painting it, but i did notice the upwards angle at the front at least on one side (the side which is the lowest now), looks like it shouldnt be there and worried me, but checking on line showed it's there for the caster angle...

when i measure from the garage floor to the bottom of the sill at the front i get 190mm on the LHS and 175 on the RHS, so swapping parts over today ive managed to reduce the side to side height difference by 5mm.


Andy Phillips (frankenfrog)

Graeme, you posted the pics while i was typing the post below...

yes, the steering arm slope on yours looks even more "slopey" than mine...

maybe when you sit in it it makes the suspension more level ?

i'll try and find some volunteers to sit whilst i take photos.

your car looks good BTW..
Andy Phillips (frankenfrog)

Just had a look at the Peter May website and he has uprated springs for racing, and these are 8" long or less.

obviously people racing will lower the cars, so maybe this also gives level suspension and steering linkages etc which gives better roadholding as well as that gained from the lower C of G..?

bit of a new subject for me so please stop me if i'm just over analysing....
Andy Phillips (frankenfrog)

Andy,
on your car I was thinking there’s more than just the GRP bonnet for the difference in weight of car and weight at the front, possibly the engine and ancillaries, g/box(?), other items(?)

the free length and spring rate effect the ride height

from Terry Horler's book – http://www.amazon.co.uk/gp/product/1906133336
the original spring free length (new) was 9.4" (9 and 13/32) (238.8mm) and 271lb/in – ‘the coil springs were made from ½in (12.7mm) diameter spring steel and were wound to give seven working coils’

interestingly although the springs got slightly longer on subsequent models the rate remained at 271lb/in even on the heavier end of line ‘rubber bumper’ model

it seems like your front springs (depending on rate) might lift the car more than the standard ones (I think no longer available)

as for the steering arm slope and lowered cars, I’ve just had a look at my car and the arms don’t seem to slope that much and my car rides at just above factory standard height (although it is difficult to see the steering arms angle and my car has the later Triumph type steering rack and has a different suspension set up to standard)

btw do you run on 14” wheels?

ever since I saw them on a friend’s car I’ve fancied a set of these, might interest you for design -http://www.spridgetwishbone.co.uk/
Nigel Atkins

Go to Kim from Magic midget for some springs. He has a nice range of heights and poundages and is an alround nice spridget chap!

As for the wishbones get some new ones!
Sounds like they are past their prime
Onno K

Here in the states we have a little gimick that seems to work... its for lowering springs ...its 2 clamps with a screw between them...you take.2 pair, place them on the coil and screw down the bolt on each pair till you get the ride hight you want

That could be a solution in your situation....probably not one MOT would like, but id think it would work

prop
Prop and the Blackhole Midget

checked corner weights today using bathroom scales, so not supremely accurate, but close enough for now....
Front RHS (drivers side) 260lb 118kg
front LHS 230lb 104kg
rear RHS 250lb 114kg
rear LHS 250lb 114kg

that makes the car just 450kg which is lighter than i expected,,, according to the book the original cars were around 700kg... i think i'll go buy another set of scales and use two together with some wood between them... they were right at the topend of the scale..

lighter weight (by 14kg 31lb) on the passenger side , which is the higher side, would compress the spring less and help explain some of the height difference, but only a little bit.
if i have got 271 lb/inch springs, 31/271 = 0.11"=2.8mm less spring compression .

all interesting stuff (to me anyway !)...

i found this website,
http://www.omniautos.force9.co.uk/sprite/m_frsus.htm
seems really good, no nonsense answers to issues...they have a design for an adjustable height spring carrier, i think i'll have a go at making some of those.. and get some new wishbones on order as well for safety reasons...


this should sort out the differing ride height issue.

Taking a look at the new website i found again.. but this time under the bonnet mods section it says...
"One piece front-end-

First if you have just got rid of the metal shroud, metal wings and metal bonnet and replaced them with a nice lightweight one piece front end remember it will be lighter and ride higher so you might want to lower the front back down so that to car sits at least level, preferably slightly nose down. "

so, as ive got GRP front AND back on my car it looks like i should be lowering front and back to bring the suspension to its correct static height..

funny how one things leads to another, then another ....

ok i'm rambling now...


Andy Phillips (frankenfrog)

I think an adjustable and perhaps removable solution would be best as you may later the cause of this anomaly

from your figures you're very slightly rear haeavy

if your car is that much lighter front and rear it would explain it sitting higher all round

and yes as we know from the Moody Blues it's a question of balance

Nigel Atkins

Definitely get new lower wishbones. You'll definitely want those anti roll bar mounting holes for a nice beefy arb. Makes all the difference although you'll then find you tear off the arb brackets on the chassis rails and thus its back to the welder...........
Matt1275Bucks

The rear springs will bias the front ride height so you need to jack the rear - remove the back wheels and support the axle - left and right on axle stands so it's level and at the correct height to ground. I then tweak any small discrepancies at the front with spacers. Ditto the rear - jack the front and wedge or shim the rear springs to bring the ride height to the right attitude and square left to right. I've tried 14" wheels - looked great but had to take them off as the tyres made the ride horrid. Darty steering? With your set up probably too much toe in - try going parallel. Your trunnions are the right way around.
F Pollock

This thread was discussed between 30/04/2013 and 04/05/2013

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